Apparatus and method for determining sphere and cylinder components of subjective refraction using objective wavefront measurement

1. A method of characterizing cylinder in a person's eye, comprising:

(a) determining an axis of said eye;

(b) providing a target image having at least one feature that may be oriented either substantially parallel or substantially perpendicular to said axis;

(c) selecting a first refractive correction (D 1 ) when the at least one feature is substantially parallel to said axis, wherein selecting a refractive correction comprises:

(i) repetitively measuring wavefronts emanating from the person's eye for different amounts of refractive correction, said act of repetitively measuring wavefronts comprising performing multiple wavefront measurements using a wavefront sensor;

(ii) producing a plurality of data sets for the plurality of refractive corrections, respectively, said data sets comprising data points indicative of the quality of vision of the person;

(iii) calculating the variation in said plurality of data points to provide an objective assessment of the refractive correction for each of said data sets;

(iv) comparing said variations and selecting an amount of refractive correction based on said comparison;

(d) selecting a second refractive correction (D 2 ) when the at least one feature is substantially perpendicular to said axis; and

(e) determining said cylinder of said patient's eye based at least in part on the values of D 1 and D 2 .

2. The method of claim 1 , wherein the step of selecting an amount of refractive correction further comprises selecting the refractive correction based on the data set having the least variation in a respective plurality of data points.

3. The method of claim 2 wherein said refractive correction comprises cylinder correction.

4. The method of claim 1 wherein:

selecting a refractive correction further comprises:

(v) providing test optics that are changeable to introduce different amounts of refractive correction, wherein said test optics introduce only spherical corrections;

(vi) repetitively measuring wavefronts emanating from the person's eye, said repetitively measuring comprising:

(A) adjusting said test optics to provide an amount of refractive correction to be tested; and

(B) performing multiple wavefront measurement using a wavefront sensor; and

said method further comprises:

obtaining a spherical equivalent value for said eye; and

determining cylinder correction for said eye based on said spherical equivalent value and said first and second refractive corrections.

5. The method of claim 1 wherein D 1 is selected based at least in part on a first plurality of data points that exhibit a least amount of variation for a given amount of refractive correction when the target image is oriented substantially parallel to the axis and D 2 is selected based at least in part on a second plurality of data points that exhibit a least amount of variation for a given amount of refractive correction when the target image is oriented substantially perpendicular to the axis.

6. An apparatus for automatically determining cylinder correction for a patient's vision, said apparatus comprising:

a target image having at least one feature that may be oriented either substantially parallel or substantially perpendicular to an axis of an eye of the patient;

test optics being changeable to provide different amounts of refractive correction;

an actuator for adjusting the test optics so as to change the amounts of refractive correction, wherein a first refractive correction has at least one feature that is substantially parallel to said axis and a second refractive correction has at least one feature that is substantially perpendicular to said axis;

a light source for directing light into an eye of the patient, said light reflecting from tissue in said eye;

a wavefront sensor for measuring a plurality of wavefronts emanating from the patient's eye for different amounts of refractive correction provided by said test optics; and

a processor configured to receive output from said wavefront sensor and to determine a cylinder correction for said patient's eye.

7. The apparatus of claim 6 , wherein said wavefront sensor comprises a Talbot based self-imaging wavefront sensor.

8. The apparatus of claim 6 , further comprising a computer readable medium having a program of instructions stored thereon for causing said processor to execute method acts comprising:

(a) calculating multiple values of a quality of vision metric indicative of the patient's quality of vision, said multiple values being derived at least in part from multiple wavefront measurements for a given refractive correction; and

(b) calculating the variation of the quality of vision metric values for a given refractive correction.

9. The apparatus of claim 8 , wherein said method acts comprise:

performing steps (a) and (b) for a plurality of values of refractive correction; and

determining said cylinder correction based on one or more refractive corrections that result in reduced variation of said quality of vision metric.

10. A method for determining cylinder correction for a patient's eye, comprising:

(a) providing a target image for viewing by the eye, the image having at least one feature that may be oriented in a desired orientation;

(b) measuring a first plurality of successive wavefronts reflected from the eye while the eye is viewing the target image oriented in a first orientation and subjected to a first refractive correction;

(c) measuring a second plurality of successive wavefronts reflected from the eye while the eye is viewing the target image oriented in the first orientation and subjected to a second refractive correction;

(d) determining a first variation associated with the first plurality of successive wavefront measurements and a second variation associated with the second plurality of successive wavefront measurements;

(e) comparing the first and second variations and selecting either the first refractive correction or the second refractive correction as a first desired refractive correction (D 1 ) based on the comparison;

(f) measuring a third plurality of successive wavefronts reflected from the eye while the eye is viewing the target image oriented in a second orientation and subjected to a third refractive correction;

(g) measuring a fourth plurality of successive wavefronts reflected from the eye while the eye is viewing the target image oriented in the second orientation and subjected to a fourth refractive correction;

(h) determining a third variation associated with the third plurality of successive wavefront measurements and a fourth variation associated with the fourth plurality of successive wavefront measurements; and

(i) comparing the third and fourth variations and selecting either the third refractive correction or the fourth refractive correction as a second desired refractive correction (D 2 ) based on the comparison; and

(j) calculating a cylinder correction for the patient's eye based at least in part on the selected first desired refractive correction (D 1 ) and second desired refractive correction (D 2 ).

11. The method of claim 10 wherein the first and second refractive corrections are selected to be within a first range of values containing a first spherical equivalent value as a median value and the third and fourth refractive corrections are selected to be within a second range of values containing a second spherical equivalent value as a median value.

12. The method of claim 10 wherein the first and second refractive corrections are selected to be within a first range of values containing a first spherical equivalent value as a median value.

13. The method of claim 10 further comprising obtaining a spherical equivalent value for the eye, wherein the cylinder correction is calculated based on the spherical equivalent value and D 1 .

14. The method of claim 10 wherein the first refractive correction comprises a first cylinder correction and the second refractive correction comprises a second cylinder correction.

15. The method of claim 10 wherein the first refractive correction comprises a first spherical correction and the second refractive correction comprises a second spherical correction.