U.S. patent application number 13/427130 was filed with the patent office on 2012-10-18 for system and method for measuring and correcting astigmatism using laser generated corneal incisions.
Invention is credited to Rudolph W. Frey.
Application Number | 20120265181 13/427130 |
Document ID | / |
Family ID | 46931851 |
Filed Date | 2012-10-18 |
United States Patent
Application |
20120265181 |
Kind Code |
A1 |
Frey; Rudolph W. |
October 18, 2012 |
SYSTEM AND METHOD FOR MEASURING AND CORRECTING ASTIGMATISM USING
LASER GENERATED CORNEAL INCISIONS
Abstract
A laser system that includes a laser source emitting a laser
beam along an axis and a keratometer. The keratometer includes a
first set of individual light sources that are equally spaced from
one another along a first ring and that direct a first light toward
an eye and a second set of individual light sources that are
equally spaced from another along a second ring and direct a second
light toward the eye, wherein the first ring and said second ring
are co-planar and concentric with one another about the axis. The
laser system includes a telecentric lens that receives the first
light and second light reflected off of the eye and a detector that
receives light from the telecentric lens and forms an image. The
laser system also includes a processor that receives signals from
said detector representative of the image and determines an
astigmatism axis of the eye based on the signals.
Inventors: |
Frey; Rudolph W.; (Winter
Park, FL) |
Family ID: |
46931851 |
Appl. No.: |
13/427130 |
Filed: |
March 22, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13017499 |
Jan 31, 2011 |
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13427130 |
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61467592 |
Mar 25, 2011 |
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61467622 |
Mar 25, 2011 |
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61300129 |
Feb 1, 2010 |
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Current U.S.
Class: |
606/5 ;
351/212 |
Current CPC
Class: |
A61B 3/1035 20130101;
A61F 9/00834 20130101; A61F 9/00825 20130101; A61B 3/107 20130101;
A61F 2009/00853 20130101; A61F 2009/00872 20130101; A61F 2009/00887
20130101; A61F 2009/0087 20130101; A61F 9/00827 20130101; A61F
2009/00889 20130101 |
Class at
Publication: |
606/5 ;
351/212 |
International
Class: |
A61B 3/107 20060101
A61B003/107; A61F 9/01 20060101 A61F009/01 |
Claims
1. A laser system comprising: a laser source emitting a laser beam
along an axis; a keratometer comprising: a first set of individual
light sources that are equally spaced from one another along a
first ring and that direct a first light toward an eye; a second
set of individual light sources that are equally spaced from
another along a second ring and direct a second light toward said
eye, wherein said first ring and said second ring are co-planar and
concentric with one another about said axis; a telecentric lens
that receives said first light and second light reflected off of
said eye; a detector that receives light from said telecentric lens
and forms an image; a processor that receives signals from said
detector representative of said image and determines an astigmatism
axis of said eye based on said signals.
2. The laser system of claim 1, wherein said processor determines a
corneal K value and orientation of said astigmatism axis based on
said signals.
3. The laser system of claim 1, wherein said keratometer is
structured so as to reduce systematic errors in use of said laser
system with said keratometer when compared with when stand-alone
keratometers are used with the laser system.
4. The laser system of claim 1, wherein said laser source and said
keratometer are housed in a common housing.
5. The laser system of claim 4, wherein said keratometer is
structured so as to reduce systematic errors in the use of said
laser system when compared with a hypothetical case when said laser
system is used with stand-alone keratometers.
6. The laser system of claim 1, wherein said processor is in
communication with said laser source and controls said laser beam
so that it cuts said eye based on said properties of said
astigmatism axis.
7. The laser system of claim 1, wherein said laser source generates
femto second pulse laser beams.
8. A method of determining properties of an eye, the method
comprising: positioning an eye so that it receives a laser beam
that is originally emitted by a laser source beam along an axis;
generating first light toward said eye from a first set of
individual light sources that are equally spaced from one another
along a first ring; generating second light toward said eye from a
second set of individual light sources that are equally spaced from
another along a second ring and direct a second light toward said
eye, wherein said first ring and said second ring are co-planar and
concentric with one another about said axis; forming an image of
light reflected off of said eye from said first light and said
second light; and determining an astigmatism axis of said eye based
on said image, wherein said laser source, said first set of
individual light sources and said second set of individual light
sources are integrated in a common housing so that systematic
effects based on said laser source, said first set of individual
light sources and said second set of individual light sources are
reduced.
9. The method of claim 8, further comprising determining a corneal
K value and orientation of said astigmatism axis.
10. The method of claim 8, wherein said astigmatism axis is not
substantially affected by systematic effects.
11. The method of claim 8, wherein prior to said positioning said
eye and generating said first light and said second light,
measuring properties of said astigmatism axis of said eye.
12. The method of claim 11, wherein said measuring properties
comprises measuring a corneal K value of said astigmatism axis.
13. The method of claim 11, wherein said measuring properties is
performed by a stand-alone keratometer.
14. The method of claim 13, wherein said determining of said axis
of astigmatism is used to compensate for cyclotorsion of said eye
that occurs between measurements made by said stand-alone
keratometer and said determining said astigmatism axis.
15. A method of repairing an eye, the method comprising:
positioning an eye so that it receives a laser beam that is
originally emitted by a laser source beam along an axis; generating
first light toward said eye from a first set of individual light
sources that are equally spaced from one another along a first
ring; generating second light toward said eye from a second set of
individual light sources that are equally spaced from another along
a second ring and direct a second light toward said eye, wherein
said first ring and said second ring are co-planar and concentric
with one another about said axis; forming an image of light
reflected off of said eye from said first light and said second
light; determining an astigmatism axis of said eye based on said
image; and controlling said laser beam so that said laser beam
performs a cutting of said eye based on said astigmatism axis of
said eye.
16. The method of claim 15, wherein said processor determines a
corneal K value and orientation of said astigmatism axis based on
said signals.
17. The method of claim 15, wherein said astigmatism axis is not
substantially affected by systematic effects.
18. The method of claim 15, wherein said cutting of said eye
generates a mark representative of an orientation of said
astigmatism axis, the method comprising performing a capsulotomy
based on said generated mark.
19. The method of claim 15, wherein said cutting of said eye
creates an LRI.
20. The method of claim 15, wherein prior to said positioning said
eye and generating said first light and said second light,
measuring properties of said astigmatism axis of said eye.
21. The method of claim 20, wherein said measuring properties
comprises measuring a corneal K value and said astigmatism
axis.
22. The method of claim 20, wherein said measuring properties is
performed by a stand-alone keratometer and said first set of
individual light sources said second set of individual light
sources are part of built-in keratometer of the same design that is
contained in a common housing with said laser source.
23. The method of claim 22, wherein said built-in keratometer
measures said axis of astigmatism to compensate for cyclotorsion of
said eye between measurements made by said stand-alone keratometer
and measurements made by said built-in keratometer.
24. A method of determining properties of an eye, the method
comprising: measuring properties of an astigmatism axis of said eye
with a stand-alone Placido ring measuring system; positioning an
eye so that it receives a laser beam that is originally emitted by
a laser source beam along an axis; generating at a built-in Placid
ring measuring system a first annular-shaped light beam directed
toward said eye, wherein said built-in Placido ring measuring
system and said laser source are in a common housing; generating at
said built-in Placido ring measuring system a second annular-shaped
light beam directed toward said eye; forming an image of light
reflected off of said eye from said first annular-shaped light beam
and said second annular-shaped light beam; and determining an
astigmatism axis of said eye based on said image.
25. The method of claim 24, wherein said built-in Placido ring
measuring system measures said axis of astigmatism to compensate
for cyclotorsion of said eye between measurements made by said
stand-alone Placido ring measuring system and measurements made by
said built-in Placido ring measuring system.
26. The method of claim 24, wherein said built-in Placido ring
measuring system is designed in all significant aspects to measure
K values and axis of astigmatism in an identical manner and to
produce identical results, except for those associated with
cyclotorsion, as said stand-alone Placido ring measuring
system.
27. A method of repairing an eye, the method comprising: measuring
properties of an astigmatism axis of said eye with a stand-alone
Placido ring measuring system; positioning an eye so that it
receives a laser beam that is originally emitted by a laser source
beam along an axis; generating at a built-in Placid ring measuring
system a first annular-shaped light beam directed toward said eye,
wherein said built-in Placido ring measuring system and said laser
source are in a common housing; generating at said built-in Placido
ring measuring system a second annular-shaped light beam directed
toward said eye; forming an image of light reflected off of said
eye from said first annular-shaped light beam and said second
annular-shaped light beam; determining an astigmatism axis of said
eye based on said image; and controlling said laser beam so that
said laser beam performs a cutting of said eye based on said
astigmatism axis.
28. The method of claim 27, wherein said cutting of said eye
generates a mark representative of an orientation of said
astigmatism axis, the method comprising performing a capsulotomy
based on said generated mark.
29. The method of claim 27, wherein said cutting of said eye
creates an LRI.
30. The method of claim 27, wherein said built-in Placido ring
measuring system measures said axis of astigmatism to compensate
for cyclotorsion of said eye between measurements made by said
stand-alone Placido ring measuring system and measurements made by
said built-in Placido ring measuring system.
31. The method of claim 27, wherein said built-in Placido ring
measuring system is designed in all significant aspects to measure
K values and axis of astigmatism in an identical manner and to
produce identical results, except for those associated with
cyclotorsion, as said stand-alone Placido ring measuring system.
Description
[0001] This application claims the benefit of priority under 35
U.S.C. .sctn.119(e)(1) of 1) U.S. Provisional Application Ser. No.
61/467,592, filed Mar. 25, 2011 and 2) U.S. Provisional Application
Ser. No. 61/467,622, filed Mar. 25, 2011, and this application is a
continuation-in-part application of U.S. patent application Ser.
No. 13/017,499, filed Jan. 31, 2011 (now pending), which claims the
benefit of priority under 35 U.S.C. .sctn.119(e)(1) of U.S.
Provisional Application Ser. No. 61/300,129, filed Feb. 1, 2010,
the entire contents of each of the above mentioned patent
applications and provisional applications is incorporated herein by
reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a system for performing an
astigmatism measurement for the purpose of correcting astigmatism.
The present invention also has to do with marking the measured axis
of astigmatism with a laser-created mark.
BACKGROUND
[0003] In known procedures for correcting astigmatism, such as
limbal relaxing incisions, LASIK or implantation of toric IOLs, it
is important to register the respective treatment or device in
precise alignment relative to the eye's axis of astigmatism. The
astigmatism is first measured by a benchtop corneal topographer,
such as the Humphrey Atlas corneal topographer manufactured by
Zeiss of Dublin, Calif. or a keratometer, such as the LenStar
keratometer manufactured by Haag Streit of Bern, Switzerland. The
patient's eye is manually marked with an ink marker to indicate the
axis of astigmatism or a reference horizontal axis or other axis
from which the astigmatism axis can be later referenced.
[0004] While each of the previously mentioned correction procedures
is performed with the patient in a reclining position, the prior
astigmatism measurement with the benchtop instrument and the
marking of the patient's eye are performed with the patient in a
sitting position. During the process of the patient being moved
from the sitting position to the reclining position, cyclotorsion
(rotation of the eye about its optical axis) generally occurs. The
registration marker is used when the patient is in the reclining,
treatment position to adjust for any rotation of the axis of
astigmatism which might occur.
[0005] The use of ink marks reduces the effect of cyclotorsion on
the astigmatism treatment; however, it is inconvenient--for best
results, it requires a separate seating of the patient at a slit
lamp--but still has limited accuracy because of the inevitable
errors in manually placing the initial marks, and the "bleeding" of
the marks as the tear film reacts with the marking ink.
[0006] The use of ink marks is avoided by the Placido ring
measurement system described in U.S. patent application Ser. No.
13/017,499 ("the '499 application"), the entire contents of which
are incorporated by reference. With the Placido ring system, the
images of the reflections of Placido rings are in the form of
circular or elliptical bands, with sharp, high contrast edges which
allow the image analysis software in the system to accurately find
the edges of each reflected circular or elliptical band. The found
edges are curve fit to an ellipse. The reflections are circular
(i.e. an ellipse of eccentricity equal to 0) if the cornea has no
astigmatism. If the cornea does have some astigmatism, the clock
angle of the minor axis of the elliptical image, gives the
orientation of the axis of astigmatism. The clock angle is measured
relative to a polar coordinate defined such that 0.degree. is in
the nasal direction; 90.degree. is superior and 180.degree.,
temporal. The length of the major and minor axes of the ellipses
provides the information from which the magnitude of the spherical
power and cylindrical power (astigmatism) of the cornea is
derived.
[0007] The Placido ring invention disclosed in the '499 application
allows for the astigmatism axis to be measured while the patient is
laying on a gurney under the laser so no manual measurement or
marking of the eye is needed. (If a toric IOL is to be used during
the corrective procedure, the laser cuts a reference mark into the
capsulotomy allowing the surgeon to accurately position the clock
angle of the IOL to the axis of astigmatism measured by the laser.
If LRIs are to be used during the corrective procedure, the laser
uses the Placido ring/keratometer measurement of axis to orient the
LRIs to the correct clock angle.)
[0008] One issue regarding the Placido ring invention described in
the '499 application is that it does not take into account that
various preoperative measurement instruments, measuring the same
parameters, generate different values of the parameters because of
differences between the measurement principles, implementation of
engineering, etc., of different instruments.
[0009] As an illustration of the variability in the value of
measured parameters, let us take a look at a cataract procedure. In
such a procedure, a number of preoperative measurements are made of
the patient's eye in order to select the correct IOL for the
patient. Among these measurements are measurements of the K values
and axis of astigmatism of the patient's cornea. The K values are
the optical power, in Diopters, of the steep axis (axis in the
plane perpendicular to the optic axis which has the highest lens
curvature) and shallow axis (axis in the planeperpendicular to the
optic axis which has the least lens curvature). The "clock" angle
of the steep and shallow axes are conventionally measured in
degrees from 0.degree. to 180.degree. in an angular coordinate
system perpendicular to and centered on the optic axis of the eye.
From the point of view of an optometrist or ophthalmologist looking
at the patient, 0.degree. is to the right, on the nasal/temporal
axis. The scale proceeds counterclockwise from 0.degree. to
180.degree.. The difference between the K value of the steep and
shallow axes is the magnitude of the astigmatism of the eye. The
angle of the steep axis, measured on the coordinate system
described above is the axis of astigmatism. The K values and axis
of astigmatism are used, along with other measurements of the eye,
in one of several common IOL power formulae (ref) to determine the
proper IOL optical power to be used for the patient.
[0010] A typical cataract procedure using a laser system can
involve the following processes: making preoperative measurements
of the patient's eye for selection of the power and other
characteristics of the IOL, placement of the patient on a gurney
under the laser, measuring the patient's axis of astigmatism by an
integral astigmatism axis measurement system built into the laser,
docking the patient's eye to the laser, performing the laser
treatment, including LRIs or capsulotomy with tagged astigmatism
axis if the patient's astigmatism is to be treated, retracting the
laser head, removing the patient's cataractous lens and implanting
an IOL is implanted. Post-operatively, the patient's surgically
repaired eye is refracted by determining the amount of refractive
correction needed to bring the patient's vision to its sharpest
distance focus. The refraction can be measured in the same units as
those used by the preoperative measurements of the patient's
cornea, i.e., Diopters of curvature along the steep and shallow
axes and axis of astigmatism. These values are generally converted
via simple mathematical relationships to the magnitudes of the
residual spherical and cylindrical power of the eye and the axis of
astigmatism. However, the refraction measures ocular, rather than
corneal optical power, i.e., the optical power of the whole eye
including the newly implanted IOL, rather than just the corneal
optical power as was measured preoperatively. In most cases, a
surgeon intends to select an IOL which brings the patient's vision
as close as possible to perfect focus for distance vision, i.e., to
bring the patient's residual optical power to zero or near zero for
both the spherical and cylindrical components of the optical
power.
[0011] A cataract surgeon may monitor the post-operative
refractions of his or her patients, grouped by which type or design
of IOL is used. If there is a bias in the clinical outcomes for a
particular type of lens, for example: patients implanted with lens
Type A have an average residual spherical power of 0.5 Diopters, an
adjustment parameter called a "lens constant" used in the IOL power
formula is changed to allow the adjusted formula to more accurately
select IOL power for future patients. The lens constant adjustment
is intended to compensate for a number of factors which can affect
clinical refractive outcomes. The most important of these factors
is a combination of variation in surgical technique and
characteristics of a particular design of IOL which affect where
along the anterior/posterior axis of the eye the IOL will tend to
position itself and which therefore directly influences the
refractive outcome. However, the lens constant also implicitly
accounts for differences in pre- and post-operative measurement
techniques and, in particular, the type of instrument used to
measure the K values and axis of astigmatism, which, as mentioned
above, vary from instrument to instrument. For example, a
keratometer which consistently measures K values a bit higher than
normal would tend to cause an IOL of higher than required power to
be selected for a treatment. Once this bias was detected (by
post-operative measurements showing that patients tended to be
overcorrected by that type of IOL as used by a particular surgeon
employing that particular keratometer and other surgical procedure
characteristics), the lens constant for that type of IOL (as used
by that surgeon, procedure, etc.) would be adjusted to eliminate
the bias.
[0012] It is helpful for this discussion to differentiate between
systematic and random measurement error. Random error occurs with
any type of instrumental measurement but can be reduced to an
arbitrarily small magnitude by averaging a sufficient number of
repeated measurements. Systematic error between instruments is due
to fundamental differences in measurement technique, calibration,
etc. and represents an irreducible bias between the two
instruments. No amount of averaging of repeated measurements can
eliminate the bias.
[0013] The foregoing process or measuring performed pre- and
post-operatively and adjusting the lens constant to improve
clinical refractive outcomes works well if a surgeon's surgical
technique is consistent from case-to-case and if all other aspects
of the surgical procedure. For example, use of a particular type of
keratometer to measure K values and axis of astigmatism are
likewise consistently followed. However, this latter condition is
not always met. For example, a surgeon may treat patients at more
than one hospital or clinic, each of which uses a different
instrument to measure K values and axis of astigmatism. In this
case, different lens constants could be used for each
surgeon/clinic combination to correctly account for differences in
refractive outcomes related to practices at each hospital or
clinic, or, more likely, a single lens constant would be used
across clinics even though a higher variability in clinical
refractive outcomes would result.
BRIEF SUMMARY
[0014] One aspect of the present invention regards a laser system
that includes a laser source emitting a laser beam along an axis
and a keratometer. The keratometer includes a first set of
individual light sources that are equally spaced from one another
along a first ring and that direct a first light toward an eye and
a second set of individual light sources that are equally spaced
from another along a second ring and direct a second light toward
the eye, wherein the first ring and said second ring are co-planar
and concentric with one another about the axis. The keratometer
also includes a telecentric lens that receives the first light and
second light reflected off of the eye and a detector that receives
light from the telecentric lens and forms an image of the
individual light sources including the first and second lights. The
keratometer further includes a processor that receives signals from
said detector representative of the image and determines an
astigmatism axis of the eye based on the signals.
[0015] A second aspect of the present invention regards a method of
determining properties of an eye, the method including positioning
an eye so that it receives a laser beam that is emitted by a laser
source beam along an axis and generating first light toward the eye
from a first set of individual light sources that are equally
spaced from one another along a first ring. The method including
generating second light toward said eye from a second set of
individual light sources that are equally spaced from another along
a second ring and direct a second light toward the eye, wherein the
first ring and the second ring are co-planar and concentric with
one another about the axis. The method further including forming an
image of light reflected off of the eye from the first light and
the second light and determining an astigmatism axis of the eye
based on the image. The laser source, the first set of individual
light sources and the second set of individual light sources are
integrated in a common housing to allow the cyclotorsion of the eye
which occurs between preoperative measurement, which is performed
with the patient in a sitting position and at the time or surgery,
when the patient is lying under the laser. The incorporation of the
laser and keratometer in a common housing also allows the user to
measure all patients with the same measuring device so that
systematic errors in determination of IOL lens constants are
avoided or reduced.
[0016] A third aspect of the present invention regards a method of
treating an eye, the method including positioning an eye so that it
receives a laser beam that is originally emitted by a laser source
beam along an axis; and generating first light toward the eye from
a first set of individual light sources that are equally spaced
from one another along a first ring. The method including
generating second light toward said eye from a second set of
individual light sources that are equally spaced from another along
a second ring and direct a second light toward the eye, wherein the
first ring and the second ring are co-planar and concentric with
one another about the axis. The method further including forming an
image of light reflected off of the eye from the first light and
the second light and determining an astigmatism axis of the eye
based on the image. The method further including controlling the
laser beam so that the laser beam performs a cutting of the eye
based on the astigmatism axis.
[0017] One or more aspects of the present invention allow for
measurement of the properties of an astigmatism axis of an eye.
[0018] One or more aspects of the present invention allow for
reducing or eliminating systematic errors during measurement of the
properties of an astigmatism axis of an eye.
BRIEF DESCRIPTION OF THE DRAWING
[0019] The accompanying drawings, which are incorporated herein and
constitute part of this specification, and, together with the
general description given above and the detailed description given
below, serve to explain features of the present invention. In the
drawings:
[0020] FIG. 1 schematically shows an embodiment of a measuring
system for measuring the corneal astigmatism axis prior to an
ophthalmological procedure being performed on the eye of a patient
in accordance with the present invention;
[0021] FIG. 2 schematically shows operation of an embodiment of a
telecentric detection system for measurements of concentric rings
of LEDs that is used with the measuring system of FIG. 1 in
accordance with the present invention;
[0022] FIG. 3 shows an example of an image of light of concentric
rings of LEDs as reflected off of a cornea and imaged by the
telecentric detection system of FIG. 2;
[0023] FIG. 4 shows picture of a common toric intraocular lens
(IOL) implanted in an eye after the corneal astigmatism axis of the
eye has been determined and marked using a treatment laser, using
the measuring system of FIG. 1 in accordance with the present
invention; and
[0024] FIG. 5 schematically shows laser cut capsulotomy openings in
the anterior crystalline lens capsule cut with a "tag" to mark the
axis of astigmatism that is measured by the measuring system of
FIG. 1 in accordance with the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] FIG. 1 schematically shows a measuring and treatment system
100 for measuring the corneal astigmatism axis and for performing
an ophthalmological procedure on the eye 102 of a patient. The
system 100 includes a keratometer 250 which includes a light
generator 203 (dashed lines) and a telecentric detection system
200. The light generator 203 includes two light sources, each
comprising a ring of 10-20 discrete LEDs 202. The telecentric
detection system 200 is used for measuring concentric rings of the
LEDs 202 and for alignment of the patient's eye with the
keratometer.The system 100 also includes a Scheimpflug-based lens
and cornea locating system 300, and a treatment laser system that
includes a treatment laser 104.
[0026] In use, the patient typically lies on a gurney or a
reclining surgical chair which is rolled into position under the
optical head of the treatment laser 104. The keratometer 250 and
the Scheimpflug-based lens and cornea locating system 300 may be
designed to work with the patient in a reclining position under the
treatment laser system since in this position the cyclotorsion of
the eye, which occurs when a patient who is in a sitting position
(for example to allow conventional astigmatism measurements to be
made) changes to a reclining position, has already occurred. It is
also advantageous that the detection system 200 and the
Scheimpflug-based lens and cornea locating system 300 are so
located such that the patient can remain stationary for both the
measurements and laser treatment, since this obviates or lessens
the time consuming step of re-aligning the patient with the laser
for the subsequent laser treatment.
[0027] After the corneal astigmatism axis is found using the
measurement of the concentric rings of LEDs 202, a medical
procedure can be performed with the laser systems described in U.S.
patents applications Ser. Nos. 11/337,127; 12/217,285; 12/217,295;
12/509,412; 12/509,021; 12/509,211 and 12/509,454, the entire
contents of each of which are incorporated herein by reference.
Possible procedures to be performed by the laser systems to correct
or reduce astigmatism are the performance of limbal relaxing
incisions or LASIK. Another possible procedure is the use of the
treatment laser to assist in cataract removal and IOL implantation.
The treatment laser is also used to create a reference mark on the
anterior capsule to allow the subsequent implantation of a toric
IOL to be correctly oriented with respect to the axis of
astigmatism.
[0028] Operation of keratometer 250 includes having the patient lie
on a patient bed in position for the laser surgery. The patient is
instructed to stare at a red fixation light generated by fixation
light source 225 that is housed in the telecentric detection system
200. The fixation light source 225 includes an LED which generates
red light. The red light is collimated and directed to a beam
combiner 227 which reflects the light to mirror 220. The red light
is then redirected toward the eye of the patient so that the red
light is aligned to be collinear with the axis of the laser beam
generated by laser 104 and centered at the middle of the concentric
rings of LEDs 202, i.e., the axis of the keratometer.
[0029] Next, the optical head of the treatment laser 104 is
aligned, using a joystick that controls a 3-axis motion control
system, to the patient's cornea. The optical head of the treatment
laser system houses both the keratometer 250 and the
Scheimpflug-based lens and cornea locating system 300 as well as
the optics that are used to guide the treatment laser beam. Thus,
aligning this optical head relative to the patient serves the
purpose of aligning all three systems (200; 300 and treatment laser
system) simultaneously relative to the patient's eye and, thus,
reduces the need for time consuming re-alignments for the
sequential operations. When the patient stares at the fixation
light generated by fixation light source 225, and when the optical
head of the treatment laser is aligned such that reflections of the
two concentric rings of LEDs 202 from the patient's cornea are
centered within the patient's pupil, as visualized on the
telecentric camera system 200, the patient's visual axis is aligned
with the keratometer 250 and treatment laser 104. A sensor, not
shown, detects when the z position (position along a direction
parallel to the axis of the laser beam passing through a concentric
rings of LEDs 202 of light generator 203 as shown in FIG. 1) is
correct for the astigmatism axis measurement; the sensor generates
a signal when the eye is at the correct distance below the light
generator 203. A software reticule is superimposed on the image of
the eye on the telecentric camera's monitor, to assist in the
assessment of centration.
[0030] After the z-position for the optical head of the treatment
laser 104 is determined, and the light generator 203 is centered
directly above the eye then measurement of the astigmatism axis is
performed using telecentric detection system 200 for measurements
of concentric rings of LEDs 202.
[0031] Telecentric system 200 is part of the keratometer 250, which
is similar to the one manufactured and sold under the tradename
LenStar LS-900 by Haag Streit of Bern, Switzerland. The keratometer
250 includes two sets of LEDs 202, wherein one set of 16 LEDs are
equally spaced from one another along a first circle or ring. The
second set of 16 LEDS 202 are equally spaced from one another along
a second circle or ring. The first and second circles are co-planar
and concentric with one another and concentric about the common
optical axis of the fixation light source 225 and treatment laser
104. The LEDs 202 are chosen to approximate point sources of light
so that the images of the reflections of the LEDs 202 from the
cornea are as compact as possible and can be located on the camera
image as accurately and precisely as possible. Each set of LEDs
202, as described above, is denoted as a ring source.
[0032] Operation of keratometer 250 is understood upon a review of
FIGS. 2-3. As shown in FIG. 2, red light 260 from the fixation
light source 225 is directed by beam combiner 227 to the eye of the
patient. When the patient stares at the red light improved
alignment of the patient's eye with the axis of the keratometer 250
is achieved. While the patient stares at the red light 260, light
201 from one or more concentric ring sources of light generator 203
is directed towards the cornea of the eye 102 and then reflected
light 214 is directed towards an objective and telecentric lens 204
of telecentric system 200. Note that the ring sources are
concentric relative to an axis of the treatment laser beam passing
through the opening of the light generator 203.
[0033] Next, the light from objective lens 204 is directed through
a telecentric stop 206 that is positioned at a focal plane of the
lens 204. The stop 206 includes an opening 208 positioned at a
focal point of the lens 204 so that only light reflected from the
cornea that was initially parallel to the axis of the objective
lens is allowed to pass through the opening 208 and be received on
the video image plane 210 of a detector 212. As shown in FIG. 1,
additional optics, such as a beam scanning system 216, beam
combiner 218 and beam splitter 220, can be used to direct the
reflected light 214 toward the lens 204.
[0034] Applying the above principles to detection system 200, one
or more concentric (relative to the axis of laser beam from optical
head 104, which is collinear with the axis of the objective lens,
204, in FIG. 2) diverging beams of light 201 are directed from the
ring sources of light source 203 toward the cornea of the eye 102.
If the cornea were perfectly spherical in shape, then the beams of
light 201 which reflect from the cornea into a direction parallel
to that of the objective lens 204 would pass through the
telecentric stop aperture 208 and form images of the discrete LEDs
in the concentric rings of light on the video image plane 210. As
shown in FIG. 2, a processor 230 analyzes overall image to find the
positions of each discrete LED 202 from the two concentric LED
rings.
[0035] For an average human cornea, with a radius of curvature of
7.8 mm, the system geometry is such that the diameters of the two
concentric rings of LEDs which are imaged by the telecentric
viewing system are approximately 2.3 mm and 1.65 mm, respectively,
as shown in FIG. 3. For corneas of different radii of curvature,
the size of the reflected rings will differ and a determination of
the size of the image of the reflected concentric rings of LEDs 202
on the telecentric camera detector 212 is used to determine the
radius of curvature of the cornea. If the cornea is astigmatic, the
cornea's shape will deviate slightly from that of a perfect sphere
in such a way as to cause the image of the reflection of the ring
sources to have a nearly elliptical shape. Based on the measurement
of the positions of the centroids of the discrete LEDs 202 which
include the two concentric rings, the shape and size of the two
circular or elliptical LED patterns formed on the video image plane
210 is determined by the processor 230, using standard numerical
methods such as those described in Turuwhenua, Jason, "An Improved
Low Order Method for Corneal Reconstruction", Optometry and Vision
Science, Vol. 85, No. 3, March 2008, pp. E211-E218. From these
data, the curvature of the cornea along the direction of a steep
and shallow meridian, i.e. the "K values", and the "clock" angle of
the axes of the steep and shallow meridian with respect to the
standard eye-fixed coordinate system, described above, can be
determined by a processor. If only the astigmatism axis is needed,
a simple method of extracting it from the reflected images is to
determine the angles of the semi-major axes of the ellipses using a
simple least squares curve fitting technique.
[0036] The choice of geometry to cause the reflected diameters of
the rings of LEDs 202 to fall into the roughly 1.5 mm to 3 mm range
results in an astigmatism (and corneal shape) measurement that is
accurate for the central 3 mm of the cornea. Such a central
region-biased measurement of optical power results in better vision
for most patients over a variety of lighting conditions and patient
activities (ref). (For some eyes the optical power of the cornea is
quite non-uniform; the average optical power over a small central
region may differ significantly from the average power averaged
over, for example, a 6 mm to 7 mm diameter circular region centered
on the optical axis of the cornea.)
[0037] Note that the incorporation of a high quality keratometer
250 into a femtosecond ophthalmic laser, being used as laser 104,
addresses the problem of higher variability in clinical refractive
outcomes resulting from variability in measurement of patients'
corneal K values and axes of astigmatism arising from use of
different types of instruments for that purpose. For purposes here,
femtosecond ophthalmic laser means a laser used in ophthalmology
for making incisions in the eye using the mechanism of
photodisruption. Such lasers have pulse widths that are generally
between 100 femtoseconds and 10,000 femtoseconds. The improvement
in clinical outcomes can be achieved in one of two ways. First, the
built-in keratometer could be used for measuring the K values and
axes of astigmatism of all patients at the time of the procedure
and those results be used for determination of the spherical and
cylindrical power in the IOL to be used for treatment. In this way,
all variability due to variation in measurement of these parameters
with different types of optical power measuring instruments would
be eliminated. The lens constants determined by the method
described above would account for other factors, such as surgical
technique/IOL characteristics, but would not be subject to
variability associated with optical power measurement.
[0038] Alternatively, the built-in keratometer could be used in
conjunction with a standalone keratometer of the same type of
design to reduce variability in the measurement of axis of
astigmatism. This use of the built-in keratometer in conjunction
with a stand-alone keratometer of the same design for pre-operative
measurements, recognizes that the measurement of K values and axis
of astigmatism depend on the type of optical design used. Although
the K values and axis of astigmatism measured on a given eye by all
types of measuring instruments will be similar, differences in
reported values may vary significantly. Instrument-to-instrument
variation may be due to the region of the cornea measured by an
instrument (for example one instrument may measure optical power
over the central 2.5 mm of the cornea; another may measure over 3.5
mm), the type of illumination source used (for example Placido
rings versus rings of discrete LEDs), how the data is analyzed,
etc. The effect of an error of as little as 10.degree. in treatment
of astigmatism axis is a 30% under correction of the astigmatism (A
M Fea, et al, Eye 20, 764-768 (2006)).
[0039] In this use of the present invention, the corneal optical
power of a patient undergoing a cataract treatment with associated
correction of astigmatism would be measured on a particular type of
standalone keratometer, for example the keratometer sold under the
tradename LenStar LS900 by Haag Streit of Bern, Switzerland). The K
values of the pre-operative measurement would be used for
determination of IOL spherical and cylindrical optical power. At
the time of surgery, with the patient on a gurney under the
femtosecond laser, the built-in keratometer would be used to
measure the axis of astigmatism of the patient's cornea. As
described above, this measurement of axis, with the patient lying
horizontally, is needed to compensate for cyclotorsion of the
patient's eye between the pre-operative keratometer measurement
made with the patient in a sitting position and that measured in
the operative position of the patient, lying on a gurney. The
built-in keratometer would be designed in all significant aspects
to measure K values and axis of astigmatism in the same manner and
to produce identical results (except for those associated with
cyclotorsion) as the pre-operative, standalone keratometer.
Therefore any bias in measurement of astigmatism axis from one type
of measurement instrument to another is eliminated and the treated
axis is as near as possible to the correct astigmatism axis of the
patient is used to treat the astigmatism with the best possible
clinical refractive outcome.
[0040] Note that the previously mentioned bias in measurement would
also be reduced or eliminated in the case where a Placido ring
system as described in U.S. patent application Ser. No. 13/017,499
is incorporated into a treatment laser and such a built-in system
is used to measure corneal K values and axes properties of the eye
in a manner as described above with respect to the built-in
keratometer. And as above, such a built-in Placido ring system,
used in conjunction with a standalone Placido ring system of
essentially the same design could be used in the same manner and
with the same benefits as is described above the built in and
standalone keratometer systems.
[0041] After the measurements of the rings of LEDs 202 previously
described are made by systems 200 and 300, the optical head of
treatment laser 104 is moved directly upward, out of the way, to
allow access to the patient's eye 102 for application of a suction
ring. In operation, a suction ring (not shown) is applied manually
to the patient's eye 102. After the suction ring is applied, the
optical head of treatment laser 104 is docked, using the previously
described joystick. Since the patient's eye 102 has not been moved
and since the treatment laser 104 and the astigmatism measuring
systems 200 and 300 are aligned to each other, the treatment laser
104 can now be used to correct or reduce the astigmatism of the eye
102, based on the previously described astigmatism axis
determination and/or the corneal shape determination, using limbal
relaxing incisions (LRIs) or LASIK, aligning the astigmatism
treatment to the measured axis of astigmatism.
[0042] The above described alignment system and process can also be
applied to procedures that involve implanting a toric intraocular
lens (IOL) to treat astigmatism. Note that IOLs are synthetic
lenses implanted into the capsular bag in the eye, after a
cataractous lens is removed. The IOL restores vision by replacing
partially opaque cataractous lens with a clear lens of appropriate
power. A conventional IOL has only spherical power. A toric IOL has
both spherical and cylindrical power and can thus correct
astigmatism in the eye.
[0043] In the case when a toric IOL is to be subsequently implanted
to treat astigmatism, the treatment laser 104 can be used to mark
the axis of astigmatism for later use in aligning the axis of
astigmatism 410 (shown in FIG. 4) of the IOL 405 (with haptics 406
used for anchoring IOL 405 in the capsular bag), with the marked
axis of astigmatism of the eye 102.
[0044] In cataract procedures, a round opening is manually torn or
cut by a laser in the crystalline lens anterior capsule. The
cataractous lens is removed through the opening and an IOL is
placed into the capsular bag, generally centered behind the
capsular opening. The treatment laser 104 can be used to cut a
small "tag" as part of the circular capsulotomy 400. The "tag"
provides a visible reference mark along which the axis of
astigmatism of the IOL 410 can be aligned. As shown in FIG. 5, the
"tags" 430 in the capsular openings can be positioned inwardly or
outwardly. The "tag" is cut in a smooth curve along the capsulotomy
cut to avoid risk of radial capsular tears during the cataract
procedure. Possible smooth shapes of the "tags" are shown
schematically in close-up 425. This method of marking the
astigmatism axis by incorporating a "tag" in the capsulotomy allows
the astigmatism mark, i.e. the "tag" to be ideally placed for use
in aligning the astigmatism axis of the IOL. The "tag" is in the
immediate vicinity of the astigmatism mark on the IOL and may in
fact be directly over the astigmatism axis mark on the IOL,
avoiding any errors in registration which might occur when aligning
the IOL mark with, for example, an ink mark on the sclera, a
considerable distance from the IOL. In summary, the "tag" provides
a visual marker so that the surgeon implanting a toric IOL can line
up the astigmatism axis of the IOL with marked axis of astigmatism
of the eye 102.
[0045] To avoid any possible distortion of the astigmatism axis of
the eye 102 which might occur when the a suction ring is placed on
the eye 102 for docking with the optical head of the treatment
laser 104, a small mark, for example a line, could be made by the
laser in the center of the lens capsule immediately after the
astigmatism axis was measured as described above. Then, after
affixing the suction ring and docking the eye 102 to the optical
head, the marks in the center of the capsule could be used, either
manually or using automatic image recognition techniques built into
a computer program, to set the position of the "tag"-marked
laser-cut capsulotomy for use in the toric IOL implantation.
[0046] Still another alternate method of marking the astigmatism
axis with the treatment laser would entail shooting several laser
shots, either at full or reduced energy at the position of the
astigmatism axis at the limbus to make a persistent visible
reference mark.
[0047] Since the x, y position of the optical head of the treatment
laser 104 is pre-aligned during the astigmatism axis measurement
process, very little adjustment is needed to dock the optical head
to the suction ring. Note that the telecentric viewing system 200
is also used as a general viewing system, to assist the laser
system associated with the optical head of the treatment laser 104
when the optical head is docked to the suction ring.
[0048] Use of the measuring system 250 built in to the above
described laser system 100 is advantageous. For example, the
measuring system 250 would allow measuring the astigmatism axis in
situ, while the patient is lying on the treatment bed, just in
advance of the laser treatment--thus eliminating the need for
pre-operative eye marks. In the case of performing limbal relaxing
incisions, the automatic measurement of the astigmatism axis by
system 100 increases the accuracy of the placement of the limbal
relaxing incisions, thereby improving the efficacy of the
treatment. The method can also be used in conjunction with the
laser to mark the astigmatism axis for cyclotorsional registration
of a toric IOL.
[0049] Despite the benefits of the method in convenience and more
accurate, automatic placement of the treatment axis for
astigmatism, and the advantage of reducing clinical outcome
variability by consistently using a built in measurement system, or
built in measurement system in conjunction with a pre-operative
standalone system of the same design, to eliminate variability in
clinical outcomes caused by determination of IOL, lens constants
with different measurement systems of different design types, there
is no laser astigmatism treatment device which currently
incorporates an astigmatism measuring system into the device. The
present invention eliminates the need for manually marking the eye
and circumvents the inaccuracies inherent in manual placing of
marks and the dispersion of the ink marks by the eye's tear film;
in addition, it provides a means to more accurately determine IOL
lens constants to reduce clinical outcome variability. The integral
astigmatism measurement, in combination with use of marks made by
the treatment laser can be used to mark the axis of astigmatism for
later registration of a toric IOL or for any subsequent refractive
treatment of the eye requiring knowledge of the axis of
astigmatism.
[0050] Since the measuring device is built into the optical head of
the treatment laser 104, the alignment of the measuring 100 to the
eye 102 reduces the time needed later to align the eye to the laser
treatment system. The system 100 also makes dual use of a camera
212 and ring light sources 202 for both the astigmatism measurement
and for general viewing of the eye during the eye docking and
lasing parts of the procedure.
[0051] It will be appreciated by those skilled in the art that
changes could be made to the embodiments described above without
departing from the broad inventive concept thereof It is
understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications within the spirit and scope of the present invention
as defined by the appended claims.
* * * * *