# US 7,744,217 B2 · Apparatus and method for determining an eyeglass prescription for a vision defect of an eye

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- Number: US 7,744,217 B2
- Document ID: US7744217B2
- Status: Granted
- Kind: B2
- Application number: 11/840,688
- Filed: 2007-08-17
- Published: 2009-01-15
- Granted: 2010-06-29
- Earliest claimed: 2007-07-09
- Assignees: Carl Zeiss Vision GmbH
- Inventors: Jesus Miguel Guillen Cabeza; Timo Kratzer
- Web page: https://patentgrep.com/patent/US7744217B2

## CPC

- A61B 3/1015: {for wavefront analysis}
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)

## Abstract

The disclosure relates to a method for determining an eyeglass prescription for a vision defect of an eye. In certain embodiments, the method includes optimizing a caustic in the area of the retina of the eye for a light ray passing through the eyeglass prescription and the eye. The disclosure further relates to an apparatus that is suitable for carrying out the method.

## Claims

### Claim 1

A method for determining an eyeglass prescription for a vision defect of an eye, the method comprising:
mathematically varying a preliminary prescription within a target space to determine the eyeglass prescription,
wherein mathematically varying the preliminary prescription comprises using an electronic processor to calculate, for each of multiple sets of parameter values, a value of a metric related to a caustic of a light ray passing through a corrective optic and the eye, each set of parameter values corresponding to a different prescription of a corrective optic, and
the eyeglass prescription is selected as the prescription for which the caustic meets predetermined requirements in an area of the retina of the eye.

### Claim 2 (depends on 1)

The method of claim 1, wherein mathematically varying the preliminary prescription comprises:
a) providing refractive properties of the eye;
b) providing the sets of parameter values describing the different prescriptions of the corrective optic;
c) providing a method for determining from the sets of parameter values a target set which provides the eyeglass prescription for the refractive properties of the eye which were established in step a);
d) determining, for a first set of the parameter values, values for at least two submetrics in associated different propagation stages of the light ray passing through the optical system comprising the eye and corrective optic corresponding to the prescription described by first set;
e) determining a value of an overall metric from a weighted sum of the submetric values, the overall metric being the metric related to the caustic of the light ray passing through the corrective optic and the eye;
f) performing the steps d) and e) for additional sets of the parameter values that are required for the determination of the target set according to the method established in step c);
g) selecting from the sets of parameter values on which the steps d) and e) were performed the target set which delivers the overall target metric; and
h) determining the eyeglass prescription by taking the target set selected in step g) into account.

### Claim 3 (depends on 1)

The method of claim 1, wherein mathematically varying the preliminary prescription comprises:
a) providing refractive properties of the eye;
b) providing the sets of parameter values describing the different prescriptions of the corrective optic;
c) providing a method for determining from the sets of parameter values a target set which provides the eyeglass prescription for the refractive properties of the eye which were established in step a);
d) determining, for a first set of the parameter values, a value for at least one metric that characterizes the energy density of the intensity distribution in the three-dimensional space of a light bundle passing through an optical system comprising the eye and a corrective optic corresponding to the prescription described by the first set;
e) performing the step d) for additional sets of the parameter values that are required for the determination of the target set according to the method established in step c);
f) selecting from the sets of parameter values on which the step d) was performed the target set which delivers the overall target metric; and
g) determining the eyeglass prescription by taking the target set selected in step f) into account.

### Claim 4 (depends on 2)

The method of claim 2, wherein the refractive properties of the eye are determined based on a wavefront emanating from the eye.

### Claim 5 (depends on 4)

The method of claim 4, wherein the wavefront is measured using a Shack-Hartmann method.

### Claim 6 (depends on 4)

The method of claim 4, wherein the wavefront is measured using a Tscherning method.

### Claim 7 (depends on 4)

The method of claim 4, wherein the wavefront is measured using a ray-tracing method.

### Claim 8 (depends on 2)

The method of claim 2, wherein the refractive properties of the eye are determined by measuring the tomography of the eye.

### Claim 9 (depends on 2)

The method of claim 2, wherein the sets of parameter values describing the different prescriptions of the corrective optic include values for sphere, cylinder and axis.

### Claim 10 (depends on 2)

The method of claim 2, wherein the sets of parameter values describing the different prescriptions of the corrective optic include values for principal curvature radii.

### Claim 11 (depends on 2)

The method of claim 2, wherein the sets of parameter values describing the different prescriptions of the corrective optic are determined from coefficients of an algebraic basis suitable for the description of the eyeglass prescription.

### Claim 12 (depends on 11)

The method of claim 11, wherein the algebraic basis comprises Zernike coefficients or Taylor coefficients.

### Claim 13 (depends on 2)

The method of claim 2, wherein the method for determining the target set is a Newton-Raphson method, a hill-climbing method, or a method where within a search space of parameter values, all of the sets of parameter values in the search space are examined with a view to finding an optimum.

### Claim 14 (depends on 2)

The method of claim 2, wherein the submetrics are ray quality metrics.

### Claim 15 (depends on 14)

The method of claim 14, wherein the ray quality metrics comprise the Strehl ratio.

### Claim 16 (depends on 14)

The method of claim 14, wherein the ray quality metrics correspond to an energy enclosed within a cross-section that is traversed by the light ray.

### Claim 17 (depends on 2)

The method of claim 2, wherein the submetrics are geometric metrics.

### Claim 18 (depends on 17)

The method of claim 17, wherein the geometric metrics include a mean curvature of a wavefront associated with the light ray.

### Claim 19 (depends on 2)

The method of claim 2, wherein all submetrics are assigned equal weight.

### Claim 20 (depends on 2)

The method of claim 2, wherein at least one of the submetrics in a preferred propagation stage is given more weight than at least one of the submetrics in the propagation stages before and/or behind the preferred propagation stage.

### Claim 21 (depends on 20)

The method of claim 20, wherein at least one of the submetrics in the propagation stages before or behind the preferred propagation stage are given less weight with increasing distance from the preferred propagation stage.

### Claim 22 (depends on 2)

The method of claim 2, wherein the overall target metric is the maximum value of the overall metric or a value which deviates from the maximum value by a minor amount.

### Claim 23 (depends on 2)

The method of claim 2, wherein the method steps a) to h) are performed for different states of accommodation of the eye.

### Claim 24 (depends on 23)

The method of claim 23, further comprising:
i) selecting a final target parameter set which delivers a final overall target metric from the overall target metrics determined for each of the different states of accommodation of the eye,
j) determining the eyeglass prescription by taking the final target parameter sets selected in step j) into account.

### Claim 25 (depends on 1)

An electronic processing system, configured to execute the method claim 1.

### Claim 26 (depends on 1)

A computer-readable medium having computer executable instructions for performing claim 1.

### Claim 27 (depends on 1, 25)

The electronic processing system of claim 25, wherein executing the method of claim 1 comprises sending data over a network.

### Claim 28 (depends on 25)

The electronic processing system of claim 25, comprising a computer with a display device and an input device, the computer being configured to execute one or more steps of the method.

### Claim 29

An apparatus comprising:
an analyzer device comprising an electronic processor configured, during operation, to determine an eyeglass prescription for a vision defect of an eye by mathematically varying a preliminary prescription within a target space,
wherein mathematically varying the preliminary prescription comprises using the electronic processor to calculate, for each of multiple sets of parameter values, a value of a metric related to a caustic of a light ray passing through a corrective optic and the eye, each set of parameter values corresponding to a different prescription of a corrective optic, and
the eyeglass prescription is selected as the prescription for which the caustic meets predetermined requirements in an area of the retina of the eye.

### Claim 30 (depends on 29)

The apparatus of claim 29, further comprising:
an input device for providing the refractive properties of the eye to the analyzer device, where the analyzer device is configured, during operation, to
i) determine values for at least two submetrics for a first set of the parameter values describing a prescription of a corrective optic, the values for the least two submetrics being determined in associated different propagation stages of a light ray passing through an optical system comprising the eye and the corrective optic corresponding to the first set of parameter values;
ii) determine a value of an overall metric from a weighted sum of the submetric values;
iii) repeat steps i) and ii) for additional sets of the parameter values, each describing different prescriptions of the corrective optic;
iv) select from the sets of parameter values on which the steps i) and ii) were performed a target set which delivers an overall target metric; and
v) determine the eyeglass prescription by taking the target set selected in step iv) into account.

### Claim 31 (depends on 29)

The apparatus of claim 29, further comprising:
an input device for providing the refractive properties of the eye to the analyzer device, where the analyzer device is configured, during operation, to
i) provide the sets of parameter values describing the different prescriptions of the corrective optic;
ii) provide a method for determining from the sets of parameter values a target set which provides the eyeglass prescription for the refractive properties of the eye which were provided in step i);
iii) determines, for a first set of the parameter values, a value for at least one metric that characterizes the energy density of the intensity distribution in the three-dimensional space of a light bundle passing through the optical system comprising the eye and a corrective optic corresponding to the prescription described by the first set;
iv) performs step iii) for additional sets of the parameter values that are needed for determining the target set in accordance with the method provided in step ii);
v) select from the sets of parameter values on which step iv) was performed the target set that delivers the overall target metric; and
vi) determine the eyeglass prescription by taking the target set determined in step v) into account.

### Claim 32 (depends on 30)

The apparatus of claim 30, wherein the analysis in the analyzer device takes place close to the location where the data are acquired.

### Claim 33 (depends on 30)

The apparatus of claim 30, wherein the analysis in the analyzer device takes place far from the location where the data are acquired.

### Claim 34 (depends on 30)

The apparatus of claim 30, wherein the input device comprises a keyboard through which data about the refractive properties of the eye can be entered.

### Claim 35 (depends on 30)

The apparatus of claim 30, wherein the input device is connected to a wavefront measurement device for measuring the refractive properties of the eye.

### Claim 36 (depends on 30)

The apparatus of claim 30, wherein the input device is connected to an aberrometer according to the Shack-Hartmann principle, the Tscherning method, or the ray-tracing method.

### Claim 37 (depends on 30)

The apparatus of claim 30, wherein the input device is connected to a tomograph for the eye.