Method and system for improving accuracy in autorefraction measurements by including measurement distance between the photoreceptors and the scattering location in an eye

1. A method for determining a distance from a photoreceptor to a scattering location of a retina of an eye of a subject, the method comprising:

performing an autorefraction;

providing an optical system including a light source;

using the optical system, directing light from the light source to form two dots of light on the eye;

receiving an adjustment of the optical system until the two dots appear to the subject to overlap; and

based on the adjustment, calculating the distance from the photoreceptor to the scattering location.

2. The method of claim 1 , further comprising directing light from the light source through two apertures of a Scheiner disk so as to project the two dots of light onto the eye of the subject.

3. The method of claim 2 , wherein receiving the adjustment includes receiving an adjustment to a distance between the light source and the Scheiner disk by moving the light source from a nominal position to a focused position until the two dots appear to the subject to overlap.

4. The method of claim 2 , wherein calculating the distance between the photoreceptors and a scattering location is based on the distance between the light source and the Scheiner disk when the two dots appear to the subject to overlap.

5. The method of claim 1 , further comprising performing an autorefraction of the eye to calculate a sphere and cylinder value for the eye.

6. The method of claim 5 , further comprising adjusting the sphere and cylinder calculation to include the calculated distance between the photoreceptor and the scattering location.

7. The method of claim 1 , wherein the distance from the photoreceptor to the scattering location is equal to a distance from the photoreceptor to a choroid of the eye.

8. A method for determining a distance from a photoreceptor to a scattering location of a retina of an eye of a subject, comprising:

performing an autorefraction;

providing an optical system including a light source;

using the optical system, directing light from the light source to the eye;

from the light, forming a speckle pattern located along an optical path between the light source and the eye;

receiving an adjustment of the optical system until the speckle pattern has a predetermined appearance to the subject; and

based on the adjustment, calculating the distance from the photoreceptor to the scattering location.

9. The method of claim 8 , wherein receiving an adjustment includes receiving an adjustment to the optical system until the speckle pattern appears to the subject to be stationary.

10. The method of claim 8 , wherein receiving an adjustment includes receiving an adjustment to the optical system until the speckle appears to the subject to have a motion that is just barely observable to move in a first direction.

11. The method of claim 10 , wherein receiving an adjustment includes receiving an adjustment to the optical system until the speckle motion is just barely visible to the subject in a direction that is opposite first direction.

12. The method of claim 8 , further comprising:

rotating the speckle pattern

focusing the eye on the rotating speckled light pattern;

adjusting a distance between the speckled light pattern and the eye until the speckled light pattern appears to be stationary;

measuring the distance between the speckled light pattern and the eye when the speckled light pattern appears to the subject to be stationary; and

calculating the distance between the photoreceptor and the scattering location is based on the distance between the speckled light pattern and the eye.

13. An ophthalmic system, comprising:

a first optical system, comprising:

a first light source;

a projecting optical system configured to deliver light from the first light onto a retina of an eye of a subject;

an imaging system configured to collect light scattered by the retina;

a sensor configured to receive light returned by the retina; and

an adjustable optical system configured for determining a distance from a photoreceptor to a scattering location of a retina of an eye.

14. The ophthalmic system of claim 13 , wherein the adjustable optical system includes a second light source and is configured to:

direct light from the second light source to the eye;

form two dots of light onto the eye using light from the second light source;

be adjusted until the two dots appear to the subject to overlap; and

based on the adjustment, calculate the distance from the photoreceptor to the scattering location;

wherein the calculated distance is used to adjust a sphere and cylinder calculation made using the projecting optical system.

15. The ophthalmic system of claim 13 , wherein the adjustable optical system includes a second light source and is configured to:

direct light from the second light source to the eye;

form a speckle pattern located along an optical path between the second light source and the eye using light from the second light source;

be adjusted until the speckle pattern has a predetermined appearance to the subject; and

based on the adjustment, calculate the distance from the photoreceptor to the scattering location;

wherein the calculated distance is used to adjust a sphere and cylinder calculation made using the projecting optical system.

16. The ophthalmic system of claim 13 , wherein the first optical system is an autorefractor.

17. The ophthalmic system of claim 13 , wherein the first optical system is a wavefront aberrometer and the sensor is a wavefront sensor.

18. The ophthalmic system of claim 13 , further comprising a treatment system configured to treat myopia and astigmatism using the Lasik procedure.

19. The ophthalmic system of claim 13 , wherein the adjustable optical system includes the first light source and is configured to:

direct light from the first light source to the eye;

form two dots of light onto the eye using light from the first light source;

be adjusted until the two dots appear to the subject to overlap; and

based on the adjustment, calculate the distance from the photoreceptor to the scattering location;

wherein the calculated distance is used to adjust a sphere and cylinder calculation made using the projecting optical system.

20. The ophthalmic system of claim 13 , wherein the adjustable optical system includes the first light source and is configured to:

direct light from the first light source to the eye;

form a speckle pattern located along an optical path between the first light source and the eye using light from the first light source;

be adjusted until the speckle pattern has a predetermined appearance to the subject; and

based on the adjustment, calculate the distance from the photoreceptor to the scattering location;

wherein the calculated distance is used to adjust a sphere and cylinder calculation made using the projecting optical system.