Apparatus and method for determining sphere and cylinder components of subjective refraction using objective wavefront measurement
View Patent ↗An apparatus for determining spherical and cylinder components of subjective refraction of a patient's vision includes a wavefront measurement device that can produce a measure of quality of vision in a return beam from the patient's eye viewing a target through a corrective test lens in the apparatus. The corrective lenses may be varied and a plurality of measurements of quality of vision may be obtained and analyzed to determine the spherical and cylinder components. Accordingly, the eye examiner may conduct a refraction examination without a subjective response from the patient.
1. A method of characterizing an eye having astigmatism, said astigmatism being defined by cylinder and axis, said method comprising:
(a) measuring said axis for said eye;
(b) disposing a target in a line of sight of said eye, the target comprising at least one feature that may be oriented in a desired orientation with respect to said eye;
(c) orienting said target such that said at least one feature is oriented either substantially parallel or substantially perpendicular to said axis, respectively;
(d) disposing test optics in said line-of-sight between said eye and said target, said test optics being changeable to introduce different amounts of defocus;
(e) measuring wavefronts emanating from said eye with a wavefront sensor for different amounts of defocus; and
(f) determining a defocus correction, D 1 , based on said wavefront measurements for different amounts of defocus.
2. The method of claim 1 wherein said at least one feature comprises a plurality of substantially parallel lines.
3. The method of claim 1 , further comprising determining quality of vision from said wavefront measurements.
4. The method of claim 3 , further comprising measuring variation in multiple measurements of the quality of vision and determining said defocus correction, D 1 , from said variation in quality of vision.
5. The method of claim 4 , wherein the defocus correction, D 1 , yields reduced variation in said quality of vision.
6. The method of claim 1 , further comprising determining a spherical equivalent for said astigmatic eye.
7. The method of claim 6 , further comprising determining said cylinder in said eye by reference to said defocus correction, D 1 , and said spherical equivalent.
8. The method of claim 1 , further comprising rotating said target by about 90° and determining a defocus correction, D 2 , for said rotated target.
9. The method of claim 8 , further comprising determining said cylinder in said eye by reference to said defocus correction values, D 1 and D 2 .
10. The method of claim 1 , wherein said test optics are changed to provide a different amounts of defocus by substituting in optics having a different amount of defocus.
11. A system for determining cylinder in an astigmatic eye, said system comprising:
a wavefront sensor for measuring wavefronts emanating from the astigmatic eye;
a target comprising at least one feature that may be oriented in a desired orientation for viewing by said astigmatic eye, cylinder in said eye being substantially undetectable by said eye when said target is suitably oriented;
test optics disposed along an optical path between said astigmatic eye and said target, said test optics being changeable to introduce different amounts of defocus; and
a processor configured to receive output from said wavefront sensor and to determine the cylinder for said eye's therefrom.
12. The system of claim 11 , further comprising a light source disposed to direct light into the astigmatic eye, said light reflecting from tissue in said eye.
13. The system of claim 11 , further comprising an actuator in communication with said processor, said actuator changing the test optics so as to vary the amount of defocus.
14. The system of claim 11 , wherein said test optics comprises optics of a phoropter.
15. The system of claim 11 wherein said at least one feature comprises a plurality of substantially parallel lines.
16. The system of claim 15 , wherein said target is adjustable such that said plurality of substantially parallel lines can be rotated.
17. The system of claim 16 , wherein said target is adjustable such that said plurality of substantially parallel lines can be rotated in response to signals from said processor.
18. The system of claim 16 , wherein said target is adjustable such that said plurality of substantially parallel lines can be rotated in response to operator control.
19. The system of claim 11 , 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 from multiple wavefront measurements, said values of said quality of vision metric indicative of quality of vision of said astigmatic eye; and
(b) calculating the variation of the quality of vision metric values for a given amount of defocus.
20. The system of claim 19 , wherein said method comprises:
performing steps (a) and (b) for a range of values of defocus provided by the test optics; and
selecting a defocus correction that yields a reduced value of variation of the quality of vision metric.