Method of verifying performance of an optical measurement instrument with a model eye and an optical measurement instrument employing such a method

1. A method, comprising:

receiving a light beam from a model eye at an optical measurement instrument having an optical axis;

producing image data, including light spot data for a plurality of light spots, from the received light beam;

determining an observed location of a corneal reflex from the model eye within an image representing the image data; and

determining an angle of misalignment between an axis normal to a front surface of the model eye and the optical axis of the optical measurement instrument from the observed location of the corneal reflex within the image,

wherein determining the angle of misalignment between the axis normal to the front surface of the model eye and the optical axis of the optical measurement instrument from the determined location of the corneal reflex within the image comprises:

establishing an expected location of the corneal reflex within the image; and

using a ray tracing algorithm to calculate the angle of misalignment between the expected location and the observed location.

2. The method of claim 1 , further comprising measuring at least one of a sphere value and a cylinder value for the model eye from the light spot data.

3. The method of claim 2 , further comprising compensating the at least one measured value to account for the angle of misalignment.

4. The method of claim 3 , further comprising:

comparing the at least one compensated measured value to a corresponding calibration value for the optical measurement instrument; and

providing an indication that the optical measurement instrument is operating properly when a difference between the compensated measured value and the corresponding calibration value is less than a specified tolerance.

5. The method of claim 1 , wherein producing the image data from the received light beam, comprises:

providing the received light beam to a Shack-Hartmann wavefront sensor; and

outputting the image data from the Shack-Hartmann wavefront sensor.

6. The method of claim 1 , further comprising:

aligning the axis normal to the model eye and the optical axis of the optical measurement instrument to within a predetermined tolerance; and

generating calibration image data while the axis normal to the model eye and the optical axis of the optical measurement instrument are aligned within the predetermined tolerance; and

processing the calibration image data to extract the calibration values.

7. The method of claim 1 , wherein determining an observed location of a corneal reflex from the model eye within an image represented by the image data comprises:

determining a boundary of a portion of the image corresponding to an iris of the model eye; and

determining the observed location of the corneal reflex with respect to the boundary.

8. The method of claim 1 , further comprising displaying the angle of misalignment to an operator of the optical measurement instrument.

9. A measurement instrument, comprising:

one or more light sources configured to illuminate a model eye;

a light spot generator configured to receive light from the model eye and to generate a plurality of light spots from the light received from the illuminated object;

a detector configured to detect the light spots and for outputting image data, including light spot data for the plurality of light spots;

a processor configured to process the image data to determine an alignment between the measurement instrument and the model eye by:

determining an observed location of a corneal reflex from the model eye within an image representing the light spot data; and

determining an angle of misalignment between an axis normal to the model eye and an optical axis of the measurement instrument from the observed location of the corneal reflex within the image,

wherein determining the angle of misalignment between the axis normal to the front surface of the model eye and the optical axis of the measurement instrument from the determined location of the corneal reflex within the image comprises:

establishing an expected location of the corneal reflex within the image; and

using a ray tracing algorithm to calculate the angle of misalignment between the expected location and the observed location.

10. The measurement instrument of claim 9 , wherein the measurement instrument is configured to measure at least one of a sphere value and a cylinder value for the model eye from the light spot data.

11. The measurement instrument of claim 10 , wherein the processor is further configured to compensate the at least one measured value to account for the angle of misalignment.

12. The measurement instrument of claim 11 , wherein the processor is further configured to:

compare the at least one compensated measured value to a corresponding calibration value for the measurement instrument; and

provide an indication that the measurement instrument is operating properly when a difference between the compensated measured value and the corresponding c calibration value is less than a specified tolerance.

13. The measurement instrument of claim 9 , wherein the detector includes a Shack-Hartmann wavefront sensor.

14. The measurement instrument of claim 9 , wherein establishing the expected location of the corneal reflex within the image comprises:

aligning the axis normal to the front surface of the model eye and the optical axis of the optical measurement instrument to within a predetermined tolerance;

generating calibration image data while the axis normal to the model eye and the optical axis of the optical measurement instrument are aligned within the predetermined tolerance; and

processing the calibration image data to extract the calibration values.

15. The measurement instrument of claim 9 , wherein determining the observed location of the corneal reflex from the model eye within the image represented by the image data comprises:

determining a boundary of a portion of the image corresponding to an iris of the model eye; and

determining the observed location of the corneal reflex with respect to the boundary.

16. The measurement instrument of claim 9 , further comprising a display, and wherein the processor is configured to display an indication of the angle of misalignment on the display.

17. A method of determining a misalignment between a measurement instrument and a model eye used to verify correct operation of the measurement instrument, by determining a difference between: (1) an observed location of a corneal reflex in an image produced by the measurement instrument from the model eye, and (2) an expected location of the corneal reflex, and using a ray tracing algorithm to calculate an amount misalignment that corresponds to a difference between the observed location and the expected location.

18. The method of claim 17 , further comprising determining the expected location of the corneal reflex from a calibration image generated when the measurement instrument is aligned with the model eye.

19. The method of claim 17 , further comprising determining the observed location of a corneal reflex by:

determining a boundary of a portion the image corresponding to an iris of the model eye; and

determining the observed location of the corneal reflex with respect to the boundary.

20. A method, comprising:

receiving a light beam from a model eye at an optical measurement instrument having an optical axis;

producing image data, including light spot data for a plurality of light spots, from the received light beam;

determining an observed location of a corneal reflex from the model eye within an image representing the image data;

defining an analysis area within an image represented by the image data, wherein the analysis area is centered on the observed location of the corneal reflex;

measuring at least one of a sphere value and a cylinder value for the model eye from a portion of the light spot data corresponding to light spots within the analysis area; and

determining an angle of misalignment between an axis normal to a front surface of the model eye and the optical axis of the optical measurement instrument from the observed location of the corneal reflex within the image,

wherein determining the angle of misalignment between the axis normal to the front surface of the model eye and the optical axis of the optical measurement instrument from the determined location of the corneal reflex within the image comprises:

establishing an expected location of the corneal reflex within the image; and

using a ray tracing algorithm to calculate the angle of misalignment between the expected location and the observed location.