Rapid, automatic measurement of the eye's wave aberration
First Claim
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;
(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.
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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.
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Citations
62 Claims
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1. A method of measuring a wavefront aberration of an eye, the method comprising:
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(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;
(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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31)
step (a) is performed with a Hartmann-Shack detector having a plurality of lenslets; and
the plurality of lenslets form the plurality of spots.
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3. The method of claim 2, wherein:
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step (d) is performed using a matrix having rows corresponding to the lenslets; and
step (d) comprises;
(i) determining which lenslets do not provide usable data; and
(ii) eliminating the rows corresponding to the lenslets which do not provide usable data.
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4. The method of claim 3, wherein step (d)(i) comprises allowing an operator to select the lenslets which do not provide usable data.
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5. The method of claim 3, wherein step (d)(i) comprises determining automatically which lenslets do not provide usable data.
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6. The method of claim 5, wherein step (d)(i) comprises determining automatically which lenslets do not provide usable data in accordance with standard deviations of intensity around the corresponding centroids.
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7. The method of claim 5, wherein step (d)(i) comprises determining automatically which lenslets do not provide usable data in accordance with overall intensity levels of the corresponding centroids.
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8. The method of claim 3, wherein:
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the matrix has two rows corresponding to each of the lenslets; and
step (d)(ii) comprises eliminating both of the rows corresponding to each of the lenslets which do not provide usable data.
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9. The method of claim 8, wherein the two rows corresponding to each of the lenslets are a row corresponding to an x coordinate and a row corresponding to ay coordinate.
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10. The method of claim 3, wherein step (d) is performed using singular value decomposition.
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11. The method of claim 1, wherein the minimum size is a diffraction limited size.
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12. The method of claim 1, wherein step (c)(ii) comprises reducing a size of each search box to be replaced by one pixel in each direction.
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13. 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.
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14. The method of claim 6, further comprising prompting an operator to select the lower threshold and the upper threshold.
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15. The method of claim 1, wherein each of the plurality of search boxes defined in step (b) is centered on a position which one of the spots would occupy in an absence of the wavefront aberration.
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16. The method of claim 15, wherein each of the plurality of search boxes defined in step (b) has a dimension equal to a spacing between the positions which the spots would occupy in the absence of the wavefront aberration.
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17. The method of claim 15, wherein each of the plurality of search boxes defined in step (b) has a dimension which is scaled down from a spacing between the positions which the spots would occupy in the absence of the wavefront aberration by a factor less than one.
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18. The method of claim 17, wherein step (b) comprises prompting an operator for the factor.
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19. The method of claim 1, wherein step (c)(ii) comprises reducing a size of each search box to be replaced by a fraction of a pixel along each side.
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20. The method of claim 19, wherein the fraction of a pixel is one-half of a pixel.
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21. The method of claim 19, wherein, for each search box of reduced size which includes at least one fractional pixel, step (c)(iii) comprises assigning to each of said at least one fractional pixel a contribution to the centroid which is equal to a corresponding fraction of an intensity detected in the fractional pixel centered in the fractional pixel.
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22. The method of claim 1, wherein step (c) further comprises:
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(v) allowing an operator to drag one of the centroids to a new location; and
(vi) recalculating the centroid which has been dragged to the new location, using a light distribution around the new location.
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23. The method of claim 1, wherein step (c) further comprises:
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(v) allowing an operator to drag a central one of the centroids to a new location; and
(vi) recalculating all of the centroids around the new location.
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24. The method of claim 1, wherein step (c)(iii) is performed without reference to a location of a previously located centroid.
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25. The method of claim 1, wherein step (c)(iii) is performed using a location of a previously located centroid as a start estimate.
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26. The method of claim 1, wherein step (c)(iii) is performed using, as a start estimate, a location which a spot would occupy in an absence of the wavefront aberration.
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27. The method of claim 1, wherein step (d) comprises calculating a number of Zernike modes by using a number of centroids which is at least twice the number of Zernike modes.
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28. The method of claim 1, wherein step (d) comprises calculating the wavefront aberration for a first pupil radius R0 of the eye and also for a second pupil radius R1 of the eye, wherein R1<
- R0.
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29. The method of claim 28, wherein the wavefront aberration is calculated for R1 by renormalizing the wavefront aberration calculated for R0.
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30. The method of claim 28, wherein step (d) further comprises prompting an operator for R1.
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31. The method of claim 30, wherein step (d) further comprises prompting an operator for a minimum Zernike mode and a maximum Zernike mode for use in calculating the wavefront aberration for R1.
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32. A system for measuring a wavefront aberration of an eye, the system comprising:
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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
computation 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. - View Dependent Claims (33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62)
the image data taking means comprises a Hartmann-Shack detector having a plurality of lenslets; and
the plurality of lenslets form the plurality of spots.
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34. The system of claim 33, wherein:
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the computation means performs step (c) using a matrix having rows corresponding to the lenslets; and
step (c) comprises;
(i) determining which lenslets do not provide usable data; and
(ii) eliminating the rows corresponding to the lenslets which do not provide usable data.
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35. The system of claim 34, further comprising interface means for allowing an operator to select the lenslets which do not provide usable data.
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36. The system of claim 34, wherein step (c)(i) comprises determining automatically which lenslets do not provide usable data.
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37. The system of claim 36, wherein step (c)(i) comprises determining automatically which lenslets do not provide usable data in accordance with standard deviations of intensity around the corresponding centroids.
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38. The system of claim 36, wherein step (c)(i) comprises determining automatically which lenslets do not provide usable data in accordance with overall intensity levels of the corresponding centroids.
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39. The system of claim 34, wherein:
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the matrix has two rows corresponding to each of the lenslets; and
step (c)(ii) comprises eliminating both of the rows corresponding to each of the lenslets which do not provide usable data.
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40. The system of claim 39, wherein the two rows corresponding to each of the lenslets are a row corresponding to an x coordinate and a row corresponding to a y coordinate.
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41. The system of claim 34, wherein step (d) is performed using singular value decomposition.
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42. The system of claim 32, wherein the minimum size is a diffraction limited size.
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43. The system of claim 32, wherein step (b)(ii) comprises reducing a size of each search box to be replaced by one pixel in each direction.
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44. The system of claim 32, 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.
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45. The system of claim 44, further comprising interface means for prompting an operator to select the lower threshold and the upper threshold.
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46. The system of claim 32, wherein each of the plurality of search boxes defined in step (a) is centered on a position which one of the spots would occupy in an absence of the wavefront aberration.
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47. The system of claim 46, wherein each of the plurality of search boxes defined in step (a) has a dimension equal to a spacing between the positions which the spots would occupy in the absence of the wavefront aberration.
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48. The system of claim 46, wherein each of the plurality of search boxes defined in step (a) has a dimension which is scaled down from a spacing between the positions which the spots would occupy in the absence of the wavefront aberration by a factor less than one.
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49. The system of claim 48, further comprising interface means for prompting an operator for the factor.
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50. The system of claim 32, wherein step (b)(ii) comprises reducing a size of each search box to be replaced by a fraction of a pixel along each side.
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51. The system of claim 50, wherein the fraction of a pixel is one-half of a pixel.
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52. The system of claim 50, wherein, for each search box of reduced size which includes at least one fractional pixel, step (b)(iii) comprises assigning to each of said at least one fractional pixel a contribution to the centroid which is equal to a corresponding fraction of an intensity detected in the fractional pixel centered in the fractional pixel.
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53. The system of claim 32, further comprising interface means for allowing an operator to drag one of the centroids to a new location, and wherein step (b) further comprises recalculating the centroid which has been dragged to the new location, using a light distribution around the new location.
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54. The system of claim 32, further comprising interface means for allowing an operator to drag a central one of the centroids to a new location, and wherein step (b) further comprises recalculating all of the centroids around the new location.
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55. The system of claim 32, wherein step (b)(iii) is performed without reference to a location of a previously located centroid.
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56. The system of claim 32, wherein step (b)(iii) is performed using a location of a previously located centroid as a start estimate.
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57. The system of claim 32, wherein step (b)(iii) is performed using, as a start estimate, a location which a spot would occupy in an absence of the wavefront aberration.
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58. The system of claim 32, wherein step (c) comprises calculating a number of Zernike modes by using a number of centroids which is at least twice the number of Zernike modes.
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59. The system of claim 32, wherein step (c) comprises calculating the wavefront aberration for a first pupil radius R0 of the eye and also for a second pupil radius R1 of the eye, wherein R1<
- R0.
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60. The system of claim 59, wherein the wavefront aberration is calculated for R1 by renormalizing the wavefront aberration calculated for R0.
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61. The system of claim 59, further comprising interface means for prompting an operator for R1.
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62. The system of claim 61, further comprising interface means for prompting an operator for a minimum Zernike mode and a maximum Zernike mode for use in calculating the wavefront aberration for R1.
Specification