U.S. patent application number 10/189779 was filed with the patent office on 2003-04-10 for method and apparatus for signal transmission and detection using a contact device.
Invention is credited to Abreu, Marcio Marc.
Application Number | 20030069489 10/189779 |
Document ID | / |
Family ID | 22675655 |
Filed Date | 2003-04-10 |
United States Patent
Application |
20030069489 |
Kind Code |
A1 |
Abreu, Marcio Marc |
April 10, 2003 |
Method and apparatus for signal transmission and detection using a
contact device
Abstract
Utilization of a contact device placed on the front part of the
eye in order to detect physical and chemical parameters of the body
as well as the non-invasive delivery of compounds according to
these physical and chemical parameters, with signals preferably
being transmitted continuously as electromagnetic waves, radio
waves, infrared and the like. One of the parameters to be detected
includes non-invasive blood analysis utilizing chemical changes and
chemical products that are found in the front part of the eye and
in the tear film. A transensor mounted in the contact device laying
on the cornea or the surface of the eye is capable of evaluating
and measuring physical and chemical parameters in the eye including
non-invasive blood analysis.
Inventors: |
Abreu, Marcio Marc; (North
Haven, CT) |
Correspondence
Address: |
JACOBSON HOLMAN PLLC
400 SEVENTH STREET N.W.
SUITE 600
WASHINGTON
DC
20004
US
|
Family ID: |
22675655 |
Appl. No.: |
10/189779 |
Filed: |
July 8, 2002 |
Related U.S. Patent Documents
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Application
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Filing Date |
Patent Number |
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10189779 |
Jul 8, 2002 |
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09827325 |
Apr 6, 2001 |
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6423001 |
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09827325 |
Apr 6, 2001 |
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09575621 |
May 22, 2000 |
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6213943 |
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09575621 |
May 22, 2000 |
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09274882 |
Mar 23, 1999 |
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6123668 |
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09274882 |
Mar 23, 1999 |
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09184127 |
Nov 2, 1998 |
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6120460 |
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09184127 |
Nov 2, 1998 |
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08707508 |
Sep 4, 1996 |
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5830139 |
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Current U.S.
Class: |
600/405 |
Current CPC
Class: |
A61B 2560/0252 20130101;
A61B 3/1241 20130101; A61B 2560/0219 20130101; A61B 5/01 20130101;
A61B 5/1455 20130101; A61B 5/6814 20130101; A61B 5/1486 20130101;
A61B 5/4839 20130101; A61B 5/18 20130101; A61B 8/56 20130101; A61B
5/416 20130101; G02C 7/04 20130101; A61B 5/14539 20130101; A61B
5/0002 20130101; A61B 5/411 20130101; A61B 5/6821 20130101; A61B
5/14532 20130101; A61B 5/14546 20130101; A61B 2562/0238 20130101;
A61B 5/031 20130101; A61B 5/14555 20130101; A61B 2560/0418
20130101; A61B 5/445 20130101; A61F 9/0017 20130101; A61B 8/06
20130101; A61B 3/16 20130101 |
Class at
Publication: |
600/405 |
International
Class: |
A61B 003/16 |
Claims
I claim:
1. A contact device for placement in contact with a portion of a
live body, said contact device comprising: a contact surface for
engagement with a portion of a live body, and a sensor mounted on
said contact surface, said contact surface being positionable so
that bodily fluids encounter said sensor, said sensor generating a
signal indicative of a property of the encountered bodily fluids,
said signal being transmitted externally of the live body for
analysis of the signal and indication of a status of certain bodily
functions.
2. A contact device as claimed in claim 1, wherein a power source
is mounted on said contact surface.
3. A contact device as claimed in claim 1, wherein a signal
transmitter is mounted on said contact surface.
4. A contact device as claimed in claim 3, wherein the signal is
transmitted through the air by said signal transmitter for receipt
at a remote location.
5. A contact device as claimed in claim 3, wherein the signal is
transmitted externally of the live body by wires.
6. A contact device as claimed in claim 1, wherein said sensor
detects glucose levels in eye tear fluid.
7. A contact device as claimed in claim 1, wherein said sensor
detects cholesterol levels in eye tear fluid.
8. A contact device as claimed in claim 1, wherein said sensor
detects oxygen levels in eye tear fluid.
9. A contact device as claimed in claim 1, wherein said sensor
detects pH levels in eye tear fluid.
10. A contact device as claimed in claim 1, wherein said sensor
detects potassium levels in eye tear fluid.
11. A contact device as claimed in claim 1, wherein said sensor
detects sodium levels in eye tear fluid.
12. A contact device for placement in contact with an eye, said
contact device comprising: a contact surface for engaging a surface
of the eye, and a sensor mounted on said contact surface, said
sensor being positionable under an eye lid of the eye.
13. A contact device as claimed in claim 1, wherein said sensor is
a pressure sensor responsive to pressure imposed by the eye lid
when the eyelids are moved into a position caused by sleeping of
the individual wearing the contact device.
14. A contact device as claimed in claim 13, wherein a signal is
generated by said pressure sensor when pressure is imposed on said
pressure sensor by closing eye lids indicative of sleep, said
signal being transmitted to an alarm circuit for alerting the
individual of the transition of the individual to a sleep
state.
15. A contact device as claimed in claim 12, wherein said sensor is
a pressure sensor responsive to pressure intentionally imposed on
said sensor by closing the eye lids for a predetermined period of
time necessary to activate an electrical circuit for performing a
function.
16. A contact device as claimed in claim 15, wherein a light
emitting diode mounted on said contact surface is activated by
intentional closure of the eye lids for a predetermined period of
time.
17. A contact device for placement in contact with an eye, said
contact device comprising: a contact surface for engaging a surface
of the eye, and a sensor mounted on said contact surface, said
sensor producing a signal indicative of a bodily function, said
signal being transmitted away from the eye for analysis and
indication of a status of the bodily function.
18. A contact device as claimed in claim 17, wherein a light source
is mounted on said contact surface, and said sensor detects light
emitted from the light source.
19. A contact device as claimed in claim 17, wherein a heater and a
storage compartment is mounted on said contact surface, said
storage compartment including chemicals or drugs for release upon
activation of said heater based upon said signal produced by said
sensor.
20. A contact device as claimed in claim 17, further comprising a
pump for injecting an individual with mediation based upon the
signal generated by said sensor.
Description
[0001] This application is a continuing application of application
Ser. No. 08/707,508, filed Sep. 4, 1996, incorporated herein in its
entirety by references.
FIELD OF THE INVENTION
[0002] The present invention includes a contact device for mounting
on a part of the body to measure bodily functions and to treat
abnormal conditions indicated by the measurements.
BACKGROUND OF THE INVENTION
[0003] The present invention relates to a tonometer system for
measuring intraocular pressure by accurately providing a
predetermined amount of applanation to the cornea and detecting the
amount of force required to achieve the predetermined amount of
applanation. The system is also capable of measuring intraocular
pressure by indenting the cornea using a predetermined force
applied using an indenting element and detecting the distance the
indenting element moves into the cornea when the predetermined
force is applied, the distance being inversely proportional to
intraocular pressure. The present invention also relates to a
method of using the tonometer system to measure hydrodynamic
characteristics of the eye, especially outflow facility.
[0004] The tonometer system of the present invention may also be
used to measure hemodynamics of the eye, especially ocular blood
flow and pressure in the eye's blood vessels. Additionally, the
tonometer system of the present invention may be used to increase
and measure the eye pressure and evaluate, at the same time, the
ocular effects of the increased pressure.
[0005] Glaucoma is a leading cause of blindness worldwide and,
although it is more common in adults over age 35, it can occur at
any age. Glaucoma primarily arises when intraocular pressure
increases to values which the eye cannot withstand.
[0006] The fluid responsible for pressure in the eve is the aqueous
humor. It is a transparent fluid produced by the eye in the ciliary
body and collected and drained by a series of channels (trabecular
meshwork, Schlemm's canal and venous system). The basic disorder in
most glaucoma patients is caused by an obstruction or interference
that restricts the flow of aqueous humor out of the eye. Such an
obstruction or interference prevents the aqueous humor from leaving
the eye at a normal rate. This pathologic condition occurs long
before there is a consequent rise in intraocular pressure. This
increased resistance to outflow of aqueous humor is the major cause
of increased intraocular pressure in glaucoma-stricken
patients.
[0007] Increased pressure within the eye causes progressive damage
to the optic nerve. As optic nerve damage occurs, characteristic
defects in the visual field develop, which can lead to blindness if
the disease remains undetected and untreated. Because of the
insidious nature of glaucoma and the gradual and painless loss of
vision associated therewith, glaucoma does not produce symptoms
that would motivate an individual to seek help until relatively
late in its course when irreversible damage has already occurred.
As a result, millions of glaucoma victims are unaware that they
have the disease and face eventual blindness. Glaucoma can be
detected and evaluated by measuring the eye's fluid pressure using
a tonometer and/or by measuring the eye fluid outflow facility.
Currently, the most frequently used way of measuring facility of
outflow is by doing indentation tonography. According to this
technique, the capacity for flow is determined by placing a
tonometer upon the eye. The weight of the instrument forces aqueous
humor through the filtration system, and the rate at which the
pressure in the eye declines with time is related to the ease with
which the fluid leaves the eye.
[0008] Individuals at risk for glaucoma and individuals who will
develop glaucoma generally have a decreased outflow facility. Thus,
the measurement of the outflow facility provides information which
can help to identify individuals who may develop glaucoma, and
consequently will allow early evaluation and institution of therapy
before any significant damage occurs.
[0009] The measurement of outflow facility is helpful in making
therapeutic decisions and in evaluating changes that may occur with
time, aging, surgery, or the use of medications to alter
intraocular pressure. The determination of outflow facility is also
an important research tool for the investigation of matters such as
drug effects, the mechanism of action of various treatment
modalities, assessment of the adequacy of antiglaucoma therapy,
detection of wide diurnal swings in pressure and to study the
pathophysiology of glaucoma.
[0010] There are several methods and devices available for
measuring intraocular pressure, outflow facility, and/or various
other glaucoma-related characteristics of the eye. The following
patents disclose various examples of such conventional devices and
methods:
1 U.S. PAT. NO. PATENTEE 5,375,595 Sinha et al. 5,295,495 Maddess
5,251,627 Morris 5,217,015 Kaye et al. 5,183,044 Nishio et al.
5,179,953 Kursar 5,148,807 Hsu 5,109,852 Kaye et al. 5,165,409 Coan
5,076,274 Matsumoto 5,005,577 Frenkel 4,951,671 Coan 4,947,849
Takahashi et al. 4,944,303 Katsuragi 4,922,913 Waters, Jr. et al.
4,860,755 Erath 4,771,792 Seale 4,628,938 Lee 4,305,399 Beale
3,724,263 Rose et al. 3,585,849 Grolman 3,545,260 Lichtenstein et
al.
[0011] Still other examples of conventional devices and/or methods
are disclosed in Morey, Contact Lens Tonometer, RCA Technical
Notes, No. 602, December 1964; Russell & Bergmanson, Multiple
Applications of the NCT: An Assessment of the Instrument's Effect
on IOP, Ophthal. Physiol. Opt., Vol. 9, April 1989, pp. 212-214;
Moses & Grodzki, The Pneumatonograph: A Laboratory Study, Arch.
Ophthalmol., Vol. 97, March 1979, pp. 547-552; and C. C. Collins,
Miniature Passive Pressure Transensor for Implanting in the Eye,
IEEE Transactions on Bio-medical Engineering, April 1967, pp.
74-83.
[0012] In general, eye pressure is measured by depressing or
flattening the surface of the eye, and then estimating the amount
of force necessary to produce the given flattening or depression.
Conventional tonometry techniques using the principle of
applanation may provide accurate measurements of intraocular
pressure, but are subject to many errors in the way they are
currently being performed. In addition, the present devices either
require professional assistance for their use or are too
complicated, expensive or inaccurate for individuals to use at
home. As a result, individuals must visit an eye care professional
in order to check their eye pressure. The frequent self-checking of
intraocular pressure is useful not only for monitoring therapy and
self-checking for patients with glaucoma, but also for the early
detection of rises in pressure in individuals without glaucoma and
for whom the elevated pressure was not detected during their office
visit.
[0013] Pathogens that cause severe eye infection and visual
impairment such as herpes and adenovirus as well as the virus that
causes AIDS can be found on the surface of the eye and in the tear
film. These microorganisms can be transmitted from one patient to
another through the tonometer tip or probe. Probe covers have been
designed in order to prevent transmission of diseases but are not
widely used because they are not practical and provide less
accurate measurements. Tonometers which prevent the transmission of
diseases, such as the "air-puff" type of tonometer also have been
designed, but they are expensive and provide less accurate
measurements. Any conventional direct contact tonometers can
potentially transmit a variety of systemic and ocular diseases.
[0014] The two main techniques for the measurement of intraocular
pressure require a force that flattens or a force that indents the
eye, called "applanation" and "indentation" tonometry
respectively.
[0015] Applanation tonometry is based on the Imbert-Fick principle.
This principle states that for an ideal dry, thin walled sphere,
the pressure inside the sphere equals the force necessary to
flatten its surface divided by the area of flattening. P=F/A (where
P=pressure, F=force, A=area). In applanation tonometry, the cornea
is flattened, and by measuring the applanating force and knowing
the area flattened, the intraocular pressure is determined.
[0016] By contrast, according to indentation tonometry (Schiotz), a
known weight (or force) is applied against the cornea and the
intraocular pressure is estimated by measuring the linear
displacement which results during deformation or indentation of the
cornea. The linear displacement caused by the force is indicative
of intraocular pressure. In particular, for standard forces and
standard dimensions of the indenting device, there are known tables
which correlate the linear displacement and intraocular
pressure.
[0017] Conventional measurement techniques using applanation and
indentation are subject to many errors. The most frequently used
technique in the clinical setting is contact applanation using
Goldman tonometers. The main sources of errors associated with this
method include the addition of extraneous pressure on the cornea by
the examiner, squeezing of the eyelids or excessive widening of the
lid fissure by the patient due to the discomfort caused by the
tonometer probe resting upon the eye, and inadequate or excessive
amount of dye (fluorescein). In addition, the conventional
techniques depend upon operator skill and require that the operator
subjectively determine alignment, angle and amount of depression.
Thus, variability and inconsistency associated with less valid
measurements are problems encountered using the conventional
methods and devices.
[0018] Another conventional technique involves air-puff tonometers
wherein a puff of compressed air of a known volume and pressure is
applied against the surface of the eye, while sensors detect the
time necessary to achieve a predetermined amount of deformation in
the eye's surface caused by application of the air puff. Such a
device is described, for example, in U.S. Pat. No. 3,545,260 to
Lichtenstein et al. Although the non-contact (air-puff) tonometer
does not use dye and does not present problems such as extraneous
pressure on the eye by the examiner or the transmission of
diseases, there are other problems associated therewith. Such
devices, for example, are expensive, require a supply of compressed
gas, are considered cumbersome to operate, are difficult to
maintain in proper alignment and depend on the skill and technique
of the operator. In addition, the individual tested generally
complains of pain associated with the air discharged toward the
eye, and due to that discomfort many individuals are hesitant to
undergo further measurement with this type of device. The primary
advantage of the non-contact tonometer is its ability to measure
pressure without transmitting diseases, but they are not accepted
in general as providing accurate measurements and are primarily
useful for large-scale glaucoma screening programs.
[0019] Tonometers which use gases, such as the pneumotonometer,
have several disadvantages and limitations. Such device are also
subject to the operator errors as with Goldman's tonometry. In
addition, this device uses freon gas, which is not considered
environmentally safe. Another problem with this device is that the
gas is flammable and as with any other aerosol-type can, the can
may explode if it gets too hot. The gas may also leak and is
susceptible to changes in cold weather, thereby producing less
accurate measurements. Transmission of diseases is also a problem
with this type of device if probe covers are not utilized.
[0020] In conventional indentation tonometry (Schiotz), the main
source of errors are related to the application of a relatively
heavy tonometer (total weight at least 16.5 g) to the eye and the
differences in the distensibility of the coats of the eye.
Experience has shown that a heavy weight causes discomfort and
raises the intraocular pressure. Moreover the test depends upon a
cumbersome technique in which the examiner needs to gently place
the tonometer onto the cornea without pressing the tonometer
against the globe. The accuracy of conventional indentation may
also be reduced by inadequate cleaning of the instrument as will be
described later. The danger of transmitting infectious diseases, as
with any contact tonometer, is also present with conventional
indentation.
[0021] A variety of methods using a contact lens have been devised,
however, such systems suffer from a number of restrictions and
virtually none of these devices is being widely utilized or is
accepted in the clinical setting due to their limitations and
inaccurate readings. Moreover. such devices typically include
instrumented contact lenses and/or cumbersome and complex contact
lenses.
[0022] Several instruments in the prior art employ a contact lens
placed in contact with the sclera (the white part of the eye). Such
systems suffer from many disadvantages and drawbacks. The
possibility of infection and inflammation is increased due to the
presence of a foreign body in direct contact with a vascularized
part of the eye. As a consequence, an inflammatory reaction around
the device may occur, possibly impacting the accuracy of any
measurement. In addition, the level of discomfort is high due to a
long period of contact with a highly sensitive area of the eye.
Furthermore, the device could slide and therefore lose proper
alignment, and again, preventing accurate measurements to be taken.
Moreover, the sclera is a thick and almost non-distensible coat of
the eye which may further impair the ability to acquire accurate
readings. Most of these devices utilize expensive sensors and
complicated electric circuitry imbedded in the lens which are
expensive, difficult to manufacture and sometimes cumbersome.
[0023] Other methods for sensing pressure using a contact lens on
the cornea have been described. Some of the methods in this prior
art also employ expensive and complicated electronic circuitry
and/or transducers imbedded in the contact lens. In addition, some
devices use piezoelectric material in the lens and the metalization
of components of the lens overlying the optical axis decreases the
visual acuity of patients using that type of device. Moreover,
accuracy is decreased since the piezoelectric material is affected
by small changes in temperature and the velocity with which the
force is applied. There are also contact lens tonometers which
utilize fluid in a chamber to cause the deformation of the cornea;
however, such devices lack means for alignment and are less
accurate, since the flexible elastic material is unstable and may
bulge forward. In addition, the fluid therein has a tendency to
accumulate in the lower portion of the chamber, thus failing to
produce a stable flat surface which is necessary for an accurate
measurement.
[0024] Another embodiment uses a coil wound about the inner surface
of the contact lens and a magnet subjected to an externally created
magnetic field. A membrane with a conductive coating is compressed
against a contact completing a short circuit. The magnetic field
forces the magnet against the eye and the force necessary to
separate the magnet from the contact is considered proportional to
the pressure. This device suffers from many limitations and
drawbacks. For example, there is a lack of accuracy since the
magnet will indent the cornea and when the magnet is pushed against
the eye, the sclera and the coats of the eye distort easily to
accommodate the displaced intraocular contents. This occurs because
this method does not account for the ocular rigidity, which is
related to the fact that the sclera of one person's eye is more
easily stretched than the sclera of another. An eye with a low
ocular rigidity will be measured and read as having a lower
intraocular pressure than the actual eye's pressure. Conversely, an
eye with a high ocular rigidity distends less easily than the
average eye, resulting in a reading which is higher than the actual
intraocular pressure. In addition, this design utilizes current in
the lens which, in turn, is in direct contact with the body. Such
contact is undesirable. Unnecessary cost and complexity of the
design with circuits imbedded in the lens and a lack of an
alignment system are also major drawbacks with this design.
[0025] Another disclosed contact lens arrangement utilizes a
resonant circuit formed from a single coil and a single capacitor
and a magnet which is movable relative to the resonant circuit. A
further design from the same disclosure involves a transducer
comprised of a pressure sensitive transistor and complex circuits
in the lens which constitute the operating circuit for the
transistor. All three of the disclosed embodiments are considered
impractical and even unsafe for placement on a person's eye.
Moreover, these contact lens tonometers are unnecessarily
expensive, complex, cumbersome to use and may potentially damage
the eye. In addition none of these devices permits measurement of
the applanated area, and thus are generally not very practical.
[0026] The prior art also fails to provide a sufficiently accurate
technique or apparatus for measuring outflow facility. Conventional
techniques and devices for measuring outflow facility are limited
in practice and are more likely to produce erroneous results
because both are subject to operator, patient and instrument
errors.
[0027] With regard to operator errors, the conventional test for
outflow facility requires a long period of time during which there
can be no tilting of the tonometer. The operator therefore must
position and keep the weight on the cornea without moving the
weight and without pressing the globe.
[0028] With regard to patient errors, if during the test the
patient blinks, squeezes, moves, holds his breath, or does not
maintain fixation, the test results will not be accurate. Since
conventional tonography takes about four minutes to complete and
generally requires placement of a relatively heavy tonometer
against the eye, the chances of patients becoming anxious and
therefore reacting to the mechanical weight placed on their eyes is
increased.
[0029] With regard to instrument errors, after each use, the
tonometer plunger and foot plate should be rinsed with water
followed by alcohol and then wiped dry with lint-free material. If
any foreign material drys within the foot plate, it can
detrimentally affect movement of the plunger and can produce an
incorrect reading.
[0030] The conventional techniques therefore are very difficult to
perform and demand trained and specialized personnel. The
pneumotonograph, besides having the problems associated with the
pneumotonometer itself, was considered "totally unsuited to
tonography." (Report by the Committee on Standardization of
Tonometers of the American Academy of Ophthalmology; Archives
Ophthalmol. , 97:547-552, 1979). Another type of tonometer (Non
Contact "Air Puff" Tonometer--U.S. Pat. No. 3,545,260) was also
considered unsuitable for tonography. (Ophthalmic &
Physiological Optics. 9(2):212-214, 1989). Presently there are no
truly acceptable means for self-measurement of intraocular pressure
and outflow facility.
[0031] In relation to an additional embodiment of the present
invention, blood is responsible not only for the transport of
oxygen, nutrients, glucose, cholesterol, electrolytes, water,
enzymes, white and red blood cells, and genetic markers, but also
provides an enormous amount of information in regards to the
overall health status of an individual. The prior art related to
analysis of blood relies primarily on invasive methods such as with
the use of needles to draw blood for further analysis and
processing. Very few and extremely limited methods for non-invasive
evaluating blood components are available.
[0032] In the prior art for example, oxygenated hemoglobin has been
indirectly measured by a pulse oximeter based on traditional near
infrared absorption spectroscopy and indirectly measures arterial
blood oxygen carried by hemoglobin (not molecular concentration of
oxygen) with sensors placed over the skin utilizing LEDs emitting
at two wave lengths around 940 and 660 nanometers. As the blood
oxygenation changes, the ratio of the light transmitted by the two
frequencies changes indicating the amount of oxygenated hemoglobin
in the arterial blood of the finger tip. The present systems are
not accurate and provide only the amount of oxygenated hemoglobin
in the finger tip.
SUMMARY OF THE INVENTION
[0033] In contrast to the various prior art devices, the apparatus
of the present invention offers an entirely new approach for the
measurement of intraocular pressure and eye hydrodynamics. The
apparatus offers a simple, accurate, low-cost and safe means of
detecting and measuring the earliest of abnormal changes taking
place in glaucoma, and provides a method for the diagnosis of early
forms of glaucoma before any irreversible damage occurs. The
apparatus of this invention provides a fast, safe, virtually
automatic, direct-reading, comfortable and accurate measurement
utilzing an easy-to-use, gentle, dependable and low-cost device,
which is suitable for home use.
[0034] Besides providing a novel method for a single measurement
and self-measurement of intraocular pressure, the apparatus of the
invention can also be used to measure outflow facility and ocular
rigidity. In order to determine ocular rigidity it is necessary to
measure intraocular pressure under two different conditions, either
with different weights on the tonometer or with the indentation
tonometer and an applanation tonometer. Moreover, the device can
perform applanation tonography which is unaffected by ocular
rigidity because the amount of deformation of the cornea is so very
small that very little is displaced with very little change in
pressure. Large variations in ocular rigidity, therefore, have
little effect on applanation measurements.
[0035] According to the present invention, a system is provided for
measuring intraocular pressure by applanation. The system includes
a contact device for placement in contact with the cornea and an
actuation apparatus for actuating the contact device so that a
portion thereof projects inwardly against the cornea to provide a
predetermined amount of applanation. The contact device is easily
sterilized for multiple use, or alternatively, can be made
inexpensively so as to render the contact device disposable. The
present invention, therefore, avoids the danger present in many
conventional devices of transmitting a variety of systemic and
ocular diseases.
[0036] The system further includes a detecting arrangement for
detecting when the predetermined amount of applanation of the
cornea has been achieved and a calculation unit responsive to the
detecting arrangement for determining intraocular pressure based on
the amount of force the contact device must apply against the
cornea in order to achieve the predetermined amount of
applanation.
[0037] The contact device preferably includes a substantially rigid
annular member, a flexible membrane and a movable central piece.
The substantially rigid annular member includes an inner concave
surface shaped to match an outer surface of the cornea and having a
hole defined therein. The subsannular member preferably has a
maximum thickness at the hole and a progressively decreasing
thickness toward a periphery of the substantially rigid annular
member.
[0038] The flexible membrane is preferably secured to the inner
concave surface of the substantially rigid annular member. The
flexible membrane is coextensive with at least the hole in the
annular member and includes at least one transparent area.
Preferably, the transparent area spans the entire flexible
membrane, and the flexible membrane is coextensive with the entire
inner concave surface of the rigid annular member.
[0039] The movable central piece is slidably disposed within the
hole and includes a substantially flat inner side secured to the
flexible membrane. A substantially cylindrical wall is defined
circumferentially around the hole by virtue of the increased
thickness of the rigid annular member at the periphery of the hole.
The movable central piece is preferably slidably disposed against
this wall in a piston-like manner and has a thickness which matches
the height of the cylindrical wall. In use, the substantially flat
inner side flattens a portion of the cornea upon actuation of the
movable central piece by the actuation apparatus.
[0040] Preferably, the actuation apparatus actuates the movable
central piece to cause sliding of the movable central piece in the
piston-like manner toward the cornea. In doing so, the movable
central piece and a central portion of the flexible membrane are
caused to project inwardly against the cornea. A portion of the
cornea is thereby flattened. Actuation continues until a
predetermined amount of applanation is achieved.
[0041] Preferably, the movable central piece includes a
magnetically responsive element arranged so as to slide along with
the movable central piece in response to a magnetic field, and the
actuation apparatus includes a mechanism for applying a magnetic
field thereto. The mechanism for applying the magnetic field
preferably includes a coil and circuitry for producing an
electrical current through the coil in a progressively increasing
manner. By progressively increasing the current, the magnetic field
is progressively increased. The magnetic repulsion between the
actuation apparatus and the movable central piece therefore
increases progressively, and this, in turn, causes a progressively
greater force to be applied against the cornea until the
predetermined amount of applanation is achieved.
[0042] Using known principles of physics, it is understood that the
electrical current passing through the coil will be proportional to
the amount of force applied by the movable central piece against
the cornea via the flexible membrane. Since the amount of force
required to achieve the predetermined amount of applanation is
proportional to intraocular pressure, the amount of current
required to achieve the predetermined amount of applanation will
also be proportional to the intraocular pressure.
[0043] The calculation unit therefore preferably includes a memory
for storing a current value indicative of the amount of current
passing through the coil when the predetermined amount of
applanation is achieved and also includes a conversion unit for
converting the current value into an indication of intraocular
pressure.
[0044] The magnetically responsive element is circumferentially
surrounded by a transparent peripheral portion. The transparent
peripheral portion is aligned with the transparent area and permits
light to pass through the contact device to the cornea and also
permits light to reflect from the cornea back out of the contact
device through the transparent peripheral portion.
[0045] The magnetically responsive element preferably comprises an
annular magnet having a central sight hole through which a patient
is able to see while the contact device is located on the patient's
cornea. The central sight hole is aligned with the transparent area
of the flexible membrane.
[0046] A display is preferably provided for numerically displaying
the intraocular pressure detected by the system. Alternatively, the
display can be arranged so as to give indications of whether the
intraocular pressure is within certain ranges.
[0047] Preferably, since different patients may have different
sensitivities or reactions to the same intraocular pressure, the
ranges are calibrated for each patient by an attending physician.
This way, patients who are more susceptible to consequences from
increased intraocular pressure may be alerted to seek medical
attention at a pressure less than the pressure at which other
less-susceptible patients are alerted to take the same action.
[0048] The detecting arrangement preferably comprises an optical
applanation detection system. In addition, a sighting arrangement
is preferably provided for indicating when the actuation apparatus
and the detecting arrangement are properly aligned with the contact
device. Preferably, the sighting arrangement includes the central
sight hole in the movable central piece through which a patient is
able to see while the device is located on the patient's cornea.
The central sight hole is aligned with the transparent area, and
the patient preferably achieves a generally proper alignment by
directing his vision through the central sight hole toward a target
mark in the actuation apparatus.
[0049] The system also preferably includes an optical distance
measuring mechanism for indicating whether the contact device is
spaced at a proper axial distance from the actuation apparatus and
the detecting arrangement. The optical distance measurement
mechanism is preferably used in conjunction with the sighting
arrangement and preferably provides a visual indication of what
corrective action should be taken whenever an improper distance is
detected.
[0050] The system also preferably includes an optical alignment
mechanism for indicating whether the contact device is properly
aligned with the actuation apparatus and the detecting arrangement.
The optical alignment mechanism preferably provides a visual
indication of what corrective action should be taken whenever a
misalignment is detected, and is preferably used in conjunction
with the sighting arrangement, so that the optical alignment
mechanism merely provides indications of minor alignment
corrections while the sighting arrangement provides an indication
of major alignment corrections.
[0051] In order to compensate for deviations in corneal thickness,
the system of the present invention may also include an arrangement
for multiplying the detected intraocular pressure by a coefficient
(or gain) which is equal to one for corneas of normal thickness,
less than one for unusually thick corneas, and a gain greater than
one for unusually thin corneas.
[0052] Similar compensations can be made for corneal curvature, eye
size, ocular rigidity, and the like. For levels of corneal
curvature which are higher than normal, the coefficient would be
less than one. The same coefficient would be greater than one for
levels of corneal curvature which are flatter than normal.
[0053] In the case of eye size compensation, larger than normal
eyes would require a coefficient which is less than one, while
smaller than normal eyes require a coefficient which is greater
than one.
[0054] For patients with "stiffer" than normal ocular rigidities,
the coefficient is less than one, but for patients with softer
ocular rigidities, the coefficient is greater than one.
[0055] The coefficient (or gain) may be manually selected for each
patient, or alternatively, the gain may be selected automatically
by connecting the apparatus of the present invention to a known
pachymetry apparatus when compensating for corneal thickness, a
known keratometer when compensating for corneal curvature, and/or a
known biometer when compensating for eye size.
[0056] The contact device and associated system of the present
invention may also be used to detect intraocular pressure by
indentation. When indentation techniques are used in measuring
intraocular pressure, a predetermined force is applied against the
cornea using an indentation device. Because of the force, the
indentation device travels in toward the cornea, indenting the
cornea as it travels. The distance traveled by the indentation
device into the cornea in response to the predetermined force is
known to be inversely proportional to intraocular pressure.
Accordingly, there are various known tables which for certain
standard sizes of indentation devices and standard forces,
correlate the distance traveled and intraocular pressure.
[0057] Preferably, the movable central piece of the contact device
also functions as the indentation device. In addition, the circuit
is switched to operate in an indentation mode. When switched to the
indentation mode, the current producing circuit supplies a
predetermined amount of current through the coil. The predetermined
amount of current corresponds to the amount of current needed to
produce one of the aforementioned standard forces.
[0058] In particular, the predetermined amount of current creates a
magnetic field in the actuation apparatus. This magnetic field, in
turn, causes the movable central piece to push inwardly against the
cornea via the flexible membrane. Once the predetermined amount of
current has been applied and a standard force presses against the
cornea, it is necessary to determine how far the movable central
piece moved into the cornea.
[0059] Accordingly, when measurement of intraocular pressure by
indentation is desired, the system of the present invention further
includes a distance detection arrangement for detecting a distance
traveled by the movable central piece, and a computation portion in
the calculation unit for determining intraocular pressure based on
the distance traveled by the movable central piece in applying the
predetermined amount of force.
[0060] Preferably, the computation portion is responsive to the
current producing circuitry so that, once the predetermined amount
of force is applied, an output voltage from the distance detection
arrangement is received by the computation portion. The computation
portion then, based on the displacement associated with the
particular output voltage, determines intraocular pressure.
[0061] In addition, the present invention includes alternative
embodiments, as will be described hereinafter, for performing
indentation-related measurements of the eye. Clearly, therefore,
the present invention is not limited to the aforementioned
exemplary indentation device.
[0062] The aforementioned indentation device of the present
invention may also be utilized to non-invasively measure
hydrodynamics of an eye including outflow facility. The method of
the present invention preferably comprises several steps including
the following:
[0063] According to a first step, an indentation device is placed
in contact with the cornea. Preferably, the indentation device
comprises the contact device of the present invention.
[0064] Next, at least one movable portion of the indentation device
is moved in toward the cornea using a first predetermined amount of
force to achieve indentation of the cornea. An intraocular pressure
is then determined based on a first distance traveled toward the
cornea by the movable portion of the indentation device during
application of the first predetermined amount of force. Preferably,
the intraocular pressure is determined using the aforementioned
system for determining intraocular pressure by indentation.
[0065] Next, the movable portion of the indentation device is
rapidly reciprocated in toward the cornea and away from the cornea
at a first predetermined frequency and using a second predetermined
amount of force during movement toward the cornea to thereby force
intraocular fluid out from the eye. The second predetermined amount
of force is preferably equal to or more than the first
predetermined amount of force. It is understood, however, that the
second predetermined amount of force may be less than the first
predetermined amount of force.
[0066] The movable portion is then moved in toward the cornea using
a third predetermined amount of force to again achieve indentation
of the cornea. A second intraocular pressure is then determined
based on a second distance traveled toward the cornea by the
movable portion of the indentation device during application of the
third predetermined amount of force. Since intraocular pressure
decreases as a result of forcing intraocular fluid out of the eye
during the rapid reciprocation of the movable portion, it is
generally understood that, unless the eye is so defective that no
fluid flows out therefrom, the second intraocular pressure will be
less than the first intraocular pressure. This reduction in
intraocular pressure is indicative of outflow facility.
[0067] Next, the movable portion of the indentation device is again
rapidly reciprocated in toward the cornea and away from the cornea,
but at a second predetermined frequency and using a fourth
predetermined amount of force during movement toward the cornea.
The fourth predetermined amount of force is preferably equal to or
greater than the second predetermined amount of force; however, it
is understood that the fourth predetermined amount of force may be
less than the second predetermined amount of force. Additional
intraocular fluid is thereby forced out from the eye.
[0068] The movable portion is subsequently moved in toward the
cornea using a fifth predetermined amount of force to again achieve
indentation of the cornea. Thereafter, a third intraocular pressure
is determined based on a third distance traveled toward the cornea
by the movable portion of the indentation device during application
of the fifth predetermined amount of force.
[0069] The differences are then preferably calculated between the
first, second, and third distances, which differences are
indicative of the volume of intraocular fluid which left the eye
and therefore are also indicative of the outflow facility. It is
understood that the difference between the first and last distances
may be used, and in this regard, it is not necessary to use the
differences between all three distances. In fact, the difference
between any two of the distances will suffice.
[0070] Although the relationship between the outflow facility and
the detected differences varies when the various parameters of the
method and the dimensions of the indentation device change, the
relationship for given parameters and dimensions can be easily
determined by known experimental techniques and/or using known
Friedenwald Tables.
[0071] Preferably, the method further comprises the steps of
plotting the differences between the first, second, and third
distance to a create a graph of the differences and comparing the
resulting graph of differences to that of a normal eye to determine
if any irregularities in outflow facility are present.
[0072] Additionally, the present invention relates to the
utilization of a contact device placed on the front part of the eye
in order to detect physical and chemical parameters of the body as
well as the non-invasive delivery of compounds according to these
physical and chemical parameters, with signals preferably being
transmitted continuously as electromagnetic waves, radio waves,
infrared and the like. One of the parameters to be detected
includes non-invasive blood analysis utilizing chemical changes and
chemical products that are found in the front part of the eye and
in the tear film. The non-invasive blood analysis and other
measurements are done using the system of my co-pending prior
application, characterized as an intelligent contact lens
system.
[0073] The word lens is used here to define an eyepiece which fits
inside the eye regardless of the presence of optical properties for
correction of imperfect vision. The word intelligent used here
defines a lens capable of signal-detection and/or
signal-transmission and/or signal-reception and/or signal-emission
and/or signal-processing and analysis as well as the ability to
alter physical, chemical, and or biological variables. When the
device is placed in other parts of the body other than the eye, it
is referred to as a contact device or intelligent contact device
(ICD).
[0074] An alternative embodiment of the present invention will now
be described. The apparatus and method is based on a different and
novel concept originated by the inventor in which a transensor
mounted in the contact device laying on the cornea or the surface
of the eye is capable of evaluating and measuring physical and
chemical parameters in the eye including non-invasive blood
analysis. The alternative embodiment preferably utilizes a
transensor mounted in the contact device which is preferably laying
in contact with the surface of the eye and is preferably activated
by the process of eye lid motion and/or closure of the eye lid. The
system preferably utilizes eye lid motion and/or closure of the eye
lid to activate a microminiature radio frequency sensitive
transensor mounted in the contact device. The signal can be
communicated by cable, but is preferably actively or passively
radio telemetered to an externally placed receiver. The signal can
then be processed, analyzed and stored.
[0075] This eye lid force and motion toward the surface of the eye
is also capable to create the deformation of any
transensor/electrodes mounted on the contact device. During
blinking, the eye lids are in full contact with the contact device
and the transensor's surface is in contact with the cornea/tear
film and/or inner surface of the eye lid and/or blood vessels on
the surface of the conjunctiva. It is understood that the
transensor used for non-invasive blood analysis is continuously
activated when placed on the eye and do not need closure of the
eyelid for activation. It is understood that after a certain amount
of time the contact device will adhere to tissues in the
conjunctiva optimizing flow of tissue fluid to sensors for
measurement of blood components.
[0076] The present invention includes apparatus and methods that
utilizes a contact device laying on the surface of the eye called
intelligent contact lens (ICL) which provides means for
transmitting physiologic, physical, and chemical information from
one location as for instance living tissue on the surface of the
eye to another remote location accurately and faithfully
reproducing the event at the receiver. In my prior copending
application, the whole mechanism by which the eye lid activate
transensors is described and a microminiature passive
pressure-sensitive radio frequency transducer is disclosed to
continuously measure intraocular pressure and eye fluid outflow
facility with both open and closed eyes.
[0077] The present invention provides a new method and apparatus to
detect physical and chemical parameters of the body and the eye
utilizing a contact device placed on the eye with signals being
transmitted continuously as electromagnetic waves, radio waves,
sound waves, infrared and the like. Several parameters can be
detected with the invention including a complete non-invasive
analysis of blood components, measurement of systemic and ocular
blood flow, measurement of heart rate and respiratory rate,
tracking operations, detection of ovulation, detection of radiation
and drug effects, diagnosis of ocular and systemic disorders and
the like. The invention also provides a new method and apparatus
for somnolence awareness, activation of devices by disabled
individuals, a new drug delivery system and new therapy for ocular
and neurologic disorders, and treatment of cancer in the eye or
other parts of the body, and an evaluation system for the overall
health status of an individual. The device of the present invention
quantifies non-invasively the amount of the different chemical
components in the blood using a contact device with suitable
electrodes and membranes laying on the surface of the eye and in
direct contact with the tear film or surface of the eye, with the
data being preferably transmitted utilizing radio waves, but
alternatively sound waves, light waves, wire, or telephone lines
can be used for transmission.
[0078] The system comprises a contact device in which a
microminiature radio frequency transensor, actively or passively
activated, such as endoradiosondes, are mounted in the contact
device which in turn is preferably placed on the surface of the
eye. A preferred method involves small passive radio telemetric
transducers capable of detecting chemical compounds, electrolytes,
glucose, cholesterol, and the like on the surface of the eye.
Besides using passive radio transmission or communication by cable,
active radio transmission with active transmitters contained a
microminiature battery mounted in the contact device can also be
used.
[0079] Several means and transensors can be mounted in the contact
device and used to acquire the signal. Active radio transmitters
using transensors which are energized by batteries or using cells
that can be recharged in the eye by an external oscillator, and
active transmitters which can be powered from a biologic source can
also be used and mounted in the contact device. The preferred
method to acquire the signal involves passive radio frequency
transensors, which contain no power source. They act from energy
supplied to it from an external source. The transensor transmits
signals to remote locations using different frequencies indicative
of the levels of chemical and physical parameters. These
intraocular recordings can then be transmitted to remote extra
ocular radio frequency monitor stations with the signal sent to a
receiver for amplification and analysis. Ultrasonic micro-circuits
can also be mounted in the contact device and modulated by sensors
which are capable of detecting chemical and physical changes in the
eye. The signal may be transmitted using modulated sound signals
particularly under water because sound is less attenuated by water
than are radio waves. The sonic resonators can be made responsive
to changes in temperature and voltage which correlate to the
presence and level of molecules such as glucose and ions in the
tear film.
[0080] Ocular and systemic disorders may cause a change in the pH,
osmolarity, and temperature of the tear film or surface of the eye
as well as change in the tear film concentration of substances such
as acid-lactic, glucose, lipids, hormones, gases, enzymes,
inflammatory mediators, plasmin, alburmin, lactoferrin, creatinin,
proteins and so on. Besides pressure, outflow facility, and other
physical characteristics of the eye, the apparatus of the invention
is also capable of measuring the above physiologic parameters in
the eye and tear film using transensor/electrodes mounted in the
contact device. These changes in pressure, temperature, pH, oxygen
level, osmolality, concentration of chemicals, and so on can be
monitored with the eyes opened or closed or during blinking. In
some instance such as with the evaluation of pH, metabolites, and
oxygen concentration, the device does not need necessarily eye lid
motion because just the contact with the transensor mounted in the
contact device is enough to activate the transensor/electrodes.
[0081] The presence of various chemical elements, gases,
electrolytes, and pH of the tear film and the surface of the eye
can be determined by the use of suitable electrodes and a suitable
permeable membrane. These electrodes, preferably microelectrodes,
can be sensitized by several reacting chemicals which are in the
tear film or the surface of the eye, in the surface of the cornea
or preferably the vascularized areas in the surface of the eye. The
different chemicals and substances diffuse through suitable
permeable membranes sensitizing suitable sensors. Electrodes and
sensors to measure the above compounds are available from several
manufacturers.
[0082] The level of oxygen can be measured in the eye with the
contact device, and in this case just the placement of the contact
device would be enough to activate the system and eye lid motion
and/or closure of the eye lid may not be necessary for its
operation. Reversible mechanical expansion methods, photometric, or
electrochemical methods and electrodes can be mounted in the device
and used to detect acidity and gases concentration. Oxygen gas can
also be evaluated according to its magnetic properties or be
analyzed by micro-polarographic sensors mounted in the contact
device. Moreover, the same sensor can measure different gases by
changing the cathode potential. Carbon dioxide, carbon monoxide,
and other gases can also be detected in a similar fashion.
[0083] Microminiature glass electrodes mounted in the contact
device can be used to detect divalent cations such as calcium, as
well as sodium and potassium ion and pH. Chloride-ion detector can
be used to detect the salt concentration in the tear film and the
surface of the eye. The signal can be radio transmitted to a
receiver and then to a screen for continuous recording and
monitoring. This allows for the continuous non-invasive measurement
of electrolytes, chemicals and pH in the body and can be very
useful in the intensive care unit setting.
[0084] A similar transensor can also be placed not in the eye, but
in contact with other mucosas and secretions in the body, such as
the oral mucosa, and the concentration of chemicals measured in the
saliva or even sweat or any other body secretion with signals being
transmitted to a remote location via ultrasonic or radio waves and
the like. However, due to the high concentration of enzymes in the
saliva and in other secretion, the electrodes and electronics could
be detrimentally affected which would impact accuracy. Furthermore,
there is a weak correlation between concentration of chemicals in
body secretions and blood.
[0085] The tear fluid proves to be the most reliable location and
indicator of the concentration of chemicals, both organic and
inorganic, but other areas of the eye can be utilized to measure
the concentration of chemicals. The tear fluid and surface of the
eye are the preferred location for these measurements because the
tear film and aqueous humor (which can be transmitted through the
intact cornea) can be considered an ultrafiltrate of the
plasma.
[0086] The apparatus and method of the present invention allows the
least traumatic way of measuring chemicals in the body without the
need of needle stick and the manipulation of blood. For instance,
this may be particularly important as compared to drawing blood
from infants because the results provided by the drawn blood sample
may not be accurate. There is a dramatic change in oxygen and
carbon dioxide levels because of crying, breath holding and even
apnea spells that occur during the process of restraining the baby
and drawing blood. Naturally, the ability to painlessly measure
blood components without puncturing the vessel is beneficial also
to any adult who needs a blood work-up, patients with diabetes who
need to check their glucose level on a daily basis, and health care
workers who would be less exposed to severe diseases such as AIDS
and hepatitis when manipulating blood. Patients in intensive care
units would benefit by having a continuous painless monitoring of
electrolytes, gases, and so on by non-invasive means using the
intelligent contact lens system, moreover, there is no time wasted
transporting the blood sample to the laboratory, the data is
available immediately and continuously.
[0087] The different amounts of eye fluid encountered in the eye
can be easily quantified and the concentration of substances
calibrated according to the amount of fluid in the eye. The
relationship between the concentration of chemical substances and
molecules in the blood and the amount of said chemical substances
in the tear fluid can be described mathematically and programmed in
a computer since the tear film can be considered an ultrafiltrate
of the plasma and diffusion of chemicals from capillaries on the
surface of the eye have a direct correspondence to the
concentration in the blood stream.
[0088] Furthermore, when the eyes are closed there is an
equilibrium between the aqueous humor and the tear fluid allowing
measurement of glucose in a steady state and since the device can
send signals through the intervening eyelid, the glucose can be
continuously monitored in this steady state condition. Optical
sensors mounted in the contact device can evaluate oxygen and other
gases in tissues and can be used to detect the concentration of
compounds in the surface of the eye and thus not necessarily have
to use the tear film to measure the concentration of said
substances. In all instances, the signals can be preferably radio
transmitted to a monitoring station. Optical, acoustic,
electromagnetic, micro-electromechanical systems and the like can
be mounted in the contact device and allow the measurement of blood
components in the tear film, surface of the eye, conjunctival
vessels, aqueous humor, vitreous, and other intraocular and
extraocular structures.
[0089] Any substance present in the blood can be analyzed in this
way since as mentioned the fluid measured is a filtrate of the
blood. Rapidly responding microelectrodes with very thin membranes
can be used to measure these substances providing a continuous
evaluation. For example, inhaled anesthetics become blood gases and
during an experiment the concentration of anesthetics present in
the blood could be evaluated in the eye fluid. Anesthetics such as
nitrous oxide and halothane can be reduced electrochemically at
noble metal electrodes and the electrodes can be mounted in the
contact device. Oxygen sensors can also be used to measure the
oxygen of the sample tear film. Measurement of oxygen and
anesthetics in the blood has been performed and correlated well
with the amount of the substances in the eye fluid with levels in
the tear fluid within 85-95% of blood levels. As can be seen, any
substances not only the ones naturally present, but also
artificially inserted in the blood can be potentially measured in
the eye fluid. A correction factor may be used to account for the
differences between eye fluid and blood. In addition, the
non-invasive measurement and detection by the ICL of exogenous
substances is a useful tool to law enforcement agents for rapidly
testing and detecting drugs and alcohol.
[0090] The evaluation of systemic and ocular hemodynamics can be
performed with suitable sensors mounted in the contact device. The
measurements of blood pulsations in the eye can be done through
electrical means by evaluating changes in impedance. Blood flow
rate can be evaluated by several techniques including but not
limited to ultrasonic and electromagnetic meters and the signals
then radio transmitted to an externally placed device. For the
measurement of blood flow, the contact device is preferably placed
in contact with the conjunctiva, either bulbar or palpebral, due to
the fact that the cornea is normally an avascular structure.
Changing in the viscosity of blood can also be evaluated from a
change in damping on a vibrating quartz micro-crystal mounted in
the contact device.
[0091] The apparatus of the invention may also measure dimension
such as the thickness of the retina, the amount of cupping in the
optic nerve head, and so on by having a microminiature ultrasound
device mounted in the contact device and placed on the surface of
the eye. Ultra sonic timer/exciter integrated circuits used in both
continuous wave and pulsed bidirectional Doppler blood flowmeters
are in the order few millimeters in length and can be mounted in
the apparatus of the invention.
[0092] For the measurement of hemodynamics, the contact device
should preferably be placed in contact with the conjunctiva and on
top of a blood vessel. Doppler blood microflowmeters are available
and continuous wave (CW) and pulsed Doppler instruments can be
mounted in the contact device to evaluate blood flow and the signal
radio transmitted to an external receiver. The Doppler flowmeters
may also use ultrasonic transducers and these systems can be
fabricated in miniature electronic packages and mounted in the
contact device with signals transmitted to a remote receiver.
[0093] Illumination of vessels, through the pupil, in the back of
the eye can be used to evaluate blood flow velocity and volume or
amount of cupping (recess) in the optic nerve head. For this use
the contact device has one or more light sources located near the
center and positioned in a way to reach the vessels that exit the
optic nerve head, which are the vessels of largest diameter on the
surface of the retina. A precise alignment of beam is possible
because the optic nerve head is situated at a constant angle from
the visual axis. Sensors can be also positioned on the opposite
side of the illumination source and the reflected beam reaching the
sensor. Multioptical filters can be housed in the contact device
with the light signal converted to voltage according to the angle
of incidence of reflected light. Moreover, the intracranial
pressure could be indirectly estimated by the evaluation of changes
and swelling in the retina and optic nerve head that occurs in
these structures due to the increased intracerebral pressure.
[0094] Fiber optics from an external light source or light sources
built in the contact device can emit a beam of plane-polarized
light from one side at three o'clock position with the beam
entering through the cornea and passing through the aqueous humor
and exiting at the nine o'clock position to reach a photodetector.
Since glucose can rotate the plane of polarization, the amount of
optical rotation would be compared to a second reference beam
projected in the same manner but with a wavelength that it is
insensitive to glucose with the difference being indicative of the
amount of glucose present in the aqueous humor which can be
correlated to plasma glucose by using a correction factor.
[0095] A dielectric constant of several thousand can be seen in
blood and a microminiature detector placed in the contact device
can identify the presence of blood in the surface of the cornea.
Moreover, blood causes the decomposition of hydrogen peroxide which
promotes an exothermic reaction that can be sensed with a
temperature-sensitive transensor. Small lamps energized by an
external radio-frequency field can be mounted in the contact device
and photometric blood detectors can be used to evaluate the
presence of blood and early detection of neovascularization in
different parts of the eye and the body.
[0096] A microminiature microphone can be mounted in the contact
device and sounds from the heart, respiration, flow, vocal and the
environment can be sensed and transmitted to a receiver. In cases
of abnormal heart rhythm, the receiver would be carried by the
individual and will have means to alert the individual through an
alarm circuit either by light or sound signals of the abnormality
present. Chances in heart beat can be detected and the patient
alerted to take appropriate action.
[0097] The contact device can also have elements which produce and
radiate recognizable signals and this procedure could be used to
locate and track individuals, particularly in military operations.
A permanent magnet can also be mounted in the contact device and
used for tracking as described above.
[0098] Life threatening injuries causing change in heart rhythm and
respiration can be detected since the cornea pulsates according to
heartbeat. Motion sensitive microminiature radio frequency
transensors can be mounted in the contact device and signals
indicative of injuries can be radio transmitted to a remote station
particularly for monitoring during combat in military
operations.
[0099] In rocket or military operations or in variable g
situations, the parameters above can be measured and monitored by
utilizing materials in the transensor such as light aluminum which
are less sensitive to gravitational and magnetic fields. Infrared
emitters can be mounted in the contact device and used to activate
distinct photodetectors by ocular commands such as in military
operations where fast action is needed without utilizing hand
movement.
[0100] Spinal cord injuries have lead thousands of individuals to
complete confinement in a wheel chair. The most unfortunate
situation occurs with quadriplegic individuals who virtually only
have useful movement of their mouth and eyes. The apparatus of the
invention allows these individuals to use their remaining movement
ability to become more independent and capable of indirect
manipulation of a variety of hardware. In this embodiment, the ICL
uses blinking or closure of the eyes to activate remotely placed
receptor photodiodes through the activation of an LED drive coupled
with a pressure sensor.
[0101] The quadriplegic patient focuses on a receptor photo diode
and closes their eyes for 5 seconds, for example. The pressure
exerted by the eyelid is sensed by the pressure sensor which is
coupled with a timing chip. If the ICL is calibrated for 5 sec,
after this amount of time elapses with eyes closed, the LED drive
activates the LED which emits infrared light though the intervening
eyelid tissue reaching suitable receptor photodiodes or suitable
optical receivers connected to a power on or off circuit. This
allows quadriplegics to turn on, turn off, or manipulate a variety
of devices using eye motion. It is understood that an alternative
embodiment can use more complex integrated circuits connected by
fine wires to the ICL placed on the eye in order to perform more
advanced functions such as using LED's of different
wavelengths.
[0102] Another embodiment according to the present invention
includes a somnolence alert device using eye motion to detect
premonitory signs of somnolence related to a physiologic condition
called Bell phenomena in which the eye ball moves up and slightly
outwards when the eyes are closed. Whenever an individual starts to
fall asleep, the eye lid comes down and the eyes will move up.
[0103] A motion or pressure sensor mounted in the superior edge of
the ICL will cause, with the Bell phenomena, a movement of the
contact device upwards. This movement of the eye would position the
pressure sensitive sensor mounted in the contact device against the
superior cul-de-sac and the pressure created will activate the
sensor which modulates a radio transmitter.
[0104] The increase in pressure can be timed and if the pressure
remains increased for a certain length of time indicating closed
eyes, an alarm circuit is activated. The signal would then be
transmitted to a receiver coupled with an alarm circuit and speaker
creating a sound signal to alert the individual at the initial
indication of falling asleep. Alternatively, the pressure sensor
can be positioned on the inferior edge of the ICL and the lack of
pressure in the inferiorly placed sensor would activate the circuit
as described above.
[0105] It is also understood that other means to activate a circuit
in the contact device such as closing an electric circuit due to
motion or pressure shift in the contact device which remotely
activate an alarm can be used as a somnolence awareness device. It
is also understood that any contact device with sensing elements
capable of sensing Bell phenomena can be used as a somnolence
awareness device. This system, device and method are an important
tool in diminishing car accidents and machinery accidents by
individuals who fall sleep while operating machinery and
vehicles.
[0106] If signs of injury in the eye are detected, such as
increased intraocular pressure (IOP), the system can be used to
release medication which is placed in the cul-de-sac in the lower
eye lid as a reservoir or preferably the contact lens device acts
as a reservoir for medications. A permeable membrane, small
fenestrations or a valve like system with micro-gates, or
micro-electronic systems housed in the contact device structure
could be electrically, magnetically, electronically, or optically
activated and the medication stored in the contact device released.
The intelligent lenses can thus be used as non-invasive drug
delivery systems. Chemical composition of the tear film, such as
the level of electrolytes or glucose, so that can be sensed and
signals radio transmitted to drug delivery pumps carried by the
patient so that medications can be automatically delivered before
symptoms occur.
[0107] A part of the contact transducer can also be released, for
instance if the amount of enzymes increases. The release of part of
the contact device could be a reservoir of lubricant fluid which
will automatically be released covering the eye and protecting it
against the insulting element. Any drugs could be automatically
released in a similar fashion or through transmission of signal to
the device.
[0108] An alternative embodiment includes the contact device which
has a compartment filled with chemical substances or drugs
connected to a thread which keeps the compartments sealed. Changes
in chemicals in the tear fluid or the surface of the eye promote
voltage increases which turns on a heater in the circuit which
melts the thread allowing discharge of the drug housed in the
compartment such as insulin if there is an increase in the levels
of glucose detected by the glucose sensor.
[0109] To measure temperature, the same method and apparatus
applies, but in this case the transmitter is comprised of a
temperature-sensitive element. A microminiature
temperature-sensitive radio frequency transensor, such as
thermistor sensor, is mounted in the contact device which in turn
is placed on the eye with signals preferably radio transmitted to a
remote station. Changes in temperature and body heat correlate with
ovulation and the thermistor can be mounted in the contact device
with signals telemetered to a remote station indicating optimum
time for conception.
[0110] The detection and transmission to remote stations of changes
in temperature can be used on animals for breeding purposes. The
intelligent contact lens can be placed on the eye of said animals
and continuous monitoring of ovulation achieved. When this
embodiment is used, the contact device with the thermistor is
positioned so that it lodges against the palpebral conjunctiva to
measure the temperature at the palpebral conjunctiva. Monitoring
the conjunctiva offers the advantages of an accessible tissue free
of keratin, a capillary level close to the surface, and a tissue
layer vascularized by the same arterial circulation as the brain.
When the lids are closed, the thermal environment of the cornea is
exclusively internal with passive prevention of heat loss during a
blink and a more active heat transfer during the actual blink.
[0111] In carotid artery disease due to impaired blood supply to
the eye, the eye has a lower temperature than that of the fellow
eye which indicates a decreased blood supply. If a temperature
difference greater than normal exists between the right and left
eye, then there is an asymmetry in blood supply. Thus, this
embodiment can provide information related to carotid and central
nervous system vascular disorders. Furthermore, this embodiment can
provide information concerning intraocular tumors such as melanoma.
The area over a malignant melanoma has an increase in temperature
and the eye harboring the malignant melanoma would have a higher
temperature than that of the fellow eye. In this embodiment the
thermistor is combined with a radio transmitter emitting an audio
signal frequency proportional to the temperature.
[0112] Radiation sensitive endoradiosondes are known and can be
used in the contact device to measure the amount of radiation and
the presence of radioactive corpuscules in the tear film or in
front of the eye which correlates to its presence in the body. The
amount of hydration and humidity of the eye can be sensed with an
electrical discharge and variable resistance moisture sensor
mounted in the contact device. Motion and deceleration can be
detected by a mounted accelerometer in the contact device. Voltages
accompanying the function of the eye, brain, and muscles can be
detected by suitable electrodes mounted in the device and can be
used to modulate the frequency of the transmitter. In the case of
transmission of muscle potentials, the contact device is placed not
on the cornea, but next to the extraocular muscle to be evaluated
and the signals remotely transmitted. A fixed frequency transmitter
can be mounted in the contact device and used as a tracking device
which utilizes a satellite tracking system by noting the frequency
received from the fixed frequency transmitter to a passing
satellite
[0113] A surface electrode mounted in the contact device may be
activated by optical or electromagnetic means in order to increase
the temperature of the eye. This increase in temperature causes a
dilation of the capillary bed and can be used in situations in
which there is hypoxia (decreased oxygenation) in the eye. The
concept and apparatus called heat stimulation transmission device
(HSTD) is based upon my experiments and in the fact that the eye
has one of largest blood supply per gram of tissue in the body and
has the unique ability to be overpefused when there is an increase
in temperature. The blood flow to the eye can thus be increased
with a consequent increase in the amount of oxygen. The electrode
can be placed in any part of the eye, inside or outside, but is
preferably placed on the most posterior part of the eye. The radio
frequency activated heating elements can be externally placed or
surgically implanted according to the area in need of increase in
the amount of oxygen in the eye. It is understood that the same
heating elements could be placed or implanted in other parts of the
body. Naturally, means that promote an increase in temperature of
the eye without using electrodes can be used as long as the
increase in temperature is sufficient to increase blood flow
without promoting any injury.
[0114] The amount of increase varies from individual to individual
and according to the status of the vascular bed of the eye. The
increase in temperature of blood in the eye raises its oxygen level
about 6% per each one degree Celsius of increase in temperature
allowing precise quantification of the increase in oxygen by using
a thermistor which simultaneously indicates temperature, or
alternatively an oxygen sensor can be used in association with the
heating element and actual amount of increase in oxygen
detected.
[0115] This increase in blood flow can be timed to occur at
predetermined hours in the case of chronic hypoxia such as in
diabetes, retinal degenerations, and even glaucoma. These devices
can be externally placed or surgically implanted in the eye or
other parts of the body according to the application needed.
[0116] Another embodiment is called over heating transmission
device (OHTD) and relates to a new method and apparatus for the
treatment of tumors in the eye or any other part of the body by
using surgically implanted or externally placed surface electrodes
next to a tumor with the electrodes being activated by optical or
electromagnetic means in order to increase the temperature of the
cancerous tissue until excessive localized heat destroys the tumor
cells. These electrodes can be packaged with a thermistor and the
increase in temperature sensed by the thermistor with the signal
transmitted to a remote station in order to evaluate the degree of
temperature increase. The OHTD includes means to detect normal from
abnormal tissue by labeling with the increase in temperature
extending only to the abnormal tissue. Furthermore, sensors
sensitive to necrotic products can be used to quantity the amount
of tissue degradation.
[0117] Another embodiment concerning therapy of eye and systemic
disorders include a neuro-stimulation transmission device (NSTD)
which relates to a system in which radio activated
micro-photodiodes or/and micro-electric circuits and electrodes are
surgically implanted or externally placed on the eye or other parts
of the body such as the brain and used to electrically stimulate
non-functioning neural or degenerated neural tissue in order to
treat patients with retinal degeneration, glaucoma, stroke, and the
like. Multiple electrodes can be used in the contact device, placed
on the eye or in the brain for electrical stimulation of
surrounding tissues with consequent regeneration of signal
transmission by axonal and neural cells and regeneration of action
potential with voltage signals being transmitted to a remote
station.
[0118] Radio and sonic transensors to measure pressure, electrical
changes, dimensions, acceleration, flow, temperature, bioelectric
activity and other important physiologic parameters and power
switches to externally control the system have been developed and
are suitable systems to be used in the apparatus of the invention.
The sensors can be automatically turned on and off with power
switches externally controlling the intelligent contact lens
system. The use of integrated circuits and advances occurring in
transducer, power source, and signal processing technology allow
for extreme miniaturization of the components which permits several
sensors to be mounted in one contact device. For instance, typical
resolutions of integrated circuits are in the order of a few
microns and very high density circuit realization can be achieved.
Radio frequency and ultrasonic microcircuits are available and can
be used and mounted in the contact device. A number of different
ultrasonic and pressure transducers are also available and can be
used and mounted in the contact device.
[0119] Technologic advances will occur which allow full and novel
applications of the apparatus of the invention such as measuring
enzymatic reactions and DNA changes that occur in the tear fluid or
surface of the eye, thus allowing an early diagnosis of disorders
such as cancer and heart diseases. HIV virus is present in tears
and AIDS could be detected with the contact device by sensors
coated with antibodies against the virus which would create a
photochemical reaction with appearance of calorimetric reaction and
potential shift in the contact device with subsequent change in
voltage or temperature that can be transmitted to a monitoring
station.
[0120] A variety of other pathogens could be identified in a
similar fashion. These signals can be radio transmitted to a remote
station for further signal processing and analysis. In the case of
the appearance of fluorescent light, the outcome could be observed
on a patient's eye simply by illuminating the eye with light going
through a cobalt filter and in this embodiment the intelligent
contact lens does not need to necessarily have signals transmitted
to a station.
[0121] The system further comprises a contact device in which a
microminiature gas-sensitive, such as oxygen-sensitive, radio
frequency transensor is mounted in the contact device which in turn
is placed on the cornea and/or surface of the eye. The system also
comprises a contact device in which a microminiature blood
velocity-sensitive radio frequency transensor is mounted in the
contact device which in turn is placed on the conjunctiva and is
preferably activated by eye lid motion and/or closure of the eye
lid. The system also comprises a contact device in which a radio
frequency transensor capable of measuring the negative resistance
of nerve fibers is mounted in the contact device which in turn is
preferably placed on the cornea and/or surface of the eye. By
measuring the electrical resistance, the effects of microorganisms,
drugs, poisons and anesthetics can be evaluated. The system also
comprises a contact device in which a microminiature
radiation-sensitive radio frequency transensor is mounted in the
contact device which in turn is preferably placed on the
cornea.
[0122] The contact device preferably includes a rigid or flexible
annular member in which a transensor is mounted in the device. The
transensor is positioned in a way to allow passage of light trough
the visual axis. The annular member preferably includes an inner
concave surface shaped to match an outer surface of the eye and
having one or more holes defined therein in which transensors are
mounted. It is understood that the contact device conforms in
general shape to the surface of the eye with its dimensions and
size chosen to achieve optimal comfort level and tolerance. It is
also understood that the curvature and shape of the contact device
is chosen to intimately and accurately fit the contact device to
the surface of the eye for optimization of sensor function. The
surface of the contact device can be porous or microporous as well
as with mircro-protuberances on the surface. It is also understood
that fenestrations can be made in the contact device in order to
allow better oxygenation of the cornea when the device is worn for
a long period of time. It is also understood that the shape of the
contact device may include a ring-like or band-like shape without
any material covering the cornea. It is also understood that the
contact device may have a base down prism or truncated edge for
better centration. It is also understood that the contact device
preferably has a myoflange or a minus carrier when a conventional
contact lens configuration is used. It is also understood that an
eliptical, half moon shape or the like can be used for placement
under the eyelid. It is understood that the contact device can be
made with soft of hard material according to the application
needed. It is also understood that an oversized corneal scleral
lens covering the whole anterior surface of the eye can be used as
well as hourglass shaped lenses and the like. It is understood also
that the external surface of the contact device can be made with
polymers which increases adherence to tissues or coating which
increases friction and adherence to tissues in order to optimize
fluid passage to sensors when measuring chemical components. It is
understood that the different embodiments which are used under the
eyelids are shaped to fit beneath the upper and/or eyelids as well
as to fit the upper or lower cul-de-sac.
[0123] The transensor may consist of a passive or active radio
frequency emitter, or a miniature sonic resonator, and the like
which can be coupled with miniature microprocessor mounted in the
contact device. The transensors mounted in the contact device can
be remotely driven by ultrasonic waves or alternatively remotely
powered by electromagnetic waves or by incident light. They can
also be powered by microminiature low voltage batteries which are
inserted into the contact device.
[0124] As mentioned, preferably the data is transmitted utilizing
radio waves, sound waves, light waves, by wire, or by telephone
lines. The described techniques can be easily extrapolated to other
transmission systems. The transmitter mounted in the contact device
can use the transmission links to interconnect to remote monitoring
sites. The changes in voltage or voltage level are proportional to
the values of the biological variables and this amplified
physiologic data signal from the transducers may be frequency
modulated and then transmitted to a remote external reception unit
which demodulates and reconstitutes the transmitted frequency
modulated data signal preferably followed by a low pass filter with
the regeneration of an analog data signal with subsequent tracing
on a strip-chart recorder.
[0125] The apparatus of the invention can also utilize a
retransmiter in order to minimize electronic components and size of
the circuit housed in the contact device. The signal from a weak
transmitter can be retransmitted to a greater distance by an
external booster transmitter carried by the subject or placed
nearby. It is understood that a variety of noise destruction
methods can be used in the apparatus of the invention.
[0126] Since the apparatus of the invention utilizes externally
placed elements on the surface of the eye that can be easily
retrieved, there is no tissue damage due to long term implantation
and if drift occurs it is possible to recalibrate the device. There
are a variety of formats that can be used in the apparatus of the
invention in which biologic data can be encoded and transmitted.
The type of format for a given application is done according to
power requirement, circuit complexity, dimensions and the type of
biologic data to be transmitted. The general layout of the
apparatus preferably includes an information source with a variety
of biological variables, a transducer, a multiplexer, a
transmitter, a transmission path and a transmission medium through
which the data is transmitted preferably as a coded and modulated
signal.
[0127] The apparatus of the invention preferably includes a
receiver which receives the coded and modulated signal, an
amplifier and low pass filter, a demultiplexer, a data processing
device, a display and recording equipment, and preferably an
information receiver, a CPU, a modem, and telephone connection. A
microprocessor unit containing an autodialing telephone modem which
automatically transmits the data over the public telephone network
to a hospital based computer system can be used. It is understood
that the system may accept digitally coded information or analog
data.
[0128] When a radio link is used, the contact device houses a radio
frequency transmitter which sends the biosignals to a receiver
located nearby with the signals being processed and digitized for
storage and analysis by microcomputer systems. When the apparatus
of the invention transmits data using a radio link, a frequency
carrier can be modulated by a subcarrier in a variety of ways:
amplitude modulation (AM), frequency modulation (FM), and code
modulation (CM). The subcarriers can be modulated in a variety of
ways which includes AM, FM, pulse amplitude modulation (PAM), pulse
duration modulation (PDM), pulse position modulation (PPM), pulse
code moduation (PCM), delta modulation (DM), and the like.
[0129] It is understood that the ICL structure and the
transducer/transmitter housing are made of material preferably
transparent to radio waves and the electronic components coated
with materials impermeable to fluids and salts and the whole unit
encased in a biocompatable material. The electronics, sensors, and
battery (whenever an active system is used), are housed in the
contact device and are hermetically sealed against fluid
penetration. It is understood that sensors and suitable electrodes
such as for sensing chemicals, pH and the like, will be in direct
contact with the tear fluid or the surface of the eye. It is also
understood that said sensors, electrodes and the like may be
covered with suitable permeable membranes according to the
application needed. The circuitry and electronics may be encased in
wax such as beeswax or paraffin which is not permeable to body
fluid. It is understood that other materials can be used as a
moisture barrier. It is also understood that various methods and
materials can be used as long as there is minimal frequency
attenuation, insulation, and biocompatibility. The components are
further encased by biocompatible materials as the ones used in
conventional contact lenses such as Hydrogel, silicone, flexible
acrylic, sylastic, or the like.
[0130] The transmitter, sensors, and other components can be
mounted and/or attached to the contact device using any known
attachment techniques, such as gluing, heat-bonding, and the like.
The intelligent contact lens can use a modular construction in its
assembly as to allow tailoring the number of components by simply
adding previously constructed systems to the contact device.
[0131] It is understood that the transmission of data can be
accomplished using preferably radio link but other means can also
be used. The choice of which energy form to be used by the ICL
depends on the transmission medium and distance, channel
requirement, size of transmitter equipment and the like. It is
understood that the transmission of data from the contact device by
wire can be used but has the disadvantage of incomplete freedom
from attached wires. However, the connection of sensors by wires to
externally placed electronics, amplifiers, and the like allows
housing of larger sensors in the contact device when the
application requires as well as the reduction of mechanical and
electrical connections in the contact device. The transmission of
data by wire can be an important alternative when there is
congested space due to sensors and electronics in the contact
device. It is understood that the transmission of data in water
from the contact device can be preferably accomplished using sound
energy with a receiver preferably using a hydrophone crystal
followed by conventional audio frequency FM decoding.
[0132] It is also understood that the transmission of data from the
contact device can be accomplished by light energy as an
alternative to radio frequency radiation. Optical transmission of
signals using all sorts of light such as visible, infrared, and
ultraviolet can be used as a carrier for the transmission of data
preferably using infrared light as the carrier for the transmission
system. An LED can be mounted in the contact device and transmit
modulated signals to remotely placed receivers with the light
emitted from the LED being modulated by the signal. When using this
embodiment, the contact device in the receiver unit has the
following components: a built in infrared light emitter (950 nm),
an infrared detector, decoder, display, and CPU. Prior to
transmission, the physiologic variables found on the eye or tear
fluid are multiplexed and encoded by pulse interval modulation,
pulse frequency modulation, or the like. The infrared transmitter
then emits short duration pulses which are sensed by a remotely
placed photodiode in the infrared detector which is subsequently
decoded, processed, and recorded. The light transmitted from the
LED is received at the optical receiver and transformed into
electrical signals with subsequent regeneration of the biosignals.
Infrared light is reflected quite well including surfaces that do
not reflect visible light and can be used in the transmission of
physiological variables and position/motion measurement. This
embodiment is particularly useful when there is limitations in
bandwidth as in radio transmission. Furthermore, this embodiment
may be quite useful with closed eyes since the light can be
transmitted through the skin of the eyelid.
[0133] It is also understood that the transmission of data from the
contact device can be accomplished by the use of sound and
ultrasound being the preferred way of transmission underwater since
sound is less strongly attenuated by water than radio waves. The
information is transmitted using modulated sound signals with the
sound waves being transmitted to a remote receiver. There is a
relatively high absorption of ultrasonic energy by living tissues,
but since the eye even when closed has a rather thin intervening
tissue the frequency of the ultrasonic energy is not restricted.
However, soundwaves are not the preferred embodiment since they can
take different paths from their source to a receiver with multiple
reflections that can alter the final signal. Furthermore, it is
difficult to transmit rapidly changing biological variables because
of the relatively low velocity of sound as compared to
electromagnetic radiation. It is possible though to easily mount an
ultrasonic endoradiosonde in the contact device such as for
transmitting pH values or temperature. An ultrasonic booster
transmitter located nearby or carried by the subject can be used to
transmit the signal at a higher power level. An acoustic tag with a
magnetic compass sensor can be used with the information
acoustically telemetered to a sector scanning sonar.
[0134] A preferred embodiment of the invention consists of
electrodes, FM transmitter, and a power supply mounted in the
contact device. Stainless steel micro cables are used to connect
the electronics to the transducers to the battery power supply. A
variety of amplifiers and FM transmitters including Colpitts
oscillator, crystal oscillators and other oscillators preferably
utilizing a custom integrated circuit approach with ultra density
circuitry can be used in the apparatus of the invention.
[0135] Several variables can be simultaneously transmitted using
different frequencies using several transmitters housed in the
contact device. Alternatively, a single transmitter (3 channel
transmitter) can transmit combined voltages to a receiver, with the
signal being subsequently decoded, separated into three parts,
filtered and regenerated as the three original voltages (different
variables such as glucose level, pressure and temperature). A
multiple channel system incorporating all signal processing on a
single integrated circuit minimizes interconnections and can be
preferably mounted in the apparatus of the invention when multiple
simultaneous signal transmission is needed such as transmitting the
level of glucose, temperature, bioelectrical, and pressure. A
single-chip processor can be combined with a logic chip to also
form a multichannel system for the apparatus of the invention
allowing measurement of several parameters as well as activation of
transducers.
[0136] It is understood that a variety of passive, active, and
inductive power sources can be used in the apparatus of the
invention. The power supply may consist of micro batteries,
inductive power link, energy from biological sources, nuclear
cells, micro power units, fuel cells which use glucose and oxygen
as energy sources, and the like. The type of power source is chosen
according to the biological or biophysical event to be
transmitted.
[0137] A variety of signal receivers can be used such a frame
aerial connected to a conventional FM receiver from which the
signal is amplified decoded and processed. Custom integrated
circuits will provide the signal processing needed to evaluate the
parameters transmitted such as temperature, pressure flow
dimensions, bioelectrical activity, concentration of chemical
species and the like. The micro transducers, signal processing
electronics, transmitters and power source can be built in the
contact device.
[0138] Power for the system may be supplied from a power cell
activated by a micropower control switch contained in the contact
device or can be remotely activated by radio frequency means,
magnetic means and the like. Inductive radio frequency powered
telemetry in which the same coil system used to transfer energy is
used for the transmission of data signal can be used in the
apparatus of the invention. The size of the system relates
primarily to the size of the batteries and the transmitter. The
size of conventional telemetry systems are proportional to the size
of the batteries because most of the volume is occupied by
batteries. The size of the transmitter is related to the operating
frequency with low frequencies requiring larger components than
higher frequency circuits. Radiation at high frequencies are more
attenuated than lower frequencies by body tissues. Thus a variety
of systems implanted inside the body requires lower frequency
devices and consequently larger size components in order for the
signal to be less atenuated. Since the apparatus of the invention
is placed on the surface of the eye there is little to no
attenuation of signals and thus higher frequency small devices can
be used. Furthermore, very small batteries can be used since the
contact device can be easily retrieved and easily replaced. The
large volume occupied by batteries and power sources in
conventional radio telemetry implantable devices can be extremely
reduced since the apparatus of the invention is placed externally
on the eye and is of easy access and retrieval, and thus a very
small battery can be utilized and replaced whenever needed.
[0139] A variety of system assemblies can be used but the densest
system assembly is preferred such as a hybrid assembly of custom
integrated circuits which permits realization of the signal
processing needed for the applications. The typical resolution of
such circuits are in the order of a few microns and can be easily
mounted in the contact device. A variety of parameters can be
measured with one integrated circuit which translates the signals
preferably into a transmission bandwidth. Furthermore, a variety of
additional electronics and a complementary metal oxide
semiconductor (CMOS) chip can be mounted in the apparatus of the
invention for further signal processing and transmission.
[0140] The micropower integrated circuits can be utilized with a
variety of transmitter modalities mounted in the intelligent
contact lens including radio links, ultrasonic link and the like. A
variety of other integrated circuits can be mounted in the contact
device such as signal processors for pressure and temperature,
power switches for external control of implanted electronics and
the like. Pressure transducers such as a capacitive pressure
transducer with integral electronics for signal processing can be
incorporated in the same silicon structure and can be mounted in
the contact device. Evolving semiconductor technology and more
sophisticated encoding methods as well as microminiature integrated
circuits amplifiers and receivers are expected to occur and can be
housed in the contact device. It is understood that a variety of
transmitters, receivers, and antennas for transmitting and
receiving signals in telemetry can be used in the apparatus of the
invention, and housed in the contact device and/or placed remotely
for receiving, processing, and analyzing the signal.
[0141] The fluid present on the front surface of the eye covering
the conjunctiva and cornea is referred as the tear film or tear
fluid. Close to 100% of the tear film is produced by the lacrimal
gland and secreted at a rate of 2 .mu.l/min. The volume of the tear
fluid is approximately 10 .mu.l. The layer of tear fluid covering
the cornea is about 8-10 .mu.m in thickness and the tear fluid
covering the conjunctiva is about 15 .mu.m thick. The pre-corneal
tear film consists of three layers: a thin lipid layer measuring
about 0.1 .mu.m consisting of the air tear interface, a mucin layer
measuring 0.03 .mu.m which is in direct contact with the corneal
epithelium, and finally the remaining layer is the thick aqueous
layer which is located between the lipid and mucin layer.
[0142] The aqueous layer is primarily derived from the secretions
of the lacrimal gland and its chemical composition is very similar
to diluted blood with a reduced protein content and slightly
greater osmotic pressure. The secretion and flow of tear fluid from
the lacrimal gland located in the supero-temporal quadrant with the
subsequent exit through the lacrimal puncta located in the
infero-medial quadrant creates a continuous flow of tear fluid
providing the ideal situation by furnishing a continuous supply of
substrate for one of the stoichiometric reactions which is the
subject of a preferred embodiment for evaluation of glucose levels.
The main component of the tear fluid is the aqueous layer which is
an ultrafiltrate of blood containing electrolytes such as sodium,
potassium, chloride, bicarbonate, calcium, and magnesium as well as
amino acids, proteins, enzymes, DNA, lipids, cholesterol,
glycoproteins, immunoglobulins, vitamins, minerals and hormones.
Moreover, the aqueous layer also holds critical metabolites such as
glucose, urea, catecholamines, and lactate, as well as gases such
as oxygen and carbon dioxide. Furthermore, any exogenous substances
found in the blood stream such as drugs, radioactive compounds and
the like are present in the tear fluid. Any compound present in the
blood can potentially noninvasively be evaluated with the apparatus
of the invention with the data transmitted and processed at a
remotely located station.
[0143] According to one preferred embodiment of the invention, the
non-invasive analysis of glucose levels will be described: Glucose
Detection:--The apparatus and methods for measurement of blood
components and chemical species in the tear fluid and/or surface of
the eye is based on electrodes associated with enzymatic reactions
providing an electrical current which can be radio transmitted to a
remote receiver providing continuous data on the concentration of
species in the tear fluid or surface of the eye. The ICL system is
preferably based on a diffusion limited sensors method that
requires no reagents or mechanical/moving parts in the contact
device. The preferred method and apparatus of the glucose detector
using ICL uses the enzyme glucose oxidase which catalyze a reaction
involving glucose and oxygen in association with electrochemical
sensors mounted in the contact device that are sensitive to either
the product of the reaction, an endogenous coreactant, or a coupled
electron carrier molecule such as the ferrocene-mediated glucose
sensors, as well as the direct electrochemical reaction of glucose
at the contact device membrane-covered catalytic metal
electrode.
[0144] Glucose and oxygen present in the tear fluid either derived
from the lacrimal gland or diffused from vessels on the surface of
the eye will diffuse into the contact device reaching an
immobilized layer of enzyme glucose oxidase mounted in the contact
device. Successful operation of enzyme electrodes demand constant
transport of the substrate to the electrode since the substrate
such as glucose and oxygen are consumed enzymatically. The ICL is
the ideal device for using enzyme electrodes since the tear fluid
flows continuously on the surface of the eye creating an optimal
environment for providing substrate for the stoichiometric
reaction. The ICL besides being a noninvasive system solves the
critical problem of sensor lifetime which occurs with any sensors
that are implanted inside the body. The preferred embodiment refers
to amperometric glucose biosensors with the biosensors based on
biocatalytic oxidation of glucose in the presence of the enzyme
oxidase. This is a two step process consisting of enzymatic
oxidation of glucose by glucose oxidase in which the co-factor
flavin-adenine dinucleotide (FAD) is reduced to FADH.sub.2 followed
by oxidation of the enzyme co-factor by molecular oxygen with
formation of hydrogen peroxide. 1
[0145] With catalase enzyme the overall reaction is
[0146] glucose+1/2O.sub.2.fwdarw.gluconic acid
[0147] Glucose concentration can be measured either by
electrochemical detection of an increase of the anodic current due
to hydrogen peroxide (product of the reaction) oxidation or by
detection of the decrease in the cathodic current due to oxygen
(co-reactant) reduction. The ICL glucose detection system
preferably has an enzyme electrode in contact with the tear fluid
and/or surface of the eye capable of measuring the oxidation
current of hydrogen peroxide created by the stoichiometric
conversion of glucose and oxygen in a layer of glucose oxidase
mounted inside the contact device. The ICL glucose sensor is
preferably electrochemical in nature and based on a hydrogen
peroxide electrode which is converted by immobilized glucose
oxidase which generates a direct current depending on the glucose
concentration of the tear fluid.
[0148] The glucose enzyme electrode of the contact device responds
to changes in the concentration of both glucose and oxygen, both of
which are substrates of the immobilized enzyme glucose oxidase. It
is also understood that the sensor in the contact device can be
made responsive to glucose only by operating in a differential
mode. The enzymatic electrodes built in the contact device are
placed in contact with the tear fluid or the surface of the eye and
the current generated by the electrodes according to the
stoichiometric conversion of glucose, are subsequently converted to
a frequency audio signal and transmitted to a remote receiver, with
the current being proportional to the glucose concentration
according to calibration factors.
[0149] The signals can be transmitted using the various
transmission systems previously described with an externally placed
receiver demodulating the audio frequency signal to a voltage and
the glucose concentration being calculated from the voltage and
subsequently displayed on a LED display. An interface card can be
used to connect the receiver with a computer for further signal
processing and analysis. During oxidation of glucose by glucose
oxidase an electrochemically oxidable molecule or any other
oxidable species generated such as hydrogen peroxide can be
detected amperometrically as a current by the electrodes. A
preferred embodiment includes a tree electrode setup consisting of
a working electrode (anode) and auxiliary electrode (cathode) and a
reference electrode connected to an amperometric detector. It
should be noted though that a glucose sensor could function well
using two electrodes. When appropriate voltage difference is
applied between the working and auxiliary electrode, hydrogen
peroxide is oxidized on the surface of the working electrode which
creates a measurable electric current. The intensity of the current
generated by the sensor is proportional to the concentration of
hydrogen peroxide which is proportional to the concentration of
glucose in the tear film and the surface of the eye.
[0150] A variety of materials can be used for the electrodes such
as silver/silver chloride coded cathodes. Anodes may be preferably
constructed as a platinum wire coated with glucose oxidase or
preferably covered by a immobilized glucose oxidase membrane.
Several possible configurations for sensors using amperometric
enzyme electrodes which involves detection of oxidable species can
be used in the apparatus of the invention. A variety of electrodes
and setups can be used in the contact device which are capable of
creating a stable working potential and output current which is
proportional to the concentration of blood components in the tear
fluid and surface of the eye. It is understood that a variety of
electrode setups for the amperometric detection of oxidable species
can be accomplished with the apparatus of the invention. It is
understood that solutions can be applied to the surface of the
electrodes to enhance transmission.
[0151] Other methods which use organic mediators such as ferrocene
which transfers electrons from glucose oxidase to a base electrode
with subsequent generation of current can be utilized. It is also
understood that needle-type glucose sensors can be placed in direct
contact with the conjunctiva or encased in a contact device for
measurement of glucose in the tear fluid. It is understood that any
sensor capable of converting a biological variable to a voltage
signal can be used in the contact device and placed on the surface
of the eye for measurement of the biological variables. It is
understood that any electrode configuration which measures hydrogen
peroxide produced in the reaction catalysed by glucose oxidase can
be used in the contact device for measurement of glucose levels. It
is understood that the following oxygen based enzyme electrode
glucose sensor can be used in the apparatus of the invention which
is based on the principal that the oxygen not consumed by the
enzymatic reactions by catalase enzyme is electrochemically reduced
at an oxygen sensor producing a glucose modulated oxygen dependent
current. This current is compared to a current from a similar
oxygen sensor without enzymes.
[0152] It is understood that the sensors are positioned in a way to
optimize the glucose access to the electrodes such as by creating
micro traumas to increase diffusion of glucose across tissues and
capillary walls, preferably positioning the sensors against
vascularized areas of the eye. In the closed eye about two-thirds
of oxygen and glucose comes by diffusion from the capillaries. Thus
positioning the sensors against the palpebral conjunctiva during
blinking can increase the delivery of substrates to the contact
device biosensor allowing a useful amount of substrates to diffuse
through the contact device biosensor membranes.
[0153] There are several locations on the surface of the eye in
which the ICL can be used to measure glucose such as: the tear film
laying on the surface of the cornea which is an ultrafiltrate of
blood derived from the main lacrimal gland; the tear meniscus which
is a reservoir of tears on the edge of the eye lid; the
supero-temporal conjunctival formix which allows direct measurement
of tears at the origin of secretion; the limbal area which is a
highly vascularized area between cornea and the sclera; and
preferably the highly vascularized conjunctiva. The contact device
allows the most efficient way of acquiring fluid by creating
micro-damage to the epithelium with a consequent loss of the blood
barrier function of said epithelium, with the subsequent increase
in tissue fluid diffusion. Furthermore, mechanical irritation
caused by an intentionally constructed slightly rugged surface of
the contact device in order to increase the flow of substrates.
Furthermore, it is understood that a heating element can be mounted
in association with the sensor in order to increase transudation of
fluid.
[0154] The samples utilized for noninvasive blood analysis may
preferably be acquired by micro-traumas to the conjunctiva caused
by the contact device which has micro projections on its surface in
contact with the conjunctiva creating an increase in the diffusion
rate of plasma components through the capillary walls toward the
measuring sensors. Moreover, the apparatus of the invention may
promote increased vascular permeability of conjunctival vessels
through an increase in temperature using surface electrodes as
heating elements. Furthermore, the sensors may be located next to
the exit point of the lacrimal gland duct in order to collect tear
fluid close to its origin. Furthermore, the sensors may be placed
inferiorly in contact with the conjunctival tear meniscus which has
the largest volume of tear fluid on the surface of the eye.
Alternatively, the sensors may be placed in contact with the limbal
area which is a substantially vascularized surface of the eye. Any
means that create a micro-disruption of the integrity of the ocular
surface or any other means that cause transudation of tissue fluid
and consequently plasma may be used in the invention.
Alternatively, the sensors may be placed against he vascularized
conjunctiva in the cul-de-sac superiorly or inferiorly.
[0155] It is also understood that the sensors can be placed on any
location on the surface of the eye to measure glucose and other
chemical compounds. Besides the conventional circular shape of
contact lenses, the shape of the contact device also includes a
flat rectangular configuration, ring like or half moon like which
are used for applications that require placement under the
palpebral conjunctiva or cul-de-sac of the eye.
[0156] A recessed region is created in the contact device for
placement of the electrodes and electronics with enzyme active
membranes placed over the electrodes. A variety of membranes with
different permeabilities to different chemical species are fitted
over the electrodes and enzyme-active membranes. The different
permeability of the membranes allows selection of different
chemicals to be evaluated and to prevent contaminants from reaching
the electrodes. Thus allowing several electroactive compounds to be
simultaneously evaluated by mounting membranes with different
permeabilities with suitable electrodes on the contact device.
[0157] It is also understood that multilayer membranes with
preferential permeability to different compounds can be used. The
contact device encases the microelectrodes forming a bioprotective
membrane such that the electrodes are covered by the enzyme active
membrane which is covered by the contact device membrane such as
polyurethane which is biocompatable and permeable to the analytes.
A membrane between the electrodes and the enzyme membrane can be
used to block interfering substances without altering transport of
peroxide ion. The permeability of the membranes are used to
optimize the concentration of the compounds needed for the
enzymatic reaction and to protect against interfering elements.
[0158] It is understood that the diffusion of substrate to the
sensor mounted in the contact device is preferably perpendicular to
the plane of the electrode surface. Alternatively, it is understood
that the membrane and surface of the contact device can be
constructed to allow selective non-perpendicular diffusion of the
substrates. It is also understood that membranes such as negatively
charged perfluorinated ionomer Nafion membrane can be used in order
to reduce interference by electroactive compounds such as
ascorbate, urate and acetaminophen. It is also understood that new
polymers and coatings under development which are capable of
preferential selection of electroactive compounds and that can
prevent degradation of electrodes and enzymes can be used in the
apparatus of the invention.
[0159] The sensors and membranes coupled with radio transmitters
can be positioned in any place in the contact device but may be
placed in the cardinal positions in a pie like configuration, with
each sensor transmitting its signal to a receiver. For example, if
four biological variables are being detected simultaneously the
four sensors signals A, B, C, and D are simultaneously transmitted
to one or more receivers. Any device utilizing the tear fluid to
non-invasively measure the blood components and signals transmitted
to a remote station can be used in the apparatus of the invention.
Preferably a small contact device, however any size or shape of
contact devices can be used to acquire the data on the surface of
the eye.
[0160] An infusion pump can be activated according to the level of
glucose detected by the ICL system and insulin injected
automatically as needed to normalize glucose levels as an
artificial pancreas. An alarm circuit can also be coupled with the
pump and activated when low or high levels of glucose are present
thus alerting the patient. It is understood that other drugs,
hormones, and chemicals can be detected and signals transmitted in
the same fashion using the apparatus of the invention.
[0161] A passive transmitter carrying a resonance circuit can be
mounted in the contact device with its frequency altered by a
change in reactance whose magnitude changes in response to the
voltage generated by the glucose sensors. As the signal from
passive transmitters falls off extremely rapidly with distance, the
antenna and receiver should be placed near to the contact device
such as in the frame of regular glasses.
[0162] It is also understood that active transmitters with
batteries housed in the contact device and suitable sensors as
previously described can also be used to detect glucose levels. It
is also understood that a vibrating micro-quartz crystal connected
to a coil and capable of sending both sound and radio impulses can
be mounted in the contact device and continuously transmit data
signals related to the concentration of chemical compounds in the
tear fluid.
[0163] An oxygen electrode consisting of a platinum cathode and a
silver anode loaded with polarographic voltage can be used in
association with the glucose sensor with the radio transmission of
the two variables. It is also understood that sensors which measure
oxygen consumption as indirect means of evaluating glucose levels
can be used in the apparatus of the invention. The membranes can be
used to increase the amount of oxygen delivered to the membrane
enzyme since all glucose oxidase systems require oxygen and can
potentially become oxygen limited. The membranes also can be made
impermeable to other electroactive species such as acetamymophen or
substances that can alter the level of hydrogen peroxide produced
by the glucose oxidase enzyme membrane.
[0164] It is understood that a polarographic Clark-type oxygen
detector electrode consisting of a platinum cathode in a
silver-to-silver-chloride anode with signals telemetered to a
remote station can be used in the apparatus of the invention. It is
also understood that other gas sensors using galvanic configuration
and the like can be used with the apparatus of the invention. The
oxygen sensor is preferably positioned so as to lodge against the
palpebral conjunctiva. The oxygen diffusing across the electrode
membrane is reduced at the cathode which produces a electrical
current which is converted to an audio frequency signal and
transmitted to a remote station. The placement of the sensor in the
conjunctiva allows intimate contact with an area vascularized by
the same arterial circulation as the brain which correlates with
arterial oxygen and provides an indication of peripheral tissue
oxygen. This embodiment allows good correlation between arterial
oxygen and cerebral blood flow by monitoring a tissue bed
vascularized by the internal carotid artery, and thus, reflects
intracranial oxygenation.
[0165] This embodiment can be useful during surgical procedures
such as in carotid endarterectomy allowing precise detection of the
side with decreased oxygenation. This same embodiment can be useful
in a variety of heart and brain operations as well as in
retinopathy of prematurity which allows close observation of the
level of oxygen administered and thus prevention of hyperoxia with
its potentially blinding effects while still delivering adequate
amount of oxygen to the infant.
[0166] Cholesterol secreted in the tear fluid correlates with
plasma cholesterol and a further embodiment utilizes a similar
system as described by measurement of glucose. However, this ICL as
designed by the inventor involves an immobilized cholesterol
esterase membrane which splits cholesterol esters into free
cholesterol and fatty acids. The free cholesterol passes through
selectively permeable membrane to both free cholesterol and oxygen
and reaches a second membrane consisting of an immobilized
cholesterol oxidase. In the presence of oxygen the free cholesterol
is transformed by the cholesterol oxidase into cholestenone and
hydrogen peroxide with the hydrogen peroxide being oxidized on the
surface of the working electrode which creates a measurable
electric current with signals preferably converted into audio
frequency signals and transmitted to a remote receiver with the
current being proportional to the cholesterol concentration
according to calibration factors. The method and apparatus
described above relates to the following reaction or part of the
following reaction. 2
[0167] A further embodiment utilizes an antimone electrode that can
be housed in the contact device and used to detect the pH and other
chemical species of the tear fluid and the surface of the eye. It
is also understood that a glass electrode with a transistor circuit
capable of measuring pH, pH endoradiosondes, and the like can be
used and mounted in the contact device and used for measurement of
the pH in the tear fluid or surface of the eye with signals
preferably radio transmitted to a remote station.
[0168] In another embodiment, catalytic antibodies immobilized in a
membrane with associated pH sensitive electrodes can identify a
variety of antigens. The antigen when interacting with the
catalytic antibody can promote the formation of acetic acid with a
consequent change in pH and current that is proportional to the
concentration of the antigens according to calibration factors.
[0169] In a further embodiment an immobilized electrocatalytic
active enzyme and associated electrode promote, in the presence of
a substrate (meaning any biological variable), an electrocatalytic
reaction resulting in a current that is proportional to the amount
of said substrate. It is understood that a variety of enzymatic and
nonenzymatic detection systems can be used in the apparatus of the
invention.
[0170] It is understood that any electrochemical sensor,
thermoelectric sensors, acoustic sensors, piezoelectric sensors,
optical sensors, and the like can be mounted in the contact device
and placed on the surface of the eye for detection and measurement
of blood components and physical parameters found in the eye with
signals preferably transmitted to a remote station. It is
understood that electrochemical sensors using amperometric,
potentiometric, conductometric, gravimetric, impedimetric, systems,
and the like can be used in the apparatus of the invention for
detection and measurement of blood components and physical
parameters found in the eye with signals preferably transmitted to
a remote station.
[0171] Some preferable ways have been described; however, any other
miniature radio transmitters can be used and mounted in the contact
device and any microminiature sensor that modulates a radio
transmitter and send the signal to a nearby radio receiver can be
used. Other microminiature devices capable of modulating an
ultrasound device, or infrared and laser emitters, and the like can
be mounted in the contact device and used for signal detection and
transmission to a remote station. A variety of methods and
techniques and devices for gaining and transmitting information
from the eye to a remote receiver can be used in the apparatus of
the invention.
[0172] It is an object of the present invention to provide an
apparatus and method for the noninvasive measurement and evaluation
of blood components.
[0173] It is also an object of the present invention to provide an
intelligent contact lens system capable of receiving, processing,
and transmitting signals such as electromagnetic waves, radio
waves, infrared and the like being preferably transmitted to a
remote station for signal processing and analysis, with transensors
and biossensors mounted in the contact device.
[0174] It is a further object of the present invention to detect
physical changes that occur in the eye, preferably using optical
emitters and sensors.
[0175] It is a further object of the present invention to provide a
novel drug delivery system and treatment of eye and systemic
diseases.
[0176] The above and other objects and advantages will become more
readily apparent when reference is made to the following
description taken in conjunction with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0177] FIG. 1 is a schematic block diagram illustrating a system
for measuring intraocular pressure in accordance with a preferred
embodiment of the present invention.
[0178] FIGS. 2A-2D schematically illustrate a preferred embodiment
of a contact device according the present invention.
[0179] FIG. 3 schematically illustrates a view seen by a patient
when utilizing the system illustrated in FIG. 1.
[0180] FIGS. 4 and 5 schematically depict multi-filter optical
elements in accordance with a preferred embodiment of the present
invention.
[0181] FIGS. 5A-5F illustrate a preferred embodiment of an
applicator for gently applying the contact device to the cornea in
accordance with the present invention.
[0182] FIG. 6 illustrates an exemplary circuit for carrying out
several aspects of the embodiment illustrated in FIG. 1.
[0183] FIGS. 7A and 7B are block diagrams illustrating an
arrangement capable compensating for deviations in corneal
thickness according to the present invention.
[0184] FIGS. 8A and 8B schematically illustrate a contact device
utilizing barcode technology in accordance with a preferred
embodiment of the present invention.
[0185] FIGS. 9A and 9B schematically illustrate a contact device
utilizing color detection technology in accordance with a preferred
embodiment of the present invention.
[0186] FIG. 10 illustrates an alternative contact device in
accordance with yet another preferred embodiment of the present
invention.
[0187] FIGS. 11A and 11B schematically illustrate an indentation
distance detection arrangement in accordance with a preferred
embodiment of the present invention.
[0188] FIG. 12 is a cross-sectional view of an alternative contact
device in accordance with another preferred embodiment of the
present invention.
[0189] FIGS. 13A-15 are cross-sectional views of alternative
contact devices in accordance with other embodiments of the present
invention.
[0190] FIG. 16 schematically illustrates an alternative embodiment
of the system for measuring intraocular pressure by applanation,
according to the present invention.
[0191] FIG. 16A is a graph depicting force (T) as a function of the
distance (x) separating a movable central piece from the pole of a
magnetic actuation apparatus in accordance with the present
invention.
[0192] FIG. 17 schematically illustrates an alternative optical
alignment system in accordance with the present invention.
[0193] FIGS. 18 and 19 schematically illustrate arrangements for
guiding the patient during alignment of his/her eye in the
apparatus of the present invention.
[0194] FIGS. 20A and 20B schematically illustrate an alternative
embodiment for measuring intraocular pressure by indentation.
[0195] FIGS. 21 and 22 schematically illustrate embodiments of the
present invention which facilitate placement of the contact device
on the sclera of the eye.
[0196] FIG. 23 is a plan view of an alternative contact device
which may be used to measure episcleral venous pressure in
accordance with the present invention.
[0197] FIG. 24 is a cross-sectional view of the alternative contact
device which may be used to measure episcleral venous pressure in
accordance with the present invention.
[0198] FIG. 25 schematically illustrates an alternative embodiment
of the present invention, which includes a contact device with a
pressure transducer mounted therein.
[0199] FIG. 25A is a cross-sectional view of the alternative
embodiment illustrated in FIG. 25.
[0200] FIG. 26 is a cross-sectional view illustrating the pressure
transducer of FIG. 25.
[0201] FIG. 27 schematically illustrates the alternative embodiment
of FIG. 25 when located in a patient's eye.
[0202] FIG. 28 illustrates an alternative embodiment wherein two
pressure transducers are utilized.
[0203] FIG. 29 illustrates an alternative embodiment utilizing a
centrally disposed pressure transducer.
[0204] FIG. 30 illustrates a preferred mounting of the alternative
embodiment to eye glass frames.
[0205] FIG. 31 is a block diagram of a preferred circuit defined by
the alternative embodiment illustrated in FIG. 25.
[0206] FIG. 32 is a schematic representation of a contact device
situated on the cornea of an eye with lateral extensions of the
contact device extending into the sclera sack below the upper and
lower eye lids and illustrating schematically the reception of a
signal transmitted from a transmitter to a receiver and the
processes performed on the transmitted signal.
[0207] FIG. 33A is an enlarged view of the contact device shown in
FIG. 32 with further enlarged portions of the contact device
encircled in FIGS. 33A being shown in further detail in FIGS. 33B
and 33C.
[0208] FIG. 34 is a schematic block diagram of a system of
obtaining sample signal measurements and transmitting and
interpreting the results of the sample signals.
[0209] FIGS. 35A and 35C schematically represent the actuation of
the contact device of the present invention by the opening and
closing of the eye lids. FIG. 35B is an enlarged detail view of an
area encircled in FIG. 35A.
[0210] FIGS. 36A through 36J schematically illustrate various
shapes of a contact device incorporating the principles of the
present invention.
[0211] FIGS. 37A and 37B schematically illustrate interpretation of
signals generated from the contact device of the present invention
and the analysis of the signals to provide different test
measurements and transmission of this data to remote locations,
such as an intensive care unit setting.
[0212] FIG. 38A schematically illustrates a contact device of the
present invention with FIG. 38B being a sectional view taken along
the section line shown in FIG. 38A.
[0213] FIG. 39A illustrates the continuous flow of fluid in the
eye. FIG. 39B schematically illustrates an alternative embodiment
of the contact device of the present invention used under the
eyelid to produce signals based upon flow of tear fluid through the
eye and transmit the signals by a wire connected to an external
device.
[0214] FIG. 40A schematically illustrates an alternative embodiment
of the present invention, used under the eye lid to produce signals
indicative of sensed glucose levels which are radio transmitted to
a remote station followed by communication through a publically
available network.
[0215] FIG. 40B schematically illustrates an alternative embodiment
of the glucose sensor to be used under the eyelid with signals
transmitted through wires.
[0216] FIG. 41 illustrates an oversized contact device including a
plurality of sensors.
[0217] FIG. 42A illustrates open eye lids positioned over a contact
device including a somnolence awareness device, whereas FIG. 42B
illustrates the closing of the eyelids and the production of a
signal externally transmitted to an alarm device.
[0218] FIG. 43 is a detailed view of a portion of an eyeball
including a heat stimulation transmission device.
[0219] FIG. 44 is a front view of a heat stimulation transmission
device mounted on a contact device and activated by a remote
hardware device.
[0220] FIG. 45 illustrates a band heat stimulation transmission
device for external use or surgical implantation in any part of the
body.
[0221] FIG. 46 illustrates a surgically implantable heat
stimulation transmission device for implantation in the eye between
eye muscles.
[0222] FIG. 47 illustrates a heat stimulation device for surgical
implantation in any part of the body.
[0223] FIG. 48 schematically illustrates the surgical implantation
of an overheating transmission device adjacent to a brain
tumor.
[0224] FIG. 49 illustrates the surgical implantation of an
overheating transmission device adjacent to a kidney tumor.
[0225] FIG. 50 illustrates an overheating transmission device and
its various components.
[0226] FIG. 51 illustrates the surgical implantation of an
overheating transmission devices adjacent to an intraocular
tumor.
[0227] FIG. 52 schematically illustrates the surgical implantation
of an overheating transmission device adjacent to a lung tumor.
[0228] FIG. 53 schematically illustrates the positioning of an
overheating transmission device adjacent to a breast tumor.
[0229] FIG. 54A is a side sectional view and FIG. 54B is a front
view of a contact device used to detect chemical compounds in the
aqueous humor located on the eye, with FIG. 54C being a side view
thereof.
[0230] FIG. 55A schematically illustrates a microphone or motion
sensor mounted on a contact device sensor positioned over the eye
for detection of heart pulsations or sound and transmission of a
signal representative of heart pulsations or sound to a remote
alarm device with FIG. 55B being an enlarged view of the alarm
device encircled in FIG. 55A.
[0231] FIG. 56 illustrates a contact device with an ultrasonic
dipolar sensor, power source and transmitter with the sensor
located on the blood vessels of the eye.
[0232] FIG. 57 schematically illustrates the location of a contact
device with a sensor placed near an extraocular muscle.
[0233] FIG. 58A is a side sectional view illustrating a contact
device having a light source for illumination of the back of the
eye. FIG. 58B illustrates schematically the transmission of light
from a light source for reflection off a blood vessel at the cup of
the optic nerve and for receipt of the reflected light by a
multioptical filter system separated from the reflecting surface by
a predetermined distance and separated from the light source by a
predetermined distance for interpretation of the measurement of the
reflected light.
[0234] FIGS. 59A through 59C illustrate positioning of contact
devices for neurostimulation of tissues in the eye and brain.
[0235] FIG. 60 is a schematic illustration of a contact device
having a fixed frequency transmitter and power source for being
tracked by an orbiting satellite.
[0236] FIG. 61 illustrates a contact device under an eyelid
including a pressure sensor incorporated in a circuit having a
power source, an LED drive and an LED for production of an LED
signal for remote activation of a device having a photodiode or
optical receiver on a receptor screen.
[0237] FIG. 62 is a cross-sectional view of a contact device having
a drug delivery system incorporated therein.
[0238] FIG. 63 schematically illustrates a block diagram of an
artificial pancreas system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Applanation
[0239] A preferred embodiment of the present invention will now be
described with reference to the drawings. According to the
preferred embodiment illustrated in FIG. 1, a system is provided
for measuring intraocular pressure by applanation. The system
includes a contact device 2 for placement in contact with the
cornea 4, and an actuation apparatus 6 for actuating the contact
device 2 so that a portion thereof projects inwardly against the
cornea 4 to provide a predetermined amount of applanation. The
system further includes a detecting arrangement 8 for detecting
when the predetermined amount of applanation of the cornea 4 has
been achieved and a calculation unit 10 responsive to the detecting
arrangement 8 for determining intraocular pressure based on the
amount of force the contact device 2 must apply against the cornea
4 in order to achieve the predetermined amount of applanation.
[0240] The contact device 2 illustrated in FIG. 1 has an
exaggerated thickness to more clearly distinguish it from the
cornea 4. FIGS. 2A-2D more accurately illustrate a preferred
embodiment of the contact device 2 which includes a substantially
rigid annular member 12, a flexible membrane 14 and a movable
central piece 16. The substantially rigid annular member 12
includes an inner concave surface 18 shaped to match an outer
surface of the cornea 4 and having a hole 20 defined therein. The
substantially rigid annular member 12 has a maximum thickness
(preferably approximately 1 millimeter) at the hole 20 and a
progressively decreasing thickness toward a periphery 21 of the
substantially rigid annular member 12. The diameter of the rigid
annular member is approximately 11 millimeters and the diameter of
the hole 20 is approximately 5.1 millimeters according to a
preferred embodiment. Preferably, the substantially rigid annular
member 12 is made of transparent polymethylmethacrylate; however,
it is understood that many other materials, such as glass and
appropriately rigid plastics and polymers, may be used to make the
annular member 12. Preferably, the materials are chosen so as not
to interfere with light directed at the cornea or reflected back
therefrom.
[0241] The flexible membrane 14 is preferably secured to the inner
concave surface 18 of the substantially rigid annular member 12 to
provide comfort for the wearer by preventing scratches or abrasions
to the corneal epithelial layer. The flexible membrane 14 is
coextensive with at least the hole 20 in the annular member 12 and
includes at least one transparent area 22. Preferably, the
transparent area 22 spans the entire flexible membrane 14, and the
flexible membrane 14 is coextensive with the entire inner concave
surface 18 of the rigid annular member 12. According to a preferred
arrangement, only the periphery of the flexible membrane 14 and the
periphery of the rigid annular member 12 are secured to one
another. This tends to minimize any resistance the flexible
membrane might exert against displacement of the movable central
piece 16 toward the cornea 4.
[0242] According to an alternative arrangement, the flexible
membrane 14 is coextensive with the rigid annular member and is
heat-sealed thereto over its entire extent except for a circular
region within approximately one millimeter of the hole 20.
[0243] Although the flexible membrane 14 preferably consists of a
soft and thin polymer, such as transparent silicone elastic,
transparent silicon rubber (used in conventional contact lens),
transparent flexible acrylic (used in conventional intraocular
lenses), transparent hydrogel, or the like, it is well understood
that other materials may be used in manufacturing the flexible
membrane 14.
[0244] The movable central piece 16 is slidably disposed within the
hole 20 and includes a substantially flat inner side 24 secured to
the flexible membrane 14. The engagement of the inner side 24 to
the flexible membrane 14 is preferably provided by glue or
thermo-contact techniques. It is understood, however, that various
other techniques may be used in order to securely engage the inner
side 24 to the flexible membrane 14. Preferably, the movable
central piece 16 has a diameter of approximately 5.0 millimeters
and a thickness of approximately 1 millimeter.
[0245] A substantially cylindrical wall 42 is defined
circumferentially around the hole 20 by virtue of the increased
thickness of the rigid annular member 12 at the periphery of the
hole 20. The movable central piece 16 is slidably disposed against
this wall 42 in a piston-like manner and preferably has a thickness
which matches the height of the cylindrical wall 42. In use, the
substantially flat inner side 24 flattens a portion of the cornea 4
upon actuation of the movable central piece 16 by the actuation
apparatus 6.
[0246] The overall dimensions of the substantially rigid annular
member 12, the flexible membrane 14 and the movable central piece
16 are determined by balancing several factors, including the
desired range of forces applied to the cornea 4 during applanation,
the discomfort tolerances of the patients, the minimum desired area
of applanation, and the requisite stability of the contact device 2
on the cornea 4. In addition, the dimensions of the movable central
piece 16 are preferably selected so that relative rotation between
the movable central piece 16 and the substantially rigid annular
member 12 is precluded, without hampering the aforementioned
piston-like sliding.
[0247] The materials used to manufacture the contact device 2 are
preferably selected so as to minimize any interference with light
incident upon the cornea 4 or reflected thereby.
[0248] Preferably, the actuation apparatus 6 illustrated in FIG. 1
actuates the movable central piece 16 to cause sliding of the
movable central piece 16 in the piston-like manner toward the
cornea 4. In doing so, the movable central piece 16 and a central
portion of the flexible membrane 14 are caused to project inwardly
against the cornea 4. This is shown in FIGS. 2C and 2D. A portion
of the cornea 4 is thereby flattened. Actuation continues until a
predetermined amount of applanation is achieved.
[0249] Preferably, the movable central piece 16 includes a
magnetically responsive element 26 arranged so as to slide along
with the movable central piece 16 in response to a magnetic field,
and the actuation apparatus 6 includes a mechanism 28 for applying
a magnetic field thereto. Although it is understood that the
mechanism 28 for applying the magnetic field may include a
selectively positioned bar magnet, according to a preferred
embodiment, the mechanism 28 for applying the magnetic field
includes a coil 30 of long wire wound in a closely packed helix and
circuitry 32 for producing an electrical current through the coil
30 in a progressively increasing manner. By progressively
increasing the current, the magnetic field is progressively
increased. The magnetic repulsion between the actuation apparatus 6
and the movable central piece 16 therefore increases progressively,
and this, in turn, causes a progressively greater force to be
applied against the cornea 4 until the predetermined amount of
applanation is achieved.
[0250] Using known principles of physics, it is understood that the
electrical current passing through the coil 30 will be proportional
to the amount of force applied by the movable central piece 16
against the cornea 4 via the flexible membrane 14. Since the amount
of force required to achieve the predetermined amount of
applanation is proportional to intraocular pressure, the amount of
current required to achieve the predetermined amount of applanation
will also be proportional to the intraocular pressure. Thus, a
conversion factor for converting a value of current to a value of
intraocular pressure can easily be determined experimentally upon
dimensions of the system, the magnetic responsiveness of the
magnetically responsive element 26, number of coil windings, and
the like.
[0251] Besides using experimentation techniques, the conversion
factor may also be determined using known techniques for
calibrating a tonometer. Such known techniques are based on a known
relationship which exists between the inward displacement of an
indentation device and the volume changes and pressure in the
indented eye. Examples of such techniques are set forth in Shiotz,
Communications: Tonometry, The Brit. J. of Ophthalmology, June
1920, p. 249-266; Friedenwald, Tonometer Calibration, Trans. Amer.
Acad. of O. & O., January-February 1957, pp. 108-126; and
Moses, Theory and Calibration of the Schiotz Tonometer VII:
Experimental Results of Tonometric Measurements: Scale Reading
Versus Indentation Volume, Investigative Ophthalmology, September
1971, Vol. 10, No. 9, pp. 716-723.
[0252] In light of the relationship between current and intraocular
pressure, the calculation unit 10 includes a memory 33 for storing
a current value indicative of the amount of current passing through
the coil 30 when the predetermined amount of applanation is
achieved. The calculation unit 10 also includes a conversion unit
34 for converting the current value into an indication of
intraocular pressure.
[0253] Preferably, the calculation unit 10 is responsive to the
detecting arrangement 8 so that when the predetermined amount of
applanation is achieved, the current value (corresponding to the
amount of current flowing through the coil 30) is immediately
stored in the memory 33. At the same time, the calculation unit 10
produces an output signal directing the current producing circuitry
32 to terminate the flow of current. This, in turn, terminates the
force against the cornea 4. In an alternative embodiment, the
current producing circuitry 32 could be made directly responsive to
the detecting arrangement 8 (i.e., not through the calculation unit
10) so as to automatically terminate the flow of current through
the coil 30 upon achieving the predetermined amount of
applanation.
[0254] The current producing circuitry 32 may constitute any
appropriately arranged circuit for achieving the progressively
increasing current. However, a preferred current producing circuit
32 includes a switch and a DC power supply, the combination of
which is capable of producing a step function. The preferred
current producing circuitry 32 further comprises an integrating
amplifier which integrates the step function to produce the
progressively increasing current.
[0255] The magnetically responsive element 26 is circumferentially
surrounded by a transparent peripheral portion 36. The transparent
peripheral portion 36 is aligned with the transparent area 22 and
permits light to pass through the contact device 2 to the cornea 4
and also permits light to reflect from the cornea 4 back out of the
contact device 2 through the transparent on peripheral portion 36.
Although the transparent peripheral portion 36 may consist entirely
of an air gap, for reasons of accuracy and to provide smoother
sliding of the movable central piece 16 through the rigid annular
member 12, it is preferred that a transparent solid material
constitute the transparent peripheral portion 36. Exemplary
transparent solid materials include polymethyl methacrylate, glass,
hard acrylic, plastic polymers, and the like.
[0256] The magnetically responsive element 26 preferably comprises
an annular magnet having a central sight hole 38 through which a
patient is able to see while the contact device 2 is located on the
patient's cornea 4. The central sight hole 38 is aligned with the
transparent area 22 of the flexible membrane 14 and is preferably
at least 1-2 millimeters in diameter.
[0257] Although the preferred embodiment includes an annular magnet
as the magnetically responsive element 26, it is understood that
various other magnetically responsive elements 26 may be used,
including various ferromagnetic materials and/or suspensions of
magnetically responsive particles in liquid. The magnetically
responsive element 26 may also consist of a plurality of small bar
magnets arranged in a circle, to thereby define an opening
equivalent to the illustrated central sight hole 38. A transparent
magnet may also be used.
[0258] A display 40 is preferably provided for numerically
displaying the intraocular pressure detected by the system. The
display 40 preferably comprises a liquid crystal display (LCD) or
light emitting diode (LED) display connected and responsive to the
conversion unit 34 of the calculation unit 10.
[0259] Alternatively, the display 40 can be arranged so as to give
indications of whether the intraocular pressure is within certain
ranges. In this regard, the display 40 may include a green LED 40A,
a yellow LED 40B, and a red LED 40C. When the pressure is within a
predetermined high range, the red LED 40C is illuminated to
indicate that medical attention is needed. When the intraocular
pressure is within a normal range, the green LED 40A is
illuminated. The yellow LED 40B is illuminated when the pressure is
between the normal range and the high range to indicate that the
pressure is somewhat elevated and that, although medical attention
is not currently needed, careful and frequent monitoring is
recommended.
[0260] Preferably, since different patients may have different
sensitivities or reactions to the same intraocular pressure, the
ranges corresponding to each LED 40A,40B,40C are calibrated for
each patient by an attending physician. This way, patients who are
more susceptible to consequences from increased intraocular
pressure may be alerted to seek medical attention at a pressure
less than the pressure at which other less-susceptible patients are
alerted to take the same action. The range calibrations may be made
using any known calibration device 40D including variable gain
amplifiers or voltage divider networks with variable
resistances.
[0261] The detecting arrangement 8 preferably comprises an optical
detection system including two primary beam emitters 44,46; two
light sensors 48,50; and two converging lenses 52,54. Any of a
plurality of commercially available beam emitters may be used as
emitters 44,46, including low-power laser beam emitting devices and
infra-red (IR) beam emitting devices. Preferably, the device 2 and
the primary beam emitters 44,46 are arranged with respect to one
another so that each of the primary beam emitters 44,46 emits a
primary beam of light toward the cornea through the transparent
area 22 of the device and so that the primary beam of light is
reflected back through the device 2 by the cornea 4 to thereby
produce reflected beams 60,62 of light with a direction of
propagation dependent upon the amount of applanation of the cornea.
The two light sensors 48,50 and two converging lenses 52,54 are
preferably arranged so as to be aligned with the reflected beams
60,62 of light only when the predetermined amount of applanation of
the cornea 4 has been achieved. Preferably, the primary beams 56,58
pass through the substantially transparent peripheral portion
36.
[0262] Although FIG. 1 shows the reflected beams 60,62 of light
diverging away from one another and well away from the two
converging lenses 52,54 and light sensors 48,50, it is understood
that as the cornea 4 becomes applanated the reflected beams 60,62
will approach the two light sensors 48,50 and the two converging
lenses 52,54. When the predetermined amount of applanation is
achieved, the reflected beams 60,62 will be directly aligned with
the converging lenses 52,54 and the sensors 48,50. The sensors
48,50 are therefore able to detect when the predetermined amount of
applanation is achieved by merely detecting the presence of the
reflected beams 60,62. Preferably, the predetermined amount of
applanation is deemed to exist when all of the sensors 48,50
receive a respective one of the reflected beams 60,62.
[0263] Although the illustrated arrangement is generally effective
using two primary beam emitters 44,46 and two light sensors 48,50,
better accuracy can be achieved in patients with astigmatisms by
providing four beam emitters and four light sensors arranged
orthogonally with respect to one another about the longitudinal
axis of the actuation apparatus 6. As in the case with two beam
emitters 44,46 and light sensors 48,50, the predetermined amount of
applanation is preferably deemed to exist when all of the sensors
receive a respective one of the reflected beams.
[0264] A sighting arrangement is preferably provided for indicating
when the actuation apparatus 6 and the detecting arrangement 8 are
properly aligned with the device 2. Preferably, the sighting
arrangement includes the central sight hole 38 in the movable
central piece 16 through which a patient is able to see while the
device 2 is located on the patient's cornea 4. The central sight
hole 38 is aligned with the transparent area 22. In addition, the
actuation apparatus 6 includes a tubular housing 64 having a first
end 66 for placement over an eye equipped with the device 2 and a
second opposite end 68 having at least one mark 70 arranged such
that, when the patient looks through the central sight hole 38 at
the mark 70, the device 2 is properly aligned with the actuation
apparatus 6 and detecting arrangement 8.
[0265] Preferably, the second end 68 includes an internal mirror
surface 72 and the mark 70 generally comprises a set of
cross-hairs. FIG. 3 illustrates the view seen by a patient through
the central sight hole 38 when the device 2 is properly aligned
with the actuation apparatus 6 and detecting arrangement 8. When
proper alignment is achieved, the reflected image 74 of the central
sight hole 38 appears in the mirror surface 72 at the intersection
of the two cross-hairs which constitute the mark 70. (The size of
the image 74 is exaggerated in FIG. 3 to more clearly distinguish
it from other elements in the drawing).
[0266] Preferably, at least one light 75 is provided inside the
tubular housing 64 to illuminate the inside of the housing 64 and
facilitate visualization of the cross-hairs and the reflected image
74. Preferably, the internal mirror surface 72 acts as a mirror
only when the light 75 is on, and becomes mostly transparent upon
deactivation of the light 75 due to darkness inside the tubular
housing 64. To that end, the second end 68 of the tubular housing
68 may be manufactured using "one-way glass" which is often found
in security and surveillance equipment.
[0267] Alternatively, if the device is to be used primarily by
physicians, optometrists, or the like, the second end 68 may be
merely transparent. If, on the other hand, the device is to be used
by patients for self-monitoring, it is understood that the second
end 68 may merely include a mirror.
[0268] The system also preferably includes an optical distance
measuring mechanism for indicating whether the device 2 is spaced
at a proper axial distance from the actuation apparatus 6 and the
detecting arrangement 8. The optical distance measurement mechanism
is preferably used in conjunction with the sighting
arrangement.
[0269] Preferably, the optical distance measuring mechanism
includes a distance measurement beam emitter 76 for emitting an
optical distance measurement beam 78 toward the device 2. The
device 2 is capable of reflecting the distance measurement beam 78
to produce a first reflected distance measurement beam 80. Arranged
in the path of the first reflected distance measurement beam 80 is
a preferably convex mirror 82. The convex mirror 82 reflects the
first reflected distance measurement beam 80 to create a second
reflected distance measurement beam 84 and serves to amplify any
variations in the first reflected beam's direction of propagation.
The second reflected distance measurement beam 84 is directed
generally toward a distance measurement beam detector 86. The
distance measurement beam detector 86 is arranged so that the
second reflected distance measurement beam 84 strikes a
predetermined portion of the distance measurement beam detector 86
only when the device 2 is located at the proper axial distance from
the actuation apparatus 6 and the detecting arrangement 8. When the
proper axial distance is lacking, the second reflected distance
measurement beam strikes another portion of the beam detector
86.
[0270] An indicator 88, such as an LCD or LED display, is
preferably connected and responsive to the beam detector 86 for
indicating that the proper axial distance has been achieved only
when the reflected distance measurement beam strikes the
predetermined portion of the distance measurement beam
detector.
[0271] Preferably, as illustrated in FIG. 1. the distance
measurement beam detector 86 includes a multi-filter optical
element 90 arranged so as to receive the second reflected distance
measurement beam 84. The multi-filter optical element 90 contains a
plurality of optical filters 92. Each of the optical filters 92
filters out a different percentage of light, with the predetermined
portion of the detector 86 being defined by a particular one of the
optical filters 92 and a filtering percentage associated
therewith.
[0272] The distance measurement beam detector 86 further includes a
beam intensity detection sensor 94 for detecting the intensity of
the second reflected distance measurement beam 84 after the beam 84
passes through the multi-filter optical element 90, Since the
multi-filter optical element causes this intensity to vary with
axial distance, the intensity is indicative of whether the device 2
is at the proper distance from the actuation apparatus 6 and the
detecting arrangement 8.
[0273] A converging lens 96 is preferably located between the
multi-filter optical element 90 and the beam intensity detection
sensor 94, for focussing the second reflected distance measurement
beam 84 on the beam intensity detection sensor 94 after the beam 84
passes through the multi-filter optical element 90.
[0274] Preferably, the indicator 88 is responsive to the beam
intensity detection sensor 94 so as to indicate what corrective
action should be taken, when the device 2 is not at the proper
axial distance from the actuation apparatus 6 and the detecting
arrangement 8, in order to achieve the proper distance. The
indication given by the indicator 88 is based on the intensity and
which of the plurality of optical filters 92 achieves the
particular intensity by virtue of a filtering percentage associated
therewith.
[0275] For example, when the device 2 is excessively far from the
actuation apparatus 6, the second reflected distance measurement
beam 84 passes through a dark one of the filters 92. There is
consequently a reduction in beam intensity which causes the beam
intensity detection sensor 94 to drive the indicator 88 with a
signal indicative of the need to bring the device 2 closer to the
actuation apparatus. The indicator 88 responds to this signal by
communicating the need to a user of the system.
[0276] Alternatively, the signal indicative of the need to bring
the device 2 closer to the actuation apparatus can be applied to a
computer which performs corrections automatically.
[0277] In like manner, when the device 2 is excessively close to
the actuation apparatus 6, the second reflected distance
measurement beam 84 passes through a lighter one of the filters 92.
There is consequently an increase in beam intensity which causes
the beam intensity detection sensor 94 to drive the indicator 88
with a signal indicative of the need to move the device 2 farther
from the actuation apparatus. The indicator 88 responds to this
signal by communicating the need to a user of the system.
[0278] In addition, computer-controlled movement of the actuation
apparatus farther away from the device 2 may be achieved
automatically by providing an appropriate computer-controlled
moving mechanism responsive to the signal indicative of the need to
move the device 2 farther from the actuation apparatus.
[0279] With reference to FIG. 3, the indicator 88 preferably
comprises three LEDs arranged in a horizontal line across the
second end 68 of the housing 64. When illuminated, the left LED
88a, which is preferably yellow, indicates that the contact device
2 is too far from the actuation apparatus 6 and the detecting
arrangement 8. Similarly, when illuminated, the right LED 88b,
which is preferably red, indicates that the contact device 2 is too
close to the actuation apparatus 6 and the detecting arrangement 8.
When the proper distance is achieved, the central LED 88c is
illuminated. Preferably, the central LED 88c is green. The LEDs
88a-88c are selectively illuminated by the beam intensity detection
sensor 94 in response to the beam's intensity.
[0280] Although FIG. 1 illustrates an arrangement of filters 92
wherein a reduction in intensity signifies a need to move the
device closer, it is understood that the present invention is not
limited to such an arrangement. The multi-filter optical element
90, for example, may be reversed so that the darkest of the filters
92 is positioned adjacent the end 68 of the tubular housing 64.
When such an arrangement is used, an increase in beam intensity
would signify a need to move the device 2 farther away from the
actuation apparatus 6.
[0281] Preferably, the actuation apparatus 6 (or at least the coil
30 thereof) is slidably mounted within the housing 64 and a knob
and gearing (e.g., rack and pinion) mechanism are provided for
selectively moving the actuation apparatus 6 (or coil 30 thereof)
axially through the housing 64 in a perfectly linear manner until
the appropriate axial distance from the contact device 2 is
achieved. When such an arrangement is provided, the first end 66 of
the housing 64 serves as a positioning mechanism for the contact
device 2 against which the patient presses the facial area
surrounding eye to be examined. Once the facial area rests against
the first end 66, the knob and gearing mechanism are manipulated to
place the actuation apparatus 6 (or coil 30 thereof) at the proper
axial distance from the contact device 2.
[0282] Although facial contact with the first end 66 enhances
stability, it is understood that facial contact is not an essential
step in utilizing the present invention.
[0283] The system also preferably includes an optical alignment
mechanism for indicating whether the device 2 is properly aligned
with the actuation apparatus 6 and the detecting arrangement 8. The
optical alignment mechanism includes two alignment beam detectors
48',50' for respectively detecting the reflected beams 60,62 of
light prior to any applanation. The alignment beam detectors
48',50' are arranged so that the reflected beams 60,62 of light
respectively strike a predetermined portion of the alignment beam
detectors 48',50' prior to applanation only when the device 2 is
properly aligned with respect to the actuation apparatus 6 and the
detecting arrangement 8. When the device 2 is not properly aligned,
the reflected beams 60,62 strike another portion of the alignment
beam detectors 48',50', as will be described hereinafter.
[0284] The optical alignment mechanism further includes an
indicator arrangement responsive to the alignment beam detectors
48',50'. The indicator arrangement preferably includes a set of
LEDs 98,100,102,104 which indicate that the proper alignment has
been achieved only when the reflected beams 60,62 of light
respectively strike the predetermined portion of the alignment beam
detectors 48',50' prior to applanation.
[0285] Preferably, each of the alignment beam detectors 48',50'
includes a respective multi-filter optical element 106,108. The
multi-filter optical elements 106,108 are arranged so as to receive
the reflected beams 60,62 of light. Each multi-filter optical
element 106,108 contains a plurality of optical filters
110.sub.10-110.sub.90 (FIGS. 4 and 5), each of which filters out a
different percentage of light. In FIGS. 4 and 5, the different
percentages are labeled between 10 and 90 percent in increments of
ten percent. It is understood, however, that many other
arrangements and increments will suffice.
[0286] For the illustrated arrangement, it is preferred that the
centrally located filters 110.sub.50 which filter out 50% of the
light represent the predetermined portion of each alignment beam
detector 48',50'. Proper alignment is therefore deemed to exist
when the reflected beams 60,62 of light pass through the filters
110.sub.50 and the intensity of the beams 60,62 is reduced by
50%.
[0287] Each of the alignment beam detectors 48',50' also preferably
includes a beam intensity detector 112,114 for respectively
detecting the intensity of the reflected beams 60,62 of light after
the reflected beams 60,62 of light pass through the multi-filter
optical elements 106,108. The intensity of each beam is indicative
of whether the device 2 is properly aligned with respect to the
actuation apparatus 6 and the detecting arrangement.
[0288] A converging lens 116,118 is preferably located between each
multi-filter optical element 106,108 and its respective beam
intensity detector 112,114. The converging lens 116,118 focusses
the reflected beams 60,62 of light onto the beam intensity
detectors 112,114 after the reflected beams 60,62 pass through the
multi-filter optical elements 106,108.
[0289] Each of the beam intensity detectors 112,114 has its output
connected to an alignment beam detection circuit which, based on
the respective outputs from the beam intensity detectors 112,114,
determines whether there is proper alignment, and if not, drives
the appropriate one or ones of the LEDs 98,100,102,104 to indicate
the corrective action which should be taken.
[0290] As illustrated in FIG. 3, the LEDs 98,100,102,104 are
respectively arranged above, to the right of, below, and to the
left of the intersection of the cross-hairs 70. No LEDs
98,100,102,104 are illuminated unless there is a misalignment.
Therefore, a lack of illumination indicates that the device 2 is
properly aligned with the actuation apparatus 6 and the detecting
arrangement 8.
[0291] When the device 2 on the cornea 4 is too high, the beams
56,58 of light strike a lower portion of the cornea 4 and because
of the cornea's curvature, are reflected in a more downwardly
direction. The reflected beams 60,62 therefore impinge on the lower
half of the multi-filter elements 106,108, and the intensity of
each reflected beam 60,62 is reduced by no more than 30%. The
respective intensity reductions are then communicated to the
alignment detection circuit 120 by the beam intensity detectors
112,114. The alignment detection circuit 120 interprets this
reduction of intensity to result from a misalignment wherein the
device 2 is too high. The alignment detection circuit 120 therefore
causes the upper LED 98 to illuminate. Such illumination indicates
to the user that the device 2 is too high and must be lowered with
respect to the actuation apparatus 6 and the detecting arrangement
8.
[0292] Similarly, when the device 2 on the cornea 4 is too low, the
beams 56,58 of light strike an upper portion of the cornea 4 and
because of the cornea's curvature, are reflected in a more upwardly
direction. The reflected beams 60,62 therefore impinge on the upper
half of the multi-filter elements 106,108, and the intensity of
each reflected beam 60,62 is reduced by at least 70%. The
respective intensity reductions are then communicated to the
alignment detection circuit 120 by the beam intensity detectors
112,114. The alignment detection circuit 120 interprets this
particular reduction of intensity to result from a misalignment
wherein the device 2 is too low. The alignment detection circuit
120 therefore causes the lower LED 102 to illuminate. Such
illumination indicates to the user that the device 2 is too low and
must be raised with respect to the actuation apparatus 6 and the
detecting arrangement 8.
[0293] With reference to FIG. 1, when the device 2 is too far to
the right, the beams 56,58 strike a more leftward side of the
cornea 4 and because of the cornea's curvature, are reflected in a
more leftward direction. The reflected beams 60,62 therefore
impinge on the left halves of the multi-filter elements 106,108.
Since the filtering percentages decrease from left to right in
multi-filter element 106 and increase from left to right in
multifilter element 108, there will be a difference in the
intensities detected by the beam intensity detectors 112,114. In
particular, the beam intensity detector 112 will detect less
intensity than the beam intensity detector 114. The different
intensities are then communicated to the alignment detection
circuit 120 by the beam intensity detectors 112,114. The alignment
detection circuit 120 interprets the intensity difference wherein
the intensity at the beam intensity detector 114 is higher than
that at the beam intensity detector 112, to result from a
misalignment wherein the device 2 is too far to the right in FIG. 1
(too far to the left in FIG. 3). The alignment detection circuit
120 therefore causes the left LED 104 to illuminate. Such
illumination indicates to the user that the device 2 is too far to
the left (in FIG. 3) and must be moved to the right (left in FIG.
1) with respect to the actuation apparatus 6 and the detecting
arrangement 8.
[0294] Similarly, when the device 2 in FIG. 1 is too far to the
left, the beams 56,58 strike a more rightward side of the cornea 4
and because of the cornea's curvature, are reflected in a more
rightwardly direction. The reflected beams 60,62 therefore impinge
on the right halves of the multi-filter elements 106,108. Since the
filtering percentages decrease from left to right in multi-filter
element 106 and increase from left to right in multifilter element
108, there will be a difference in the intensities detected by the
beam intensity detectors 112,114. In particular, the beam intensity
detector 112 will detect more intensity than the beam intensity
detector 114. The different intensities are then communicated to
the alignment detection circuit 120 by the beam intensity detectors
112,114. The alignment detection circuit 120 interprets the
intensity difference wherein the intensity at the beam intensity
detector 114 is lower than that at the beam intensity detector 112,
to result from a misalignment wherein the device 2 is too far to
the left in FIG. 1 (too far to the right in FIG. 3). The alignment
detection circuit 120 therefore causes the right LED 100 to
illuminate. Such illumination indicates to the user that the device
2 is too far to the right (in FIG. 3) and must be moved to the left
(right in FIG. 1) with respect to the actuation apparatus 6 and the
detecting arrangement 8.
[0295] The combination of LEDs 98,100,102,104 and the alignment
detection circuit 120 therefore constitutes a display arrangement
which is responsive to the beam intensity detectors 112,114 and
which indicates what corrective action should be taken, when the
device 2 is not properly aligned, in order to achieve proper
alignment. Preferably, the substantially transparent peripheral
portion 36 of the movable central piece 16 is wide enough to permit
passage of the beams 56,58 to the cornea 4 even during
misalignment.
[0296] It is understood that automatic alignment correction may be
provided via computer-controlled movement of the actuation
apparatus upwardly, downwardly, to the right, and/or to the left,
which computer-controlled movement may be generated by an
appropriate computer-controlled moving mechanism responsive to the
optical alignment mechanism.
[0297] The optical alignment mechanism is preferably used in
conjunction with the sighting arrangement, so that the optical
alignment mechanism merely provides indications of minor alignment
corrections while the sighting arrangement provides an indication
of major alignment corrections. It is understood, however, that the
optical alignment mechanism can be used in lieu of the sighting
mechanism if the substantially transparent peripheral portion 36 is
made wide enough.
[0298] Although the foregoing alignment mechanism uses the same
reflected beams 60,62 used by the detecting arrangement 8, it is
understood that separate alignment beam emitters may be used in
order to provide separate and distinct alignment beams. The
foregoing arrangement is preferred because it saves the need to
provide additional emitters and thus is less expensive to
manufacture.
[0299] Nevertheless, optional alignment beam emitters 122,124 are
illustrated in FIG. 1. The alignment mechanism using these optional
alignment beam emitters 122,124 would operate in essentially the
same manner as its counterpart which uses the reflected beams
60,62.
[0300] In particular, each of the alignment beam emitters 122,124
emits an optical alignment beam toward the device 2. The alignment
beam is reflected by the cornea 4 to produce a reflected alignment
beam. The alignment beam detectors 48',50' are arranged so as to
receive, not the reflected beams 60,62 of light, but rather the
reflected alignment beams when the alignment beam emitters 122,124
are present. More specifically, the reflected alignment beams
strike a predetermined portion of each alignment beam detector
48',50' prior to applanation only when the device 2 is properly
aligned with respect to the actuation apparatus 6 and the detecting
arrangement 8. The rest of the system preferably includes the same
components and operates in the same manner as the system which does
not use the optional, alignment beam emitters 122, 124.
[0301] The system may further include an applicator for gently
placing the contact device 2 on the cornea 4. As illustrated in
FIGS. 5A-5F, a preferred embodiment of the applicator 127 includes
an annular piece 127A at the tip of the applicator 127. The annular
piece 127A matches the shape of the movable central piece 16.
Preferably, the applicator 127 also includes a conduit 127CN having
an open end which opens toward the annular piece 127A. An opposite
end of the conduit 127CN is connected to a squeeze bulb 127SB. The
squeeze bulb 127SB includes a one-way valve 127V which permits the
flow of air into the squeeze bulb 127SB, but prevents the flow of
air out of the squeeze bulb 127SB through the valve 127V. When the
squeeze bulb 127SB is squeezed and then released, a suction effect
is created at the open end of the conduit 127CN as the squeeze bulb
127SB tries to expand to its pre-squeeze shape. This suction effect
may be used to retain the contact device 2 at the tip of the
applicator 127.
[0302] In addition, a pivoted lever system 127B is arranged to
detach the movable central piece 16 from the annular piece 127A
when a knob 127C at the base of the applicator 127 is pressed,
thereby nudging the contact device 2 away from the annular piece
127A.
[0303] Alternatively, the tip of the applicator 127 may be
selectively magnetized and demagnetized using electric current
flowing through the annular piece 127A. This arrangement replaces
the pivoted lever system 127B with a magnetization mechanism
capable of providing a magnetic field which repels the movable
central piece 16, thereby applying the contact device 2 to the
cornea 4.
[0304] A preferred circuit arrangement for implementing the above
combination of elements is illustrated schematically in FIG. 6.
According to the preferred circuit arrangement, the beam intensity
detectors 112,114 comprise a pair of photosensors which provide a
voltage output proportional to the detected beam intensity. The
output from each beam intensity detector 112,114 is respectively
connected to the non-inverting input terminal of a filtering
amplifier 126,128. The inverting terminals of the filtering
amplifiers 126,128 are connected to ground. The amplifiers 126,128
therefore provide a filtering and amplification effect.
[0305] In order to determine whether proper vertical alignment
exists, the output from the filtering amplifier 128 is applied to
an inverting input terminal of a vertical alignment comparator 130.
The vertical alignment comparator 130 has its non-inverting input
terminal connected to a reference voltage Vref.sub.1. The reference
voltage Vref.sub.1 is selected so that it approximates the output
from the filtering amplifier 128 whenever the light beam 62 strikes
the central row of filters 110.sub.40-60 of the multi-filter
optical element 108 (i.e., when the proper vertical alignment is
achieved).
[0306] Consequently, the output from the comparator 130 is
approximately zero when proper vertical alignment is achieved, is
significantly negative when the contact device 2 is too high, and
is significantly positive when the contact device 2 is too low.
This output from the comparator 130 is then applied to a vertical
alignment switch 132. The vertical alignment switch 132 is
logically arranged to provide a positive voltage to an AND-gate 134
only when the output from the comparator 130 is approximately zero,
to provide a positive voltage to the LED 98 only when the output
from the comparator 130 is negative, and to provide a positive
voltage to the LED 102 only when the output from the comparator 130
is positive. The LEDs 98,102 are thereby illuminated only when
there is a vertical misalignment and each illumination clearly
indicates what corrective action should to be taken.
[0307] In order to determine whether proper horizontal alignment
exists, the output from the filtering amplifier 126 is applied to a
non-inverting input terminal of a horizontal alignment comparator
136, while the inverting input terminal of the horizontal alignment
comparator 136 is connected to the output from the filtering
amplifier 128. The comparator 136 therefore produces an output
which is proportional to the difference between the intensities
detected by the beam intensity detectors 112,114. This difference
is zero whenever the light beams 60,62 strike the central column of
filters 110.sub.20, 110.sub.50, 110.sub.80 of the multi-filter
optical elements 106,108 (i.e., when the proper horizontal
alignment is achieved).
[0308] The output from the comparator 136 is therefore zero when
the proper horizontal alignment is achieved, is negative when the
contact device 2 is too far to the right (in FIG. 1), and is
positive when the contact device 2 is too far to the left (in FIG.
1). This output from the comparator 130 is then applied to a
horizontal alignment switch 138. The horizontal alignment switch
138 is logically arranged to provide a positive voltage to the
AND-gate 134 only when the output from the comparator 136 is zero,
to provide a positive voltage to the LED 104 only when the output
from the comparator 136 is negative, and to provide a positive
voltage to the LED 100 only when the output from the comparator 136
is positive. The LEDs 100, 104 are thereby illuminated only when
there is a horizontal misalignment and each illumination clearly
indicates what corrective action should be taken.
[0309] In accordance with the preferred circuit arrangement
illustrated in FIG. 6, the beam intensity detection sensor 94 of
the distance measurement beam detector 86 includes a photosensor
140 which produces a voltage output proportional to the detected
beam intensity. This voltage output is applied to the non-inverting
input terminal of a filtering amplifier 142. The inverting terminal
of the filtering amplifier 142 is connected to ground. Accordingly,
the filtering amplifier 142 filters and amplifies the voltage
output from the photosensor 140. The output from the filtering
amplifier 142 is applied to the non-inverting input terminal of a
distance measurement comparator 144. The comparator 144 has its
inverting terminal connected to a reference voltage Vref.sub.2.
Preferably, the reference voltage Vref.sub.2 is selected so as to
equal the output of the filtering amplifier 142 only when the
proper axial distance separates the contact device 2 from the
actuation apparatus 6 and detecting arrangement 8.
[0310] Consequently, the output from the comparator 144 is zero
whenever the proper axial distance is achieved, is negative
whenever the second reflected beam 84 passes through a dark portion
of the multi-filter optical element 90 (i.e., whenever the axial
distance is too great), and is positive whenever the second
reflected beam 84 passes through a light portion of the
multi-filter optical element 90 (i.e., whenever the axial distance
is too short).
[0311] The output from the comparator 144 is then applied to a
distance measurement switch 146. The distance measurement switch
146 drives the LED 88c with positive voltage whenever the output
from the comparator 144 is zero, drives the LED 88b only when the
output from the comparator 144 is positive, and drives the LED 88a
only when the output from the comparator 144 is negative. The LEDs
88a,88b are thereby illuminated only when the axial distance
separating the contact device 2 from the actuation apparatus 6 and
the detecting arrangement 8 is improper. Each illumination clearly
indicates what corrective action should be taken. Of course, when
the LED 88c is illuminated, no corrective action is necessary.
[0312] With regard to the detecting arrangement 8, the preferred
circuit arrangement illustrated in FIG. 6 includes the two light
sensors 48,50. The outputs from the light sensors 48,50 are applied
to and added by an adder 147. The output from the adder 147 is then
applied to the non-inverting input terminal of a filtering
amplifier 148. The inverting input terminal of the same amplifier
148 is connected to ground. As a result, the filtering amplifier
148 filters and amplifies the sum of the output voltages from the
light sensor 48,50. The output from the filtering amplifier 148 is
then applied to the non-inverting input terminal of an applanation
comparator 150. The inverting input terminal of the applanation
comparator 150 is connected to a reference voltage Vref.sub.3.
Preferably, the reference voltage Vref.sub.3 is selected so as to
equal the output from the filtering amplifier 148 only when the
predetermined amount of applanation is achieved (i.e., when the
reflected beams 60,62 strike the light sensors 48,50). The output
from the applanation comparator 150 therefore remains negative
until the predetermined amount of applanation is achieved.
[0313] The output from the applanation comparator 150 is connected
to an applanation switch 152. Th applanation switch 152 provides a
positive output voltage when the output from the applanation
comparator 150 is negative and terminates its positive output
voltage whenever the output from the applanation comparator 150
becomes positive.
[0314] Preferably, the output from the applanation switch 152 is
connected to an applanation speaker 154 which audibly indicates
when the predetermined amount of applanation has been achieved. In
particular, the speaker 154 is activated whenever the positive
output voltage from the applanation, switch 152 initially
disappears.
[0315] In the preferred circuit of FIG. 6, the coil 30 is
electrically connected to the current producing circuitry 32 which,
in turn, includes a signal generator capable of producing the
progressively increasing current in the coil 30. The current
producing circuitry 32 is controlled by a start/stop switch 156
which is selectively activated and deactivated by an AND-gate
158.
[0316] The AND-gate 158 has two inputs, both of which must exhibit
positive voltages in order to activate the start/stop switch 156
and current producing circuitry 32. A first input 160 of the two
inputs is the output from the applanation switch 152. Since the
applanation switch 152 normally has a positive output voltage, the
first input 160 remains positive and the AND-gate is enabled at
least with respect to the first input 160. However, whenever the
predetermined amount of applanation is achieved (i.e. whenever the
positive output voltage is no longer present at the output from the
applanation switch 152), the AND-gate 158 deactivates the current
producing circuitry 32 via the start/stop switch 156.
[0317] The second input to the AND-gate 158 is the output from
another AND-gate 162. The other AND-gate 162 provides a positive
output voltage only when a push-action switch 164 is pressed and
only when the contact device 2 is located at the proper axial
distance from, and is properly aligned both vertically and
horizontally with, the actuation apparatus 6 and the detecting
arrangement 8. The current producing circuitry 32 therefore cannot
be activated unless there is proper alignment and the proper axial
distance has been achieved. In order to achieve such operation, the
output from the AND-gate 134 is connected to a first input of the
AND-gate 162 and the push-action switch 164 is connected to the
second input of the AND-gate 162.
[0318] A delay element 163 is located electrically between the
AND-gate 134 and the AND-gate 162. The delay element 163 maintains
a positive voltage at the first input terminal to the AND-gate 162
for a predetermined period of time after a positive voltage first
appears at the output terminal of the AND-gate 134. The primary
purpose of the delay element 163 is to prevent deactivation of the
current producing circuitry 32 which would otherwise occur in
response to changes in the propagation direction of the reflected
beams 60,62 during the initial stages of applanation. The
predetermined period of time is preferably selected pursuant to the
maximum amount of time that it could take to achieve the
predetermined amount of applanation.
[0319] According to the preferred circuitry illustrated in FIG. 6,
misalignment and improper axial separation of the contact device 2
with respect to the actuation apparatus 6 and detecting arrangement
8 is audibly announced by a speaker 166 and causes deactivation of
a display 167. The display 167 and speaker 166 are connected and
responsive to an AND-gate 168. The AND-gate 168 has an inverting
input connected to the push-action switch 164 and another input
connected to a three-input OR-gate 170.
[0320] Therefore, when the push-action switch 164 is activated, the
inverting input terminal of the AND-gate 168 prevents a positive
voltage from appearing at the output from the AND-gate 168.
Activation of the speaker 166 is thereby precluded. However, when
the push-action switch is not activated, any positive voltage at
any of the three inputs to the OR-gate 170 will activate the
speaker 166. The three inputs to the OR-gate 170 are respectively
connected to outputs from three other OR-gates 172,174,176. The
OR-gates 172,174,176, in turn, have their inputs respectively
connected to the LEDs 100.104, LEDs 98,102, and LEDs 88a,88b.
Therefore, whenever any one of these LEDs 88a, 88b, 98, 100, 102,
104 is activated, the OR-gate 170 produces a positive output
voltage. The speaker 166, as a result, will be activated whenever
any one of the LEDs 88a,88b,98,100,102,104 is activated while the
push-action switch 164 remains deactivated.
[0321] Turning now to the current producing circuitry 32, the
output from the current producing circuitry 32 is connected to the
coil 30. The coil 30, in turn, is connected to a current-to-voltage
transducer 178. The output voltage from the current-to-voltage
transducer 178 is proportional to the current flowing through the
coil 30 and is applied to the calculation unit 10.
[0322] The calculation unit 10 receives the output voltage from the
transducer 178 and converts this output voltage indicative of
current to an output voltage indicative of intraocular pressure.
Initially, an output voltage from the filtering amplifier 142
indicative of the axial distance separating the contact device 2
from the actuation apparatus 6 and the detecting arrangement 8, is
multiplied by a reference voltage Vref.sub.4 using a multiplier
180. The reference voltage Vref.sub.4 represents a distance
calibration constant. The output from the multiplier 180 is then
squared by a multiplier 182 to create an output voltage indicative
of distance squared (d.sup.2).
[0323] The output from the multiplier 182 is then supplied to an
input terminal of a divider 184. The other input terminal of the
divider 184 receives the output voltage indicative of current from
the current-to-voltage transducer 178. The divider 184 therefore
produces an output voltage indicative of the current in the coil 30
divided by the distance squared (I/d.sup.2).
[0324] The output voltage from the divider 184 is then applied to a
multiplier 186. The multiplier 186 multiplies the output voltage
from the divider 184 by a reference voltage Vref.sub.5. The
reference voltage Vref.sub.5 corresponds to a conversion factor for
converting the value of (I/d.sup.2) to a value indicative of force
in Newtons being applied by the movable central piece 16 against
the cornea 4. The output voltage from the multiplier 186 is
therefore indicative of the force in Newtons being applied by the
movable central piece 16 against the cornea.
[0325] Next, the output voltage from the multiplier 186 is applied
to an input terminal of a divider 188. The other input terminal of
the divider 188 receives a reference voltage Vref.sub.6. The
reference voltage Vref.sub.6 corresponds to a calibration constant
for converting force (in Newtons) to pressure (in Pascals)
depending on the surface area of the movable central piece's
substantially flat inner side 24. The output voltage from the
divider 188 is therefore indicative of the pressure (in Pascals)
being exerted by the cornea 4 against the inner side of the movable
central piece 16 in response to displacement of the movable central
piece 16.
[0326] Since the pressure exerted by the cornea 4 depends upon the
surface area of the substantially flat inner side 24, the output
voltage from the divider 188 is indicative of intraocular pressure
only when the cornea 4 is being applanated by the entire surface
area of the inner side 24. This, in turn, corresponds to the
predetermined amount of applanation.
[0327] Preferably, the output voltage indicative of intraocular
pressure is applied to an input terminal of a multiplier 190. The
multiplier 190 has another input terminal connected to a reference
voltage Vref.sub.7. The reference voltage Vref.sub.7 corresponds to
a conversion factor for converting pressure in Pascals to pressure
in millimeters of mercury (mmHg). The voltage output from the
multiplier 190 therefore is indicative of intraocular pressure in
millimeters of mercury (mmHg) whenever the predetermined amount of
applanation is achieved.
[0328] The output voltage from the multiplier 190 is then applied
to the display 167 which provides a visual display of intraocular
pressure based on this output voltage. Preferably, the display 167
or calculation unit 10 includes a memory device 33 which stores a
pressure value associated with the output voltage from the
multiplier 190 whenever the predetermined amount of applanation is
achieved. Since the current producing circuitry 32 is automatically
and immediately deactivated upon achieving the predetermined amount
of applanation, the intraocular pressure corresponds to the
pressure value associated with the peak output voltage from the
multiplier 190. The memory therefore can be triggered to store the
highest pressure value upon detecting a drop in the output voltage
from the multiplier 190. Preferably, the memory is automatically
reset prior to any subsequent measurements of intraocular
pressure.
[0329] Although FIG. 6 shows the display 167 in digital form, it is
understood that the display 167 may have any known form. The
display 167 may also include the three LEDs 40A,40B,40C illustrated
in FIG. 1 which give a visual indication of pressure ranges which,
in turn, are calibrated for each patient.
[0330] As indicated above, the illustrated calculation unit 10
includes separate and distinct multipliers 180,182,186,190 and
dividers 184,188 for converting the output voltage indicative of
current into an output voltage indicative of intraocular pressure
in millimeters of mercury (mmHg). The separate and distinct
multipliers and dividers are preferably provided so that variations
in the system's characteristics can be compensated for by
appropriately changing the reference voltages Vref.sub.4,
Vref.sub.5, Vref.sub.6 and/or Vref.sub.7. It is understood,
however, that when all of the system's characteristics remain the
same (e.g., the surface area of the inner side 24 and the desired
distance separating the contact device 2 from the actuation
apparatus 6 and detecting arrangement 8) and the conversion factors
do not change, that a single conversion factor derived from the
combination of each of the other conversion factors can be used
along with a single multiplier or divider to achieve the results
provided by the various multipliers and dividers shown in FIG.
6.
[0331] Although the above combination of elements is generally
effective at accurately measuring intraocular pressure in a
substantial majority of patients, some patients have unusually thin
or unusually thick corneas. This, in turn, may cause slight
deviations in the measured intraocular pressure. In order to
compensate for such deviations, the circuitry of FIG. 6 may also
include a variable gain amplifier 191 (illustrated in FIG. 7A)
connected to the output from the multiplier 190. For the majority
of patients, the variable gain amplifier 191 is adjusted to provide
a gain (g) of one. The variable gain amplifier 191 therefore would
have essentially no effect on the output from the multiplier
190.
[0332] However, for patients with unusually thick corneas, the gain
(g) is adjusted to a positive gain less than one. A gain (g) of
less than one is used because unusually thick corneas are more
resistant to applanation and consequently result in a pressure
indication that exceeds, albeit by a small amount, the actual
intraocular pressure. The adjustable gain amplifier 191 therefore
reduces the output voltage from the multiplier 190 by a selected
percentage proportional to the cornea's deviation from normal
corneal thickness.
[0333] For patients with unusually thin corneas, the opposite
effect would be observed. Accordingly, for those patients, the gain
(g) is adjusted to a positive gain greater than one so that the
adjustable gain amplifier 191 increases the output voltage from the
multiplier 190 by a selected percentage proportional to the
cornea's deviation from normal corneal thickness.
[0334] Preferably, the gain (g) is manually selected for each
patient using any known means for controlling the gain of a
variable gain amplifier, for example, a potentiometer connected to
a voltage source. As indicated above, the particular gain (g) used
depends on the thickness of each patient's cornea which, in turn,
can be determined using known corneal pachymetry techniques. Once
the corneal thickness is determined, the deviation from the normal
thickness is calculated and the gain (g) is set accordingly.
[0335] Alternatively, as illustrated in FIG. 7B, the gain (g) may
be selected automatically by connecting an output (indicative of
corneal thickness) from a known pachymetry apparatus 193 to a
buffer circuit 195. The buffer circuit 195 converts the detected
corneal thickness to a gain signal associated with the detected
thickness' deviation from the normal corneal thickness. In
particular, the gain signal produces a gain (g) of one when the
deviation is zero, produces a gain (g) greater than one when the
detected corneal thickness is less than the normal thickness, and
produces a gain (g) less than one when the detected corneal
thickness is greater than the normal thickness.
[0336] Although FIGS. 7A and 7B illustrate a configuration which
compensates only for corneal thickness, it is understood that
similar configurations can be used to compensate for corneal
curvature, eye size, ocular rigidity, and the like. For levels of
corneal curvature which are higher than normal, the gain would be
less than one. The gain would be greater than one for levels of
corneal curvature which are flatter than normal. Typically, each
increase in one diopter of corneal curvature is associated with a
0.34 mm Hg increase in pressure. The intraocular pressure rises 1
mm Hg for very 3 diopters. The gain therefore can be applied in
accordance with this general relationship.
[0337] In the case of eye size compensation, larger than normal
eyes would require a gain which is less than one, while smaller
than normal eyes would require a gain which is greater than
one.
[0338] For patients with "stiffer" than normal ocular rigidities,
the gain is less than one, but for patients with softer ocular
rigidities, the gain is greater than one.
[0339] As when compensating for corneal thickness, the gain may be
manually selected for each patient, or alternatively, the gain may
be selected automatically by connecting the apparatus of the
present invention to a known keratometer when compensating for
corneal curvature, and/or a known biometer when compensating for
eye size.
[0340] Despite not being illustrated, it is understood that the
system includes a power supply mechanism for selectively powering
the system using either batteries or household AC current.
[0341] Operation of the preferred circuitry will now be described.
Initially, the contact device 2 is mounted on the corneal surface
of a patient and tends to locate itself centrally at the front of
the cornea 4 in essentially the same way as conventional contact
lenses. The patient then looks through the central sight hole 38 at
the intersection of the cross-hairs which define the mark 70,
preferably, while the light 75 provided inside the tubular housing
64 is illuminated to facilitate visualization of the cross-hairs
and the reflected image 74. A rough alignment is thereby
achieved.
[0342] Next, the preferred circuitry provides indications of
misalignment or improper axial distance should either or both
exist. The patient responds to such indications by taking the
indicated corrective action.
[0343] Once proper alignment is achieved and the proper axial
distance exists between the actuation apparatus 6 and the contact
device 2, push-action switch 164 is activated and the AND-gate 158
and start/stop switch 156 activate the current producing circuitry
32. In response to activation, the current producing circuitry 32
generates the progressively increasing current in the coil 30. The
progressively increasing current creates a progressively increasing
magnetic field in the coil 30. The progressively increasing
magnetic field, in turn, causes axial displacement of the movable
central piece 16 toward the cornea 4 by virtue of the magnetic
field's repulsive effect on the magnetically responsive element 26.
Since axial displacement of the movable central piece 16 produces a
progressively increasing applanation of the cornea 4, the reflected
beams 60,62 begin to swing angularly toward the light sensors
48,50. Such axial displacement and increasing applanation continues
until both reflected beams 60,62 reach the light sensors 48,50 and
the predetermined amount of applanation is thereby deemed to exist.
At that instant, the current producing circuit 32 is deactivated by
the input 160 to AND-gate 158; the speaker 154 is momentarily
activated to give an audible indication that applanation has been
achieved; and the intraocular pressure is stored in the memory
device 33 and is displayed on display 167.
[0344] Although the above-described and illustrated embodiment
includes various preferred elements, it is understood that the
present invention may be achieved using various other individual
elements. For example, the detecting arrangement 8 may utilize
various other elements, including elements which are typically
utilized in the art of barcode reading.
[0345] With reference to FIGS. 8A and 8B, a contact device 2' may
be provided with a barcode-like pattern 300 which varies in
response to displacement of the movable central piece 16'. FIG. 8A
illustrates the preferred pattern 300 prior to displacement of the
movable central piece 16'; and FIG. 8B shows the preferred pattern
300 when the predetermined amount of applanation is achieved. The
detecting arrangement therefore would include a barcode reader
directed generally toward the contact device 2' and capable of
detecting the differences in the barcode pattern 300.
[0346] Alternatively, as illustrated in FIGS. 9A and 9E, the
contact device 2' may be provided with a multi-color pattern 310
which varies in response to displacement of the movable central
piece 16'. FIG. 9A schematically illustrates the preferred color
pattern 310 prior to displacement of the movable central piece 16',
while FIG. 9B schematically shows the preferred pattern 310 when
the predetermined amount of applanation is achieved. The detecting
arrangement therefore would include a beam emitter for emitting a
beam of light toward the pattern 310 and a detector which receives
a reflected beam from the pattern 310 and detects the reflected
color to determine whether applanation has been achieved.
[0347] Yet another way to detect the displacement of the movable
central piece 16 is by using a two dimensional array photosensor
that senses the location of a reflected beam of light. Capacitive
and electrostatic sensors, as well as changes in magnetic field can
then be used to encode the position of the reflected beam and thus
the displacement of the movable central piece 16.
[0348] According to yet another alternative embodiment illustrated
in FIG. 10, a miniature LED 320 is inserted into the contact device
2'. The piezoelectric ceramic is driven by ultrasonic waves or is
alternatively powered by electromagnetic waves. The brightness of
the miniature LED 320 is determined by the current flowing through
the miniature LED 320 which, in turn, may be modulated by a
variable resistance 330. The motion of the movable central piece
16' varies the variable resistance 330. Accordingly, the intensity
of light from the miniature LED 320 indicates the magnitude of the
movable central piece's displacement. A miniature, low-voltage
primary battery 340 may be inserted into the contact device 2' for
powering the miniature LED 320.
[0349] With regard to yet another preferred embodiment of the
present invention, it is understood that a tear film typically
covers the eye and that a surface tension resulting therefrom may
cause underestimation of the intraocular pressure. Accordingly, the
contact device of the present invention preferably has an inner
surface of hydrophobic flexible material in order to decrease or
eliminate this potential source of error.
[0350] It should be noted that the drawings are merely schematic
representations of the preferred embodiments. Therefore, the actual
dimensions of the preferred embodiments and physical arrangement of
the various elements is not limited to that which is illustrated.
Various arrangements and dimensions will become readily apparent to
those of ordinary skill in the art. The size of the movable central
piece, for example, can be modified for use in animals or
experimental techniques. Likewise, the contact device can be made
with smaller dimensions for use with infants and patients with eye
lid abnormalities.
[0351] One preferred arrangement of the present invention includes
a handle portion extending out from below the housing 64 and
connected distally to a platform. The platform acts as a base for
placement on a planar surface (e.g., a table), with the handle
projecting up therefrom to support the actuation apparatus 6 above
the planar surface.
Indentation
[0352] The contact device 2 and associated system illustrated in
FIGS. 1-5 may also be used to detect intraocular pressure by
indentation. When indentation techniques are used in measuring
intraocular pressure, a predetermined force is applied against the
cornea using an indentation device. Because of the force, the
indentation device travels in toward the cornea, indenting the
cornea as it travels. The distance travelled by the indentation
device into the cornea in response to the predetermined force is
known to be inversely proportional to intraocular pressure.
Accordingly, there are various known tables which, for certain
standard sizes of indentation devices and standard forces,
correlate the distance travelled and intraocular pressure.
[0353] In utilizing the illustrated arrangement for indentation,
the movable central piece 16 of the contact device 2 functions as
the indentation device. In addition, the current producing circuit
32 is switched to operate in an indentation mode. When switched to
the indentation mode, the current producing circuit 32 supplies a
predetermined amount of current through the coil 30. The
predetermined amount of current corresponds to the amount of
current needed to produce one of the aforementioned standard
forces.
[0354] The predetermined amount of current creates a magnetic field
in the actuation apparatus 6. This magnetic field, in turn, causes
the movable central piece 16 to push inwardly against the cornea 4
via the flexible membrane 14. Once the predetermined amount of
current has been applied and a standard force presses against the
cornea, it is necessary to determine how far the movable central
piece 16 moved into the cornea 4.
[0355] Accordingly, when measurement of intraocular pressure by
indentation is desired, the system illustrated in FIG. 1 further
includes a distance detection arrangement for detecting a distance
travelled by the movable central piece 16, and a computation
portion 199 in the calculation unit 10 for determining intraocular
pressure based on the distance travelled by the movable central
piece 16 in applying the predetermined amount of force.
[0356] A preferred indentation distance detection arrangement 200
is illustrated in FIGS. 11A and 11B and preferably includes a beam
emitter 202 and a beam sensor 204. Preferably, lenses 205 are
disposed in the optical path between the beam emitter 202 and beam
sensor 204. The beam emitter 202 is arranged so as to emit a beam
206 of light toward the movable central piece 16. The beam 206 of
light is reflected back from the movable central piece 16 to create
a reflected beam 208. The beam sensor 204 is positioned so as to
receive the reflected beam 208 whenever the device 2 is located at
the proper axial distance and in proper alignment with the
actuation apparatus 6. Preferably, the proper distance and
alignment are achieved using all or any combination of the
aforementioned sighting mechanism, optical alignment mechanism and
optical distance measuring mechanism.
[0357] Once proper alignment and the proper axial distance are
achieved, the beam 206 strikes a first portion of the movable
central piece 16, as illustrated in FIG. 11A. Upon reflection of
the beam 206, the reflected beam 208 strikes a first portion of the
beam sensor 204. In FIG. 11A, the first portion is located on the
beam sensor 204 toward the right side of the drawing.
[0358] However, as indentation progresses, the movable central
piece 16 becomes more distant from the beam emitter 202. This
increase in distance is illustrated in FIG. 11A. Since the movable
central piece 16 moves linearly away, the beam 206 strikes
progressively more to the left on the movable central piece 16. The
reflected beam 206 therefore shifts toward the left and strikes 204
at a second portion which is to the left of the first portion.
[0359] The beam sensor 204 is arranged so as to detect the shift in
the reflected beam 206, which shift is proportional to the
displacement of the movable central piece 16. Preferably, the beam
sensor 204 includes an intensity responsive beam detector 212 which
produces an output voltage proportional to the detected intensity
of the reflected beam 208 and an optical filter element 210 which
progressively filters more light as the light's point of incidence
moves from one portion of the filter to an opposite portion.
[0360] In FIGS. 11A and 11B, the optical filter element 210
comprises a filter with a progressively increasing thickness so
that light passing through a thicker portion has a more
significantly reduced intensity than light passing through a
thinner portion of the filter. Alternatively, the filter can have a
constant thickness and progressively increasing filtering density
whereby a progressively increasing filtering effect is achieved as
the point of incidence moves across a longitudinal length of the
filter.
[0361] When, as illustrated in FIG. 11A, the reflected beam 208
passes through a thinnest portion of the optical filter element 210
(e.g., prior to indentation), the reflected beam's intensity is
reduced by only a small amount. The intensity responsive beam
detector 212 therefore provides a relatively high output voltage
indicating that no movement of the movable central piece 16 toward
the cornea 4 has occurred.
[0362] However, as indentation progresses, the reflected beam 208
progressively shifts toward thicker portions of the optical filter
element 210 which filter more light. The intensity of the reflected
beam 208 therefore decreases proportionally to the displacement of
the movable central piece 16 toward the cornea 4. Since the
intensity responsive beam detector 212 produces an output voltage
proportional to the reflected beam's intensity, this output voltage
decreases progressively as the displacement of the movable central
piece 16 increases. The output voltage from the intensity
responsive beam detector 212 is therefore indicative of the movable
central piece's displacement.
[0363] Preferably, the computation portion 199 is responsive to the
current producing circuitry 32 so that, once the predetermined
amount of force is applied, the output voltage from the beam
detectors 212 is received by the computation portion 199. The
computation portion then, based on the displacement associated with
the particular output voltage, determines intraocular pressure.
Preferably, the memory 33 includes a memory location for storing a
value indicative of the intraocular pressure.
[0364] Also, the computation portion 199 preferably has access to
an electronically or magnetically stored one of the aforementioned
known tables. Since the tables indicate which intraocular pressure
corresponds with certain distances traveled by the movable central
piece 16, the computation portion 199 is able to determine
intraocular pressure by merely determining which pressure
corresponds with the distance traveled by the movable central piece
16.
[0365] The system of the present invention may also be used to
calculate the rigidity of the sclera. In particular, the system is
first used to determine intraocular pressure by applanation and
then is used to determine intraocular pressure by indentation. The
differences between the intraocular pressures detected by the two
methods would then be indicative of the sclera's rigidity.
[0366] Although the foregoing description of the preferred systems
generally refers to a combined system capable of detecting
intraocular pressure by both applanation and indentation, it is
understood that a combined system need not be created. That is, the
system capable of determining intraocular pressure by applanation
may be constructed independently from a separate system for
determining intraocular pressure by indentation and vice versa.
Measuring Hydrodynamics of the Eye
[0367] The indentation device of the present invention may also be
utilized to non-invasively measure hydrodynamics of an eye
including outflow facility. The method of the present invention
preferably comprises several steps including the following:
[0368] According to a first step, an indentation device is placed
in contact with the cornea. Preferably, the indentation device
comprises the contact device 2 illustrated in FIGS. 1 and
2A-2D.
[0369] Next, at least one movable portion of the indentation device
is moved in toward the cornea using a first predetermined amount of
force to achieve indentation of the cornea. When the indentation
device is the contact device 2. the movable portion consists of the
movable central piece 16.
[0370] An intraocular pressure is then determined based on a first
distance traveled toward the cornea by the movable portion of the
indentation device during application of the first predetermined
amount of force. Preferably, the intraocular pressure is determined
using the aforementioned system for determining intraocular
pressure by indentation Next, the movable portion of the
indentation device is rapidly reciprocated in toward the cornea and
away from the cornea at a first predetermined frequency and using a
second predetermined amount of force during movement toward the
cornea to thereby force intraocular fluid out from the eye. The
second predetermined amount of force is preferably equal to or
greater than the first predetermined amount of force. It is
understood, however, that the second predetermined amount of force
may be less than the first predetermined amount of force. The
reciprocation, which preferably continues for 5 seconds, should
generally not exceed 10 seconds induration.
[0371] The movable portion is then moved in toward the cornea using
a third predetermined amount of force to again achieve indentation
of the cornea.
[0372] A second intraocular pressure is then determined based on a
second distance traveled toward the cornea by the movable portion
of the indentation device during application of the third
predetermined amount of force. This second intraocular pressure is
also preferably determined using the aforementioned system for
determining intraocular pressure by indentation. Since intraocular
pressure decreases as a result of forcing intraocular fluid out of
the eye during the rapid reciprocation of the movable portion, it
is generally understood that, unless the eye is so defective that
no fluid flows out therefrom, the second intraocular pressure will
be less than the first intraocular pressure. This reduction in
intraocular pressure is indicative of outflow facility.
[0373] Next, the movable portion of the indentation device is again
rapidly reciprocated in toward the cornea and away from the cornea,
but at a second predetermined frequency and using a fourth
predetermined amount of force during movement toward the cornea.
The fourth predetermined amount of force is preferably equal or
greater than the second predetermined amount of force. It is
understood, however, that the fourth predetermined amount of force
may be less than the second predetermined amount of force.
Additional intraocular fluid is thereby forced out from the eye.
This reciprocation, which also preferably continues for 5 seconds,
should generally not exceed 10 seconds in duration.
[0374] The movable portion is subsequently moved in toward the
cornea using a fifth predetermined amount of force to again achieve
indentation of the cornea.
[0375] Thereafter, a third intraocular pressure is determined based
on a third distance traveled toward the cornea by the movable
portion of the indentation device during application of the fifth
predetermined amount of force.
[0376] The differences are then preferably calculated between the
first, second, and third distances, which differences are
indicative of the volume of intraocular fluid which left the eye
and therefore are also indicative of the outflow facility. It is
understood that the difference between the first and last distances
may be used, and in this regard, it is not necessary to use the
differences between all three distances. In fact, the difference
between any two of the distances will suffice.
[0377] Although the relationship between the outflow facility and
the detected differences varies when the various parameters of the
method and the dimensions of the indentation device change, the
relationship for given parameters and dimensions can be easily
determined by known experimental techniques and/or using known
Friedenwald Tables.
[0378] The method of the present invention is preferably carried
out using an indenting surface which is three millimeters in
diameter and a computer equipped with a data acquisition board. In
particular, the computer generates the predetermined forces via a
digital-to-analog (D/A) converter connected to the current
generating circuitry 32. The computer then receives signals
indicative of the first, second, and third predetermined distances
via an analog-to-digital (A/D) converter. These signals are
analyzed by the computer using the aforementioned relationship
between the differences in distance and the outflow facility. Based
on this analysis, the computer creates an output signal indicative
of outflow facility. The output signal is preferably applied to a
display screen which, in turn, provides a visual indication of
outflow facility.
[0379] Preferably, the method further comprises the steps of
plotting the differences between the first, second, and third
distances to a create a graph of the differences and comparing the
resulting graph of differences to that of a normal eye to determine
if any irregularities in outflow facility are present. As indicated
above, however, it is understood that the difference between the
first and last distances may be used, and in this regard, it is not
necessary to use the differences between all three distances. In
fact, the difference between any two of the distances will
suffice.
[0380] Preferably, the first predetermined frequency and second
predetermined frequency are substantially equal and are
approximately 20 Hertz. Generally, any frequencies up to 35 Hertz
can be used, though frequencies below 1 Hertz are generally less
desirable because the stress relaxation of the eye's outer coats
would contribute to changes in pressure and volume.
[0381] The fourth predetermined amount of force is preferably at
least twice the second predetermined amount of force, and the third
predetermined amount of force is preferably approximately half of
the first predetermined amount of force. It is understood, however,
that other relationships will suffice and that the present method
is not limited to the foregoing preferred relationships.
[0382] According to a preferred use of the method, the first
predetermined amount of force is between 0.01 Newton and 0.015
Newton; the second predetermined amount of force is between 0.005
Newton and 0.0075 Newton; the third predetermined amount of force
is between 0.005 Newton and 0.0075 Newton; the fourth predetermined
amount of force is between 0.0075 Newton and 0.0125 Newton; the
fifth predetermined amount of force is between 0.0125 Newton and
0.025 Newton; the first predetermined frequency is between 1 Hertz
and 35 Hertz; and the second predetermined frequency is also
between 1 Hertz and 35 Hertz. The present method, however, is not
limited to the foregoing preferred ranges.
[0383] Although the method of the present invention is preferably
carried out using the aforementioned device, it is understood that
various other tonometers may be used. The method of the present
invention therefore is not limited in scope to its use in
conjunction with the claimed system and illustrated contact
device.
Alternative Embodiments of the Contact Device
[0384] Although the foregoing description utilizes an embodiment of
the contact device 2 which includes a flexible membrane 14 on the
inside surface of the contact device 2, it is readily understood
that the present invention is not limited to such an arrangement.
Indeed, there are many variations of the contact device which fall
well within the scope of the present invention.
[0385] The contact device 2, for example, may be manufactured with
no flexible membrane, with the flexible membrane on the outside
surface of the contact device 2 (i.e., the side away from the
cornea), with the flexible membrane on the inside surface of the
contact device 2, or with the flexible membrane on both sides of
the contact device 2.
[0386] Also, the flexible membrane (s) 14 can be made to have an
annular shape, thus permitting light to pass undistorted directly
to the movable central piece 16 and the cornea for reflection
thereby.
[0387] In addition, as illustrated in FIG. 12, the movable central
piece 16 may be formed with a similar annular shape so that a
transparent central portion thereof merely contains air. This way,
light passing through the entire contact device 2 impinges directly
on the cornea without undergoing any distortion due to the contact
device 2.
[0388] Alternatively, the transparent central portion can be filled
with a transparent solid material. Examples of such transparent
solid materials include polymethyl methacrylate, glass, hard
acrylic, plastic polymers, and the like. According to a preferred
arrangement, glass having an index of refraction substantially
greater than that of the cornea is utilized to enhance reflection
of light by the cornea when the light passes through the contact
device 2. Preferably, the index of refraction for the glass is
greater than 1.7, compared to the typical index of refraction of
1.37 associated with the cornea.
[0389] It is understood that the outer surface of the movable
central piece 16 may be coated with an anti-reflection layer in
order to eliminate extraneous reflections from that surface which
might otherwise interfere with operation of the alignment mechanism
and the applanation detecting arrangement.
[0390] The interconnections of the various components of the
contact device 2 are also subject to modification without departing
from the scope and spirit of the present invention. It is
understood therefore that many ways exist for interconnecting or
otherwise maintaining the working relationship between the movable
central piece 16, the rigid annular member 12, and the membranes
14.
[0391] When one or two flexible membranes 14 are used, for example,
the substantially rigid annular member 12 can be attached to any
one or both of the flexible membrane(s) 14 using any known
attachment techniques, such as gluing, heat-bonding, and the like.
Alternatively, when two flexible membranes 14 are used, the
components may be interconnected or otherwise maintained in a
working relationship, without having to directly attach the
flexible membrane 14 to the substantially rigid annular member 12.
Instead, the substantially rigid annular member 12 may be retained
between the two flexible membranes 14 by bonding the membranes to
one another about their peripheries while the rigid annular member
12 is sandwiched between the membranes 14.
[0392] Although the movable central piece 16 may be attached to the
flexible membrane(s) 14 by gluing, heat-bonding, and the like, it
is understood that such attachment is not necessary. Instead, one
or both of the flexible membranes 14 can be arranged so as to
completely or partially block the movable central piece 16 and
prevent it from falling out of the hole in the substantially rigid
annular member 12. When the aforementioned annular version of the
flexible membranes 14 is used, as illustrated by way of example in
FIG. 12, the diameter of the hole in at least one of the annular
flexible membranes 14 is preferably smaller than that of the hole
in the substantially rigid annular member 12 so that a radially
inner portion 14A of the annular flexible membrane 14 overlaps with
the movable central piece 16 and thereby prevents the movable
central piece 16 from falling out of the hole in the substantially
rigid annular member 12.
[0393] As illustrated in FIG. 13A, another way of keeping the
movable central piece 16 from falling out of the hole in the
substantially rigid annular member 12 is to provide arms 16A which
extend radially out from the movable central piece 16 and are
slidably received in respective grooves 16B. The grooves 16B are
formed in the rigid annular member 12. Each groove 16B has a
longitudinal dimension (vertical in FIG. 13) which is selectively
chosen to restrict the range of movement of the movable central
piece 16 to within predetermined limits. Although FIG. 13 shows an
embodiment wherein the grooves are in the substantially rigid
annular member 12 and the arms extend out from the movable central
piece 16, it is understood that an equally effective arrangement
can be created by reversing the configuration such that the grooves
are located in the movable central piece 16 and the arms extend
radially in from the substantially rigid annular member 12.
[0394] Preferably, the grooves 16B include resilient elements, such
as miniature springs, which bias the position of the movable
central piece 16 toward a desired starting position. In addition,
the arms 16A may include distally located miniature wheels which
significantly reduce the friction between the arms 16A and the
walls of the grooves 16B.
[0395] FIG. 13B illustrates another way of keeping the movable
central piece 16 from falling out of the hole in the substantially
rigid annular member 12. In FIG. 13B, the substantially rigid
annular member 12 is provided with radially inwardly extending
flaps 12F at the outer surface of the annular member 12. One of the
aforementioned annular membranes 14 is preferably disposed on the
inner side of the substantially rigid annular member 12.
Preferably, a portion of the membrane 14 extends radially inwardly
past the walls of the rigid annular member's hole. The combination
of the annular membrane 14 and the flaps 12F keeps the movable
central piece 16 from falling out of the hole in the substantially
rigid annular member 12.
[0396] The flaps 12F may also be used to achieve or facilitate
actuation of the movable central piece 16. In a magnetically
actuated embodiment, for example, the flaps 12F may be magnetized
so that the flaps 12F move inwardly in response to an externally
applied magnetic field.
[0397] With reference to FIG. 14, an alternative embodiment of the
contact device 2 is made using a soft contact lens material 12A
having a progressively decreasing thickness toward its outer
circumference. A cylindrical hole 12B is formed in the soft contact
lens material 12A. The hole 12B, however, does not extend entirely
through the soft contact lens material 12A. Instead, the hole has a
closed bottom defined by a thin portion 12C of the soft contact
lens material 12A. The movable central piece 16 is disposed
slidably within the hole 12B, and preferably, the thin portion 12C
is no more than 0.2 millimeters thick, thereby allowing the movable
central piece 16 to achieve applanation or indentation when moved
against the closed bottom of the hole toward the cornea with very
little interference from the thin portion 12C.
[0398] Preferably, a substantially rigid annular member 12D is
inserted and secured to the soft contact material 12A to define a
more stable wall structure circumferentially around the hole 12B.
This, in turn, provides more stability when the movable central
piece 16 moves in the hole 12B.
[0399] Although the soft lens material 12A preferably comprises
Hydrogel, silicone, flexible acrylic, or the like, it is understood
that any other suitable materials may be used. In addition, as
indicated above, any combination of flexible membranes may be added
to the embodiment of FIG. 14. Although the movable central piece 16
in FIG. 14 is illustrated as being annular, it is understood that
any other shape may be utilized. For example, any of the previously
described movable central pieces 16 would suffice.
[0400] Similarly, the annular version of the movable central piece
16 may be modified by adding a transparent bottom plate (not
illustrated) which defines a flat transparent bottom surface of the
movable central piece 16. When modified in this manner, the movable
central piece 16 would have a generally cup-shaped appearance.
Preferably, the flat transparent bottom surface is positioned
toward the cornea to enhance the flattening effect of the movable
central piece 16; however, it is understood that the transparent
plate can be located on the outside surface of the movable central
piece 16 if desired.
[0401] Although the movable central piece 16 and the hole in the
substantially rigid annular member 12 (or the hole in the soft
contact lens material 12A) are illustrated as having complementary
cylindrical shapes, it is understood that the complementary shapes
are not limited to a cylinder, but rather can include any shape
which permits sliding of the movable central piece 16 with respect
to its surrounding structure.
[0402] It is also understood that the movable central piece 16 may
be mounted directly onto the surface of a flexible membrane 14
without using a substantially rigid annular member 12. Although
such an arrangement defines a working embodiment of the contact
device 2, its stability, accuracy, and level of comfort are
significantly reduced compared to that of a similar embodiment
utilizing the substantially rigid annular member 12 with a
progressively tapering periphery.
[0403] Although the illustrated embodiments of the movable central
piece 16 include generally flat outside surfaces with well defined
lateral edges, it is understood that the present invention is not
limited to such arrangements. The present invention, for example,
can include a movable central piece 16 with a rounded outer surface
to enhance comfort and/or to coincide with the curvature of the
outer surface of the substantially rigid annular member 12. The
movable central piece can also be made to have any combination of
curved and flat surfaces defined at its inner and outer surfaces,
the inner surface being the surface at the cornea and the outer
surface being the surface directed generally away from the
cornea.
[0404] With reference to FIG. 15, the movable central piece 16 may
also include a centrally disposed projection 16P directed toward
the cornea. The projection 16P is preferably created by extending
the transparent solid material in toward the cornea at the center
of the movable central piece 16.
Alternative Embodiment for Measuring Intraocular Pressure by
Applanation
[0405] With reference to FIG. 16, an alternative embodiment of the
system for measuring intraocular pressure by applanation will now
be described. The alternative embodiment preferably utilizes the
version of the contact device 2 which includes a transparent
central portion.
[0406] According to the alternative embodiment, the schematically
illustrated coil 30 of the actuation apparatus includes an iron
core 30A for enhancing the magnetic field produced by the coil 30.
The iron core 30A preferably has an axially extending bore hole 30B
(approximately 6 millimeters in diameter) which permits the passage
of light through the iron core 30A and also permits mounting of two
lenses L3 and L4 therein.
[0407] In order for the system to operate successfully, the
strength of the magnetic force applied by the coil 30 on the
movable central piece 16 should be sufficient to applanate
patients' corneas over at least the full range of intraocular
pressures encountered clinically (i.e. 5-50 mm Hg). According to
the illustrated alternative embodiment, intraocular pressures
ranging from 1 to over 100 mm of mercury can be evaluated using the
present invention. The forces necessary to applanate against such
intraocular pressures may be obtained with reasonably
straightforward designs and inexpensive materials as will be
demonstrated by the following calculations:
[0408] It is known that the force F exerted by an external magnetic
field on a small magnet equals the magnet's magnetic dipole moment
m multiplied by the gradient of the external field's magnetic
induction vector "grad B" acting in the direction of the magnet's
dipole moment.
F=m*grad B (1)
[0409] The magnetic dipole moment m for the magnetic version of the
movable central piece 16 can be determined using the following
formula:
m=(B*V)/u.sub.0 (2)
[0410] where B is the magnetic induction vector just at the surface
of one of the poles of the movable central piece 16, V is its
volume, and u.sub.0 is the magnetic permeability of free space
which has a value of 12.57*10.sup.-7 Henry/meter.
[0411] A typical value of B for magnetized Alnico movable central
pieces 16 is 0.5 Tesla. If the movable central piece 16 has a
thickness of 1 mm, a diameter of 5 mm, and 50% of its initial
volume is machined away, its volume V=9.8 cubic millimeters
(9.8*10.sup.-9 cubic meters. Substituting these values into
Equation 2 yields the value for the movable central piece's
magnetic dipole moment, namely, m=0.00390 Amp*(Meter).sup.2.
[0412] Using the foregoing calculations, the specifications of the
actuation apparatus can be determined. The magnetic field gradient
"grad B" is a function of the distance x measured from the front
face of the actuation apparatus and may be calculated as follows: 1
grad B = u 0 * X * N * I * ( RAD ) 2 * { [ ( x + L ) 2 + RAD 2 ] -
3 / 2 - [ x 2 + RAD 2 ] - 3 / 2 } 2 * L ( 3 )
[0413] where X is the magnetic susceptibility of the iron core, N
is the number of turns in the coil's wire, I is the electric
current carried by the wire, L is the length of the coil 30, and
RAD is the radius of the coil 30.
[0414] The preferred values for these parameters in the alternative
embodiment are: X=500, N=200, I=1.0 Amp, L=0.05 meters, and
RAD=0.025 meters. It is understood, however, that the present
invention is not limited to these preferred parameters. As usual,
u.sub.0=12.57*10.sup.-7 Henry/meter.
[0415] The force F exerted by the magnetic actuation apparatus on
the movable central piece 16 is found from Equation 1 using the
aforementioned preferred values as parameters in Equation 3, and
the above result for m=0.00390 Amp*(Meter)2. A plot of F as a
function of the distance x separating the movable central piece 16
from the pole of the magnetic actuation apparatus appears as FIG.
16A.
[0416] Since a patient's cornea 4, when covered by the contact
device 2 which holds the movable central piece 16, can be placed
conveniently at a distance x=2.5 cm (0.025 m) from the actuation
apparatus, it is noted from FIG. 16A that the magnetic actuation
force is approximately F=0.063 Newtons.
[0417] This force is then compared to F.sub.required which is the
force actually needed to applanate a cornea 4 over a typical
applanation area when the intraocular pressure is as high as 50 mm
Hg. In Goldman tonometry, the diameter of the applanated area is
approximately 3.1 mm and therefore the typical applanated AREA will
equal 7.55 mm.sup.2. The typical maximum pressure of 50 mm Hg can
be converted to metric form, yielding a pressure of 0.00666
Newtons/mm.sup.2. The value of F.sub.required then can be
determined using the following equation:
F.sub.required=PRESSURE*AREA (4)
[0418] After mathematical substitution, F.sub.required=0.050
Newtons. Comparing the calculated magnetic actuation force F to the
force required F it becomes clear that F.sub.required is less than
the available magnetic driving force F. Therefore, the maximum
force needed to applanate the cornea 4 for intraocular pressure
determinations is easily achieved using the actuation apparatus and
movable central piece 16 of the present invention.
[0419] It is understood that, if a greater force becomes necessary
for whatever reason (e.g, to provide more distance between the
contact device 2 and the actuation apparatus), the various
parameters can be manipulated and/or the current in the coil 30 can
be increased to achieve a satisfactory arrangement.
[0420] In order for the actuation apparatus to properly actuate the
movable central piece 16 in a practical way, the magnetic actuation
force (and the associated magnetic field) should increase from
zero, reach a maximum in about 0.01 sec., and then return back to
zero in approximately another 0.01 sec. The power supply to the
actuation apparatus therefore preferably includes circuitry and a
power source capable of driving a "current pulse" of peak magnitude
in the 1 ampere range through a fairly large inductor (i.e. the
coil 30).
[0421] For "single-pulse" operation, a DC-voltage power supply can
be used to charge a capacitor C through a charging resistor. One
side of the capacitor is grounded while the other side ("high"
side) may be at a 50 volt DC potential. The "high" side of the
capacitor can be connected via a high current-carrying switch to a
"discharge circuit" consisting of the coil 30 and a damping
resistor R. This arrangement yields an R-L-C series circuit similar
to that which is conventionally used to generate large pulses of
electrical current for such applications as obtaining large pulsed
magnetic fields and operating pulsed laser power systems. By
appropriately choosing the values of the electrical components and
the initial voltage of the capacitor, a "current pulse" of the kind
described above can be generated and supplied to the coil 30 to
thereby operate the actuation apparatus.
[0422] It is understood, however, that the mere application of a
current pulse of the kind described above to a large inductor, such
as the coil 30, will not necessarily yield a zero magnetic field
after the current pulse has ended. Instead, there is usually an
undesirable residual magnetic field from the iron-core 30A even
though no current is flowing in the coil 30. This residual field is
caused by magnetic hysteresis and would tend to produce a magnetic
force on the movable central piece 16 when such a force is not
wanted.
[0423] Therefore, the alternative embodiment preferably includes
means for zeroing the magnetic field outside the actuation
apparatus after operation thereof Such zeroing can be provided by a
demagnetizing circuit connected to the iron-core 30A.
[0424] Methods for demagnetizing an iron-core are generally known
and are easy to implement. It can be done, for example, by
reversing the current in the coil repeatedly while decreasing its
magnitude. The easiest way to do this is by using a step-down
transformer where the input is a sinusoidal voltage at 60 Hz which
starts at a "line voltage" of 110 VAC and is gradually dampened to
zero volts, and where the output of the transformer is connected to
the coil 30.
[0425] The actuation apparatus therefore may include two power
circuits, namely, a "single pulse" current source used for
conducting applanation measurements and a "demagnetization circuit"
for zeroing the magnetic field of the coil 30 immediately after
each applanation measurement.
[0426] As illustrated in FIGS. 16 and more specifically in FIG. 17,
the alternative embodiment used for applanation also includes an
alternative optical alignment system. Alignment is very important
because, as indicated by the graph of FIG. 16A, the force exerted
by the actuation apparatus on the movable central piece 16 depends
very much on their relative positions. In addition to the movable
central piece's axial location with respect to the actuation
apparatus (x-direction), the magnetic force exerted on the movable
central piece 16 also depends on its lateral (y-direction) and
vertical (z-direction) positions, as well as on its orientation
(tip and tilt) with respect to the central axis of the actuation
apparatus.
[0427] Considering the variation of force F with axial distance x
shown in FIG. 16A, it is clear that the movable central piece 16
should be positioned in the x-direction with an accuracy of about
+/-1 mm for reliable measurements. Similarly, since the diameter of
the coil 30 is preferably 50 mm, the location of the movable
central piece 16 with respect to the y and z directions (i.e.
perpendicular to the longitudinal axis of the coil 30) should be
maintained to within +/-2 mm (a region where the magnetic field is
fairly constant) of the coil's longitudinal axis.
[0428] Finally, since the force on the movable central piece 16
depends on the cosine of the angle between the coil's longitudinal
axis and the tip or tilt angle of the movable central piece 16, it
is important that the range of the patient's gaze with respect to
the coil's longitudinal axis be maintained within about +/-2
degrees for reliable measurements.
[0429] In order to satisfy the foregoing criteria, the alternative
optical alignment system facilitates precise alignment of the
patient's corneal vertex (situated centrally behind the movable
central piece 16) with the coil's longitudinal axis, which precise
alignment can be achieved independently by a patient without the
assistance of a trained medical technician or health care
professional.
[0430] The alternative optical alignment system functions according
to how light reflects and refracts at the corneal surface. For the
sake of simplicity, the following description of the alternative
optical alignment system and FIGS. 16 and 17 does not refer
specifically to the effects of the movable central piece's
transparent central portion on the operation of the optical system,
primarily because the transparent central portion of the movable
central piece 16 is preferably arranged so as not to affect the
behavior of optical rays passing through the movable central piece
16.
[0431] Also, for the sake of simplicity, FIG. 17 does not show the
iron core 30A and its associated bore 30B, though it is understood
that the alignment beam (described hereinafter) passes through the
bored hole 30B and that the lenses L3 and L4 are mounted within the
bored hole 30B.
[0432] As illustrated in FIG. 16. a point-like source 350 of light
such as an LED is located at the focal plane of a positive (i.e.,
convergent) lens L1. The positive lens L1 is arranged so as to
collimate a beam of light from the source 350. The collimated beam
passes through a beam splitter BS1 and a transmitted beam of the
collimated beam continues through the beam splitter BS1 to a
positive lens L2. The positive lens L2 focuses the transmitted beam
to a point within lens L3 located at the focal plane of a lens L4.
The light rays passing through L4 are collimated once again and
enter the patient's eye where they are focused on the retina 5. The
transmitted beam is therefore perceived by the patient as a
point-like light.
[0433] Some of the rays which reach the eye are reflected from the
corneal surface in a divergent manner due to the cornea's
preapplanation curvature, as shown in FIG. 18, and are returned
back to the patient's eye by a partially mirrored planar surface of
the lens L4. These rays are perceived by the patient as an image of
the corneal reflection which guides the patient during alignment of
his/her eye in the instrument as will be described hereinafter.
[0434] Those rays which are reflected by the convex cornea 4 and
pass from right-to-left through the lens L4 are made somewhat more
convergent by the lens L4. From the perspective of lens L3, these
rays appear to come from a virtual point object located at the
focal point. Therefore, after passing through L3, the rays are once
again collimated and enter the lens L2 which focuses the rays to a
point on the surface of the beam splitter BS1. The beam splitter
BS1 is tilted at 45 degrees and consequently deflects the rays
toward a lens L5 which, in turn, collimates the rays. These rays
then strike the surface of a tilted reflecting beam splitter BS2.
The collimated rays reflected from the beam splitter BS2 enter lens
L6 which focuses them onto the small aperture of a silicon
photodiode which functions as an alignment sensor D1.
[0435] Therefore, when the curved cornea 4 is properly aligned, an
electric current is produced by the alignment sensor D1. The
alignment system is very sensitive because it is a confocal
arrangement (i.e., the point image of the alignment light due to
the corneal reflection--Purkinje image--in its fiducial position is
conjugate to the small light-sensitive aperture of the silicon
photodiode). In this manner, an electrical current is obtained from
the alignment sensor only when the cornea 4 is properly aligned
with respect to the lens L4 which, in turn, is preferably mounted
at the end of the magnetic actuation apparatus. The focal lengths
of all the lenses shown in FIG. 17 are preferably 50 mm except for
the lens L3 which preferably has a focal length of 100 MM.
[0436] An electrical circuit capable of operating the alignment
sensor D1 is straight-forward to design and build. The silicon
photodiode operates without any bias voltage ("photovoltaic mode")
thus minimizing inherent detector noise. In this mode, a voltage
signal, which corresponds to the light level on the silicon
surface, appears across a small resistor spanning the diode's
terminals. Ordinarily this voltage signal is too small for display
or subsequent processing; however, it can be amplified many orders
of magnitude using a simple transimpedance amplifier circuit.
Preferably, the alignment sensor D1 is utilized in conjunction with
such an amplified photodiode circuit.
[0437] Preferably, the circuitry connected to the alignment sensor
D1 is arranged so as to automatically activate the actuation
apparatus immediately upon detecting via the sensor D1 the
existence of proper alignment. If, however, the output from the
alignment sensor D1 indicates that the eye is not properly aligned,
the circuitry preferably prevents activation of the actuation
apparatus. In this way, the alignment sensor D1, not the patient,
determines when the actuation apparatus will be operated.
[0438] As indicated above, the optical alignment system preferably
includes an arrangement for guiding the patient during alignment of
his/her eye in the instrument. Such arrangements are illustrated,
by way of example, in FIGS. 18 and 19.
[0439] The arrangement illustrated in FIG. 18 allows a patient to
precisely position his/her eye translationally in all x-y-z
directions. In particular, the lens L4 is made to include a piano
surface, the piano surface being made partially reflective so that
a patient is able to see a magnified image of his/her pupil with a
bright point source of light located somewhere near the center of
the iris. This point source image is due to the reflection of the
incoming alignment beam from the curved corneal surface (called the
first Purkinje image) and its subsequent reflection from the
mirrored or partially reflecting piano surface of the lens L4.
Preferably, the lens L4 makes the reflected rays parallel as they
return to the eye which focuses them onto the retina 5.
[0440] Although FIG. 18 shows the eye well aligned so that the rays
are focused at a central location on the surface of the retina 5,
it is understood that movements of the eye toward or away
(x-direction) from the lens L4 will blur the image of the corneal
reflection, and that movements of the eye in either the y or z
direction will tend to displace the corneal reflection image either
to the right/left or up/down.
[0441] The patient therefore performs an alignment operation by
gazing directly at the alignment light and moving his/her eye
slowly in three dimensions until the point image of the corneal
reflection is as sharp as possible (x-positioning) and merges with
the point image of the alignment light (y & z positioning)
which passes straight through the cornea 4.
[0442] As illustrated in FIG. 19, the lens L4 need not have a
partially reflective portion if the act of merely establishing a
proper direction of gaze provides sufficient alignment.
[0443] Once alignment is achieved, a logic signal from the optical
alignment system activates the "pulse circuit" which in turn,
powers the actuation apparatus. After the actuation apparatus is
activated, the magnetic field at the patient's cornea increases
steadily for a time period of about 0.01 sec. The effect of this
increasing field is to apply a steadily increasing force to the
movable central piece 16 resting on the cornea which, in turn,
causes the cornea 4 to flatten increasingly over time. Since the
size of the applanation area is proportional to the force on the
movable central piece 16 (and Pressure=Force/Area), the intraocular
pressure (IOP) is found by determining the ratio of the force to
the area applanated by the force.
[0444] In order to detect the applanated area and provide an
electrical signal indicative of the size of the applanated area,
the alternative embodiment includes an applanation sensor D2. The
rays that are reflected from the applanated corneal surface are
reflected in a generally parallel manner by virtue of the flat
surface presented by the applanated cornea 4. As the rays pass from
right-to-left through the lens L4, they are focused within the lens
L3 which, in turn, is in the focal plane of the lens L2.
Consequently, after passing through the lens L2, the rays are once
again collimated and impinge on the surface of beam splitter BS1.
Since the beam splitter BS1 is tilted at 45 degrees, the beam
splitter BS1 deflects these collimated rays toward the lens L5
which focuses the rays to a point at the center of beam splitter
BS2. The beam splitter BS2 has a small transparent portion or hole
in its center which allows the direct passage of the rays on to the
lens L7 (focal length of preferably 50 mm). The lens L7 pertains to
an applanation sensing arm of the alternative embodiment. The focal
spot on the beam splitter BS2 is in the focal plane of the lens
L7.
[0445] Consequently, the rays emerging from the lens L7 are once
again collimated. These collimated rays impinge on the mirror M1,
preferably at a 45 degree angle, and are deflected toward a
positive lens L8 (focal length of 50 mm) which focuses the rays
onto the small aperture of a silicon photodiode which defines the
applanation sensor D2. It is understood that rays which impinge
upon the cornea 4 slightly off center tend to be reflected away
from the lens L4 when the cornea's curvature remains undisturbed.
However, as applanation progresses and the cornea becomes
increasingly flat, more of these rays are reflected back into the
lens L4. The intensity of light on the applanation sensor D2
therefore increases, and as a result, an electric current is
generated by the applanation sensor D2, which electric current is
proportional to the degree of applanation.
[0446] Preferably, the electrical circuit utilized by the
applanation sensor D2 is identical or similar to that used by the
alignment sensor D1.
[0447] The electric signal indicative of the area of applanation
can then be combined with signals indicative of the time it takes
to achieve such applanation and/or the amount of current (which, in
turn, corresponds to the applied force) used to achieve the
applanation, and this combination of information can be used to
determines the intraocular pressure using the equation
Pressure=Force/Area.
[0448] The following are preferred operational steps for the
actuation apparatus during a measurement cycle:
[0449] 1) While the actuation apparatus is OFF, there is no
magnetic field being directed toward the contact device 2.
[0450] 2) When the actuation apparatus is turned ON, the magnetic
field initially remains at zero.
[0451] 3) Once the patient is in position, the patient starts to
align his/her eye with the actuation apparatus. Until the eye is
properly aligned, the magnetic field remains zero.
[0452] 4) When the eye is properly aligned (as automatically sensed
by the optical alignment Sensor), the magnetic field (driven by a
steadily increasing electric current) starts to increase from
zero.
[0453] 5) During the time period of the current increase
(approximately 0.01 sec.), the force on the movable central piece
also increases steadily.
[0454] 6) In response to the increasing force on the movable
central piece, the surface area of the cornea adjacent to the
movable central piece is increasingly flattened.
[0455] 7) Light from the flattened surface area of the cornea is
reflected toward the detecting arrangement which detects when a
predetermined amount of applanation has been achieved. Since the
amount of light reflected straight back from the cornea is
proportional to the size of the flattened surface area, it is
possible to determine exactly when the predetermined amount of
applanation has been achieved, preferably a circular area of
diameter 3.1 mm, of the cornea. It is understood, however, that any
diameter ranging from 0.10 mm to 10 mm can be utilized.
[0456] 8) The time required to achieve applanation of the
particular surface area (i.e, the predetermined amount of
applanation) is detected by a timing circuit which is part of the
applanation detecting arrangement. Based on prior calibration and a
resulting conversion table, this time is converted to an indication
of intraocular pressure. The longer the time required to applanate
a specific area, the higher the intraocular pressure, and vice
versa.
[0457] 9) After the predetermined amount of applanation is
achieved, the magnetic field is turned OFF.
[0458] 10) The intraocular pressure is then displayed by a readout
meter, and all circuits are preferably turned completely OFF for a
period of 15 seconds so that the automatic measurement cycle will
not be immediately repeated if the patient's eye remains aligned.
It is understood, however, that the circuits may remain ON and that
a continuous measurement of intraocular pressure may be achieved by
creating an automatic measurement cycle. The data provided by this
automatic measurement cycle then may be used to calculate blood
flow.
[0459] 11) If the main power supply has not been turned OFF, all
circuits are turned back ON after 15 seconds and thus become ready
for the next measurement.
[0460] Although there are several methods for calibrating the
various elements of the system for measuring intraocular pressure
by applanation, the following are illustrative examples of how such
calibration can be achieved:
[0461] Initially, after manufacturing the various components, each
component is tested to ensure the component operates properly. This
preferably includes verifying that there is free piston-like
movement (no twisting) of the movable central piece in the contact
device; verifying the structural integrity of the contact device
during routine handling; evaluating the magnetic field at the
surface of the movable central piece in order to determine its
magnetic dipole moment (when magnetic actuation is utilized):
verifying that the electrical current pulse which creates the
magnetic field that actuates the magnetically responsive element of
the movable central piece, has an appropriate peak magnitude and
duration, and ensuring that there is no "ringing"; verifying the
efficacy of the "demagnetization circuit" at removing any residual
magnetization in the iron-core of the actuation apparatus after it
has been pulsed; measuring the magnetic field as a function of time
along and near the longitudinal axis of the coil where the movable
central piece will eventually be placed; determining and plotting
grad B as a function of time at several x-locations (i.e., at
several distances from the coil); and positioning the magnetic
central piece (contact device) at several x-locations along the
coil's longitudinal axis and determining the force F acting on it
as a function of time during pulsed-operation of the actuation
apparatus.
[0462] Next, the optical alignment system is tested for proper
operation. When the optical alignment system comprises the
arrangement illustrated in FIGS. 16 and 17, for example, the
following testing and calibration procedure may be used:
[0463] a) First, a convex glass surface (one face of a lens) having
a radius of curvature approximately the same as that of the cornea
is used to simulate the cornea and its surface reflection.
Preferably, this glass surface is placed in a micrometer-adjusted
mounting arrangement along the longitudinal axis of the coil. The
micrometer-adjusted mounting arrangement permits rotation about two
axes (tip & tilt) and translation in three-dimensional x-y-z
space.
[0464] b) With the detector Dl connected to a voltage or current
meter, the convex glass surface located at its design distance of
25 mm from lens L4 will be perfectly aligned (tip/tilt/x/y/z) by
maximizing the output signal at the read-out meter.
[0465] c) After perfect alignment is achieved, the alignment
detection arrangement is "detuned" for each of the positional
degrees of freedom (tip/tilt/x/y/z) and curves are plotted for each
degree of freedom to thereby define the system's sensitivity to
alignment.
[0466] d) The sensitivity to alignment will be compared to the
desired tolerances in the reproducibility of measurements and also
can be based on the variance of the magnetic force on the movable
central piece as a function of position.
[0467] e) Thereafter, the sensitivity of the alignment system can
be changed as needed by such procedures as changing the size of the
aperture in the silicon photodiode which functions as the alignment
sensor D1, and/or changing an aperture stop at lens L4.
[0468] Next, the detection arrangement is tested for proper
operation. When the detection arrangement comprises the optical
detection arrangement illustrated in FIG. 16, for example, the
following testing and calibration procedure may be used:
[0469] a) A flat glass surface (e.g., one face of a short polished
rod) with a diameter of preferably 4-5 mm is used to simulate the
applanated cornea and its surface reflection.
[0470] b) A black, opaque aperture defining mechanism (which
defines clear inner apertures with diameters ranging from 0.5 to 4
mm and which has an outer diameter the same as that of the rod) is
arranged so as to partially cover the face of the rod, thus
simulating various stages of applanation.
[0471] c) The flat surfaced rod is placed in a mount along the
longitudinal axis of the coil in a micrometer-adjusted mounting
arrangement that can rotate about two axes (tip & tilt) and
translate in three-dimensional x-y-z space.
[0472] d) The applanation sensor D2 is then connected to a voltage
or current meter, while the rod remains located at its design
distance of 25 mm from the lens L4 where it is perfectly aligned
(tip/tilt/x/y/z) by maximizing the output signal from the
applanation sensor D2. Alignment, in this case, is not sensitive to
x-axis positioning.
[0473] e) After perfect alignment is achieved, the alignment is
"detuned" for each of the positional degrees of freedom
(tip/tilt/x/y/z) and curves are plotted for each degree of freedom
thus defining the system's sensitivity to alignment. Data of this
kind is obtained for the variously sized apertures (i.e. different
degrees of applanation) at the face of the rod.
[0474] f) The sensitivity to alignment is then compared to the
tolerances required for reproducing applanation measurements which
depends, in part, on the results obtained in the aforementioned
testing and calibration method associated with the alignment
apparatus.
[0475] g) The sensitivity of the applanation detecting arrangement
is then changed as needed by such procedures as changing the size
of the aperture in front of the applanation sensor D2 and/or
changing the aperture stop (small hole) at the beam splitter
BS2.
[0476] Further calibration and in-vitro measurements can be carried
out as follows: After the aforementioned calibration and testing
procedures have been carried out on the individual subassemblies,
all parts can be combined and the system tested as an integrated
unit. For this purpose, ten enucleated animal eyes and ten
enucleated human eyes are measured in two separate series. The
procedures for both eye types are the same. The eyes are mounted in
non-magnetic holders, each having a central opening which exposes
the cornea and part of the sclera. A 23 gauge needle attached to a
short piece of polyethylene tubing is then inserted behind the
limbus through the sciera and ciliary body and advanced so that the
tip passes between the lens and iris. Side ports are drilled in the
cannulas about 2 mm from the tip to help avoid blockage of the
cannula by the iris or lens. This cannula is attached to a pressure
transducer with an appropriate display element. A normal saline
reservoir of adjustable height is also connected to the pressure
transducer tubing system. The hydrostatic pressure applied to the
eye by this reservoir is adjustable between 0 and 50 mm Hg, and
intraocular pressure over this range can be measured directly with
the pressure transducer.
[0477] In order to verify that the foregoing equipment is properly
set up for each new eye, a standard Goldman applanation tonometer
can be used to independently measure the eye's intraocular pressure
at a single height of the reservoir. The intraocular value measured
using the Goldman system is then compared to a simultaneously
determined intraocular pressure measured by the pressure
transducer. Any problems encountered with the equipment can be
corrected if the two measurements are significantly different.
[0478] The reservoir is used to change in 5 mm Hg sequential steps
the intraocular pressure of each eye over a range of pressures from
5 to 50 mm Hg. At each of the pressures, a measurement is taken
using the system of the present invention. Each measurement taken
by the present invention consists of recording three separate
time-varying signals over the time duration of the pulsed magnetic
field. The three signals are: 1) the current flowing in the coil of
the actuation apparatus as a function of time, labelled I (t), 2)
the voltage signal as a function of time from the applanation
detector D2, labelled APPLN (t), and 3) the voltage signal as a
function of time from the alignment sensor D1, labelled ALIGN (t).
The three signals, associated with each measurement, are then
acquired and stored in a computer equipped with a multi-input "data
acquisition and processing" board and related software.
[0479] The computer allows many things to be done with the data
including: 1) recording and storing many signals for subsequent
retrieval, 2) displaying graphs of the signals versus time, 3)
numerical processing and analyses in any way that is desired, 4)
plotting final results, 5) applying statistical analyses to groups
of data, and 6) labeling the data (e.g. tagging a measurement set
with its associated intraocular pressure).
[0480] The relationship between the three time-varying signals and
intraocular pressure are as follows:
[0481] 1. I(t) is an independent input signal which is consistently
applied as current pulse from the power supply which activates the
actuation apparatus. This signal I (t) is essentially constant from
one measurement to another except for minor shot-to-shot
variations. I (t) is a "reference" waveform against which the other
waveforms, APPLN (t) and ALIGN (t) are compared as discussed
further below.
[0482] 2. APPLN(t) is a dependent output signal. APPLN(t) has a
value of zero when I(t) is zero (i.e. at the very beginning of the
current pulse in the coil of the actuation apparatus. The reason
for this is that when I=0, there is no magnetic field and,
consequently, no applanation force on the movable central piece. As
I (t) increases, so does the extent of applanation and,
correspondingly, so does APPLN(t). It is important to note that the
rate at which APPLN(t) increases with increasing I(t) depends on
the eye's intraocular pressure. Since eyes with low intraocular
pressures applanate more easily than eves with high intraocular
pressures in response to an applanation force, it is understood
that APPLN(t) increases more rapidly for an eye having a low
intraocular pressure than it does for an eye having a high
intraocular pressure. Thus, APPLN (t) increases from zero at a rate
that is inversely proportional to the intraocular pressure until it
reaches a maximum value when full applanation is achieved.
[0483] 3. ALIGN(t) is also a dependent output signal. Assuming an
eye is aligned in the setup, the signal ALIGN(t) starts at some
maximum value when I(t) is zero (i.e. at the very beginning of the
current pulse to the coil of the actuation apparatus). The reason
for this is that when I=0, there is no magnetic field and,
consequently, no force on the movable central piece which would
otherwise tend to alter the cornea's curvature. Since corneal
reflection is what gives rise to the alignment signal, as I(t)
increases causing applanation (and, correspondingly, a decrease in
the extent of corneal curvature), the signal ALIGN (t) decreases
until it reaches zero at full applanation. It is important to note
that the rate at which ALIGN (t) decreases with increasing I(t)
depends on the eye's intraocular pressure. Since extraocular
pressure applanate more easily than eyes with high intraocular
pressure, it is understood that ALIGN (t) decreases more rapidly
for an eye having a low intraocular pressure than for an eye having
a high intraocular pressure. Thus, ALIGN(t) decreases from some
maximum value at a rate that is inversely proportional to the
intraocular pressure until it reaches zero when full applanation is
achieved.
[0484] From the foregoing, it is clear that the rate of change of
both output signals, APPLN and ALIGN, in relation to the input
signal I is inversely proportional to the intraocular pressure.
[0485] Therefore, the measurement of intraocular pressure using the
present invention may depend on determining the SLOPE of the "APPLN
versus I" measurement data (also, although probably with less
certainty, the slope of the "ALIGN versus I" measurement data).
[0486] For the sake of brevity, the following description is
limited to the "APPLN versus I" data; however, it is understood
that the "ALIGN versus I" data can be processed in a similar
manner.
[0487] Plots of "APPLN versus I" can be displayed on the computer
monitor for the various measurements (all the different intraocular
pressures for each and every eye) and regression analysis (and
other data reduction algorithms) can be employed in order to obtain
the "best fit" SLOPE for each measurement. Time can be spent in
order to optimize this data reduction procedure. The end result of
a series of pressure measurements at different intraocular
pressures on an eye (determined by the aforementioned pressure
transducer) will be a corresponding series of SLOPE's (determined
by the system of the present invention).
[0488] Next, a single plot is prepared for each eye showing SLOPE
versus intraocular pressure data points as well as a best fitting
curve through the data. Ideally, all curves for the 10 pig eyes are
perfectly coincident--with the same being true for the curves
obtained for the 10 human eyes. If the ideal is realized, any of
the curves can be utilized (since they all are the same) as a
CALIBRATION for the present invention. In practice, however, the
ideal is probably not realized.
[0489] Therefore, all of the SLOPE versus intraocular pressure data
for the 10 pig eyes is superimposed on a single plot (likewise for
the SLOPE versus intraocular pressure data for the 10 human eyes).
Such superimposing generally yields an "averaged" CALIBRATION
curve, and also indication of the reliability associated with the
CALIBRATION.
[0490] Next, the data in the single plots can be analyzed
statistically (one for pig eyes and one for human eyes) which, in
turn, shows a composite of all the SLOPE versus intraocular
pressure data. From the statistical analysis, it is possible to
obtain: 1) an averaged CALIBRATION curve for the present invention
from which one can obtain the "most likely intraocular pressure"
associated with a measured SLOPE value, 2) the Standard Deviation
(or Variance) associated with any intraocular pressure
determination made using the present invention, essentially the
present invention's expected "ability" to replicate measurements,
and 3) the "reliability" or "accuracy" of the present invention's
CALIBRATION curve which is found from a "standard-error-of-the
mean" analysis of the data.
[0491] In addition to data obtained with the eyes aligned. It is
also possible to investigate the sensitivity of intraocular
pressure measurements made using the present invention, to
translational and rotational misalignment.
Alternative Embodiment for Measuring Intraocular Pressure by
Indentation
[0492] With reference to FIGS. 20A and 20B, an alternative
embodiment for measuring intraocular pressure by indentation will
now be described.
[0493] The alternative embodiment includes an indentation distance
detection arrangement and contact device. The contact device has a
movable central piece 16 of which only the outside surface is
illustrated in FIGS. 20A and 20B. The outside surface of the
movable central piece 16 is at least partially reflective.
[0494] The indentation distance detection arrangement includes two
converging lenses L1 and L2; a beam splitter BS1; a light source LS
for emitting a beam of light having a width w; and a light detector
LD responsive to the diameter of a reflected beam impinging on a
surface thereof.
[0495] FIG. 20A illustrates the alternative embodiment prior to
actuation of the movable central piece 16. Prior to actuation, the
patient is aligned with the indentation distance detection
arrangement so that the outer surface of the movable central piece
16 is located at the focal point of the converging lens L2. When
the movable central piece 16 is so located, the beam of light from
the light source LS strikes the beam splitter BS and is deflected
through the converging lens L1 to impinge as a point on the
reflective outer surface of the movable central piece 16. The
reflective outer surface of the movable central piece 16 then
reflects this beam of light back through the converging lens L1,
through the beam splitter BS, and then through the converging lens
L2 to strike a surface of the light detector LD. Preferably, the
light detector LD is located at the focal point of the converging
lens L2 so that the reflected beam impinges on a surface of the
light detector LD as a point of virtually zero diameter when the
outer surface of the movable central piece remains at the focal
point of the converging lens L1.
[0496] Preferably, the indentation distance detection arrangement
is connected to a display device so as to generate an indication of
zero displacement when the outer surface of the movable central
piece 16 has yet to be displaced, as shown in FIG. 20A.
[0497] By subsequently actuating the movable central piece 16 using
an actuating device (preferably, similar to the actuating devices
described above), the outer surface of the movable central piece 16
moves progressively away from the focal point of the converging
lens L1, as illustrated in FIG. 20B. As a result, the light beam
impinging on the reflective outer surface of the movable central
piece 16 has a progressively increasing diameter. This progressive
increase in diameter is proportional to the displacement from the
focal point of the converging lens L1. The resulting reflected beam
therefore has a diameter proportional to the displacement and
passes back through the converging lens L1, through the beam
splitter BS, through the converging lens C2 and then strikes the
surface of the light detector LD with a diameter proportional to
the displacement of the movable central piece 16. Since the light
detector LD is responsive, as indicated above, to the diameter of
the reflected light beam, any displacement of the movable central
piece 16 causes a proportional change in output from the light
detector LD.
[0498] Preferably, the light detector LD is a photoelectric
converter connected to the aforementioned display device and
capable of providing an output voltage proportional to the diameter
of the reflected light beam impinging upon the light detector LD.
The display device therefore provides a visual indication of
displacement based on the output voltage from the light detector
LD.
[0499] Alternatively, the output from the light detector LD may be
connected to an arrangement, as described above, for providing an
indication of intraocular pressure based on the displacement of the
movable central piece 16.
Additional Capabilities
[0500] Generally, the present apparatus and method makes it
possible to evaluate intraocular pressure, as indicated above, as
well as ocular rigidity, eye hydrodynamics such as outflow facility
and inflow rate of eye fluid, eye hemodynamics such as the pressure
in the episcleral veins and the pulsatile ocular blood flow, and
has also the ability to artificially increase intraocular pressure,
as well as the continuous recording of intraocular pressure.
[0501] With regard to the measurement of intraocular pressure by
applanation, the foregoing description sets forth several
techniques for accomplishing such measurement, including a variable
force technique wherein the force applied against the cornea varies
with time. It is understood, however, that a variable area method
can also be implemented.
[0502] The apparatus can evaluate the amount of area applanated by
a known force. The pressure is calculated by dividing the force by
the amount of area that is applanated. The amount of area
applanated is determined using the optical means and/or filters
previously described.
[0503] A force equivalent to placing 5 gram of weight on the
cornea, for example, will applanate a first area if the pressure is
30 mmHg, a second area if the pressure is 20 mmHg, a third area if
the pressure is 15 mmHg and so on. The area applanated is therefore
indicative of intraocular pressure.
[0504] Alternatively, intraocular pressure can be measured using a
non-rigid interface and general applanation techniques. In this
embodiment, a flexible central piece enclosed by the magnet of the
movable central piece is used and the transparent part of the
movable central piece acts like a micro-balloon. This method is
based on the principle that the interface between two spherical
balloons of unequal radius will be flat if the pressures in the two
balloons are equal. The central piece with the balloon is pressed
against the eye until the eye/central piece interface is planar as
determined by the aforementioned optical means.
[0505] Also, with regard to the previously described arrangement
which measures intraocular pressure by indentation, an alternative
method can be implemented with such an embodiment wherein the
apparatus measures the force required to indent the cornea by a
predetermined amount. This amount of indentation is determined by
optical means as previously described. The movable central piece is
pressed against the cornea to indent the cornea, for example, 0.5
mm (though it is understood that virtually any other depth can be
used). Achievement of the predetermined depth is detected by the
previously described optical means and filters. According to
tables, the intraocular pressure can be determined thereafter from
the force.
[0506] Yet another technique which the present invention
facilitates use of is the ballistic principle. According to the
ballistic principle, a parameter of a collision between the known
mass of the movable central piece and the cornea is measured. This
measured parameter is then related theoretically or experimentally
to the intraocular pressure. The following are exemplary
parameters:
[0507] Impact acceleration
[0508] The movable central piece is directed at the cornea at a
well defined velocity. It collides with the cornea and, after a
certain time of contact, bounces back. The time-velocity
relationships during and after impact can be studied. The
applanating central piece may have a spring connecting to the rigid
annular member of the contact device. If the corneal surface is
hard, the impact time will be short. Likewise, if the corneal
surface is soft the impact time will be longer. Optical sensors can
detect optically the duration of impact and how long it takes for
the movable central piece to return to its original position.
[0509] Impact duration
[0510] Intraocular pressure may also be estimated by measuring the
duration of contact of a spring driven movable central piece with
the eye. The amount of time that the cornea remains flattened can
be evaluated by the previously described optical means.
[0511] Rebound velocity
[0512] The distance traveled per unit of time after bouncing is
also indicative of the rebound energy and this energy is
proportional to intraocular pressure.
[0513] Vibration principle
[0514] The intraocular pressure also can be estimated by measuring
the frequency of a vibrating element in contact with the contact
device and the resulting changes in light reflection are related to
the pressure in the eye.
[0515] Time
[0516] The apparatus of the present invention can also be used, as
indicated above, to measure the time that it takes to applanate the
cornea. The harder the cornea, the higher the intraocular pressure
and thus the longer it takes to deform the cornea. On the other
hand, the softer the cornea, the lower the intraocular pressure and
thus the shorter it takes to deform the cornea. Thus, the amount of
time that it takes to deform the cornea is proportional to the
intraocular pressure.
[0517] Additional uses and capabilities of the present invention
relate to alternative methods of measuring outflow facility
(tonography). These alternative methods include the use of
conventional indentation techniques, constant depth indentation
techniques, constant pressure indentation techniques, constant
pressure applanation techniques, constant area applanation
techniques, and constant force applanation techniques.
[0518] 1. Conventional Indentation
[0519] When conventional indentation techniques are utilized, the
movable central piece of the present invention is used to indent
the cornea and thereby artificially increase the intraocular
pressure. This artificial increase in intraocular pressure forces
fluid out of the eye more rapidly than normal. As fluid leaves the
eye, the pressure gradually returns to its original level. The rate
at which the intraocular pressure falls depends on how well the
eye's drainage system is functioning. The drop in pressure as a
function of time is used to calculated the C value or coefficient
of outflow facility. The C value is indicative of the degree to
which a change in intraocular pressure will cause a change in the
rate of fluid outflow. This, in turn, is indicative of the
resistance to outflow provided by the eye's drainage system. The
various procedures for determining outflow facility are generally
known as tonography and the C value is typically expressed in terms
of microliters per minute per millimeter of mercury. The C value is
determined by raising the intraocular pressure using the movable
central piece of the contact device and observing the subsequent
decay in intraocular pressure with respect to time. The elevated
intraocular pressure increases the rate of aqueous outflow which,
in turn, provides a change in volume. This change in volume can be
calculated from the Friedenwald tables which correlate volume
change to pressure changes. The rate of volume decrease equals the
rate of outflow. The change in intraocular pressure during the
tonographic procedure can be computed as an arithmetical average of
pressure increments for successive {fraction (1/2)} minute
intervals. The C value is derived then from the following equation:
C=.DELTA.V/t*(Pave-Po), in which t is the duration of the
procedure, Pave is the average pressure elevation during the test
and can be measured, Po is the initial pressure and it is also
measured, and .DELTA.V is difference between the initial and final
volumes and can be obtained from known tables. The Flow ("F") of
fluid is then calculated using the formula: F=C*(Po-Pv), in which
Pv is the pressure in the episcleral veins which can be measured
and generally has a constant value of 10.
[0520] 2. Constant Depth Indentation
[0521] When constant depth indentation techniques are utilized, the
method involves the use of a variable force which is necessary to
cause a certain predetermined amount of indentation in the eye. The
apparatus of the present invention is therefore configured so as to
measure the force required to indent the cornea by a predetermined
amount. This amount of indentation may be detected using optical
means as previously described. The movable central piece is pressed
against the cornea to indent the eye, for example, by approximately
0.5 mm. The amount of indentation is detected by the optical means
and filters previously described. With the central piece indenting
the cornea using a force equivalent to a weight of 10 grams, a 0.5
mm indentation will be achieved under normal pressure conditions
(e.g. , intraocular pressure of 15 mm Hg) and assuming there is an
average corneal curvature. With that amount of indentation and
using standard dimensions for the central piece, 2.5 mm of fluid
will be displaced. The force recorded by the present invention
undergoes a slow decline and it levels off at a more or less steady
state value after 2 to 4 minutes. The decay in pressure is measured
based on the difference between the value of the first indentation
of the central piece and the final level achieved after a certain
amount of time. The pressure drop is due to the return of pressure
to its normal value, after it has been artificially raised by the
indentation caused by the movable central piece. A known normal
value of decay is used as a reference and is compared to the values
obtained. Since the foregoing provides a continuous recording of
pressure over time, this method can be an important tool for
physiological research by showing, for example, an increase in
pressure during forced expiration. The pulse wave and pulse
amplitude can also be evaluated and the pulsatile blood flow
calculated.
[0522] 3. Constant Pressure Indentation
[0523] When constant pressure indentation techniques are utilized,
the intraocular pressure is kept constant by increasing the
magnetic field and thereby increasing the force against the cornea
as fluid leaks out of the eye. At any constant pressure, the force
and rate of outflow are linearly related according to the
Friedenwald tonometry tables. The intraocular pressure is
calculated using the same method as described for conventional
indentation tonometry. The volume displacement is calculated using
the tonometry tables. The facility of outflow (C) may be computed
using two different techniques. According to the first technique, C
can be calculated from two constant pressure tonograms at different
pressures according to the equation,
C={[(.DELTA.V.sub.1/t.sub.1)-(.DELTA.V.sub.2/t-
.sub.2)]/(P.sub.1-P.sub.2)}, in which 1 corresponds to a
measurement at a first pressure and 2 corresponds to a measurement
at a second pressure (which is higher than the first pressure). The
second way to calculate C is from one constant pressure tonogram
and an independent measure of intraocular pressure using
applanation tonometry (P.sub.3), in
C=[(.DELTA.V/t)/(P-P.sub.a-.DELTA.P.sub.c)], where .DELTA.P.sub.c
is a correction factor for rise in episcleral venous pressure with
indentation tonometry and P is the intraocular pressure obtained
using indentation tonometry.
[0524] 4. Constant Pressure Applanation
[0525] When constant pressure applanation techniques are utilized,
the intraocular pressure is kept constant by increasing the
magnetic field and thus the force as fluid leaks out of the eye. If
the cornea is considered to be a portion of a sphere, a
mathematical formula relates the volume of a spherical segment to
the radius of curvature of the sphere and the radius of the base of
the segment. The volume displaced is calculated based on the
formula V=A.sup.2/(4*.pi.*R), in which V is volume, A is the area
of the segment base, and R is the radius of curvature of the sphere
(this is the radius of curvature of the cornea). Since
A=weight/pressure, then V=W.sup.2/(4*.pi.*R*P.sup.2). The weight is
constituted by the force in the electromagnetic field, R is the
curvature of the cornea and can be measured with a keratometer, P
is the pressure in the eye and can be measured using the same
method as described for conventional applanation tonometry. It is
therefore possible to calculate the volume displaced and the C
value or outflow facility. The volume displaced, for example, can
be calculated at 15 second intervals and is plotted as a function
of time.
[0526] 5. Constant Area Applanation
[0527] When constant area applanation techniques are utilized, the
method consists primarily of evaluating the pressure decay curve
while the flattened area remains constant. The aforementioned
optical applanation detecting arrangements can be used in order to
keep constant the area flattened by the movable central piece. The
amount of force necessary to keep the flattened area constant
decreases and this decrease is registered. The amount of volume
displaced according to the different areas of applanation is known.
For instance, a 5 mm applanating central piece displaces 4.07
mm.sup.3 of volume for the average corneal radius of 7.8 mm. Using
the formula .DELTA.V/.DELTA.t=V(R*.DELTA.P), it is possible to
calculate R which is the reciprocal of C. Since a continuous
recording of pressure over time, is provided, this method can be an
important tool for research and evaluation of blood flow.
[0528] 6. Constant Force Applanation
[0529] When constant force applanation techniques are utilized, the
same force is constantly applied and the applanated area is
measured using any of the aforementioned optical applanation
detection arrangements. Once the area flattened by a known force is
measured, the pressure can be calculated by dividing the force by
the amount of area that is applanated. As fluid leaves the eye the
amount of area applanated increases with time. This method consists
primarily of evaluating a resulting area augmentation curve while
the constant force is applied. The amount of volume displaced
according to the different areas of applanation is known. Using the
formula .DELTA.V/.DELTA.t=V(R*.DELTA.P), it is possible to
calculate R which is the reciprocal of C.
[0530] Still additional uses of the present invention relate to
detecting the frequency response of the eye, using indentation
tonometry. In particular, if an oscillating force is applied using
the movable central piece 16, the velocity of the movable central
piece 16 is indicative of the eye's frequency response. The system
oscillates at the resonant frequency determined primarily by the
mass of the movable central piece 16. By varying the frequency of
the force and by measuring the response, the intraocular pressure
can be evaluated. The evaluation can be made by measuring the
resonant frequency and a significant variation in resonant
frequency can be obtained as a function of the intraocular
pressure.
[0531] The present invention may also be used with the foregoing
conventional indentation techniques, but where the intraocular
pressure used for calculation is measured using applanation
principles. Since applanation virtually does not disturb the
hydrodynamic equilibrium because it displaces a very small volume,
this method can be considered more accurate than intraocular
pressure measurements made using traditional indentation
techniques.
[0532] Another use of the present invention involves a time related
way of measuring the resistance to outflow. In particular, the
resistance to outflow is detected by measuring the amount of time
necessary to transfigure the cornea with either applanation or
indentation. The time necessary to displace, for example, 5
microliters of eye fluid would be 1 second for normal patients and
above 2 seconds for glaucoma-stricken individuals.
[0533] Yet another use of the present invention involves measuring
the inflow of eye fluid. In particular, this measurement is made by
applying the formula F=.DELTA.P/R, in which .DELTA.P is P-Pv, and P
is the steady state intraocular pressure and PV is the episcleral
venous pressure which, for purposes of calculation is considered
constant at 10. R is the resistance to outflow, which is the
reciprocal of C that can be calculated. F, in units of volume/min,
can then be calculated.
[0534] The present invention is also useful at measuring ocular
rigidity, or the distensibility of the eye in response to an
increased intraocular pressure. The coefficient of ocular rigidity
can be calculated using a nomogram which is based on two tonometric
readings with different weights. A series of conversion tables to
calculate the coefficient of ocular rigidity was developed by
Friedenwald. The technique for determining ocular rigidity is based
on the concept of differential tonometry, using two indentation
tonometric readings with different weights or more accurately,
using one indentation reading and one applanation reading and
plotting these readings on the nomogram. Since the present
invention can be used to measure intraocular pressure using both
applanation and indentation techniques, a more accurate evaluation
of the ocular rigidity can be achieved.
[0535] Measurements of intraocular pressure using the apparatus of
the present invention can also be used to evaluate hemodynamics, in
particular, eye hemodynamics and pulsatile ocular blood flow. The
pulsatile ocular blood flow is the component of the total ocular
arterial inflow that causes a rhythmic fluctuation of the
intraocular pressure. The intraocular pressure varies with each
pulse due to the pulsatile influx of a bolus of arterial blood into
the eye with each heartbeat. This bolus of blood enters the
intraocular arteries with each heartbeat causing a temporary
increase in the intraocular pressure. The period of inflow causes a
stretching of the eye walls with a concomitant increase in pressure
followed by a relaxation to the previous volume and a return to the
previous pressure as the blood drains from the eye. If this process
of expansion during systole (contraction of the heart) and
contraction during diastole (relaxation of the heart) occurs at a
certain pulse rate, then the blood flow rate would be the
incremental change in eye volume times the pulse rate.
[0536] The fact that intraocular pressure varies with time
according to the cardiac cycle is the basis for measuring pulsatile
ocular blood flow. The cardiac cycle is approximately in the order
of 0.8 Hz. The present invention can measure the time variations of
intraocular pressure with a frequency that is above the fundamental
human heart beat frequency allowing the evaluation and recording of
intraocular pulse. In the normal human eye, the intraocular pulse
has a magnitude of approximately 3 mm Hg and is practically
synchronous with the cardiac cycle.
[0537] As described, measurements of intraocular pressure show a
time variation that is associated with the pulsatile component of
arterial pressure. Experimental results provide means of
transforming ocular pressure changes into eye volume changes. Each
bolus of blood entering the eye increases the ocular volume and the
intraocular pressure. The observed changes in pressure reflect the
fact that the eye volume must change to accommodate changes in the
intraocular blood volume induced by the arterial blood pulse. This
pulse volume is small relative to the ocular volume, but because
the walls of the eye are stiff, the pressure increase required to
accommodate the pulse volume is significant and can be measured.
Therefore, provided that the relationship between the increased
intraocular pressure and increased ocular volume is known, the
volume of the bolus of fluid can be determined. Since this
relationship between pressure change and volume change has been
well established (Friedenwald 1937, McBain 1957, Ytteborg 1960,
Eisenlohr 1962, McEwen 1965), the pressure measurements can be used
to obtain the volume of a bolus of blood and thereby determine the
blood flow.
[0538] The output of the tonometer for the instantaneous pressure
can be converted into instantaneous change in eye volume as a
function of time. The time derivative of the change in ocular
volume is the net instantaneous pulsatile component of the ocular
blood flow. Under these conditions, the rate of pulsatile blood
flow through the eye can be evaluated from the instantaneous
measurement of intraocular pressure. In order to rapidly quantify
and analyze the intraocular pulse, the signal from the tonometer
may be digitalized and fed into a computer.
[0539] Moreover, measurements of intraocular pressure can be used
to obtain the intraocular volume through the use of an
independently determined pressure-volume relationship such as with
the Friedenwald equation (Friedenwald, 1937). A mathematical model
based on experimental data from the pressure volume relationship
(Friedenwald 1937, McBain 1957, Eisenlohr 1962, McEwen 1965) can
also be used to convert a change in ocular pressure into a change
in ocular volume.
[0540] In addition, a model can also be constructed to estimate the
ocular blood flow from the appearance of the intraocular pressure
waveform. The flow curve is related to parameters that come from
the volume change curve. This curve is indirectly measured since
the intraocular pressure is the actual measured quantity which is
transformed into volume change through the use of the measured
pressure-volume relation. The flow is then computed by taking the
change in volume Vmax-Vmin multiplied by a constant that is related
to the length of the time interval of the inflow and the total
pulse length. Known mathematical calculations can be used to
evaluate the pulsatile component of the ocular blood flow. Since
the present invention can also be used to measure the ocular
rigidity, this parameter of coefficient of ocular rigidity can be
used in order to more precisely calculate individual differences in
pulsatile blood flow.
[0541] Moreover, since the actuation apparatus 6 and contact device
2 of the present invention preferably include transparent portions,
the pulsatile blood flow can be directly evaluated optically to
quantify the change in size of the vessels with each heart beat. A
more precise evaluation of blood flow therefore can be achieved by
combining the changes in intraocular pulse with changes in vessel
diameter which can be automatically measured optically.
[0542] A vast amount of data about the vascular system of the eye
and central nervous system can be obtained after knowing the
changes in intraocular pressure over time and the amount of
pulsatile ocular blood flow. The intraocular pressure and
intraocular pulse are normally symmetrical in pairs of eyes.
Consequently, a loss of symmetry may serve as an early sign of
ocular or cerebrovascular disease. Patients afflicted with
diabetes, macular degeneration, and other vascular disorders may
also have a decreased ocular blood flow and benefit from evaluation
of eye hemodynamics using the apparatus of the present
invention.
[0543] The present invention may also be used to artificially
elevate intraocular pressure. The artificial elevation of
intraocular pressure is an important tool in the diagnosis and
prognosis of eye and brain disorders as well as an important tool
for research.
[0544] Artificial elevation of intraocular pressure using the
present invention can be accomplished in different ways. According
to one way, the contact device of the present invention is modified
in shape for placement on the sclera (white of the eye). This
arrangement, which will be described hereinafter, is illustrated in
FIGS. 21-22, wherein the movable central piece 16 may be larger in
size and is preferably actuated against the sclera in order to
elevate the intraocular pressure. The amount of indentation can be
detected by the optical detection system previously described.
[0545] Another way of artificially increasing the intraocular
pressure is by placing the contact device of the present invention
on the cornea in the same way as previously described, but using
the movable central piece to apply a greater amount of force to
achieve deeper indentation. This technique advantageously allows
visualization of the eye while exerting the force, since the
movable central portion of the contact device is preferably
transparent. According to this technique, the size of the movable
central piece can also be increased to indent a larger area and
thus create a higher artificial increase of intraocular pressure.
Preferably, the actuation apparatus also has a transparent central
portion, as indicated above, to facilitate direct visualization of
the eye and retina while the intraocular pressure is being
increased. When the intraocular pressure exceeds the ophthalmic
arterial diastolic pressure, the pulse amplitude and blood flow
decreases rapidly. Blood flow becomes zero when the intraocular
pressure is equal or higher than the ophthalmic systolic pressure.
Thus, by allowing direct visualization of the retinal vessels, one
is able to determine the exact moment that the pulse disappears and
measure the pressure necessary to promote the cessation of the
pulse which, in turn, is the equivalent of the pulse pressure in
the ophthalmic artery. The present invention thus allows the
measurement of the pressure in the arteries of the eye.
[0546] Also, by placing a fixation light in a back portion of the
actuation apparatus and asking the patient to indicate when he/she
can no longer see the light, one can also record the pressure at
which a patient's vision ceases. This also would correspond to the
cessation of the pulse in the artery of the eye. The pressure in
which vessels open can also be determined by increasing intraocular
pressure until the pulse disappears and then gradually decreasing
the intraocular pressure until the pulse reappears. Thus, the
intraocular pressure necessary for vessels to open can be
evaluated.
[0547] It is important to note that the foregoing measurements can
be performed automatically using an optical detection system, for
example, by aiming a light beam at the pulsating blood vessel. The
cessation of pulsation can be optically recognized and the pressure
recorded. An attenuation of pulsations can also be used as the end
point and can be optically detected. The apparatus also allows
direct visualization of the papilla of the optic nerve while an
increased intraocular pressure is produced. Thus, physical and
chemical changes occurring inside the eye due to the artificial
increase in intraocular pressure may be evaluated at the same time
that pressure is measured.
[0548] Advantageously, the foregoing, test can be performed on
patients with media opacities that prevent visualization of the
back of the eye. In particular, the aforementioned procedure
wherein the patient indicates when vision ceases is particular
useful in patients with media opacities. The fading of the
peripheral vision corresponds to the diastolic pressure and fading
of the central vision corresponds to the systolic pressure.
[0549] The present invention, by elevating the intraocular
pressure, as indicated above and by allowing direct visualization
of blood vessels in the back of the eye, may be used for tamponade
(blockade of bleeding by indirect application of pressure) of
hemorrhagic processes such as those which occur, for example, in
diabetes and macular degeneration. The elevation of intraocular
pressure may also be beneficial in the treatment of retinal
detachments.
[0550] As yet another use of the present invention, the
aforementioned apparatus also can be used to measure outflow
pressure of the eye fluid. In order to measure outflow pressure in
the eye fluid, the contact device is placed on the cornea and a
measurable pressure is applied to the cornea. The pressure causes
the aqueous vein to increase in diameter when the pressure in the
cornea equals the outflow pressure. The pressure on the cornea is
proportional to the outflow pressure. The flow of eye fluid out of
the eye is regulated according to Poiseuille's Law for laminar
currents. If resistance is inserted into the formula, the result is
a formula similar to Ohm's Law. Using these known formulas, the
rate of flow (volume per time) can be determined. The change in the
diameter of the vessel which is the reference point can be detected
manually by direct observation and visualization of the change in
diameter or can be done automatically using an optical detection
system capable of detecting a change in reflectivity due to the
amount of fluid in the vein and the change in the surface area. The
actual cross-section of the vein can be detected using an optical
detection system.
[0551] The eye and the brain are hemodynamically linked by the
carotid artery and the autonomic nervous system. Pathological
changes in the carotid, brain, heart, and the sympathetic nervous
system can secondarily affect the blood flow to the eye. The eye
and the brain are low vascular resistance systems with high
reactivity. The arterial flow to the brain is provided by the
carotid artery. The ophthalmic artery branches off of the carotid
at a 90 degree angle and measures approximately 0.5 mm in diameter
in comparison to the carotid which measures 5 mm in diameter. Thus,
most processes that affect the flow to the brain will have a
profound effect on the eye. Moreover, the pulsation of the central
retinal artery may be used to determine the systolic pressure in
the ophthalmic artery, and due to its anatomic relationship with
the cerebral circulatory system, the pressure in the brain's
vessels can be estimated. Total or partial occlusion of the
vascular system to the brain can be determined by evaluating the
ocular blood flow. There are numerous vascular and nervous system
lesions that alter the ocular pulse amplitude and/or the
intraocular pressure curve of the eye. These pathological
situations may produce asymmetry of measurements between the two
eyes and/or a decrease of the central retinal artery pressure,
decrease of pulsatile blood flow and alter the pulse amplitude.
[0552] An obstruction in the flow in the carotid (cerebral
circulation) can be evaluated by analyzing the ocular pulse
amplitude and area, pulse delay and pulse width, form of the wave
and by harmonic analysis of the ocular pulse.
[0553] The eye pulsation can be recorded optically according to the
change in reflection of the light beam projected to the cornea. The
same system used to record distance traveled by the movable central
piece during indentation can be used on the bare cornea to detect
the changes in volume that occurs with each pulsation. The optical
detection system records the variations in distance from the
surface of the cornea that occurs with each heart beat. These
changes in the position of the cornea are induced by the volume
changes in the eye. From the pulsatile character of these changes,
the blood flow to the eye can be calculated.
[0554] With the aforementioned technique of artificial elevation of
pressure, it is possible to measure the time necessary for the eye
to recover to its baseline and this recovery time is an indicator
of the presence of glaucoma and of the coefficient of outflow
facility.
[0555] The present invention may also be used to measure pressure
in the vessels on the surface of the eye, in particular the
pressure in the episcleral veins. The external pressure necessary
to collapse a vein is utilized in this measurement. The method
involves applying a variable force over a constant area of
conjunctive overlying the episcleral vein until a desired end point
is obtained. The pressure is applied directly onto the vessel
itself and the preferred end point is when the vessel collapses.
However, different end points may be used, such as blanching of the
vessel which occurs prior to the collapse. The pressure of the end
point is determined by dividing the force applied by the area of
the applanating central piece in a similar way as is used for
tonometry. The vessel may be observed through a transparent
applanating movable central piece using a slit-lamp biomicroscope.
The embodiment for this technique preferably includes a modified
contact device which fits on the sclera (FIG. 23). The preferred
size of the tip ranges from 250 micrometers to 500 micrometers.
Detection of the end point can be achieved either manually or
automatically.
[0556] According to the manual arrangement, the actuation apparatus
is configured for direct visualization of the vessel through a
transparent back window of the actuation apparatus, and the time of
collapse is manually controlled and recorded. According to an
automatic arrangement, an optical detection system is configured so
that, when the blood stream is no longer visible, there is a change
in a reflected light beam in the same way as described above for
tonometry, and consequently, the pressure for collapse is
identifiable automatically. The end point marking in both
situations is the disappearance of the blood stream, one detected
by the operator's vision and the other detected by an optical
detection system. Preferably, in both cases, the contact device is
designed in a way to fit the average curvature of the sclera and
the movable central piece, which can be a rigid or flexible
material, is used to compress the vessel.
[0557] The present invention may also be used to provide real-time
recording of intraocular pressure. A built-in single chip
microprocessor can be made responsive to the intraocular pressure
measurements over time and can be programmed to create and display
a curve relating pressure to time. The relative position of the
movable central piece can be detected, as indicated above, using an
optical detection system and the detected position in combination
with information regarding the amount of current flowing through
the coil of the actuation apparatus can be rapidly collected and
analyzed by the microprocessor to create the aforementioned
curve.
[0558] It is understood that the use of a microprocessor is not
limited to the arrangement wherein curves are created. In fact,
microprocessor technology may be used to create at least the
aforementioned calculation unit 10 of the present invention. A
microprocessor preferably evaluates the signals and the force that
is applied. The resulting measurements can be recorded or stored
electronically in a number of ways. The changes in current over
time, for example, can be recorded on a strip-chart recorder. Other
methods of recording and storing the data can be employed. Logic
microprocessor control technology can also be used in order to
better evaluate the data.
[0559] Still other uses of the present invention relate to
evaluation of pressure in deformable materials in industry and
medicine. One such example is the use of the present invention to
evaluate soft tissue, such as organs removed from cadavers. Cadaver
dissection is a fundamental method of learning and studying the
human body. The deformability of tissues such as the brain, liver,
spleen, and the like, can be measured using the present invention
and the depth of indentation can be evaluated. In this regard, the
contact device of the present invention can be modified to fit over
the curvature of an organ. When the movable central piece rests
upon a surface, it can be actuated to project into the surface a
distance which is inversely proportional to the tension of the
surface and rigidity of the surface to deformation. The present
invention can also be used to evaluate and quantify the amount of
cicatrization, especially in burn scar therapy. The present
invention can be used to evaluate the firmness of the scar in
comparison to normal skin areas. The scar skin tension is compared
to the value of normal skin tension. This technique can be used to
monitor the therapy of patients with burn scars allowing a
numerical quantification of the course of cicatrization. This
technique can also be used as an early indicator for the
development of hypenrophic (thick and elevated) scarring. The
evaluation of the tissue pressure and deformability in a variety of
conditions such as: a) lymphoedema b) post-surgical effects, such
as with breast surgery, and c) endoluminal pressures of hollow
organs, is also possible with the apparatus. In the above cases,
the piston-like arrangement provided by the contact device does not
have to be placed in an element that is shaped like a contact lens.
To the contrary, any shape and size can be used, with the bottom
surface preferably being flat and not curved like a contact
lens.
[0560] Yet another use of the present invention relates to
providing a bandage lens which can be used for extended periods of
time. Glaucoma and increased intraocular pressure are leading
causes for rejection of corneal transplants. Many conventional
tonometers in the market are unable to accurately measure
intraocular pressure in patients with corneal disease. For patients
with corneal disease and who have recently undergone corneal
transplant, a thinner and larger contact device is utilized and
this contact device can be used for a longer period of time. The
device also facilitates measurement of intraocular pressure in
patients with corneal disease which require wearing of contact
lenses as part of their treatment.
[0561] The present invention may also be modified to non-invasively
measure infant intracranial pressure, or to provide instantaneous
and continuous monitoring of blood pressure through an intact wall
of a blood vessel. The present invention may also be used in
conjunction with a digital pulse meter to provide synchronization
with the cardiac cycle. Also, by providing a contact microphone,
arterial pressure can be measured. The present invention may also
be used to create a dual tonometer arrangement in one eye. A first
tonometer can be defined by the contact device of the present
invention applied over the cornea, as described above. The second
tonometer can be defined by the previously mentioned contact device
which is modified for placement on the temporal sclera. In using
the dual tonometer arrangement, it is desirable to permit looking
into the eye at the fundus while the contact devices are being
actuated. Accordingly, at least the movable central piece of the
contact device placed over the cornea is preferably transparent so
that the fundus can be observed with a microscope.
[0562] Although the foregoing illustrated embodiments of the
contact device generally show only one movable central piece 16 in
each contact device 2, it is understood that more than one movable
central piece 16 can be provided without departing from the scope
and spirit of the present invention. Preferably, the multiple
movable central pieces 16 would be concentrically arranged in the
contact device 2, with at least one of the flexible membranes 14
interconnecting the concentrically arranged movable central pieces
16. This arrangement of multiple movable central pieces 16 can be
combined with any of the aforementioned features to achieve a
desired overall combination.
[0563] Although the foregoing preferred embodiments include at
least one magnetically actuated movable central piece 16, it is
understood that there are many other techniques for actuating the
movable central piece 16. Sound or ultrasound generation
techniques, for example, can be used to actuate the movable central
piece. In particular, the sonic or ultrasonic energy can be
directed to a completely transparent version of the movable central
piece which, in turn, moves in toward the cornea in response to the
application of such energy.
[0564] Similarly, the movable central piece may be provided with
means for retaining a static electrical charge. In order to actuate
such a movable central piece, an actuation mechanism associated
therewith would create an electric field of like polarity, thereby
causing repulsion of the movable central piece away from the source
of the electric field.
[0565] Other actuation techniques, for example, include the
discharge of fluid or gas toward the movable central piece, and
according to a less desirable arrangement, physically connecting
the movable central piece to a mechanical actuation device which,
for example, may be motor driven and may utilize a strain
gauge.
[0566] Alternatively, the contact device may be eliminated in favor
of a movable central piece in an actuation apparatus. According to
this arrangement, the movable central piece of the actuation
apparatus may be connected to a slidable shaft in the actuation
apparatus, which shaft is actuated by a magnetic field or other
actuation means. Preferably, a physician applies the movable
central piece of the actuation apparatus to the eye and presses a
button which generates the magnetic field. This, in turn, actuates
the shaft and the movable central piece against the eye.
Preferably, the actuation apparatus, the shaft, and the movable
central piece of the actuation apparatus are appropriately arranged
with transparent portions so that the inside of the patient's eye
remains visible during actuation.
[0567] Any of the above described detection techniques, including
the optical detection technique, can be used with the alternative
actuation techniques.
[0568] Also, the movable central piece 16 may be replaced by an
inflatable bladder (not shown) disposed of the substantially rigid
annular member 12. When inflated, the bladder extends out of the
hole in the substantially rigid annular member 12 and toward the
cornea.
[0569] Similarly, although some of the foregoing preferred
embodiments utilize an optical arrangement for determining when the
predetermined amount of applanation has been achieved, it is
understood that there are many other techniques for determining
when applanation occurs. The contact device, for example, may
include an electrical contact arranged so as to make or break an
electrical circuit when the movable central piece moves a distance
corresponding to that which is necessary to produce applanation.
The making or breaking of the electrical circuit is then used to
signify the occurrence of applanation.
[0570] It is also understood that, after applanation has occurred,
the time which it takes for the movable central piece 16 to return
to the starting position after termination of the actuating force
will be indicative of the intraocular pressure, when the
intraocular pressure is high, the movable central piece 16 returns
more quickly to the starting position. Similarly, for lower
intraocular pressures, it takes longer for the movable central
piece 16 to return to its starting position. Therefore, the present
invention can be configured to also consider the return time of the
movable central piece 16 in determining the measured intraocular
pressure.
[0571] As indicated above, the present invention may be formed with
a transparent central portion in the contact device. This
transparent central portion advantageously permits visualization of
the inside of the eye (for example, the optic nerve) while the
intraocular pressure is artificially increased using the movable
central piece. Some of the effects of increased intraocular
pressure on the optic nerve, retina, and vitreous are therefore
readily observable through the present invention, while intraocular
pressure is measured simultaneously.
[0572] With reference to FIGS. 21 and 22, although the foregoing
examples describe placement of the contact device 2 on the cornea,
it is understood that the contact device 2 of the present invention
may be configured with a quasi-triangular shape (defined by the
substantially rigid annular member) to facilitate placement of the
contact device 2 on the sclera of the eve.
[0573] With reference to FIGS. 23 and 24, the contact device 2 of
the present invention may be used to measure episcleral venous
pressure. Preferably, when episcleral venous pressure is to be
measured, the movable central piece 6 has a transparent centrally
disposed frustoconical projection 16P. The embodiment illustrated
FIG. 24 advantageously permits visualization of the subject in
through at least the transparent central portion of the movable
central piece 16.
[0574] Furthermore, as indicated above, the present invention may
also be used to measure pressure in other parts of the body (for
example, scar pressure in the context of plastic surgery) or on
surfaces of various objects. The contact device of the present
invention, therefore, is not limited to the corneal-conforming
curved shape illustrated in connection with the exemplary
embodiments, but rather may have various other shapes including a
generally flat configuration.
Alternative Embodiment Actuated by Closure of the Eye Lid
[0575] With reference to FIGS. 25-31, an alternative embodiment of
the system will now be described. The alternative apparatus and
method uses the force and motion generated by the eye lid during
blinking and/or closure of the eyes to act as the actuation
apparatus and activate at least one transducer 400 mounted in the
contact device 402 when the contact device 402 is on the cornea.
The method and device facilitate the remote monitoring of pressure
and other physiological events by transmitting the information
through the eye lid tissue, preferably via electromagnetic waves.
The information transmitted is recovered at a receiver 404 remotely
placed with respect to the contact device 402, which receiver 404
is preferably mounted in the frame 408 of a pair of eye glasses.
This alternative embodiment also facilitates utilization of
forceful eye lid closure to measure outflow facility. The
transducer is preferably a microminiature pressure-sensitive
transducer 400 that alters a radio frequency signal in a manner
indicative of physical pressure exerted on the transducer 400.
[0576] Although the signal response from the transducer 400 can be
communicated by cable, it is preferably actively or passively
transmitted in a wireless manner to the receiver 404 which is
remotely located with respect to the contact device 402. The data
represented by the signal response of the transducer 400 can then
be stored and analyzed. Information derived from this data can also
be communicated by telephone using conventional means.
[0577] According to the alternative embodiment, the apparatus
comprises at least one pressure-sensitive transducer 400 which is
preferably activated by eye lid closure and is mounted in the
contact device 402. The contact device 402, in turn, is located on
the eye. In order to calibrate the system, the amount of motion and
squeezing of the contact device 402 during eye lid motion/closure
is evaluated and calculated. As the upper eyelid descends during
blinking, it pushes down and squeezes the contact device 402,
thereby forcing the contact device 402 to undergo a combined
sliding and squeezing motion.
[0578] Since normal individuals involuntarily blink approximately
every 2 to 10 seconds, this alternative embodiment of the present
invention provides frequent actuation of the transducer 400. In
fact, normal individuals wearing a contact device 402 of this type
will experience an increase in the number of involuntary blinks,
and this, in turn, tends to provide quasi-continuous measurements.
During sleep or with eyes closed, since there is uninterrupted
pressure by the eye lid, the measurements can be taken
continuously.
[0579] As indicated above, during closure of the eye, the contact
device 402 undergoes a combined squeezing and sliding motion caused
by the eye lid during its closing phase. Initially the upper eye
lid descends from the open position until it meets the upper edge
of the contact device 402, which is then pushed downward by
approximately 0.5 mm to 2 mm. This distance depends on the type of
material used to make the structure 412 of the contact device 402
and also depends on the diameter thereof.
[0580] When a rigid structure 412 is used, there is little initial
overlap between the lid and the contact device 402. When a soft
structure 412 is used, there is a significant overlap even during
this initial phase of eye lid motion. After making this initial
small excursion the contact device 402 comes to rest, and the eye
lid then slides over the outer surface of the contact device 402
squeezing and covering it. It is important to note that if the
diameter of the structure 412 is greater than the lid aperture or
greater than the corneal diameter, the upper lid may not strike the
upper edge of the contact device 402 at the beginning of a
blink.
[0581] The movement of the contact device 402 terminates
approximately at the corneo-scleral junction due to a slope change
of about 13 degrees in the area of intersection between cornea
(radius of 9 mm) and sclera (radius of 11.5 mm). At this point the
contact device 402, either with a rigid or soft structure 412,
remains immobile and steady while the eye lid proceeds to cover it
entirely.
[0582] When a rigid structure 412 is used, the contact device 402
is usually pushed down 0.5 mm to 2 mm before it comes to rest. When
a soft structure 412 is used, the contact device 402 is typically
pushed down 0.5 mm or less before it comes to rest. The larger the
diameter of the contact device 402, the smaller the motion, and
when the diameter is large enough there may be zero vertical
motion. Despite these differences in motion, the squeezing effect
is always present, thereby allowing accurate measurements to be
taken regardless of the size of the structure 412. Use of a thicker
structure 412 or one with a flatter surface results in an increased
squeezing force on the contact device 402.
[0583] The eye lid margin makes a re-entrant angle of about 35
degrees with respect to the cornea. A combination of forces,
possibly caused by the contraction of the muscle of Riolan near the
rim of the eye lid and of the orbicularis muscle, are applied to
the contact device 402 by the eye lid. A horizontal force (normal
force component) of approximately 20,000 to 25,000 dynes and a
vertical force (tangential force component) of about 40 to 50 dynes
is applied on the contact device 402 by the upper eye lid. In
response to these forces, the contact device 402 moves both toward
the eye and tangentially with respect thereto. At the moment of
maximum closure of the eye, the tangential motion and force are
zero and the normal force and motion are at a maximum.
[0584] The horizontal lid force of 20,000 to 25,000 dynes pressing
the contact device 402 against the eye generates enough motion to
activate the transducer 400 mounted in the contact device 402 and
to permit measurements to be performed. This eye lid force and
motion toward the surface of the eye are also capable of
sufficiently deforming many types of transducers or electrodes
which can be mounted in the contact device 402. During blinking,
the eye lids are in full contact with the contact device 402 and
the surface of each transducer 400 is in contact with the
cornea/tear film and/or inner surface of the eye lid.
[0585] The microminiature pressure-sensitive radio frequency
transducer 400 preferably consists of an endoradiosonde mounted in
the contact device 402 which, in turn, is preferably placed on the
cornea and is activated by eye lid motion and/or closure. The force
exerted by the eye lid on the contact device 402, as indicated
above, presses it against the cornea.
[0586] According to a preferred alternative embodiment illustrated
in FIG. 26, the endoradiosonde includes two opposed matched coils
which are placed within a small pellet. The flat walls of the
pellet act as diaphragms and are attached one to each coil such
that compression of the diaphragm by the eye lid brings the coils
closer to one another. Since the coils are very close to each
other, minimal changes in their separation affect their resonant
frequency.
[0587] A remote grid-dip oscillator 414 may be mounted at any
convenient location near the contact device 402, for example, on a
hat or cap worn by the patient. The remote grid-dip oscillator 414
is used to induce oscillations in the transducer 400. The resonant
frequency of these oscillations is indicative of intraocular
pressure.
[0588] Briefly, the contact of the eye lid with the diaphragms
forces a pair of parallel coaxial archimedean-spiral coils in the
transducer 400 to move closer together. The coils constitute a
high-capacitance distributed resonant circuit having a resonant
frequency that varies according to relative coil spacing. When the
coils approach one another, there is an increase in the capacitance
and mutual inductance, thereby lowering the resonant frequency of
the configuration. By repeatedly scanning the frequency of an
external inductively coupled oscillating detector of the grid-dip
type, the electromagnetic energy which is absorbed by the
transducer 400 at its resonance is sensed through the intervening
eye lid tissue.
[0589] Pressure information from the transducer 400 is preferably
transmitted by radio link telemetry. Telemetry is a preferred
method since it can reduce electrical noise pickup and eliminates
electric shock hazards. FM (frequency modulation) methods of
transmission are preferred since FM transmission is less noisy and
requires less gain in the modulation amplifier, thus requiring less
power for a given transmission strength. FM is also less sensitive
to variations in amplitude of the transmitted signal.
[0590] Several other means and transducers can be used to acquire a
signal indicative of intraocular pressure from the contact device
402. For example, active telemetry using transducers which are
energized by batteries or using cells that can be recharged in the
eye by an external oscillator, and active transmitters which can be
powered from a biologic source can also be used.
[0591] The preferred method to acquire the signal, however,
involves at least one of the aforementioned passive pressure
sensitive transducers 400 which contain no internal power source
and operate using energy supplied from an external source to modify
the frequency emitted by the external source. Signals indicative of
intraocular ocular pressure are based on the frequency modification
and are transmitted to remote extra-ocular radio frequency
monitors. The resonant frequency of the circuit can be remotely
sensed, for example, by a grid-dip meter.
[0592] In particular, the grip-dip meter includes the
aforementioned receiver 404 in which the resonant frequency of the
transducer 400 can be measured after being detected by external
induction coils 415 mounted near the eye, for example, in the
eyeglass frames near the receiver or in the portion of the eyeglass
frames which surround the eye. The use of eyeglass frames is
especially practical in that the distance between the external
induction coils 415 and the radiosonde is within the typical
working limits thereof. It is understood, however, that the
external induction coils 415, which essentially serve as a
receiving antenna for the receiver 404 can be located any place
that minimizes signal attenuation. The signal from the external
induction coils 415 (or receiving antenna) is then received by the
receiver 404 for amplification and analysis.
[0593] When under water, the signal may be transmitted using
modulated sound signals because sound is less attenuated by water
than are radio waves. The sonic resonators can be made responsive
to changes in temperature and voltage.
[0594] Although the foregoing description includes some preferred
methods and devices in accordance with the alternative embodiment
of the present invention, it is understood that the invention is
not limited to these preferred devices and methods. For example,
many other types of miniature pressure sensitive radio transmitters
can be used and mounted in the contact device, and any
microminiature pressure sensor that modulates a signal from a radio
transmitter and sends the modulated signal to a nearby radio
receiver can be used.
[0595] Other devices such as strain gauges, preferably
piezoelectric pressure transducers, can also be used on the cornea
and are preferably activated by eye lid closure and blinking. Any
displacement transducer contained in a distensible case also can be
mounted in the contact device. In fact, many types of pressure
transducers can be mounted in and used by the contact device.
Naturally, virtually any transducer that can translate the
mechanical deformation into electric signals is usable.
[0596] Since the eye changes its temperature in response to changes
in pressure, a pressure-sensitive transducer which does not require
motion of the parts can also be used, such as a thermistor.
Alternatively, the dielectric constant of the eye, which also
changes in response to pressure changes, can be evaluated to
determine intraocular pressure. In this case, a pressure-sensitive
capacitor can be used. Piezoelectric and piezo-resistive
transducers, silicon strain gauges, semiconductor devices and the
like can also be mounted and activated by blinking and/or closure
of the eyes.
[0597] In addition to providing a novel method for performing
single measurements, continuous measurements, and self-measurement
of intraocular pressure during blinking or with the eyes closed,
the apparatus can also be used to measure outflow facility and
other physiological parameters. The inventive method and device
offer a unique approach to measuring outflow facility in a
physiological manner and undisturbed by the placement of an
external weight on the eye.
[0598] In order to determine outflow facility in this fashion, it
is necessary for the eye lid to create the excess force necessary
to squeeze fluid out of the eye. Because the present invention
permits measurement of pressure with the patient's eyes closed, the
eye lids can remain closed throughout the procedure and
measurements can be taken concomitantly. In particular, this is
accomplished by forcefully squeezing the eye lids shut. Pressures
of about 60 mm Hg will occur, which is enough to squeeze fluid out
of the eye and thus evaluate outflow facility. The intraocular
pressure will decrease over time and the decay in pressure with
respect to time correlates to the outflow facility. In normal
individuals, the intraocular fluid is forced out of the eye with
the forceful closure of the eye lid and the pressure will decrease
accordingly; however, in patients with glaucoma, the outflow is
compromised and the eye pressure therefore does not decrease at the
same rate in response to the forceful closure of the eye lids. The
present system allows real time and continuous measurement of eye
pressure and, since the signal can be transmitted through the eye
lid to an external receiver, the eyes can remain closed throughout
the procedure.
[0599] Telemetry systems for measuring pressure, electrical
changes, dimensions, acceleration, flow, temperature, bioelectric
activity, chemical reactions, and other important physiological
parameters and power switches to externally control the system can
be used in the apparatus of the invention. The use of integrated
circuits and technical advances occurring in transducer, power
source, and signal processing technology allow for extreme
miniaturization of the components which, in turn, permits several
sensors to be mounted in one contact device, as illustrated for
example in FIG. 28.
[0600] Modern resolutions of integrated circuits are in the order
of a few microns and facilitate the creation of very high density
circuit arrangements. Preferably, the modern techniques of
manufacturing integrated circuits are exploited in order to make
electronic components small enough for placement on the eyeglass
frame 408. The receiver 404, for example, may be connected to
various miniature electronic components 418, 419 420, as
schematically illustrated in FIG. 31, capable of processing,
storing, and even displaying the information derived from the
transducer 400.
[0601] Radio frequency and ultrasonic micro-circuits are available
and can be mounted in the contact device for use thereby. A number
of different ultrasonic and pressure transducers are also available
and can be used and mounted in the contact device. It is understood
that further technological advances will occur which will permit
further applications of the apparatus of the invention.
[0602] The system may further comprise a contact device for
placement on the cornea and having a transducer capable of
detecting chemical changes in the tear film. The system may further
include a contact device for placement on the cornea and having a
microminiature gas-sensitive radio frequency transducer (e.g.,
oxygen-sensitive). A contact device having a microminiature blood
velocity-sensitive radio frequency transducer may also be used for
mounting on the conjunctiva and is preferably activated by eye lid
motion and/or closure of the eye lid.
[0603] The system also may comprise a contact device in which a
radio frequency transducer capable or measuring the negative
resistance of nerve fibers is mounted in the contact device which,
in turn, is placed on the cornea and is preferably activated by eye
lid motion and/or closure of the eye lid. By measuring the
electrical resistance, the effects of microorganisms, drugs,
poisons and anesthetics can be evaluated.
[0604] The system of the present invention may also include a
contact device in which a microminiature radiation-sensitive radio
frequency transducer is mounted in the contact device which, in
turn, is placed on the cornea and is preferably activated by eye
lid motion and/or closure of the eye lid.
[0605] In any of the foregoing embodiments having a transducer
mounted in the contact device, a grid-dip meter can be used to
measure the frequency characteristics of the tuned circuit defined
by the transducer.
[0606] Besides using passive telemetry techniques as illustrated by
the use of the above transducers, active telemetry with active
transmitters and a microminiature battery mounted in the contact
device can also be used.
[0607] The contact device preferably includes a rigid or flexible
transparent structure 412 in which at least one of the transducers
400 is mounted in hole(s) formed in the transparent structure 412.
Preferably, the transducers 400 is/are positioned so as to allow
the passage of light through the visual axis. The structure 412
preferably includes an inner concave surface shaped to match an
outer surface of the cornea.
[0608] As illustrated in FIG. 29, a larger transducer 400 can be
centrally arranged in the contact device 402, with a transparent
portion 416 therein preserving the visual axis of the contact
device 402.
[0609] The structure 412 preferably has a maximum thickness at the
center and a progressively decreasing thickness toward a periphery
of the structure 412. The transducers is/are preferably secured to
the structure 412 so that the anterior side of each transducer 400
is in contact with the inner surface of the eye lid during blinking
and so that the posterior side of each transducer 400 is in contact
with the cornea, thus allowing eye lid motion to squeeze the
contact device 402 and its associated transducers 400 against the
cornea.
[0610] Preferably, each transducer 400 is fixed to the structure
412 in such a way that only the diaphragms of the transducers
experience motion in response to pressure changes. The transducers
400 may also have any suitable thickness, including matching or
going beyond the surface of the structure 412.
[0611] The transducers 400 may also be positioned so as to bear
against only the cornea or alternatively only against the inner
surface of the eye lid. The transducers 400 may also be positioned
in a protruding way toward the cornea in such a way that the
posterior part flattens a portion of the cornea upon eye lid
closure. Similarly, the transducers 400 may also be positioned in a
protruding way toward the inner surface of the eye lid so that the
anterior part of the transducer 400 is pressed by the eye lid, with
the posterior part being covered by a flexible membrane allowing
interaction with the cornea upon eye lid closure.
[0612] A flexible membrane of the type used in flexible or hydrogel
lenses may encase the contact device 402 for comfort as long as it
does not interfere with signal acquisition and transmission.
Although the transducers 400 can be positioned in a manner to
counterbalance each other, as illustrated in FIG. 28, it is
understood that a counter weight can be used to maintain proper
balance.
[0613] FIG. 32 illustrates the contact device 500 placed on the
surface of the eye with mounted sensor 502, transmitter 504, and
power source 506 which are connected by fine wire 508 (shown only
partially extending from sensor 502 and from transmitter 504),
encased in the contact device. The contact device shown measures
approximately 24 mm in its largest diameter with its corneal
portion 510 measuring approximately 111 mm in diameter with the
remaining 13 mm subdivided between 8 mm of a portion 512 under the
upper eyelid 513 and 5 mm of a portion 514 under the lower eyelid
515. The contact device in FIG. 32 has microprotuberances 516 in
its surface which increases friction and adhesion to the
conjunctiva allowing diffusion of tissue fluid from the blood
vessels into the sensor selective membrane surface 518. The tissue
fluid goes through membranes in the sensor and reaches an electrode
520 with generation of current proportional to the amount of
analyte found in the tear fluid 522 moving in the direction of
arrows 524. A transmitter 504 transmitting a modulated signal 526
to a receiver 528 with the signal 526 being amplified and filtered
in amplifier and filter 529, decoded in demultiplexer 530,
processed in CPU 532, displayed at monitor 534, and stored in
memory 536.
[0614] The contact device 540 shown in FIG. 33A includes two
sensors, one sensor 542 for detection of glucose located in the
main body 544 of the contact device and a cholesterol sensor 546
located on a myoflange 548 of the contact device 540. Forming part
of the contact device is a heating electrode 550 and a power source
552 next to the cholesterol sensor 546 with the heating electrode
550 increasing the local temperature with subsequent transudation
of fluid in the direction of arrows 553 toward the cholesterol
sensor 546.
[0615] In one embodiment the cholesterol sensor shown in FIG. 33C
includes an outer selectively permeable membrane 554, and
mid-membranes 556, 558 with immobilized cholesterol esterase and
cholesterol oxidase enzymes and an inner membrane 560 permeable to
hydrogen peroxide. The external membrane 554 surface has an area
preferably no greater than 300 square micrometers and an overall
thickness of the multiple membrane layers is in the order of 30-40
micrometers. Covered by the inner membrane are a platinum electrode
562 and two silver electrodes 564 measuring 0.4 mm (platinum wire)
and 0.15 mm (silver wire). Fine wires 566, 568 connect the
cholesterol sensor 546 to the power source 552 and transmitter 570.
The glucose sensor 542 includes a surrounding irregular external
surface 572 to increase friction with the sensor connected by fine
wires 574, 576 to the power source 578 and transmitter 570. The
power source 578 is connected to the sensor in order to power the
sensor 542 for operation.
[0616] The transmitter includes integrated circuits for receiving
and transmitting the data with the transmitters being of ultra
dense integrated hybrid circuits measuring approximately 500
microns in its largest dimension. The corneal tissue fluid diffuses
in the direction of arrows 580 toward the glucose sensor 542 and
reaches an outer membrane 582 permeable to glucose and oxygen
followed by an immobilized glucose oxidase membrane 584 and an
inner membrane 586 permeable to hydrogen peroxide. The tissue fluid
then reaches the one platinum 588 and two silver 590 electrodes
generating a current proportional to the concentration of glucose.
The dimensions of the glucose sensor are similar to the dimensions
of the cholesterol sensor.
[0617] FIG. 34 illustrates by, a block diagram, examples of signals
obtained for measuring various biological variables such as glucose
600, cholesterol 602 and oxygen 604 in the manner as exemplified in
FIGS. 33A-33C. A glucose signal 606, a cholesterol signal 608 and
an oxygen signal 610 are generated by transducers or sensors as
shown in FIGS. 33B and 33C. The signals are transmitted to a
multiplexer 612 which transmits the signals as a coded signal by
wire 614 to a transmitter 616. A coded and modulated signal is
transmitted, as represented by line 618, by radio, light, sound,
wire telephone or the like with noise suppression to a receiver
620. The signal is then amplified and filtered at amplifier and
filter 622. The signal passes through a demultiplexer 624 and the
separated signals are amplified at 626, 628, 630, respectively and
transmitted and displayed at display 632 of a CPU and recorded for
transmission by modem 634 to a hospital network, for example.
[0618] FIGS. 35A-35C illustrate an intelligent contact lens being
activated by closure of the eyelids with subsequent increased
diffusion of blood components to the sensor. During movement of the
eye lids from the position shown in FIG. 35C to the position shown
in FIG. 35A by blinking and/or closure of the eye, a combination of
forces are applied to the contact device 636 by the eyelid with a
horizontal force (normal force component) of approximately 25,000
dynes which causes an intimate interaction between the contact
device and the surface of the eye with a disruption of the lipid
layer of the tear film allowing direct interaction of the outer
surface of the contact device with the palpebral conjunctiva as
well as a direct interaction of the inner surface of the contact
device with the aqueous layer of the tear film and the epithelial
surface of the cornea and bulbar conjunctiva. Blinking promotes a
pump system which extracts fluid from the supero-temporal corner of
the eye and delivery of fluid to the puncta in the infero-medial
corner of the eye creating a continuous flow which bathes the
contact device. During blinking, the close interaction with the
palpebral conjunctiva, bulbar conjunctiva, and cornea, the slightly
rugged surface of the contact device creates microdisruption of the
blood barrier and of the epithelial surface with transudation and
increased flow of tissue fluid toward the surface of the contact
device. The tear fluid then diffuses through the selectively
permeable membranes located on the surface of the contact device
636 and subsequently reaching the electrodes of the sensor 638
mounted in the contact device. In the preferred embodiment for
glucose measurement, glucose and oxygen flow from the capillary
vessels 640 toward a selectively permeable outer membrane and
subsequently reach a mid-membrane with immobilized glucose oxidase
enzyme. At this layer of immobilized glucose oxidase enzyme, a
enzymatic oxidation of glucose in the presence of the enzyme
oxidase and oxygen takes place with the formation of hydrogen
peroxide and gluconic acid. The hydrogen peroxide then diffuses
through an inner membrane and reaches the surface of a platinum
electrode and it is oxidized on the surface of the working
electrode creating a measurable electrical current. The intensity
of the current generated is proportional to the concentration of
hydrogen peroxide which is proportional to the concentration of
glucose. The electrical current is subsequently converted to a
frequency audio signal by a transmitter mounted in the contact
device with signals being transmitted to a remote receiver using
preferably electromagnetic energy for subsequent amplification,
decoding, processing, analysis, and display.
[0619] In FIGS. 36A through 36J, various shapes of contact devices
are shown for use in different situations. In FIG. 36A, a contact
device 642 is shown of an elliptical, banana or half moon shape for
placement under the upper or lower eye lid. FIGS. 36B and 36C show
a contact device 644 having, in side view a wide base portion 646
as compared to an upper portion 648. FIG. 36D shows a contact
device 650 having a truncated lens portion 652.
[0620] In FIGS. 36E and 36F, the contact device 654 is shown in
side view in FIG. 36E and includes a widened base portion 656 which
as shown in FIG. 36F is of a semi-truncated configuration.
[0621] FIG. 36G shows a contact device 658, having a corneal
portion 650 and a scleral portion 652. In FIG. 36H, an oversized
contact device 664, includes a corneal portion 666 and a scleral
portion 668.
[0622] A more circular shaped contact device 670 is shown in FIG.
36I having a corneal-scleral lens 672.
[0623] The contact device 674 shown in FIG. 36J is similar to the
ones shown in FIGS. 32, 33A, 35A and 35C. The contact device
includes a main body portion 676 with upper myoflange or minus
carrier 678 and lower myoflange or minus carrier 680.
[0624] In FIG. 37A, an upper contact device 682 is placed under an
upper eye lid 684. Similarly, a lower contact device 686 is placed
underneath a lower eye lid 688. Upper contact device 682 includes
an oxygen sensor/transmitter 690 and a glucose transmitter 692.
Similarly, the lower contact device includes a temperature sensor
transmitter 694 and a pH sensor/transmitter 696.
[0625] Each of these four sensors outputs a signal to respective
receivers 698, 700, 702 and 704, for subsequent display in CPU
displays 706, 708, 710, 712, respectively. The CPUs display an
indication of a sensed oxygen output 714, temperature output 716,
pH output 718 and glucose output 720.
[0626] In FIG. 37B, a single contact device 722, in an hour glass
shape, includes an upper sodium sensor/transmitter 724 and a lower
potassium sensor/transmitter 726. The two sensors send respective
signals to receivers 728 and 730 for display in CPUs 732, 734 for
providing a sodium output indicator 736 and a potassium output
indicator 738.
[0627] In FIG. 38A, a contact device 740 is shown which may be
formed of an annular band 742 so as to have a central opening with
the opening overlying a corneal portion or if the contact device
includes a corneal portion, the corneal portion lays on the surface
of the cornea. Limited to annular band 742 is a sensor 744
positioned on the scleral portion of the contact device so as to be
positioned under an eye lid. The sensor is connected by wires 746a,
746b to transmitter 748 which is in communication with the power
source 750 by wires 752a, 752b. The intelligent contact lens device
740 is shown in section in FIG. 38B with the power source 750 and
sensor 744 located on opposite ends of the contact device on the
scleral portion of the contact device.
[0628] FIG. 39A schematically illustrates the flow of tear fluid as
illustrated by arrows 754 from the right lacrimal gland 756 across
the eye to the lacrimal punctum 758a and 758. Taking advantage of
the flow of tear fluid, in FIG. 39B, a contact device 760 is
positioned in the lower cul-de-sac 762 beneath the lower eye lid
764 so that a plurality of sensors 764a, 764b and 764c in wire
communication with a power source 766 and transducer 768 can be
connected by a wire 770 to an external device. The flow of tear
fluid from the left lacrimal gland 762 to the lacrimal punctum 764a
and 764b is taken advantage of to produce a reading indicative of
the properties to be detected by the sensors.
[0629] In FIG. 40A, a contact device 772 is positioned in the
cul-de-sac 774 of the lower eye lid 776. The contact device
includes a needle-type glucose sensor 778 in communication with a
transmitter 780 and a power source 782. A signal 782 is transmitted
to a receiver, demultiplexer and amplifier 784 for transmission to
a CPU and modem 786 and subsequent transmission over a public
communication network 788 for receipt and appropriate action at an
interface 790 of a hospital network.
[0630] In FIG. 40B, a similar arrangement to that shown in FIG. 40A
is used except the glucose sensor 792 is a needle type sensor with
a curved shape so as to be placed directly against the eye lid. The
sensor 792 is silicone coated or encased by coating with silicone
for comfortable wear under the eye lid 794. Wires 796a and 796b
extend from under the eye lid and are connected to an external
device. The sensor 792 is placed in direct contact with the
conjunctiva with signals and power source connected by wires to
external devices.
[0631] FIG. 41 shows an oversized contact device 798 including
sensors 800a, 800b, 800c and the scleral portion of the contact
device to be positioned under the upper eye lid. In addition,
sensors 802a, 802b, 802c are to be positioned under the lower eye
lid in contact with the bulbar and/or palpebral conjunctiva. In
addition, sensors 804a-d are located in the corneal portion in
contact with the tear film over the cornea.
[0632] FIG. 42A shows a contact device 806 having a sensor 808 and
a transmitter 810 in position, at rest, with the eye lids open.
However, in FIG. 42B, when the eye lids move towards a closed
position, and the individual is approaching a state of sleep, the
Bell phenomenon will move the eye and therefore the contact device
upward in the direction of arrows 812. The pressure produced from
the eye lid as the contact device moves up, will produce a signal
814 from the sensor 808 which is transmitted to a receive 816. The
signal passes through an amplifier and filter 818 to a
demultiplexer 820 for activation of an alarm circuit 822 and
display of data at 824. The alarm should be sufficient to wake a
dozing driver or operator of other machinery to alert the user of
signs of somnolence.
[0633] In FIG. 43, a heat stimulation transmission device 825 for
external placement on the surface of the eye is shown for placement
on the scleral and corneal portions of the eye. The device 825
includes a plurality of sensors 826 spaced across the device 825.
With reference to FIG. 44, the device 825 includes heating elements
828a-c, a thermistor 830, an oxygen sensor 832, and a preferably
inductively activated power source 834. Signals generated by the
sensors are transmitted by transmitter 836 to hardware 838 which
provides an output representative of a condition detected by the
sensors.
[0634] In FIG. 46, an annular band 840 includes a plurality of
devices 842a-e. The annular band shaped heat stimulation
transmission device 840 can be used externally or internally by
surgical implication in any part of the body promoting increase of
oxygen from a remotely situated stimulating source. Another
surgically implantable device 844 is shown in FIG. 46. In this
example, the heat stimulation transmission device 844 is implanted
between eye muscles 846, 848. Another example of a surgically
implantable heat stimulation transmission device 850 is shown in
FIG. 47, having four heating elements 852, a temperature sensor 854
and an oxygen sensor 856, with a power source 858 and a transmitter
860 for transmitting signal 852.
[0635] FIGS. 48, 49 and 51 through 53 illustrate the use of an
overheating transmission device, as shown in FIG. 50, for the
destruction of tumor cells after the implantation of the
overheating transmission device by surgery. As shown in FIG. 50,
the overheating transmission device 864 includes a plurality of
heating elements 866a, 866b, 866c, a temperature sensor 868, a
power source 870 which is inductively activated and a transmitter
872 for transmitting a signal 874. By activation of the device 864,
an increase in temperature results in the immediately adjacent
area. This can cause the destruction of tumor cells from a remote
location.
[0636] In FIG. 48, the device 864 is located adjacent to a brain
tumor 876. In FIG. 49, the device 864 is located adjacent to a
kidney tumor 878.
[0637] In FIG. 51, the device 864 is located adjacent to an
intraocular tumor 880. In FIG. 52, a plurality of devices 864 are
located adjacent to a lung tumor 882. In FIG. 53, a device 864 is
located externally on the breast, adjacent to a breast tumor
884.
[0638] In FIGS. 54A and 54B, a contact device 886 is located on the
eye 888. The contact device is used to detect glucose in the
aqueous humor by emitting light from light emitting optical fiber
890, which is sensitive to glucose, as compared to a reference
optical fiber light source 892, which is not sensitive to glucose.
Two photo detectors 894a, 894b measure the amount of light passing
from the reference optical fiber 892 and the emitting optical fiber
890 sensitive to glucose and transmit the received signals by wires
896a, 896b for analysis.
[0639] In FIG. 54C, a glucose detecting contact device 900 is used
having a power source 902, an emitting light source 904 sensitive
to glucose and a reference light source 906, non-sensitive to
glucose. Two photo detectors 908a and 908b, provide a signal to a
transmitter 910 for transmission of a signal 912 to a remote
location for analysis and storage.
[0640] In FIG. 55A, a contact device 914 is positioned on an eye
916 for detection of heart pulsations or heart sounds as
transmitted to eye 916 by the heart 918 as a normal bodily
function. A transmitter provides a signal 920 indicative of the
results of the heart pulsations or heart sound. A remote alarm
device 922 may be worn by the individual. The details of the alarm
device are shown in FIG. 55B where the receiver 924 receives the
transmitted signal 920 and conveys the signal to a display device
926 as well as to an alarm circuit 928 for activation of an alarm
if predetermined parameters are exceeded.
[0641] In FIG. 56, a contact device 930 is shown. The contact
device includes an ultra sound sensor 932, a power source 934 and a
transmitter 936 for conveying a signal 938. The ultra sound sensor
932 is placed on a blood vessel 940 for measurement of blood flow
and blood velocity. The result of this analysis is transmitted by
signal 938 to a remote receiver for analysis and storage.
[0642] In FIG. 57, an oversized contact device 940 includes a
sensor 942, a power source 944 and a transmitter 946 for
transmitting a signal 948. The sensor 942 is positioned on the
superior rectus muscle for measurement of eye muscle potential. The
measured potential is transmitted by signal 948 to a remote
receiver for analysis and storage.
[0643] In FIG. 58A, a contact device 950 includes a light source
952, a power source 954, multioptical filter system 956 and a
transmitter 958 for transmission of a signal 960. The light source
952 emits a beam of light to the optic nerve head 962. The beam of
light is reflected on to the multioptical filter system 956 for
determination of the angle of reflection.
[0644] As shown in FIG. 58B, since the distance X of separation
between the multioptical filter system and the head of the optic
nerve 962 remains constant as does the separation distance Y
between the light source 952 and the multoptical filter system 956,
a change in the point P which is representative of the head of the
optic nerve will cause a consequent change in the angle of
reflection so that the reflected light will reach a different point
on the multioptical filter system 956. The change of the reflection
point on multioptical filter system 956 will create a corresponding
voltage change based on the reflection angle. The voltage signal is
transmitted as an audio frequency signal 960 to a remote location
for analysis and storage.
[0645] In FIGS. 59A through 59C, a neuro stimulation transmission
device 964 is shown. In FIG. 59A, the device 964 is surgically
implanted in the brain 966. The device 964 includes
microphotodiodes or electrodes 968 and a power source/transmitter
970. The device is implanted adjacent to the occipital cortex
972.
[0646] In FIG. 59B, the device 964 is surgically implanted in the
eye 974 on a band 976 including microphotodiodes 978a, 978b with a
power source 980 and a transmitter 982.
[0647] In FIG. 59C, the device 964 is externally placed on the eye
974 using an oversized contact device 984 as a corneal scleral
lens. The device includes an electrode 986 producing a
microcurrent, a microphotodiode or electrode 988, a power source
990 and a transmitter 992 for transmission of a signal to a remote
location for analysis and storage.
[0648] In FIG. 60, a contact device 1000 includes a power source
1002 and a fixed frequency transmitter 1004. The transmitter 1004
emits a frequency which is received by an orbiting satellite 1006.
Upon detection of the frequency of the signal transmitted by the
transmitter 1004, the satellite can transmit a signal for remote
reception indicative of the location of the transmitter 1004 and
accordingly the exact location of the individual wearing the
contact device 1000. This would be useful in military operations to
constantly monitor the location of all personal.
[0649] In FIG. 61, a contact device 1008 is located below the lower
eye lid 1010. The contact device includes a pressure sensor, an
integrated circuit 1012, connected to an LED drive 1014 and an LED
1016. A power source 1018 is associated with the device located in
the contact device 1008.
[0650] By closure of the eye 1020 by the eye lids, the pressure
sensor 1012 would be activated to energize the LED drive and
therefore the LED for transmission of a signal 1020 to a remote
photodiode or optical receiver 1022 located on a receptor system.
The photodiode or optical receiver 1022, upon receipt of the signal
1020, can transmit a signal 1024 for turning on or off a circuit.
This application has may uses for those individuals limited in
their body movement to only their eyes.
[0651] In FIG. 62, a contact device 1026 includes compartments
1028, 1030 which include a chemical or drug which can be dispensed
at the location of the contact device 1026. The sensor 1032
provides an signal indicative of a specific condition or parameter
to be measured. Based upon the results of the analysis of this
signal, when warranted, by logic circuit 1034, a heater device 1036
can be activated to melt a thread or other closure member 1038
sealing the compartments 1028, 1030 so as to allow release of the
chemical or drug contained in the compartments 1028, 1030. The
system is powered by power source 1040 based upon the biological
variable signal generated as a result of measurement by sensor
1032.
[0652] According to the system shown in FIG. 63, a glucose sensor
1042, positioned on the eye 1044, can generate a glucose level
signal 1046 to a receiver 1048 associated with an insulin pump 1050
for release of insulin into the blood stream 1052. The associated
increase in insulin will again be measured on the eye 1044 by the
sensor 1042 so as to control the amount of insulin released by the
insulin pump 1050. A constant monitoring system is thereby
established
[0653] While the present invention has been described with
reference to preferred embodiments thereof, it is understood that
the present invention is not limited to those embodiments, and by
the scope of the appended claims.
* * * * *