U.S. patent application number 10/653552 was filed with the patent office on 2005-08-11 for apparatus and method for determining subjective responses using objective characterization of vision based on wavefront sensing.
Invention is credited to Dreher, Andreas W., Lai, Shui T..
Application Number | 20050174535 10/653552 |
Document ID | / |
Family ID | 34826311 |
Filed Date | 2005-08-11 |
United States Patent
Application |
20050174535 |
Kind Code |
A1 |
Lai, Shui T. ; et
al. |
August 11, 2005 |
Apparatus and method for determining subjective responses using
objective characterization of vision based on wavefront sensing
Abstract
An apparatus for determining the refraction of a patient's eye
includes a wavefront measurement device that determines aberrations
in a return beam from the patient's eye viewing a target through a
corrective test lens in the apparatus. The wavefront measurement
device preferably outputs an display representative of the quality
of vision afforded the patient through the test lens. The display
may be, e.g., a representation of a Snellen chart convolved with
the optical characteristics of the patient's vision, an overall
quality of vision scale, or the optical contrast function, all of
which are based on the wavefront measurements of the patient's eye.
The examiner may use the display information to conduct a
refraction examination or other vision tests without the subjective
response from the patient.
Inventors: |
Lai, Shui T.; (Encinitas,
CA) ; Dreher, Andreas W.; (Escondido, CA) |
Correspondence
Address: |
MORRISON & FOERSTER LLP
3811 VALLEY CENTRE DRIVE
SAN DIEGO
CA
92130
US
|
Family ID: |
34826311 |
Appl. No.: |
10/653552 |
Filed: |
September 2, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10653552 |
Sep 2, 2003 |
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PCT/US03/04921 |
Feb 13, 2003 |
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Current U.S.
Class: |
351/205 |
Current CPC
Class: |
A61B 3/1015 20130101;
A61B 3/032 20130101 |
Class at
Publication: |
351/205 |
International
Class: |
A61B 003/10 |
Claims
What is claimed is:
1. An apparatus for determining the refraction of a patient's eye
focused on a physical target, said apparatus comprising: a light
source; optics directing light from said light source to the
patient's eye, said light reflecting from a surface of said eye,
said reflected light comprising a plurality of wavefronts; a
wavefront measurement device positioned along a first optical path
to said eye to measure the shape of said wavefronts reflected from
the patient's eye; and at least one test lens disposable along a
second optical path between the patient's eye and the physical
target, wherein said optics and said at least one test lens are
arranged such that when said patient looks at said physical target
through said test lens, said light from said light source is
directed through said eye so as to determine said refraction from
said wavefronts returning from said eye.
2. The apparatus of claim 1, further comprising a beamsplitter for
merging said first optical path from said wavefront sensor to said
eye and said second optical path from said eye to said physical
target such that they overlap in a region between said beam
splitter and said eye.
3. The apparatus of claim 1, wherein said test lens is disposed in
said region between said patient's eye and said beamsplitter where
said first and second optical paths overlap.
4. The apparatus of claim 1, wherein said test lens is disposed in
said second optical path from said eye to said physical target
outside said first optical path from said wavefront sensor to said
eye.
5. The apparatus of claim 1, wherein said test lens is positioned
an optical path length of approximately z.sub.o from said physical
target, said eye being adjusted to focus on said physical target
said distance, z.sub.o, away from said eye.
6. The apparatus of claim 5, wherein said test lens is positioned
an optical path length of about z.sub.o-y.sub.o from said physical
target, where y.sub.o corresponds to the optical path length from
said test lens to said patient's eye.
7. The apparatus of claim 6, wherein said optical path length
distance, z.sub.o-y.sub.o, between said lens and said physical
target is about 8 feet or greater.
8. The apparatus of claim 6, wherein said distance, z-y.sub.o,
between said lens and said physical target is about 20 feet.
9. The apparatus of claim 6, wherein said distance, y.sub.o,
between said eye and said test lens is between about 0.8 and 1.6
centimeters.
10. The apparatus of claim 6, wherein said distance, y.sub.o,
between said eye and said test lens is between about 0.5 and 4.0
centimeters.
11. The apparatus of claim 1, further comprising a housing
containing said wavefront measurement device, said housing
including a substantial ly transparent window disposed in said
second optical path between said patient's eye and said physical
target such said patient's eye can focus on said physical
target.
12. The apparatus of claim 11, wherein said test lens is contained
in said housing.
13. The apparatus of claim 1, wherein said light source is selected
from the group consisting of (i) a laser and (ii) a light emitting
diode.
14. The apparatus of claim 1, wherein said wavefront measurement
device includes at least one light detector receiving the light
returning from the patient's eye and sending a signal to at least
one processor, said at least one processor generating at least one
diagnostic output based on said wavefront measurements.
15. A method of quantifying the quality of a person's vision,
comprising: providing a test lens through which said person views a
physical target spaced from the test lens; directing light into an
eye of the person when the person looks through the test lens at
said physical target, some of the light reflecting from tissue in
said eye such that said light propagates through an ocular lens and
cornea of said eye and exits said eye; measuring a wavefront of
said reflected light emanating from the person's eye; determining
one or more values of a figure of merit using said wavefront
measurement, said figure of merit indicative of quality of a
person's vision; and producing a graphic based on said one or more
values of said figure of merit, said graphic indicative of the
quality of a person's vision.
16. The method of claim 15, wherein said figure of merit comprises
a function selected from the group consisting of a point spread
function, a modulation transfer function, and an optical transfer
function.
17. The method of claim 15, wherein said figure of merit is
selected from the group consisting of (i) a sum of terms based on
Zernike coefficients and (ii) a weighted sum of terms based on
Zernike coefficients.
18. The method of claim 17, wherein said figure of merit includes a
sum of squared Zernike coefficients.
19. The method of claim 15, wherein said figure of merit comprises
a Quality of Vision Factor (QVF) defined as 1 QVF = - P n Z n 2
wherein Z.sub.n corresponds to coefficients for Zernike polynomials
and P.sub.n correspond to psychometric weight factors.
20. The method of claim 15, wherein said graphic is selected from
the group consisting of a pie chart, a bar chart, and a line
chart.
21. The apparatus of claim 15, wherein the graphic is color-coded
in correspondence with said value of said figure of merit.
22. The method of claim 15, wherein said graphic comprises an image
of said target convolved with a function derived from wavefront
measurement, said graphic appearing more distorted with increasing
aberration.
23. The method of claim 22, wherein said graphic comprises an image
of said target convolved with a point spread function derived from
wavefront measurement.
24. The method of claim 23, wherein said point spread function is
derived by squaring the magnitude of the Fourier transform of the
wavefront.
25. The method of claim 15, further comprising varying said test
lens and determining said one or more figure of merit values for
different lenses.
26. The method of claim 25, further comprising identifying the lens
that provides an extreme value of said figure of merit
corresponding to a maximal quality of vision.
27. The method of claim 26, wherein said extreme value comprises a
peak average value of said figure of merit.
28. The method of claim 27, wherein said extreme value comprises a
maximum point spread function.
29. The method of claim 15, further comprising directing said light
through said test lens into said eye.
30. The method of claim 15, further comprising situating said test
lens such that said light is directed into said eye without passing
through said test lens.
31. A method of characterizing a person's vision, comprising: (a)
providing corrective optics for testing said vision, said
corrective optics being variable to provide different amounts of
optical correction; (b) directing a light beam into an eye of the
person, light from said light beam reflecting from tissue in said
eye such that said light propagates through an ocular lens and
cornea of said eye and exits said eye, said reflected light
comprising a plurality of wavefronts; (c) repetitively measuring
said wavefronts emanating from the person's eye with said
corrective optics adjusted to a substantially fixed amount of
optical correction thereby producing a set of data points
indicative of the quality of vision of the person for a given
amount of optical correction; and (d) determining the average and
variation in said plurality of data points to provide an objective
assessment of said correction.
32. The method of claim 31, wherein said determining the variation
in said plurality of data points comprises determining the standard
deviation.
33. The method of claim 31, further comprising comparing said
variations and selecting an amount of optical correction based on
said comparison.
34. The method of claim 33, wherein the optical correction is
selected substantially equal to the amount yielding the least
variation.
35. The method of claim 33, wherein the optical correction is
selected substantially equal to the amount yielding the minimum
standard deviation.
36. The method of claim 31, wherein said reflected light emanating
from the person's eye is repetitively measured for an amount of
optical correction such that the time period between the repeat
measurements is sufficiently long to permit the eye to adjust its
focus.
37. The method of claim 36, wherein said time period between repeat
measurements ranges between about 0.1 to 5 seconds.
38. The method of claim 31, wherein said corrective optics
comprises a plurality of test lens in a phoropter system.
39. The method of claim 31, wherein said corrective optics
comprises an optical system having variable optical power.
40. The method of claim 31, further comprising selecting the amount
of optical correction for said person based as least in part on the
optical correction that yields reduced aberration in said
wavefronts.
41. The method of claim 40, further comprising selecting the amount
of optical power that provides a peak value of a figure of merit on
the quality of vision of the patient.
42. The method of claim 31, wherein said optical correction
selected is substantially equal to an amount between the optical
correction yielding the least variation and the optical correction
yielding the peak value of figure of merit on the quality of
vision.
43. An apparatus for automatically determining correction for a
patient's vision, said apparatus comprising: test optics for
testing said vision, said test optics being variable to provide
different amounts of optical correction; a light source and
associated optics for directing light into an eye of the patient,
said light reflecting from tissue in said eye, said reflected light
comprising a plurality of wavefronts that propagate through an
ocular lens and cornea in said eye; a wavefront sensor including
one or more optical detectors for measuring said wavefronts
emanating from the patient's eye, said wavefront sensor having an
electrical output representative of said wavefront; an electrical
processor configured to receive said electrical output from said
wavefront sensor and determine the quality of said patient's vision
therefrom; and a mechanical actuator electrically connected to said
processor, said mechanical actuator adjusting the test optics so as
to vary the amounts of optical correction.
44. The apparatus of claim 43, further comprising a computer
readable medium having a program of instructions stored thereon for
causing said electrical processor to execute method steps for
determining the quality of said patient's vision, comprising: (a)
calculating a value of a figure of merit indicative of the
patient's quality of vision, said value being derived at least in
part from a measurement of one of the wavefronts from the patient's
eye; (b) retrieving another wavefront measurement from the
wavefront sensor; (c) repeating steps (a) and (b) N times; (c)
calculating the average and variation of the figure of merit values
and storing the average and variation as a data set for a given
optical correction; (d) instructing the actuator to alter the test
optics to provide a different optical correction; (e) repeating
steps (a) through (d) until a predetermined end point has been
reached; and (f) selecting the optical correction that yields (i)
the maximum average value of the figure of merit, (ii) the minimum
variation of the figure of merit, or (iii) a value between those of
(i) and (ii).
45. The apparatus of claim 43, further comprising a display
electrically connected to said electrical processor so as to
receive input from said electrical processor such that said
electrical processor can output results of said measurements to
said display.
46. The apparatus of claim 45, wherein said electrical processor
and display are configured to provide a graphical representation of
a target image as seen by the patient, said graphical
representation generated by a convolution of said target image with
a function derived from said wavefront measurements, said image
being distorted an amount indicative of distortion in the patient's
vision.
47. The apparatus of claim 45, wherein said electrical processor
and display are configured to provide information selected from the
group consisting of (1) a numerical and/or graphic representative
of the effectiveness of application of different amount of optical
power; and (2) a numerical and/or graphic display of the contrast
function of the patient's vision.
48. The apparatus of claim 43, wherein said electrical processor
includes electronic circuitry configured to select a prescription
suitable for correction and an output for outputting said
prescription.
49. The apparatus of claim 43, wherein said test optics comprise a
plurality of test lens that can be separately introduced into an
optical path between the patient's eye and a target to adjust the
patient's vision.
50. A method of determining correction for a person's vision,
comprising: directing light into an eye of the person, said light
reflecting from tissue in said eye, said reflected light comprising
a plurality of wavefronts that propagates through an ocular lens
and cornea in said eye; measuring said wavefronts with a wavefront
sensor; representing at least one of said wavefronts by a sum of
orthogonal components, .epsilon.K.sub.nQ.sub.n, where Q.sub.n
corresponds to said orthogonal components and K.sub.n corresponds
to coefficients having values selected to substantially match said
sum with said wavefront; weighting said orthogonal components with
psychometric weight factors P.sub.n based on the relative influence
of the orthogonal component Q.sub.n on human vision; and designing
optical correction based on said wavefront representation and said
psychometric weight factors.
51. The method of claim 50, wherein said orthogonal components
comprise Zernike polynomials.
52. The method of claim 50, wherein said psychometric weight
factors P.sub.n is obtained from a normative data base generated by
quantifying the effects of the respective orthogonal components
Q.sub.n in a normative population group.
53. A method of quantifying accommodation in an eye having a
cornea, an ocular lens, and a retina, said method comprising:
directing a light beam into the eye, light from said light beam
reflecting from tissue in said eye such that said light propagates
through the ocular lens and cornea of said eye and exits said eye;
repetitively measuring wavefronts associated with said reflected
light emanating from the eye for a set of conditions that induce an
amount of accommodation, thereby producing a set of data points
indicative of the quality of vision for said plurality of
wavefronts measured under said set of conditions; and determining
the average and variation in said plurality of data points to
provide a measurement of the amount of accommodation.
54. The method of claim 53, further comprising repeating said
measuring and determining steps for different sets of conditions
for inducing different amounts of accommodation, thereby producing
a plurality of average values which if plotted form a curve having
a maximum.
55. The method of claim 53, further comprising providing at least
one target a distance from said eye.
56. The method of claim 55, wherein said first set of conditions
includes a first target distance and said second set of conditions
includes a second target distance, said first and second target
distances being different so as to introduce different amounts of
accommodation.
57. The method of claim 53, further comprising providing optics
through which said eye can view at least one target, said optics
having spherical power to move the image of the target behind the
retina.
58. The method of claim 54, further comprising providing optics
through which said eye can view at least one target, said optics
having spherical power to move the image of the target behind the
retina.
59. The method of claim 58, wherein said maximum is a plateau
having a width, said method further comprising determining the
accommodating power of a person from the width of the plateau in
units of optical power.
60. The method of claim 53, wherein said determining the variation
in said plurality of data points comprises determining the standard
deviation from the data points.
61. A computer readable medium having a program of instructions
stored thereon for causing an electrical processor to execute
method steps for identifying optical correction for a person's eye
based on wavefront measurements of light reflected from said
person's eye, comprising: (a) calculating a value of a figure of
merit indicative of the person's quality of vision, said value
being derived at least in part from a measurement of a wavefront
from said person's eye; (b) retrieving another wavefront
measurement; (c) repeating steps (a) and (b) N times; (c)
calculating the average and variation of the figure of merit values
and storing the average and variation as a data set for a given
optical correction; (d) repeating steps (a) through (d) for
different optical correction; and (e) selecting the optical
correction that yields (i) the maximum average value of the figure
of merit, (ii) the minimum variation of the figure of merit, or
(iii) a value between those of (i) and (ii).
62. The method of claim 41, the figure of merit on the quality of
vision of the patient being selected from the group consisting of
(a) QVF, defined as 2 QVF = - P n Z n 2 wherein Z.sub.n corresponds
to coefficients for Zernike polynomials and P.sub.n correspond to
psychometric weight factors, (b) a point spread function, and (c) a
sum of squared Zernike coefficients.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to methods and
apparatus for determining a person's visual characteristics, and
more particularly to apparatus and methods for determining the
refraction of the eye.
[0003] 2. Description of the Related Art
[0004] Phoropters are apparatus used by optometrists to determine a
patient's visual characteristics, so that proper eye diagnoses can
be made and eyewear can be prescribed. In conventional phoropters,
a patient looks through the phoropter, in which various test lenses
are disposed, at a target eye chart, referred to as a "Snellen
chart," while an optometrist moves the test corrective lenses into
the patient's field of view. In some applications, the target may
be positioned at a predetermined distance from the patient. The
patient is then asked to verbally compare the quality of the
perceived image as afforded by one lens versus the prior lens
presented. The optometrist takes note of either an improvement or a
deterioration in the patient's vision through such lenses.
Systematically, the test progresses towards the "best" test lens
entirely based on the patient's responses. The lens parameters are
then used as the basis for a prescription for eyewear.
[0005] Unfortunately, as recognized herein, the patient can become
fatigued during the process and/or misjudge the vision afforded by
the various lenses. This can lead to the selection of a less than
optimum prescription. Moreover, some patients, such as a very ill
or a very young patient, might not be capable of articulating the
quality of vision the various lenses afford the patient.
[0006] Objective methods of determining the patient's refraction
errors have been proposed, but these other methods introduce
further complications that are not present when using phoropters.
In a retinoscopy method, for example, a streak of light is
projected to a patient's retina, and the characteristics of the
reflected light at the patient's corneal plane is analyzed to
determine whether the patient is myopic, or hyperopic, and with or
without astigmatism. However, the method does not provide
sufficient accuracy for prescribing spectacle lenses. Consequently,
its measurement results are typically used only as a starting point
of a standard phoropter measurement.
[0007] Another objective measurement instrument for determining
refractive errors is an autorefractor, which, owing to its speed of
use, is more popular than retinoscopy. To use the autorefractor, a
patient is asked to look inside an enclosed box that is part of the
autorefractor. A target image is optically projected into patient's
eye, and a series of lenses is automatically moved into position of
the patient's line of sight to the target, to neutralize the
patient's refractive errors (autorefraction). Unfortunately, the
measurement outcome often differs from the patient's ideal
prescription. Accordingly, like retinoscopy, autorefractor outcomes
typically are used only as starting points for standard phoropter
measurements.
[0008] Moreover, both retinoscopy and autorefraction fail to
account for the accommodation effect of the patient, that is, for
the propensity of a patient to alter his or her focus or sight to
make the best of the vision test. An autorefractor measurement
essentially is a snapshot of the patient's vision at a particular
instant at which the autorefractor has identified a so-called
neutralization point, and at this point if it happens that the
patient focuses his vision for seeing an image at a distance other
than what is intended, or if the patient is momentarily looking
elsewhere other than the target, the output of the autorefractor is
erroneous. Such deceptive focussing on the part of the patient can
arise because the patient is conscious of the working distance
inside the box, and when an image of an object presented to the
patient which is modeled to be located at, e.g., twenty feet, the
patient automatically focuses for an image at a much closer
distance, knowing the actual size of the box. Examination results
that include patient accommodation effects are inaccurate for
prescribing spectacle lenses.
[0009] Another limitation of the autorefractor is that the examiner
has no control over which lens is to be used in the test. The
result is that repeated measurements are likely to provide
different results for the same eye from the same patient, which
results in laborious and time consuming tests and retests when
using the device to finalize a prescription.
[0010] Thus, what is needed are improved methods and apparatus for
measuring the optical properties of a person's eye.
SUMMARY OF THE INVENTION
[0011] One aspect of the invention comprises an apparatus for
determining the refraction of a patient's eye focused on a physical
target. The apparatus comprises a light source and optics that
direct light from the light source to the patient's eye. The light
reflects from a surface of the eye. This reflected light comprises
a plurality of wavefronts. The apparatus further comprises a
wavefront measurement device positioned along a first optical path
to the eye to measure the shape of the wavefronts reflected from
the patient's eye along this first optical path. At least one test
lens is disposed along a second optical path between the patient's
eye and the physical target. The optics and the at least one test
lens are arranged such that when the patient looks at the physical
target through the test lens, the light from the light source is
directed through the eye so as to determine the refraction from the
wavefronts returning from the eye.
[0012] Another aspect of the invention comprises a method of
quantifying the quality of a person's vision. In this method, a
test lens is provided through which the person views a physical
target spaced from the test lens. Light is directed into an eye of
the person when the person looks through the test lens at the
physical target. Some of the light reflects from tissue in the eye
such that the light propagates through an ocular lens and cornea of
the eye and exits the eye. A wavefront of the reflected light
emanating from the person's eye is measured. One or more values of
a figure of merit are determined using the wavefront measurement.
The figure of merit is indicative of quality of a person's vision.
A graphic based on the one or more values of the figure of merit is
produced. This graphic is indicative of the quality of a person's
vision.
[0013] Yet another aspect of the invention comprises a method of
characterizing a person's vision. In this method, corrective optics
are provided for testing the vision. The corrective optics are
variable to provide different amounts of optical correction for
reducing optical aberration. A light beam is directed into an eye
of the person. Light from this light beam reflects from tissue in
the eye such that the light propagates through an ocular lens and
cornea of the eye and exits the eye. The reflected light comprises
a plurality of wavefronts. The wavefronts emanating from the
person's eye are repetitively measured with the corrective optics
adjusted to a substantially fixed amount of optical correction. A
set of data points indicative of the quality of vision of the
person for a given amount of optical correction are thereby
produced. The average and variation in the plurality of data points
are determined to provide an objective assessment of the
correction.
[0014] In various embodiments, the corrective optics may be altered
to provide different amounts of optical correction. The reflected
light from the person's eye is repeatedly measured for each of the
different amounts of optical correction, thereby yielding a set of
data points for the different amounts of optical correction. The
average and variation in the plurality of data points is determined
for the different amounts of optical correction.
[0015] Another aspect of the invention comprises an apparatus for
automatically determining correction for a patient's vision. This
apparatus includes test optics for testing the vision, the test
optics are variable to provide different amounts of optical
correction. The apparatus further includes a light source and
associated optics for directing light into an eye of the patient.
The light from the light source reflects from tissue in the eye.
This reflected light comprises a plurality of wavefronts that
propagate through an ocular lens and cornea in the eye. In
addition, a wavefront sensor that comprises one or more optical
detectors for measuring the wavefronts emanating from the patient's
eye is included in the apparatus. The wavefront sensors has an
electrical output representative of the wavefront. An electrical
processor is configured to receive the electrical output from the
wavefront sensor and determine the quality of the patient's vision
therefrom. Furthermore, a mechanical actuator is electrically
connected to the processor. The mechanical actuator adjusts the
test optics so as to vary the amounts of optical correction.
[0016] Still another aspect of the invention comprises a method of
determining correction for a person's vision. In this method light
is directed into an eye of the person. The light reflects from
tissue in the eye. This reflected light comprises a plurality of
wavefronts that propagates through an ocular lens and cornea in the
eye. The wavefronts are measured with a wavefront sensor. At least
one of the wavefronts is represented by a series of orthogonal
components, .epsilon.K.sub.nQ.sub.n- , where Q.sub.n corresponds to
the orthogonal components and K.sub.n corresponds to coefficients
having values selected to substantially match the sum with the
wavefront. The orthogonal components are weighted with psychometric
weight factors P.sub.n based on their relative influence on human
vision. Optical correction is designed based on the wavefront
representation and the psychometric weight factors.
[0017] Another aspect of the invention comprises a method of
quantifying accommodation in an eye having a cornea, an ocular
lens, and a retina. In this method, a light beam is directed into
the eye. Light from the light beam is reflected from tissue in the
eye such that the light propagates through the ocular lens and
cornea of the eye and exits the eye. Wavefronts associated with the
reflected light emanating from the eye are repetitively measured
for a set of conditions that induce an amount of accommodation. A
set of data points indicative of the quality of vision for the
plurality of wavefronts measured under this set of conditions are
thereby produced. The average and variation in the plurality of
data points are determined to provide a measurement of the amount
of accommodation.
[0018] In various embodiments, the reflected light from the eye is
repetitively measured for another set of conditions that induce a
different amount of accommodation thereby yielding an additional
set of data points for this different amount of accommodation. The
variation in the plurality of data points is determined to provide
a measurement of this different amount of accommodation.
[0019] Yet another aspect of the invention comprises a computer
readable medium having a program of instructions stored thereon for
causing an electrical processor to execute method steps for
identifying optical correction for a person's eye based on
wavefront measurements of light reflected from said person's eye.
These method steps comprise:
[0020] (a) calculating a value of a figure of merit indicative of
the person's quality of vision, said value being derived at least
in part from a measurement of a wavefront from said person's
eye;
[0021] (b) retrieving another wavefront measurement;
[0022] (c) repeating steps (a) and (b) N times;
[0023] (c) calculating the average and variation of the figure of
merit values and storing the average and variation as a data set
for a given optical correction;
[0024] (d) repeating steps (a) through (d) for different optical
correction; and
[0025] (e) selecting the optical correction that yields (i) the
maximum average value of the figure of merit, (ii) the minimum
variation of the figure of merit, or (iii) a value between those of
(i) and (ii).
[0026] Yet another aspect of the invention comprises a phoropter
that includes plural test lenses that can be disposed into a line
of sight defined between a patient and a target, such that a
patient looking at the target perceives light from the lens. A
wavefront measurement apparatus is positioned to detect aberrations
in light returning from the patient. These aberrations are caused
by the eye of the patient.
[0027] The phoropter may further comprise a processor that outputs
a diagnostic signal that corresponds to an objective assessment of
the patient's quality of vision. The processor may be in
communication with a display device for generating at least one
visual display representative of an effectiveness of a test lens in
correcting the patient's vision. The processor may employ the
objective assessment of the patient's quality of vision to select a
next test lens to determine a successive objective measurement of
the quality of vision corresponding to the next test lens. In some
embodiments, the processor may determine the standard deviation of
the objective measurement of the patient's quality of vision and
one or more successive objective measurements of the quality of
vision for different test lenses and identify a substantially
optimal vision correction lens for the patient. The objective
assessment of the patient's quality of vision may also be useful
for generating an image representation of the target.
[0028] In one preferred embodiment, a wavefront measurement
apparatus includes a light source, such as a laser or light
emitting diode (LED), for generating the light and a light detector
that outputs a signal representative of the aberrations. Also, the
apparatus includes a processor that receives the signal from the
light detector and outputs a diagnostic signal representative
thereof. The diagnostic signal is.degree. useful for generating an
image representative of the test object, and/or for generating at
least one visual display representative of an effectiveness of the
lens in correcting a patient's vision. The visual display can
include a bar chart, a pie chart, and/or a line chart, and it can
be color coded. The display may include, for example, (1) an image
generated by a convolution of the image of the test object based on
the wavefront returning from the patient's eye and through the
lens, (2) a numerical and/or graphic display representative of the
effectiveness of the lens, or (3) a numerical and/or graphic
display of the contrast function of the patient's vision.
[0029] In still another aspect of the invention, a method for
indicating the quality of a patient's vision includes providing a
device through which a patient can look at a target. The method
also includes directing a laser beam into the eye of the patient
when the patient looks at the target, and then detecting
aberrations in a wavefront of the light beam as the light beam
returns from the patient's eye. Based on the wavefront, the method
indicates a quality of a patient's vision. In various preferred
embodiments the refraction for the patient is determined.
[0030] In some embodiments, this method may further include
prescribing ophthalmic lenses for the patient. Ophthalmic lenses
for correcting refractive errors of the patient may be prescribed
and/or dispensed that are designed to reduce or correct (i) the low
order aberrations including sphere, cylinder, and axis, or (ii) low
order aberration in (i) and higher order aberrations including the
third order and possibly higher Zernike terms.
[0031] In still another aspect, a method for indicating the quality
of a patient's vision includes providing a device into which a
patient can look, and that generates a substantially instantaneous
visual indication of a quality of a patient's vision. The method
may further include indicating the quality of a patient's vision by
using at least one visual display representative of the
effectiveness of a first lens in correcting the patient's vision.
The display representing the effectiveness of the first lens may be
evaluated and a second test lens may be selected. The second test
lens may be positioned in the patient's line of sight and at least
a second visual display representative of an effectiveness of the
second test lens in correcting the patient's vision may be
generated. Selecting the second test lens may include determining
at least one of (a) the onset of the patient's accommodation, and
(b) the range of the patient's accommodation. Fogging may be
employed to select a more suitable lens for the patient.
[0032] In yet another aspect, a device for aiding a practitioner in
knowing the integrated effect of a patient's eye and a test lens
placed in front of the eye includes means for sensing an optical
wavefront returning from the eye through the lens. Means are
coupled to the wavefront sensing means for generating an indication
of the integrated effect of the eye and the test lens.
[0033] In another aspect, a device for generating an indication of
the quality of vision of a patient viewing a target includes a
light beam generator directing light into the eye of the patient,
and a wavefront sensing device detecting an optical wavefront
returned from the eye of the patient while the patient is looking
at the target. A computing device receives input from the wavefront
sensing device that is representative of the wavefront. The
computing device outputs a substantially continuous update of at
least one of: a point spread function (PSF) and a modulation
transfer function (MTF), while the patient is looking at the
target. A display device displays at least one of: a simulated
image of the target at the patient's retina, a quality of vision
indicator indicating the quality of vision, and a graph indicating
a contrast function of the patient, based at least in part on at
least one of the point spread function and the modulation transfer
function.
[0034] In yet another aspect, a vision quantifying device includes
a beamsplitter through which a patient can look at a target. A
source of light emits light into an eye of the patient, which
reflects from the eye as a return beam. A processor receives a
signal representative of a wavefront of the return beam and
generates at least one signal in response thereto, and a display
receives the signal and presents a visual indication of the
patient's sight.
[0035] Another aspect of the invention is to provide automatic
refraction correction. The patient looks at a target. A test lens
is positioned between the target and the patient's eye, and in the
line of sight of the patient. A light beam is directed through the
test lens and into the patient's eye. Using a portion of that light
reflected from a surface within the eye, a wavefront profile is
reconstructed. From the reconstructed wavefront profile, a quality
vision factor ("QVF") may be calculated. In order to improve the
accuracy of the measurements of the patient's eye, a number of
measurements of the returning wavefront profile are taken, and the
corresponding QVF values for each of the measurements for that
particular test lens, is analyzed. The analysis of this data
provides for a determination that the correction with that
particular lens is optimal. If the correction is not optimal, a
next test lens is selected, and the process is then repeated for
the next test lens after it is positioned by mechanical means in
the patient's line of sight. On the other hand, if the correction
with that particular lens is optimal, then the process ends
resulting in the proper refractive correction having been
identified.
[0036] The details of the present invention, both as to its
structure and operation, can be understood in reference to the
accompanying drawings, in which like reference numerals refer to
like parts.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is a perspective view of one embodiment of an
apparatus for characterizing a patient's vision, in one intended
environment;
[0038] FIG. 2 is a perspective view of the apparatus, showing the
patient;
[0039] FIG. 3 is a block diagram of the components of one preferred
apparatus;
[0040] FIG. 4 is a flow chart of the some preferred logic;
[0041] FIGS. 5-9 are exemplary non-limiting diagrams of quality of
vision displays; and
[0042] FIG. 10 is a flow chart showing an automatic refraction
method described herein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0043] Although this invention will be described in terms of
certain preferred embodiments, other embodiments that are apparent
to those of ordinary skill in the art, including embodiments that
do not provide all of the benefits and features set forth herein,
are also within the scope of this invention. Accordingly, the scope
of the invention is defined only by reference to the appended
claims.
[0044] Referring initially to FIGS. 1 and 2, an exemplary apparatus
is shown, generally designated 10, and includes a housing 12 that
can be mounted on a movable stand 14 for positioning the housing 12
in front of a patient 15 who might sit in an examination chair 16.
As can be appreciated in cross-reference to FIGS. 1 and 2, the
patient 15 can position his or her head against the housing 12.
Alternatively, the housing 12 can be supported on the head of the
patient 15 and/or be suspended from a flexible overhanging arm
which may be attached to a stand, to provide weight balance and to
facilitate mounting and dismounting of the head mounted-apparatus.
In other embodiments, the apparatus can be co-mounted with a
conventional phoropter (not shown), in which case the test lenses,
described more fully below, can be established by the lenses of the
conventional phoropter. Other configurations may also be
practicable.
[0045] Now referring to FIG. 3, the patient 15 can look through the
housing 12 to a target 18, such as but not limited to a Snellen
chart. The target 18 can be positioned at any appropriate distance
from the patient 15, e.g., twenty feet or closer. Preferably, the
target 18 is a distance z.sub.o of about 8 to 20 feet from the
patient's eye 15. Since the target 18 can be positioned at a
distance that actually is the distance intended, the above-noted
patient accommodation effects related to autorefractors, are
reduced or eliminated. In some cases, a mirror may be inserted in
the optical path between the system 10 and the target 18 to
introduce a turn in the optical path. These reflectors may be
employed, for example, to accommodate suitable placement of the
target 18 such as on the ceiling of an office where the vision
tests are being administered.
[0046] FIG. 3 shows one exemplary implementation of the housing 12.
While FIG. 3 shows that various components are located inside the
housing 12 and various other components such as the output display
are located outside the housing 12, it is to be understood that the
principles advanced herein apply to systems having multiple
housings, or a single housing. Additionally, other component and
configurations may be included in the design.
[0047] In the embodiment shown, the patient looks at the target 18
through a transparent window within the housing 12, such as can be
established by a primary beamsplitter 20 or other optical element.
Interposed in the line of sight of the patient 15 are one or more
movable test lens 22. By "movable" is meant physically movable by
hand or computer or electronically-controlled mechanism as
indicated as "M" in FIG. 3, and more fully disclosed below, such
that the lens is selectively interposed in or out of the line of
sight of the patient 15. The test lens may also be movable in the
sense that a variable focal length lens can be used, with its
optical characteristics being variable in accordance with
principles known in the art, for example those utilized in various
designs of autorefractors. In certain embodiments, the test lens 22
can be, but should not be limited to, a single concave convex lens,
or a combination of optical components such as lenses, and may
include a cylindrical lens and a prism.
[0048] The test lens 22 may be disposed in an optical path between
the primary beamspiitter 20 and the patient's eye 15 as depicted in
FIG. 3. The distance y.sub.o between the test lens 22 and the eye
is relatively small, compared, for example, to the distance to the
target 18. The separation between the eye 15 and the lens 22 may,
e.g., be between about 0.8 and 1.6 centimeters in some embodiments.
In the case, where this separation is small, the distance from the
test lens 22 to the physical target, z.sub.o-y.sub.0, is
approximately equal to the distance z.sub.o from the eye to the
target 18.
[0049] As also shown, a light source such as but not limited to a
laser 24 generates a light beam 26 that can be directed, in one
preferred embodiment, toward a laser beamsplitter 28. The laser
beamsplitter 28 reflects the light beam 26 toward the primary
beamsplitter 20, which in turn reflects the beam through the test
lens 22 and onto the eye of the patient.
[0050] Note that in certain embodiments, the test lens 22 may be
inserted in the optical path between the beamsplitter 20 and the
target such that the laser beam 26 does not pass therethrough.
However, in either case where the test lens 22 is employed,
preferably the vision is at least partially corrected. Measurements
may be more accurate when vision is good and the eye is not
stressed and is operating more normally.
[0051] With reference again to FIG. 3, after reaching the eye, the
beam 26 is reflected therefrom, back through the lens 22, and is
reflected off the primary beamsplitter 20. The beam passes through
the laser beamsplitter 28, and a portion of the beam is reflected
off a pupil detection beamsplitter 30 toward a pupil light detector
32 through one or more focussing lenses 33, for purposes to be
shortly disclosed. A portion of the return beam passes through the
pupil detection beamsplitter 30 and propagates through an optical
relay unit 34, which focuses the beam onto a wavefront analyzer
optics 36. The wavefront analyzer optics 36 generates a signal
representative of the wavefront of the return beam, and a wavefront
detector 38 transforms the signal into an electrical signal for
analysis by a processor 40. In one preferred embodiment, the
processor 40 can be associated with control electronics known in
the art for undertaking control of one or more components (e.g.,
the light source 24) of the system 10 as more fully set forth
below. Also, the processor 40 can generate the below-described
visual indications of the patient's vision as corrected by the test
lens 22 and can cause the indications to be displayed on a display
device 42, such as a video monitor, that can be mounted on the
housing 12 or apart therefrom. The display device 42 can be a
liquid crystal display that can be mounted on the housing 12 of the
system 10, or a stand-alone display unit conveniently located for
the examiner's viewing. Suitable displays may include, but not be
limited to, numerical and/or graphical representations indicative
of the patient's quality of vision, as described more fully
below.
[0052] If desired, an illumination light 44, e.g., a ring-shaped
fiber optic, can be mounted on the housing 12 and can be connected
to the processor 40 to control the pupil size of the patient 15.
The illumination light 44 can be a source of diffused light. The
light intensity of the illumination light 44 may be controlled by
the processor 40 in response to feedback from the pupil light
detector 32, which can comprise, e.g., a CCD camera, or reticon
detector array to monitor the size of the pupil, so that a
predetermined pupil size can be maintained for the patient during
the measurement. The locations of the pupil detection unit,
including the components, beamsplitter 30, lens 33, and pupil light
detector 32, can be in other appropriate locations along the
optical path of the return light from the eye, including locations
inside the optical relay unit 34.
[0053] As a further improvement to the accuracy of the refraction
measurement, the system also monitors the first Purkinge image, an
image formed by reflection at the anterior surface of the cornea of
the light beam 26. The position of this image relative to the pupil
boundary is an indication of gazing direction of the patient under
examination. Unless the patient has strabismus in that eye, the
relative position of the First Perkinge image is a well defined
bright spot, and it is typically inside the pupil boundary.
Therefore, in a preferred but non-limiting embodiment, the pupil
detector 32 can also function as a patient gazing monitor. In this
case, the relative position of the First Perkinge image to the
pupil is determined by processing of the image data from the CCD
camera, for example, using data filtering, contrast enhancement,
and pupil boundary determination methods known in the art.
[0054] In various embodiments, software processing can be done in
real time in a matter of a fraction of a second. The objective of
this analysis is to determine whether the patient is looking at the
target, or momentarily drifting off. The information is
electromagnetically transmitted to the central control unit 40. If
the patient is not looking at the target, the data set from the
wavefront detector unit 38 is rejected, and preferably is not
displayed or accumulated for data analysis.
[0055] As indicated above, the following comments are germane to
implementation details of preferred, non-limiting embodiments. The
light source 24 can be a diode laser that emits light at near
infrared wavelengths. Moreover, the light detectors 32, 38 can be
implemented by CCD arrays or linear reticon arrays or other
detection devices. Further, the primary beamsplitter 20 can be
coated to transmit visible light and to reflect infrared light. On
the other hand, the laser beamsplitter 28 can be a polarization
dependent reflector, in which case the laser light is polarized,
and a quarter wave plate (not shown) is disposed in the beam path
to the patient 15 such that the return beam is rotated ninety
degrees (90.degree.) upon double passing the quarter wave plate for
facilitating passage thereof through the laser beamsplitter 28
toward the wavefront analyzer optics 36. Alternatively, the laser
beamsplitter 28 can be plate coated for high transmission and low
reflectivity at forty five degrees (45.degree.) incident angle,
such that only a small portion of the laser light is reflected into
the eye, but a high percentage of the return light propagates
through the laser beamsplitter 28.
[0056] Continuing with the implementation details of a preferred,
non-limiting embodiment, the optical relay unit 34 can include two
convex lenses F1 and F2 that together establish a telescope. The
lenses F1, F2 are separated from each other by a distance equal to
the sum of their focal lengths, with the focal plane of the first
lens F1 being located at the front surface of the test lens 22,
i.e., the surface facing the primary beamsplitter 20. In the case
where the lens 22 is not between the patient's eye 15 and the
primary beamsplitter 20 (e.g., wherein the test lens is between the
primary beamsplitter and the target 18), the focal plane of the
first lens F1 is preferably located at the front of the eye, i.e.
the front of the cornea. The focal plane of the second lens F2 is
located at the image plane of the wavefront analyzer optics 36. The
purpose of the telescope structure of the relay unit 34 is to relay
the wavefront at the exit surface of the test lens 22 to the image
plane of the wavefront analyzer optics 36. Alternative relay optics
can be used to achieve the same or different purpose.
[0057] With respect to the non-limiting details of the wavefront
analyzer optics 36, the optics 36 can include an array of lenslets
arranged as in a Shack-Hartmann wavefront sensor, an example of
which can be found in page 37, "Customized Corneal Ablation The
Quest for Super Vision" edited by MacRae, et. al. published by
Slack Incorporated, 2001, incorporated herein by reference. Various
Shack-Hartmann wavefront sensors and processors are available, for
example, from commercial vendors such as Wavefront Sciences, in
Albuquerque, N. Mex., Zeiss/Humphrey Instruments, in Dublin,
Calif., or Bausch and Lomb, in Irvine, Calif. More preferably, the
optics 36 can include ruled reticles such as those disclosed in
co-pending application U.S. patent application Ser. No. 10/014,037,
entitled "SYSTEM AND METHOD FOR WAVEFRONT MEASUREMENT", filed Dec.
10, 2001, and U.S. patent application Ser. No. 10/314,906, entitled
"SYSTEMS AND METHODS FOR WAVEFRONT MEASUREMENT", filed Dec. 9,
2002, both of which are incorporated herein by reference, which use
a self-imaging diffraction principle to detect the wavefront in the
return beam.
[0058] Regardless of the type of wavefront analyzer optics 36 used,
the processor 40 analyzes the profile of the wavefront of the light
returned from the patient's eye, and quantifies the wavefront
aberrations in two regimes: low order aberrations, including
spherical refractive error, cylinder, and axis, and higher order
aberrations, including coma, spherical aberrations and other higher
order terms that can be described by Zernike polynomials.
Quantitative data representing the patient's quality of vision are
then graphically presented on the display device 42.
[0059] Now referring to FIG. 4, an exemplary mode of operation of
an apparatus such as depicted in FIG. 3 can be seen. The patient 15
views the target 18 through the system 10, and in particular
through the transparent window that is established by the primary
beamsplitter 20. At block 44, the examiner initiates the vision
test by inserting a selected test lens 22 in the line of sight of
the patient, or by configuring a variable focal length lens 22 to
have a predetermined focal length. Inserting means either manual
positioning or positioning using a motor or other translation or
rotation mechanism. In certain embodiments, the processor 40 can
select a particular lens 22 and cause it to be automatically moved
in the line of sight, in accordance with discussion below.
[0060] Various steps represented by blocks in FIG. 4 involve
calculations, and other types of activities that can be automated
and at least partially implemented using for example computer
logic. In particular, in accordance with processes and methods
described and shown herein. These methods and processes include,
but are not limited to, those depicted in at least some of the
blocks in the flow chart of FIG. 4 as well as the flow chart in
FIG. 10, which is described more fully below. These and other
representations of the methods and processes described herein
illustrate the structure of the logic of various embodiments of the
present invention which may be embodied in computer program
software. Moreover, those skilled in the art will appreciate that
the flow charts and description included herein illustrate the
structures of logic elements, such as computer program code
elements or electronic logic circuits. Manifestly, various
embodiments include a machine component that renders the logic
elements in a form that instructs a digital processing apparatus
(that is, a computer, controller, processor, etc.) to perform a
sequence of function steps corresponding to those shown.
[0061] In other words, the logic may be embodied by a computer
program that is executed by the processor 40 as a series of
computer- or control element-executable instructions. These
instructions may reside, for example, in RAM or on a hard drive or
optical drive, or the instructions may be stored on magnetic tape,
electronic read-only memory, or other appropriate data storage
device.
[0062] Proceeding to block 46 in FIG. 4, the processor 40
determines the point spread function (PSF) that is derived from
using, for instance, the terms of Zernike polynomials, which is in
turn derived from the wavefront passing through the wavefront
analyzer optics 36 and transformed into an electrical signal by the
wavefront detector 38 when the wavefront data is acquired. The
processor 40 may Fourier transform the signal from the wavefront
detector 38 using the following equation:
PSF(x,y)=.vertline.FT(P(x,y)).vertline..sup.2
[0063] wherein FT designates a Fourier Transform calculation and
P(x, y) is the spatial distribution of the wavefront profile of
light with the same phase (i.e., phase front) returned at the
corneal plane.
[0064] Proceeding to block 48, if desired, an Optical Transfer
Function (OTF) can be calculated from an inverse operation of
Fourier Transform as follows:
OTF(f.sub.x,f.sub.y)=FT.sup.-1(PSF(x,y)),
[0065] wherein f.sub.x, f.sub.y are spatial frequencies in x and y
directions, respectively, that are orthogonal to each other.
[0066] Moreover, a Modulation Transfer Function (MTF) can be
determined as the amplitude of the OTF:
MTF(f.sub.x,f.sub.y)=.vertline.OTF(f.sub.x,f.sub.y)
[0067] The above functions are used to generate visual indications
of the quality of vision that is afforded by the test lens 22
currently being viewed by the patient 15. For instance, once the
PSF is determined at block 46, the logic can flow to block 50 to
determine a convolution function G as follows:
G(X.sub.img,
Y.sub.img)=.intg..intg.PSF(x-x.sub.img,y-img)f(x.sub.img,y.su-
b.img)dxdy,
[0068] wherein f(x.sub.img, y.sub.img) is the test target 18 (FIG.
3), i.e., an ideal image function, x.sub.img-x.sub.img is the
difference in the x-dimension between each point in the PSF and the
corresponding ideal point in the ideal image, and y-y.sub.img is
the difference in the y-dimension between each point in the PSF and
the corresponding ideal point in the ideal image.
[0069] The convolutional function G can be used at output state 52
to generate an appropriately blurred image, point by point, of an
ideal image as affected by the imperfection of the patient's eye in
combination with the lens 22. For example, when the target 18 is a
Snellen chart, the ideal image function can be the letter "E" or a
series of other letters, e.g., of various physical sizes as
conventionally used in the various lines in the Snellen chart. FIG.
5 shows one such blurred image at 54, which can be presented on the
display 42. Alternatively, the target can be a picture, and the
convolved image G(x.sub.img, y.sub.img) Of the picture is blurred
point by point, according to the PSF, which represents an image of
the target formed at the patient's retina.
[0070] Accordingly, the letters in the simulated blurred image have
the same blurring as perceived by the patient 15. In this way, the
examiner can visualize the clarity and sharpness of the image as a
result of the lens 22 as it is perceived by the patient 15.
[0071] Alternatively or in addition to the image shown in FIG. 5,
the processor 40 can generate the displays shown in FIGS. 6-8 as
follows. At block 56 the wavefront profile, as indicated by the
above-mentioned linear combination of Zernike polynomials, is
filtered to eliminate terms with coefficient below a threshold
amplitude. Moving to block 58, a psychometric weighting factor "P"
is inserted for each of the remaining Zernike terms as shown in the
following. This weighting factor "P" represents the effect of the
brain to discriminate objects despite certain types of ocular
aberrations. For example, most people can discern a letter in a
Snellen chart with a certain amount of defocus while the same
amplitude of aberration in coma would not allow the same patient to
discern that letter. To compensate for this, a Quality of Vision
Factor (QVF) is determined as follows:
QVF=exp.sup.-.epsilon.nPnZn.sup..sup.2)
[0072] wherein P.sub.n is the psychometric weight factor for the
corresponding n.sup.th term of the Zernike polynomials, and Z.sub.n
is the coefficient of the n.sup.th term of the Zernike polynomials
in the PSF.
[0073] The psychometric weighting factors "P.sub.n" can be
determined by presenting a particular aberration to a normative
group of people representing an average population distribution,
for example, between about two hundred to several thousand people,
depending on the accuracy level desired and the range of the
scatter value of each type of aberration measurement. The patients
are presented one at a time with particular types of aberrations
selected from the Zernike polynomials, and then the patients are
scored for the extent of success in discerning the target, for
example, by the number of letters correctly read on the Snellen
chart, or other standardized vision test chart. Other methods based
on contrast level, standardized letter size, sine or square wave
patterns can also be used. For example, success of patients in
discerning graphics consisting of lines having various cycles per
degree may be employed to test contrast sensitivity.
[0074] The optical element for introducing such aberration can be
an aberration plate on which a selected type of aberration has been
imprinted. For example, the aberration type can be a coma, or a
trefoil, having a refractive index profile to produce the proper
phase changes as specified by the corresponding Zernike
polynomial.
[0075] The relative effect of each type of aberration is tabulated
for the group and averaged to obtain statistically meaningful
weight factors. For most practical purposes, Zernike coefficients
for terms higher than the sixth order (term number twenty nine or
higher) minimally contribute to the overall aberration profile of
normal eyes. The method of producing various types of aberrations
with desired amplitudes according to each of the Zernike terms is
set forth in co-pending U.S. patent application Ser. No. 09/875,447
filed Jun. 4, 2001 and entitled "WAVEFRONT ABERRATOR AND METHOD OF
MANUFACTURING", which is incorporated herein by reference. In the
event that no data for the psychometric weight factors are
available, all weighting factors P.sub.n can be set to unity.
[0076] Once the QVF has been determined, one or more of the
displays shown in FIGS. 6-8 can be generated and displayed as
indicated in block 60. For example, as shown in FIG. 6, a bar chart
display can be generated to present an overall indication of the
patient's quality of vision as afforded by the lens 22 under test.
As shown, the indicator can be in the form of a graduated bar 62,
the height of which is proportional to the QVF determined at block
60, with zero indicating poor vision and perfect vision being
indicated by a bar extending from the bottom to the top 64 of the
scale. If desired, the display scale can be a log scale, in which
case the "best" is indicated by the bar 62 being at zero, and
rising logarithmetrically with worse vision using a
root-mean-square function of the QVF. Enhancements to the bar 62
such as color-coding can be used. For instance, the bar 62 can be
colored red for poor vision and green for good vision, with other
colors being used to indicate intermediate qualities of vision. In
lieu of the bar chart of FIG. 6, the QVF can be used to generate a
pie chart as shown in FIG. 7, with the size of a pie slice 66
relative to the entire circle being linearly or logarithmetrically
proportional to the QVF.
[0077] The system 10 can substantially continuously measure the
wavefront profile of the light beam returned from the patient's
eye. Accordingly, in one preferred, non-limiting embodiment, a
sequence of QVF measurements (e.g., twenty) for a single test lens
22 can be made in a second or two and grouped together.
[0078] As described earlier, the measurement accuracy can be
improved by monitoring the gazing direction of the patient, and the
computing device in block 40 can reject the data points acquired
when the patient was not looking at the designated target.
Furthermore, the computing device can also accumulate data and
perform calculations for average values and standard deviation for
selected subsets of measurement.
[0079] FIG. 8 shows a resulting display. As can be appreciated from
the exemplary embodiment shown, five lenses 22 have been tested and
several QVF values obtained over a short period for each. Each
group of QVF values is plotted as a respective vertical line 68 on
a plot of QVF versus lens, with the length of each error bar line
68 representing the standard deviation of the measurements for that
particular lens and the center of each line representing the mean
QVF value. The prescription can be based not only on a high mean
QVF value, as indicated at points 70 and 72, but also on a small
standard deviation, as indicated by bar 74. That is, the lens
corresponding to the bar 74 might be selected because its QVF
values had a small standard deviation from each other and it had a
high mean QVF value, even if not as high as the point 70. This
recognizes that some patients prefer a lens power which may not
necessarily provide the sharpest image but which does result in
more comfort, since a patient does relatively little searching for
the "better focus" using lenses that exhibit smaller standard
deviations in the QVF. An example case is a patient who has not had
a vision check for an extended period of time and requires
correction of more than 1.5 diopters in cylinder. The patient may
feel uncomfortable with the full correction as afforded by the
sharpest image; rather the patient may prefer a smaller amount of
correction which represents improvement in his vision, yet that
does not cause dizziness or head strains. Therefore, embodiments of
the present invention may provide objective data based on the
subjective response of the patient to a test lens set 22 presented
to the patient.
[0080] Determining the variation in the figure of merit preferably
involves performing multiple measurements with consecutive
measurements separated by a sufficiently long time interval. This
time interval is preferably long enough to permit the eye to adjust
its focus. Thus, the variation in data points should reflect
adjustments made by the eye such as are present when the eye is
straining to focus or accommodate. The time period between
consecutive measurements is therefore preferably between about 0.1
to 5 seconds, however, values outside this range are also
possible.
[0081] Accordingly, various test conditions may be presented to the
patient under examination to investigate the subjective responses
to such conditions. For example, as described above with reference
to FIG. 8, objective measurements are performed to determine the
subjective response of the patient to different optical correction.
By taking into account the subjective aspect of the patients vision
experience, a prescription for correction of the refractive errors
that is superior to that obtained with conventional objective
measurement approaches is possible. Other conditions can be altered
and the subjective response of the patient determined using the
objective measurements described herein. Fogging and testing for
the range of the accommodative ability are some other examples of
how conditions that affect vision may be controlled and tested. In
each of these cases, the apparatus and methods described herein
advantageously can enables quantification of the subjective
response of the patient by performing objective measurements, i.e.,
without any verbal communication with the patient.
[0082] As recognized herein, to determine a patient's ability to
resolve patterns having varying levels of contrast, the patient can
be presented with a series of standardized patterns of sine wave
gratings of increasing spatial frequency frequencies, with the
patient offering subjective responses. The resulting examination
report can be a curve that depicts a cutoff contrast intensity at
various spatial frequencies. Embodiments of the present invention
can provide a quantitative evaluation of a patient's ability to
handle contrast, which can be generated in addition to or in lieu
of those displays discussed above. Such a display can be generated
at output state 76 in FIG. 4 and is shown in FIG. 9, showing a
curve 78 depicting actual patient optical contrast function (OCF)
and a reference curve 80 depicting a diffraction-limited reference.
To determine OCF, the following relation may be used:
OCF=MTF.times.M.sub.iat.
[0083] wherein MTF is the modulation transfer function determined
at block 48 and M.sub.iat is a mathematical function accounting for
the low frequency filtering of the neural system, the value of
which linearly increases with spatial frequencies with a slope of
unity in a log-log scale plot and reaches the maximum value of one
at and above the spatial frequency of seven cycles per degree.
[0084] Accordingly, the OCF does not include the effect of the
brain processing at frequencies higher than seven cycles per
degree, but it does provide valuable information about the
patient's ability to discern sine gratings of various spatial low
frequencies based on a patient's optics.
[0085] The above process of measuring (and displaying) indications
of the improvement in vision afforded by a particular test lens 22
to the patient 15 can be continued at block 82 until the "best"
test lens is found. This can be done by the examiner manually
swapping lenses 22 as, e.g., in a conventional phoropter. As
mentioned above, in other embodiments, the positioning of test
lenses 22 can be done automatically by the processor 40 controlling
the moving mechanism "M", which can include a motor (or actuator)
and coupling structure connecting the motor/actuator to one or more
lenses 22. With this configuration, the mechanism follows an
instruction from the processor 40 to insert the particular lens in
the line of sight of the patient, as requested by the
processor.
[0086] When done by the processor 40, the sequence of test lenses
22 to be used in an examination may be programmed into the
processor 40 in accordance with examination strategy and routines
known in the art. The starting lens can be selected based on the
patient's current spectacle prescription or based on the wavefront
measurement without any test lens 22 in the patient's line of
sight. Consequently, in reconstructing the return beam wavefront
without a test lens 22 being in the beam path, the processor 40
essentially models the uncorrected aberrations of the patient's eye
in Zernike terms.
[0087] Recall that the second order Zernike terms represent
defocus, astigmatism and axis information. Based on the patient's
pupil size and the uncorrected wavefront error amplitudes, the
processor 40 can determine the equivalent diopter power in sphere
and cylinder and its axis, and select the appropriate lens 22 being
used to start the examination. In selecting test lenses 22, the
processor 40 can use the above-disclosed QVF values or other
figures of merit in lieu of subjective responses from the patient,
and can then execute the examination strategy as if it is performed
with the subjective response from the patient.
[0088] The automatic refraction process is depicted in FIG. 10, and
generally designated 100. Process 100 begins with a first step 102
wherein the patient looks at a target. In step 104 a test lens is
positioned between the target and the patient's eye, and in the
line of sight of the patient. A light beam is directed through the
test lens and into the patient's eye in step 106. As discussed
earlier, the test lens may be positioned outside of the light beam,
yet in the line of sight of the patient, positioned between the
beam splitter 20 and the target 18 in FIG. 3. In this
configuration, the patient's vision is affected by the test lens as
he is looking at the target, but the wavefront emerging from the
patient's eye is directed to the wavefront sensor without passing
through the test lens, and thus this wavefront contains both the
low order and higher order aberrations of the patient's eye.
[0089] In step 108, the light returning from the patient's eye is
detected. From this detected light, the wavefront profile may be
reconstructed, as shown in step 110. From the reconstructed
wavefront profile, the quality vision factor ("QVF") may be
calculated in step 112. In order to improve the accuracy of the
measurements of the patient's eye, "N" number of measurements are
performed using the returning light. Accordingly, "N" wavefront
measurements are taken, thereby yielding N wavefront profiles and
corresponding QVF values. These successive measurements are taken
by returning from step 112 to step 108, in which the returning
light is again detected. Steps 108 through 112 are executed "N"
times for the test lens. As described above, the "N" measurements
are spaced apart in time by a sufficient amount to allow the
patient to adjust their focus. For example, this time interval is
preferably long enough to permit the muscles in the eye to
readjust.
[0090] Once "N" measurements have been taken and the QVF for each
measurement has been calculated, the QVF for that particular test
lens is analyzed in step 114. The analysis of this data provides
for a determination whether the correction with that particular
lens is optimal. This decision is made in step 116, and if the
correction is not optimal, a next test lens is selected in step
120, and the process returns to step 104 where the next test lens
is positioned in the patient's line of sight. On the other hand, if
the correction with that particular lens is optimal, then the
process ends in step 122 resulting in the proper refractive
correction having been identified. In other embodiments, the
optimal lens may not be identified immediately after that
particular lens is tested on the patient. Instead, the suitable
lens may be selected after trying one or more additional test lens.
Such is the case wherein a figure of merit analysis like that
illustrated in FIG. 8 is employed.
[0091] In a typical refraction process, a series of lenses in 1/4
diopters increments are used to determine the patient's optical
correction. However, in various embodiments of the present
invention, more or less than the typical number of lenses may be
used, and the diopter increments can be in 1/8 instead of 1/4,
depending upon the magnitude of correction necessary. Also, as
shown in FIG. 10, a number ("N") of measurements of the returning
light are performed in steps 108 through 112 to calculate the QVF
for the particular test lens. In some embodiments, for example,
5-20 separate measurements (i.e., "N" equals 5-20) are performed to
provide an accurate measurement of the QVF. However, more or less
measurements may be performed depending upon the particular
wavefront sensor device used, and the magnitude of correction
necessary.
[0092] The prescription can be determined by a person viewing the
display, e.g., of FIG. 8, or automatically by the processor 40
based on a high QVF value and low standard deviation, as follows:
The examiner, or the processor 40 will examine the curve shown in
FIG. 8, which connects the average values of the QVF's for various
lens sets presented to the patient. Certain embodiments may include
the step of performing a best fit to the average values, using a
polynomial of up to 4 orders, for example. The processor 40
searches for the maximum value, of the "peak" of the curve. This
can be accomplished by monitoring the peak value of the curve, or
the slope of the curve, e.g., from decreasing lens power, from
right to left, in FIG. 8. When the curve reaches its maximum value,
the slope changes sign, and the maximum is at the zero slope value.
Now, the processor 40 sends the peak value of the QVF and the
corresponding lens power to the display or a printer.
[0093] Additionally, the processor 40 may also search for the
minimum value among the standard deviation in the data set such as
shown in FIG. 8. A figure (not shown) similar to FIG. 8 showing
standard deviations versus lens power can be useful in determining
the minimum value. Again curve fitting can be employed. The minimum
value may be identified for example by detecting the sign change in
the slope as described above for determining the maximum QVF value.
Again, this minimum standard deviation value and the corresponding
lens power are sent to the display device or a printer for record.
For example, on the display or the printout the processor may
indicate that lens power with the maximum QVF value provides for
the sharpest image, while the lens power with the minimum standard
deviation provides for the most comfortable prescription to the
patient.
[0094] In certain embodiments both the average value of the figure
of merit and its variation, e.g., the standard deviation, may be
employed together to determine the suitable correction. The optical
correction selected may for example be substantially equal to an
amount between the optical correction yielding the least variation
and the optical correction yielding the least aberration.
[0095] While FIG. 3 illustrates a system 10 wherein the return beam
from the lens 22 is detected and analyzed and, hence, the
integrated effect on the wavefront introduced by the eye and lens
22 is measured, it is to be understood that as mentioned above the
return beam from the eye can also be analyzed without passing
through the lens 22. The test lens 22 may for example be located
between the primary beamsplitter 20 and the target 18. In such an
embodiment, the effect of the lens 22, which has a known deviation
from spherical, can be accounted for by adding or subtracting the
lens 22 effect as appropriate from the eye-only wavefront. To
facilitate this, in some embodiments a sensor (not shown) can be
provided that senses which lens 22 is moved into the patient's line
of sight. The sensor sends a signal representative of the lens 22
(and, hence, of the optical contribution of the lens) to the
processor 40.
[0096] In any case, it may now be appreciated that if desired, the
examiner can use conventional tactics in the steps of selecting
test lenses 22 as if the whole process were done using a
conventional phoropter that requires subjective responses from the
patient. For example, the examiner can use "fogging" in accordance
with principles known in the art to form an artificial image before
the retina of the patient to cause the patient to relax the
above-mentioned accommodative power. However, as a result of the
display capability of the system 10, the examiner can identify the
test lens 22 with which the patient achieves good vision without
accommodation, regardless of patient verbal cooperation or ability
to judge and articulate which lens 22 is preferable.
[0097] Advantageously, embodiments described herein may be suitable
for quantifying accommodation. For example, the variation in the
vision figure of merit may be determined for a variety of
conditions that may induce differing amounts of accommodation.
These conditions may include, for instance, distances from the eye
to the target. Additionally, these conditions may include different
amounts of optical power in the case wherein optics are inserted in
the optical path between the eye and the target. By varying these
conditions, the eye may accommodate. This accommodation may be
characterized, for example, by determining the average value of the
N measurements and the variation in the figure of merit values with
varying condition and its corresponding accommodation response of
the patient. In one approach the examiner may observe the displays
and continue to decrease the focusing power (or increase minus
power) of the test lenses being used, thereby moving the image
behind the patient's retina. For example, if the patient is under
the age of 40 years old, the patient's accommodative power may be
in the range of 1 to 5 diopters, with younger patients tending to
have greater accommodative power. For young hyperopic patients,
determining the onset of accommodation is typically an important
task to avoid an over minus corrective power in prescribing
spectacle lenses. Using a preferred method, the examiner may find
both the accommodative onset and the range of accommodation. The
examiner may start with a higher corrective power lens than what is
optimal for the patient that causes the image of the target to fall
in front of the retina. The approximate optimal power may be
determined from an autorefractor measurement, or measured directly
from the patient's spectacle lenses. The starting power for the
test lens is then preferably chosen to be 1 to 3 diopters higher
than the approximate optimal power. The quality of vision and the
figure of merit value is below the optimal value at this point.
Then the examiner may decrease the corrective power of the test
lens, thereby bringing the target into sharper focus, and an
improved figure of merit of vision which is also shown by the
increase of the average value of the figure of merit. This
continues until a peak average value of the figure of merit is
reached. This peak value is noted as the actual optimal refractive
correction for the patient. So far, the examiner has performed a
process that in many respects is similar to a traditional fogging,
except that the entire procedure is done using a objective method
and no verbal communication is needed. For older patients who have
no accommodative power, any further decrease of the refractive
power of the test lens would cause the figure of merit value to
drop. However, for the young patients, accommodation would be
applied to cancel the over minus effect of the test lens, so that
the patient's focusing effort results in a sharp image of the
target. The average value of the figure of merit does not drop
appreciably at this point, but only slightly and leveling to form a
plateau. Until the over minus power exceeds the accommodative range
of the patient, the figure of merit value curve starts to drop. The
width of the plateau is an indication of the patient's range of
accommodative power. One aspect of this method is that while the
patient may be able to see the target with reasonable sharpness
using his accommodation, the extra efforts to drive the
accommodation causes the focusing power of the eye to be unstable,
which is manifested in the variation of the figure of merit value,
or more specifically from the standard deviation calculation based
on the number of repeated measurements. The error bars representing
the standard deviation if plotted over the average value curve as a
function of the diopter power of the test lenses, similar to the
one shown in FIG. 8 would typically show larger standard deviations
with more efforts to accomplish focusing when looking through the
over minus power lenses (curve not shown). For a young hyperopic
patient, who has not had his eye properly corrected, he may be
conditioned to accommodate and often times the patient actually
prefers to accommodate while looking at distant objects. In this
case, the standard deviation error bar may be smaller than at the
zero accommodation point where the curve first reaches its maximum
value. If in fact this is the case, a prescription may, for
example, be chosen to be a mid point between the zero accommodation
point and the point with the minimum standard deviation. This
example illustrates an aspect of this method in that the figure of
merit data together with its standard deviations over N
measurements, N may be in the range of, e.g., 3 to 10, are
manifesting the subjective response of the patient as he reacts to
various test lenses or other stimuli. Therefore, the aspect of
using the average and the deviation of a figure of merit of vision
has the ability of detecting subjective responses by studying the
variation of the figure of merit over repeated measurements of the
same test lens while the entire measurement is performed in an
objective manner. The examiner can thereby determine the range of
accommodation of the patient based on the objective measurements
provided by the apparatus 10 and also provide a prescription to
reduce accommodation or hyperopia errors.
[0098] As described above, in various embodiments, repetitive
measurements used in determining optical correction, accommodation,
or other vision properties are spaced apart over time intervals
that are sufficiently long to allow the person under examination to
adjust the focus of their eye. Consequently, the information
gathered by the system represents the physical response of the
person to the various conditions to which they are exposed. Thus,
by allowing the person time to adjust to the various test
conditions, and measuring the quality of vision responding to such
conditions repeatedly, objective measurements can be obtained of
the subjective responses of the patient without communicating with
the person verbally, which is required when performing a manifest
refraction using a conventional phoropter.
[0099] Specific examples of conditions that may be modified to
characterize a person vision may include but are not limited to
variations in test optics that are positioned in the line of sight
as well as changes in the target distance. The target distance can
be modified by moving the physical target. In addition, the
apparent distance of the target can be changed by manipulating the
beam of light from the target to the eye.
[0100] The apparent distance of the target can be controlled by
altering the beam of light from the target to the eye. The
patient's eye collects a portion of the light emanating from the
target. The divergence angle of these collected rays will depend on
the location of the target. For example, as is well known, light
from a point object at the infinity is collimated (i.e., the
divergence is approximately zero). An object at a closer distance
will have a larger angle of divergence. As a result, the eye will
perceive the target to be at different locations based on the
divergence of the rays of light entering the patient's eye. Thus,
by adjusting the divergence properties of the rays of light or the
associated wavefronts, the apparent distance of the target seen by
the patient may be controlled. This may be accomplished for example
by adjusting the optics. Such adjustments to the viewing conditions
to which a patient is exposed may help the examiner characterize
the patients vision and provide suitable correction.
[0101] Once the appropriate lens 22 has been identified, the
examiner may indicate this decision by pressing a "finish" button
(not shown), and a printout of the examination result can be output
using a printer or similar device (not shown) that is connected to
the processor 40. The processor 40 may also automatically transmit
the prescription via modem, internet or other appropriate
communication medium to a remote location for lens manufacturing. A
prescription to correct low order aberrations including sphere,
cylinder and axis, can be used for prescribing conventional
ophthalmic lenses, or a "supervision" prescription to correct
higher or even all orders of aberrations can be used to provide
improved vision lenses, such as are described in co-pending U.S.
patent application Ser. No. 10/044,304, filed Oct. 25, 2001 and
entitled "EYEGLASS MANUFACTURING METHOD USING VARIABLE INDEX
LAYER", which is incorporated herein by reference.
[0102] Accordingly, the apparatus and methods described herein
advantageously enable quantification of the subjective response of
the patient by performing objective measurements, i.e., without
relying on verbal communication with the patient regarding the
quality of their vision. Namely, objective measurements can be
performed that determine the subjective response of the patient to
different optical correction. By taking into account the subjective
aspect of the patient's vision, a prescription for correction of
the refractive errors can be obtained that is superior to that
determined by conventional objective measurement approaches.
[0103] Those skilled in the art will appreciate that the methods
and designs described above have additional applications and that
the relevant applications are not limited to those specifically
recited above. Also, the present invention may be embodied in other
specific forms without departing from the essential characteristics
as described herein. The embodiments described above are to be
considered in all respects as illustrative only and not restrictive
in any manner.
* * * * *