Rapid, automatic measurement of the eye's wave aberration

• US 6,299,311 B1
• Filed: 03/24/2000
• Issued: 10/09/2001
• Est. Priority Date: 10/21/1999
• Status: Expired due to Term

• Current Assignee: University of Rochester
• Original Assignee: University of Rochester
• Inventors: Williams, David R., Singer, Benjamin D., Yoon, Geun-Young, Hofer, Heidi, Vaughn, William J.
• Primary Examiner(s): MANUEL, GEORGE C
• Application Number:
  US09/533,809
• Time in Patent Office: 564 Days
• Field of Search: 351/205, 351/211, 351/212, 351/219, 351/221, 351/246, 351/247, 356/121, 356/122, 356/123
• US Class Current: 351/221
• CPC Class Codes: A61B 3/1015 for wavefront analysis
• CPC Class Codes: G01J 9/00 Measuring optical phase difference devices or arrangements for controlling the phase of light beams G02F1/01; Determining degree of coherence; Measuring optical wavelength spectrometry G01J3/00

Abstract

A wavefront aberration of an eye is determined, e.g., in real time. The eye is illuminated, and the light reflected from the retina is converted into spots with a device such as a Hartmann-Shack detector. The displacement of each spot from where it would be in the absence of aberration allows calculation of the aberration. Each spot is located by an iterative technique in which a corresponding centroid is located in a box drawn on the image data, a smaller box is defined around the centroid, the centroid is located in the smaller box, and so on. The wavefront aberration is calculated from the centroid locations by using a matrix in which unusable data can be eliminated simply by eliminating rows of the matrix. Aberrations for different pupil sizes are handled in data taken for a single pupil size by renormalization.

Claims

1. A method of measuring a wavefront aberration of an eye, the method comprising:

(a) taking image data from the eye, the image data comprising a plurality of spots having positions determined by the wavefront aberration;

(b) defining a plurality of search boxes in the image data;

(c) determining the positions of the spots by;

(i) locating a centroid in each of the search boxes;

(ii) replacing each of the search boxes with a search box of reduced size, the search box of reduced size being clipped to fit entirely within the search box which is replaced;

(iii) locating the centroid in each of the search boxes of reduced size; and

(iv) repeating steps (ii) and (iii) until each of the search boxes of reduced size reaches a minimum size; and

(d) calculating the wavefront aberration in accordance with the positions of the spots.

2. The method of claim 1, wherein step (c)(ii) comprises forming the search box of reduced size by:

(A) reducing a size of the search box to be replaced by one pixel in each direction to form a pixel-reduced search box;

(B) centering the pixel-reduced search box on the centroid located in step (c)(i); and

(C) clipping the pixel-reduced search box to the boundaries of the search box to be replaced to fit entirely within the search box to be replaced.

3. The method of claim 1, wherein the minimum size in step (c)(iv) is a diffraction limited size.

4. The method of claim 1, wherein steps (c)(i) and (c)(iii) are performed only in accordance with pixels in the image data whose intensities lie between a lower threshold and an upper threshold.

5. The method of claim 4, further comprising prompting an operator to select the lower threshold and the upper threshold.

6. A method of measuring a wavefront aberration of an eye, the method comprising:

(a) taking image data from the eye, the image data comprising a plurality of spots having positions determined by the wavefront aberration;

(b) defining a plurality of search boxes in the image data by;

(i) defining a central search box;

(ii) defining a first set of search boxes relative to the central search box;

(iii) locating centroids in the first set of search boxes; and

(iv) defining successive sets of search boxes, each successive set defined in accordance with locations of centroids in a previous set;

(c) determining the positions of the spots by;

(i) locating a centroid in each of the search boxes;

(ii) replacing each of the search boxes with a search box of reduced size;

(iii) locating the centroid in each of the search boxes of reduced size; and

(iv) repeating steps (ii) and (iii) until each of the search boxes of reduced size reaches a minimum size; and

(d) calculating the wavefront aberration in accordance with the positions of the spots.

7. The method of claim 6, wherein the central search box is defined about a center point which is a position which one of the spots at a center of the image data would occupy in an absence of the wavefront aberration.

8. The method of claim 6, wherein step (a) comprises forming the spots by a plurality of lenslets having a lenslet spacing C.

9. The method of claim 8, wherein at least some of the plurality of search boxes have linear dimensions scaled from C by a factor of less than one.

10. The method of claim 9, further comprising prompting an operator for the factor.

11. The method of claim 8, wherein the central search box is defined about a center point which is a position which one of the spots at a center of the image would occupy in an absence of the wavefront aberration.

12. The method of claim 11, wherein:

the first set of search boxes defined in step (b)(ii) have centers spaced from the center point of the central search box by C; and

each successive set of search boxes defined in step (b)(iv) have centers spaced from the centroids in the previous set by C.

13. The method of claim 6, wherein, in step (c)(ii), the search box of reduced size is clipped to fit entirely within the search box which is replaced.

14. A method of measuring a wavefront aberration of an eye, the method comprising:

(a) taking image data from the eye while correcting for a spatial inhomogeneity in a retina of the eye, the image data comprising a plurality of spots having positions determined by the wavefront aberration;

(b) defining a plurality of search boxes in the image data;

(c) determining the positions of the spots by

(i) locating a centroid in each of the search boxes;

(ii) replacing each of the search boxes with a search box of reduced size;

(iii) locating the centroid in each of the search boxes of reduced size; and

(iv) repeating steps (ii) and (iii) until each of the search boxes of reduced size reaches a minimum size; and

(d) calculating the wavefront aberration in accordance with the positions of the spots.

15. The method of claim 14, wherein step (a) comprises illuminating the eye with near infrared light.

16. The method of claim 14, wherein said step of correcting for the spatial inhomogeneity of the retina of the eye comprises illuminating the eye with light of a coherence length selected such that the spatial inhomogeneity does not appear in the image data.

17. The method of claim 16, wherein the coherence length is 30 microns.

18. The method of claim 16, wherein said step of correcting for the spatial inhomogeneity of the retina of the eye comprises:

(i) providing an optical scanning device;

(ii) illuminating the eye with light which has been scanned by the optical scanning device; and

(iii) causing the light emerging from the eye to be scanned again by the optical scanning device and subsequently made indent on a detector such that the light is stationary as the light is made indent on the detector.

19. The method of claim 18, wherein:

the detector comprises a camera having a frame time; and

the optical scanning device performs a plurality of scans within a single one of said frame time.

20. The method of claim 19, wherein the optical scanning device has a scanning frequency of 400-600 Hz.

21. The method of claim 19, wherein the optical scanning device scans with an angular extent of less than 0.5 degrees.

22. The method of claim 18, wherein the optical scanning device comprises a single scanning/de-scanning mirror which scans both the light which illuminates the eye and the light emerging from the eye.

23. A method of measuring a wavefront aberration of an eye, the method comprising:

(a) taking image data from a plurality of locations in the eye, the image data comprising a plurality of spots corresponding to the plurality of locations and having positions determined by the wavefront aberration, the data from the plurality of locations in the eye being taken by scanning light into the eye such that the plurality of spots are separated in time;

(b) defining a plurality of search boxes in the image data;

(c) determining the positions of the spots by

(i) locating a centroid in each of the search boxes;

(ii) replacing each of the search boxes with a search box of reduced size, the search box of reduced size being clipped to fit entirely within the search box which is replaced;

(iii) locating the centroid in each of the search boxes of reduced size; and

(iv) repeating steps (ii) and (iii) until each of the search boxes of reduced size reaches a minimum size; and

(d) calculating the wavefront aberration in accordance with the positions of the spots.

24. A device for measuring a wavefront aberration of an eye, the device comprising:

image data taking means for taking image data from the eye, the image data comprising a plurality of spots having positions determined by the wavefront aberration; and

data processing means, receiving the image data, for;

(a) defining a plurality of search boxes in the image data;

(b) determining the positions of the spots by;

(i) locating a centroid in each of the search boxes;

(ii) replacing each of the search boxes with a search box of reduced size, the search box of reduced size being clipped to fit entirely within the search box which is replaced;

(iii) locating the centroid in each of the search boxes of reduced size; and

(iv) repeating steps (ii) and (iii) until each of the search boxes of reduced size reaches a minimum size; and

(c) calculating the wavefront aberration in accordance with the positions of the spots.

25. The device of claim 24, wherein the data processing means performs step (b)(ii) by forming the search box of reduced size by:

(A) reducing a size of the search box to be replaced by one pixel in each direction to form a pixel-reduced search box;

(B) centering the pixel-reduced search box on the centroid located in step (c)(i); and

(C) clipping the pixel-reduced search box to the boundaries of the search box to be replaced to fit entirely within the search box to be replaced.

26. The device of claim 24, wherein the minimum size in step (b)(iv) is a diffraction limited size.

27. The device of claim 24, wherein steps (b)(i) and (b)(iii) are performed only in accordance with pixels in the image data whose intensities lie between a lower threshold and an upper threshold.

28. The device of claim 27, wherein the data processing means comprises interface means for prompting an operator to select the lower threshold and the upper threshold.

29. A device for measuring a wavefront aberration of an eye, the device comprising:

image data taking means for taking image data from the eye, the image data comprising a plurality of spots having positions determined by the wavefront aberration; and

data processing means, receiving the image data, for;

(a) defining a plurality of search boxes in the image data by;

(i) defining a central search box;

(ii) defining a first set of search boxes relative to the central search box;

(iii) locating centroids in the first set of search boxes; and

(iv) defining successive sets of search boxes, each successive set defined in accordance with locations of centroids in a previous set;

(b) determining the positions of the spots by;

(i) locating a centroid in each of the search boxes;

(ii) replacing each of the search boxes with a search box of reduced size;

(iii) locating the centroid in each of the search boxes of reduced size; and

(iv) repeating steps (ii) and (iii) until each of the search boxes of reduced size reaches a minimum size; and

(c) calculating the wavefront aberration in accordance with the positions of the spots.

30. The device of claim 29, wherein the central search box is defined about a center point which is a position which one of the spots at a center of the image data would occupy in an absence of the wavefront aberration.

31. The device of claim 29, wherein the image data taking means comprises a plurality of lenslets having a lenslet spacing C for forming the spots.

32. The device of claim 31, wherein at least some of the plurality of search boxes have linear dimensions scaled from C by a factor of less than one.

33. The device of claim 32, wherein the data processing means comprises interface means for prompting an operator for the factor.

34. The device of claim 31, wherein the central search box is defined about a center point which is a position which one of the spots at a center of the image would occupy in an absence of the wavefront aberration.

35. The device of claim 34, wherein:

the first set of search boxes defined in step (a)(ii) have centers spaced from the center point of the central search box by C; and

each successive set of search boxes defined in step (b)(iv) have centers spaced from the centroids in the previous set by C.

36. The device of claim 29, wherein, in step (b)(ii), the search box of reduced size is clipped to fit entirely within the search box which is replaced.

37. A device for measuring a wavefront aberration of an eye, the device comprising:

image data taking means for taking image data from the eye while correcting for a spatial inhomogeneity in a retina of the eye, the image data comprising a plurality of spots having positions determined by the wavefront aberration; and

data processing means, receiving the image data, for;

(a) defining a plurality of search boxes in the image data;

(b) determining the positions of the spots by

(i) locating a centroid in each of the search boxes;

(ii) replacing each of the search boxes with a search box of reduced size;

(iii) locating the centroid in each of the search boxes of reduced size; and

(iv) repeating steps (ii) and (iii) until each of the search boxes of reduced size reaches a minimum size; and

(c) calculating the wavefront aberration in accordance with the positions of the spots.

38. The device of claim 37, wherein the image data taking means comprises means for illuminating the eye with near infrared light.

39. The device of claim 37, wherein the image data taking means comprises means for illuminating the eye with light of a coherence length selected such that the spatial inhomogeneity does not appear in the image data.

40. The device of claim 39, wherein the coherence length is 30 microns.

41. The device of claim 39, wherein the image data taking means comprises:

a detector; and

an optical scanning device for illuminating the eye with light which has been scanned by the optical scanning device and scanning again the light emerging from the eye, the light emerging from the eye and scanned again being subsequently made indent on the detector such that the light is stationary as the light is made indent on the detector.

42. The device of claim 41, wherein:

the detector comprises a camera having a frame time; and

the optical scanning device performs a plurality of scans within a single one of said frame time.

43. The device of claim 42, wherein the optical scanning device has a scanning frequency of 400-600 Hz.

44. The device of claim 42, wherein the optical scanning device scans with an angular extent of less than 0.5 degrees.

45. The device of claim 41, wherein the optical scanning device comprises a single scanning/de-scanning mirror which scans both the light which illuminates the eye and the light emerging from the eye.

46. A device for measuring a wavefront aberration of an eye, the method comprising:

image data taking means for taking image data from a plurality of locations in the eye, the image data comprising a plurality of spots corresponding to the plurality of locations and having positions determined by the wavefront aberration, the image data taking means comprising a scanner, the data from the plurality of locations in the eye being taken by scanning light into the eye with the scanner such that the plurality of spots are separated in time; and

data processing means, receiving the image data, for;

(a) defining a plurality of search boxes in the image data;

(b) determining the positions of the spots by

(i) locating a centroid in each of the search boxes;

(ii) replacing each of the search boxes with a search box of reduced size, the search box of reduced size being clipped to fit entirely within the search box which is replaced;

(iii) locating the centroid in each of the search boxes of reduced size; and

(iv) repeating steps (ii) and (iii) until each of the search boxes of reduced size reaches a minimum size; and

(c) calculating the wavefront aberration in accordance with the positions of the spots.