U.S. patent application number 17/558091 was filed with the patent office on 2022-04-14 for arrangement for eye pressure measurements.
The applicant listed for this patent is PHOTONO OY. Invention is credited to Edward HAGGSTROM, Antti KONTIOLA, Heikki NIEMINEN, Ari SALMI.
Application Number | 20220110523 17/558091 |
Document ID | / |
Family ID | |
Filed Date | 2022-04-14 |
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United States Patent
Application |
20220110523 |
Kind Code |
A1 |
KONTIOLA; Antti ; et
al. |
April 14, 2022 |
ARRANGEMENT FOR EYE PRESSURE MEASUREMENTS
Abstract
An intraocular pressure measurement arrangement is disclosed for
measuring pressure of an eye of a patient. The arrangement can
include at least one source for producing mechanical waves of
several frequencies from a distance to the eye of the patient to
generate at least one surface wave to the eye, a detector for
detecting at least one surface wave from a distance from the eye to
extract surface wave information, and a device for determining
pressure information of the eye based on the surface wave
information.
Inventors: |
KONTIOLA; Antti; (Helsinki,
FI) ; HAGGSTROM; Edward; (Helsinki, FI) ;
SALMI; Ari; (Helsinki, FI) ; NIEMINEN; Heikki;
(Helsinki, FI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
PHOTONO OY |
Helsinki |
|
FI |
|
|
Appl. No.: |
17/558091 |
Filed: |
December 21, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15257522 |
Sep 6, 2016 |
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17558091 |
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PCT/FI2015/050133 |
Mar 3, 2015 |
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15257522 |
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International
Class: |
A61B 3/16 20060101
A61B003/16; A61B 5/00 20060101 A61B005/00; A61B 8/10 20060101
A61B008/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 4, 2014 |
FI |
20145205 |
Claims
1. An intraocular pressure measurement arrangement for measuring
pressure of an eye of a patient, the intraocular pressure
arrangement comprising: a contactless nonlinear wave generator that
is locatable at a first distance from the eye, the nonlinear wave
generator being configured to generate, when being the first
distance away from the eye, a nonlinear acoustic wave or a
nonlinear mechanical wave at an output of the contactless nonlinear
wave generator, the generated nonlinear acoustic wave or the
nonlinear mechanical wave coupling to the eye through air and then
generating at least one surface wave to the eye, wherein the
nonlinear acoustic wave or the nonlinear mechanical wave is a
transient or shock wave; a contactless wave detector that is
locatable at a detection distance from the eye, the wave detector
being configured to detect the generated at least one surface wave
from the detection distance from the eye, the detected at least one
surface wave containing surface wave information; and an
intraocular pressure measurement unit comprising a processor
operatively connected to an output of the wave detector to receive
the detected at least one surface wave containing the surface wave
information and to extract surface wave information, the
intraocular pressure measurement unit configured to determine
pressure information of the eye based on said surface wave
information and provide the determined pressure information of the
eye as an output of the intraocular pressure measurement
arrangement, wherein the contactless nonlinear wave generator
comprises one of the following: i) a spark gap and a membrane
located between the spark gap and the eye when a spark in the spark
gap generates the nonlinear acoustic wave or the nonlinear
mechanical wave coupling to the eye through air, or ii) means for
generating a mechanical impact between two hard surfaces to
generate the nonlinear acoustic wave or the nonlinear mechanical
wave coupling to the eye through air.
2. The intraocular pressure measurement arrangement according to
claim 1, wherein the nonlinear wave generator is configured to
generate the acoustic wave or the nonlinear mechanical wave so that
upon coupling to the eye, the generated nonlinear acoustic wave or
the nonlinear mechanical wave generates the at least one surface
wave as a membrane wave.
3. The intraocular pressure measurement arrangement according to
claim 1, wherein, the nonlinear wave generator is configured to
generate the acoustic wave or the nonlinear mechanical wave so that
upon coupling to the eye, the generated acoustic wave or the
nonlinear mechanical wave generates said at least one surface wave
and generates resonant vibrations to the eye, the generated
resonant vibrations containing resonance information; and said wave
detector is configured to detect the resonant vibrations from the
detection distance from the eye; and said intraocular pressure
measurement unit is configured to determine the pressure
information of the eye based on the surface wave information and
the resonance information.
4. The intraocular pressure measurement arrangement according to
claim 1, wherein the wave detector comprises at least one
interferometer.
5. The intraocular pressure measurement arrangement according to
claim 1, wherein the wave detector is configured to detect at least
in two different detection locations in order to improve
measurement accuracy and to obtain higher signal-to-noise
ratio.
6. The intraocular pressure measurement arrangement according to
claim 1, wherein the arrangement comprises means for controlling at
least one distance among an excitation distance and a detection
distance.
7. The intraocular pressure measurement arrangement according to
claim 1, wherein the wave detector comprises at least one of an
optical interferometer, an optical coherence tomograph, a laser
Doppler vibrometer, and an ultrasonic transducer.
8. The intraocular pressure measurement arrangement according to
claim 3, wherein the wave detector is configured to detect the
resonance vibrations based on detection of a first arriving signal
(FAS).
9. The intraocular pressure measurement arrangement according to
claim 1, wherein the nonlinear wave generator is configured for
producing surface waves of plural frequencies from the first
distance to the eye of the patient in response to at least one of
the patient heartbeat and breathing.
10. The intraocular pressure measurement arrangement according to
claim 1, wherein the contactless nonlinear wave generator comprises
the spark gap and the membrane located between the spark gap and
the eye when a spark in the spark gap generates the nonlinear
acoustic wave or the nonlinear mechanical wave coupling to the eye
through air.
11. The intraocular pressure measurement arrangement according to
claim 1, wherein the contactless nonlinear wave generator comprises
the means for generating a mechanical impact between two hard
surfaces to generate the nonlinear acoustic wave or the nonlinear
mechanical wave coupling to the eye through air.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 15/257,522 filed on Sep. 6, 2016, which is a continuation
of PCT International Application No. PCT/FI2015/050133 filed on
Mar. 3, 2015, which claims priority to FI Application No. 20145205
filed on Mar. 4, 2014, the contents of which are hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] Intraocular pressure (IOP) plays a major role in the
pathogenesis of open angle glaucoma, a leading cause of blindness.
There are about 150 million people with glaucoma globally, about
half of which are unknowingly affected and without diagnosis. The
prevalence of glaucoma increases with aging of the human population
and it is expected that this will increase by 30% the number of
glaucoma cases during the next decade. The only way to currently
treat glaucoma is by lowering the intraocular pressure (IOP).
[0003] An IOP measurement is the most practical way of screening
open angle glaucoma. However, screening large parts of the
population is needed to find undiagnosed cases.
[0004] The other type of glaucoma is the narrow angle glaucoma that
causes a sudden IOP increase that may cause blindness in a few
days. Since one per mille of the population is affected with acute
narrow angle closure glaucoma, it is mandatory to diagnose acute
glaucoma by measuring IOP in community emergency departments of
general medicine. Consequently it would be beneficial if every
doctor's office would have means to measure IOP.
STATE OF THE ART
[0005] Contact methods (e.g. Goldmann tonometry, Mackay-Marg
tonometry) for measuring IOP mostly require use of an anesthetic to
carry out the measurement and are thus impractical e.g. for
screening large human populations.
[0006] The US patent application document US 2010/0249569 A1
presents a non-contact ultrasonic tonometer for IOP measurements,
which employs piezo-electric transducers to excite wave signals
into the eye. The position of said transducers have to be exactly
measured, which makes the IOP measurement procedure complex and
slow. Also temperature variations cause error and uncertainty in
the IOP measurement information together with possible errors in
said position measurements. The shape of the eye also introduces
bias (=error) into the measurement.
[0007] The patent document U.S. Pat. No. 6,030,343 A presents a
method that is based on an airborne ultrasonic beam that is
reflected from the cornea--the same beam measures and actuates the
eye. The actuation is done by a narrow band ultrasonic tone burst,
which deforms the cornea, and the system measures the phase shift
from the deformed eye.
[0008] The prior art solutions suffer from difficulties to achieve
a convenient and low-cost device for measuring IOP precisely and
comfortably for the patient by non-contact measurements.
SHORT DESCRIPTION OF THE INVENTION
[0009] The object of the present invention is to achieve a
contactless, fast and advanced device and method to measure IOP
without need for anaesthetics. An object of the invention is to
achieve an IOP reading that is both precise., i.e. unbiased and
features small uncertainty in the IOP estimate. This is achieved by
an IOP measurement arrangement for measuring the pressure in an eye
of a patient. The arrangement comprises at least one source for
producing mechanical waves of several frequencies from a distance
to the eye of the patient to generate at least one surface wave to
the eye, means for detecting at least one surface wave from a
distance from the eye to extract surface wave information, and
means to determine pressure information of the eye based on said
surface wave information.
[0010] An object of the invention is also an intraocular pressure
measurement method for measuring pressure in an eye of a patient.
In the method is produced mechanical waves of several frequencies
from a distance to the eye of the patient to generate at least one
surface wave to the eye, is detected at least one surface wave from
a distance from the eye to extract surface wave information, and is
determined pressure information of the eye based on said surface
wave information.
[0011] The invention is based on utilization of mechanical waves of
several frequencies, which are sent from a distance through air to
the eye of the patient to generate at least one surface wave to the
eye, and on utilization of a detection, in which is detected at
least one surface wave from a distance from the eye to form surface
wave information for determination of pressure information of the
eye.
[0012] The invention enables patient and user friendly use with no
need to touch sensitive surfaces of an eye together with advanced
methods to process measurement information in order to extract
qualified pressure information of the eye. One benefit is that the
invention can be utilized from one patient to another with less
risk for contamination as contact to the eye is avoided.
SHORT DESCRIPTION OF FIGURES
[0013] FIG. 1 presents first exemplary embodiment according to the
present invention.
[0014] FIG. 2 presents second exemplary embodiment according to the
present invention.
[0015] FIG. 3 presents preferred embodiment according to the
present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Essentially, excitation and/or detection of electromagnetic
waves is to be performed by means of a beam of electromagnetic
waves produced e.g. by a laser, pulsed laser or a plasma source
(focused laser or a spark gap), which is for example mediated via
an electromagnetic waveguide (e.g. an optical fiber, collimator,
lenses, masks and/or an arrangement of mirrors) and targeted onto
the eye of a patient or onto a spot in the vicinity of the
patient's eye. An input of the electromagnetic wave into or onto
the eye is followed by electromagnetic-mechanical conversion (e.g.
photo-acoustic conversion) that generates little heat and
significant mechanical vibration into the eye's tissues or a plasma
source that launches sound waves that impinge on the eye to create
a wave in it. Correspondingly, mechanical vibrations of the eye
tissue are detected (e.g. by means of optical interferometry,
optical coherence tomography, laser Doppler vibrometry or
ultrasound transducer). The objective is thereby to generate
mechanical wave or waves (e.g. ultrasonic waves) in the eye and to
detect said waves in the eye. The potential applications relate
especially to determination of IOP, i.e. an eye pressure.
[0017] In the embodiments according to the present invention is
presented non-contacting photoacoustic and ultrasonic intraocular
pressure (IOP) measurement techniques, which may have e.g.
following requirements: non-contact excitation and detection
methods, which are safe for the patient, determination of
essentially accurate intraocular pressure (IOP) values, possibility
to follow-up of patient's IOP values, and said techniques can be
used by a health care professional and/or by a patient in a
convenient and ergonomic way with lowered risk for contamination
from patient to patient.
[0018] There are several physical interactions that could be
exploited for the IOP measurement. Next will be explained these
interactions in order to evaluate their usability for a non-contact
ultrasonic IOP measurement:
[0019] A) Physical systems such as the eye may vibrate at certain
resonance frequencies when they are mechanically or
photo-acoustically disturbed. These frequencies depend on the
mechanical properties of the components of the eye, and on the IOP
as well as on eye size and shape as well as properties of the eye
socket. Measurement of the resonance frequencies is rather easy to
implement, and preliminary data can be utilized to support the
viability of the resonance measurements. Guided waves, e.g. Lamb
waves or quasi-Lamb waves or membrane waves that propagate on
curved structures can also be used in said measurements.
[0020] B) Lamb waves are guided waves that travel along a
structure. They are dispersive, i.e. the phase velocity of a Lamb
wave depends on the frequency of the wave. Thus, with a single
broadband excitation one can measure the dispersion relation of the
waves, which is closely related to both the elasticity of the
structure and stress caused by external pressure such as for
example the IOP. Broadband dispersion measurements provide more
accurate IOP estimates than narrow band measurements. Several
independent measurements can be performed on different parts of the
eye, which increases accuracy and decreases the confounding effect
of the elasticity of e.g. the cornea of the eye as well as the
effect of the eye socket. Preliminary data support the viability of
the proposed method. Localized testing along lines can be
performed, which could allow spatial averaging and could provide
localized data as well as anisotropy data.
[0021] C) Bulk wave velocities, i.e. longitudinal and shear
ultrasonic wave velocities, probe mechanical properties of measured
materials. The propagation velocity of the longitudinal wave
depends on the static pressure loading the material (e.g. liquid)
in which it propagates, and said phenomena can be utilized to
determine e.g. IOP. Bulk waves are simple to generate and measure,
but for accurate e.g. IOP measurements other measurements than bulk
wave measurements are needed, because bulk wave measurements itself
are unlikely to achieve high accuracy.
[0022] D) Ultrasonic waves, both Lamb and bulk waves, loose energy
as a function of propagation distance. This energy loss decreases
as a function of pressure for bulk waves, but in loaded plates
(e.g. the eye) due to the loading on the surface by the IOP, the
effect is reversed. Quantitative measurements can be performed to
calibrate the effects of external pressure on Lamb wave
attenuation. Attenuation analysis is likely to be useful when
combined with other properties (e.g. speed of sound,
dispersion).
[0023] FIG. 1 presents a first exemplary embodiment according to
the present invention, in which a spark gap 210 is placed near but
not in contact with the sclera of the eye 202. The spark generates
a wave that upon contacting the sclera launches two kinds of
vibrations: first, elastic waves (Lamb S.sub.0 and A.sub.0 guided
ultrasonic modes), followed by a resonant vibration of the sclera
and the cornea. The vibration can be picked up e.g. with a custom
made one-point interferometer 212 capable of detecting the
time-of-arrival of the wave. The mode map i.e. frequency-velocity
chart of Lamb waves traveling along the sclera depends on the
intra-ocular pressure (IOP). Also resonant frequencies depend on
IOP. This kind of embodiment is affordable and simple to produce
and allows adding detectors to increase the measurement accuracy.
Also a high signal-to-noise ratio can be achieved by this kind of
implementation.
[0024] The spark gap 210 produces a bright flash of light that
might harm the eye 202. This can be avoided with a thin black
membrane not in contact with the eye. The membrane passes the
acoustic pressure wave and blocks the light from reaching the eye.
The weak mechanical and/or acoustic nonlinear wave, which is e.g.
transient, broadband or shock wave, generated by the spark can be
audible and does not induce tissue-breaking stress. The intensity
of the emitted wave can be controlled to ensure that there is no
risk to the hearing. Also the detectors can use very low power
lasers (even Class 1) in order to introduce no safety risks to the
eye.
[0025] The first exemplary embodiment can be further improved by
incorporating a custom made one-point interferometer capable of
measuring vibration as a function of time. This increases costs,
but allows simultaneous measurement of both the resonance and the
traveling Lamb waves, thus yielding more accurate IOP measurement
information.
[0026] FIG. 2 presents a second exemplary embodiment according to
the present invention, in which is utilized a pulsed e.g. KrF
excimer laser 210 (e.g. 248 nm) to excite mechanical wave(s) and
e.g. a laser Doppler vibrometer (LDV) as detecting means 212. The
excimer laser can be focused on either the sclera or the cornea of
the eye 202 or close to them both, launching Lamb waves to the eye
which are detected by a detection system 212, e.g. the LDV. Several
parameters can concurrently be detected and correlated and
calibrated to IOP: speed of sound, attenuation, vibration spectrum
of the received signal, detected resonance frequency, etc.
[0027] UV wavelengths (or 1300-1550 nm IR (infrared)) absorb
strongly into the cornea, and are thus unlikely to traverse the
sclera. Interferometers use generally a Class 1 beam, which is safe
to the eye. The generated Lamb waves do not cause discomfort or
damage. E.g. the 248 nm wavelength absorbs extremely well into both
the cornea and the sclera, thus not damaging eye structures beneath
them. Benefits of the second embodiment are also low intensity
values which causes no discomfort to the patient and high
absorption coefficient which improves signal to noise ratio and
hence both precision and accuracy of the IOP estimate. Also e.g.
phase-delayed laser diodes can be used to shape the spectrum of the
transmit signal to increase the signal to noise ratio in the four
modes in the mode map that is analyzed.
[0028] In the first and second exemplary embodiment according to
the present invention is accomplished photoacoustic IOP
measurements based on Lamb wave velocity dispersion and resonant
frequencies of the eye/sclera. A bi-modality embodiment, i.e.
concurrent use of Lamb wave measurements and resonance measurements
can be accomplished e.g. by four detection points to pick up the
wave excited in the middle to allow four simultaneous and
independent measurements. This provides precision. The sensor 212
can also comprise e.g. ultrasonic transducers coupled to air which
to serve as distance and tilt measurement devices. An IOP
measurement device (e.g. FIG. 3) according to the present can
comprise e.g. a spark gap 210 in the middle of the device,
detection means to pick up the excited waves from four points
around an excitation point on the surface of the eye 210 and a
built-in ultrasonic sensor 220 detecting the distance of the device
from the eye and the tilt of the device. The device can further
comprise direction lights or a display unit to indicate into which
direction it should be tilted. This makes it more operator
friendly.
[0029] FIG. 3 presents a first preferred intraocular pressure (IOP)
measurement arrangement according to the present invention for
measuring the pressure in an eye 202 of a patient. The arrangement
comprises at least one source 210 for producing mechanical waves of
several frequencies from a distance 200 through air to the eye 202
of the patient. Said waves generate at least one surface wave to
the eye, and more specifically to a certain surface area of the eye
and near the surface area of the eye. The invention can enable
probing a certain site of the eye if one wants to and even a
certain direction along the eye ball. The surface waves preferably
comprise modes, e.g. Lamb S.sub.0 and A.sub.0 guided ultrasonic
modes, and also resonant vibrations that are generated to the eye.
The source 210 is preferably a spark gap 210 that generates by at
least one spark an acoustic nonlinear wave, e.g. shock wave that
couples to the eye 202 through the air and generates e.g. both Lamb
waves and resonant vibrations to the surface of the eye 202 and
into the eye 202. The surface wave or waves are detected by means
212 for detecting from a distance 201 from the eye 202 to form
surface wave information. Preferably also resonant vibrations are
detected by means 212 for detecting from a distance 201 from the
eye 202 to form resonance information. Detection of the propagating
waves can be based on e.g. the time-of-arrival of the first
arriving signal (FAS), whereas the detection of the resonances can
be based on e.g. the Fourier transform of the measured signal.
[0030] As is apparent to a person skilled in the art the mechanical
nonlinear wave can also be generated by a mechanical impact of a
combination of two hard surfaces or corners or edges (210) as the
source (210) for producing nonlinear acoustic or mechanical waves,
e.g. shock waves, of several frequencies from a distance (200) said
waves coupling to the eye (202) of the patient. For example it is
commonly known that a hammer strike can produce nonlinear wide
spectrum acoustic signal including ultrasonic frequencies.
[0031] The distance 200 or the distance 201, or both of them, can
be optimized by means 220 for controlling distance. The means 220
can be implemented e.g. by ultrasonic transducers coupled to air
for distance or tilt measurements and aiding the operator to
position the device. Also accelerometers or gyroscopes can be used
to detect the best position and time moment for the measurements.
The means 220 for controlling and setting an optimized distance
200, 201 from the source 210 and from the means 212 to the surface
of the eye 202 can also be implemented by an embodiment, in which
the means 220 comprises at least one laser emitting visible light,
and at least two e.g. light guides having first ends and second
ends, said first ends connected to said laser for receiving said
visible light. The means 220 can also comprise positioning means
for moving the source 210 for producing mechanical waves or the
detecting means 212 into different points e.g. along a
predetermined path. Each of said second ends provides a light beam,
and these light beams are directed towards a surface of the eye 202
with an angle of convergence K. The light beams are adjusted to
intersect in a predetermined focus point, which is visible on the
surface of the eye and which indicates the proper position and
distance 200, 201 from the source 210 and from the means 212 to the
surface of the eye 202.
[0032] The arrangement in FIG. 3 also comprises means 216 for
determining pressure information of the eye based on the surface
wave information and preferably based also on the resonance
information. The means 216 can be implemented by e.g. a processor
unit in an IOP measurement device or by a separate computer unit to
which measurement information is sent from the IOP measurement unit
via a wireless or wired connection link. The means 212 for
detecting can be implemented for example by means of optical
interferometry, i.e. by an optical interferometer, by means of
optical coherence tomography, i.e. by an optical coherence
tomography device, or by means of laser Doppler vibrometry, i.e. by
a laser Doppler vibrometer, or by ultrasonic measurements using at
least one ultrasonic transducer, or with a combination of the
different techniques. In the first preferred arrangement the means
212 for detecting at least one surface wave comprises at least one
interferometer 212, which can measure the vibrations as a function
of time, and which allows simultaneous measurement of both the
resonance vibrations and of the surface waves, i.e. the Lamb waves,
thus yielding a precise and accurate estimate of the pressure of
the eye 202. The invention can permit use of one cheap single point
interferometer or more of them to detect time of arrival.
[0033] There can be either at least two wave sources 210 or
detecting means 212, or at least two of both, to improve
measurement accuracy in forming the surface wave information and
the resonance information. In the preferred arrangement of FIG. 3
the detecting means 212 are in three different detection locations
in order to improve measurement accuracy and precision and to
obtain higher signal-to-noise ratio.
[0034] Heartbeat, eye blinking, and respiration cause temporal
fluctuations in intraocular pressure. Of these, the heartbeat
causes relatively constant pulsatile peaks in IOP, normally between
2-3 mmHg. This difference is called ocular pulse amplitude. This
amplitude depends on heart rate and axial length and there is a
positive linear correlation between ocular pulse amplitude and IOP.
High IOP causes high ocular pulse amplitude. Several other
parameters, including ocular rigidity affects the magnitude of the
ocular pulse amplitude. These pressure peaks cause vibrations and
waves along the eyeball (sclera and cornea) and also internally
(e.g. iris), and said waves and vibrations can be detected e.g.
optically. The device according to the present invention can be
used to measure, monitor, and analyze these heart beat induced
changes in said vibrations and waves to estimate IOP also without
external stimulus.
[0035] Embodiments according to the present invention can improve
comfort, accuracy, and precision of the IOP measurement by
utilizing at least one of the following features: 1) employing
non-contacting measurement (comfort), 2) employing a localized and
directional measurement (reduces eye shape -induced bias (error) to
improve accuracy), 3) employing a slow wave form (symmetric &
asymmetric Lamb waves, which reduces the confidence limits of the
sound velocity estimate=improves the precision of the elasticity
estimate=improves the precision of the IOP estimate, 4) employing a
broadband signal which allows mapping several propagating modes to
gain precision in the sound velocity estimate (improves precision
and potentially accuracy of the tester) 5) employing a geometric
transmit and receive array or phased array (improved SNR which
reduces the confidence limits of the sound velocity estimate due to
larger signals and due to ability to fit the estimate with a
regression line, this improves precision), 6) the array approach
also allows tuning the modes to be employed for improved SNR and
consequently precision and accuracy of the tester/test, 7)
employing both the travelling wave approach described above and the
resonance concept known to the state of the art. Since these
measurements are independent of each other a more sensitive and
robust tester follows (it should improve both precision and
accuracy). The measurement can be generalized to other physical
parameters such as sound attenuation (absorption, scattering) and
sound velocity dispersion.
[0036] In one embodiment according to the present invention can be
utilized patient heartbeat or breathing or both of them as a source
for producing surface waves of several frequencies from a distance
200 to the eye 202 of the patient. In another embodiment according
to the present invention can be utilized means 210 to generate tiny
plasma burst as the source 210 for producing acoustic waves of
several frequencies from a distance 200 to the eye 202 of the
patient. Said generation can be made by sparking or by focusing a
laser ray to one point on the surface of the eye or close to the
surface of the eye. In one further embodiment according to the
present invention can be utilized means 210 to generate chemical
reaction as the source 210 for producing acoustic waves of several
frequencies from a distance 200 to the eye 202 of the patient.
[0037] In embodiments according to the present invention can be
utilized mode tuning by phase delayed excitation in source 210 for
producing mechanical waves of several frequencies from a distance
200 through air to the eye 202 of the patient. An improved signal
to noise ratio (SNR) and improved time of flight (TOF) estimate can
be achieved by mode tuning performed on the basis of phase delayed
excitation. Precision and accuracy of IOP measurements according to
the present invention can thus be increased.
[0038] Also, in an embodiment according to the present invention a
photoacoustic laser-based excitation can be performed by having a
ring shaped form to the surface of the eye or close to that surface
in order to amplify the surface wave in the middle of the ring
shape. This enables easier and more accurate detection to be
performed by the detection means. It also permits a cheaper
receiver to be used. The user can combine the use of a shaped, i.e.
circle or line or crescent source with the phased array concept
having many dots, lines or crescents for improved precision and
accuracy in the IOP measurement.
[0039] On the basis of the present invention can be implemented an
ideal tonometer capable of measuring intraocular pressure with fast
comfortable measurements without anesthetic and disposable waste
operated also by an unskilled operator.
[0040] Although the invention has been presented in reference to
the attached figures and specification, the invention is by no
means limited to those, as the invention is subject to variations
within the scope allowed for by the claims.
* * * * *