Method and apparatus for measuring properties of the eye using an virtual object

• US 6,059,773 A
• Filed: 08/04/1997
• Issued: 05/09/2000
• Est. Priority Date: 08/12/1996
• Status: Expired due to Fees

• Current Assignee: Visionrx, LLC
• Original Assignee: Visionrx.Com, Inc.
• Inventors: Stewart, Jeffrey L., Maloney, Robert K., Truax, Bruce E.
• Primary Examiner(s): Dvorak, Linda C. M.
• Assistant Examiner(s): YARNELL, BRYAN KEITH
• Application Number:
  US08/910,494
• Time in Patent Office: 1,009 Days
• Field of Search: 606/4-6, 606/10-12, 351/205, 351/206, 351/207, 351/211-215, 600/473, 600/476, 356/2
• US Class Current: 606/4
• CPC Class Codes: A61B 3/107 for determining the shape or measuring the curvature of the cornea

Abstract

A technique for evaluating the topography of a cornea in which a virtual object of a keratoscope pattern isured. The topography system includes a structured light source to create the keratoscope pattern or another diagnostic pattern, an optical assembly to focus the created pattern upon or behind the cornea, and for capturing the image reflected off the patient'"'"'s eye and directing the reflected image toward an imaging system for processing. Light emitted by the light source is preferably not in the visible range, to minimize discomfort to the patient. Since the topography is evaluated with a projected virtual image, there is no nose or brow shadow, thereby allowing better corneal coverage. The optical system includes an aperture stop which is preferably conjugate with a point behind the corneal surface approximating the center of a normal cornea. Thus, wide angle capture is achieved as reflected rays reaching the imaging system appear as if they originated at the center of the cornea. A pupil detection mechanism is disclosed which is performed independently of the diagnostic pattern illumination, thereby facilitating pupil detection. In an alternate embodiment, the diagnostic pattern is generated using a variable light pattern generator, which provides flexibility in selecting target images to achieve various diagnostic abilities. The topography system may be reconfigured to serve as a visual field measuring device, or a perimeter.

Claims

1. An apparatus for obtaining the topography of an object, comprising:

means for illuminating the object with light that forms a virtual object of a diagnostic pattern a distance behind the object;

means for capturing light reflected from the object; and

means for forming an image from said reflected light, wherein abnormalities in the shape of the object are observed in distortions in the reflected image of the diagnostic pattern.

2. The apparatus of claim 1 further comprising means for processing said reflected image of the diagnostic pattern.

3. The apparatus of claim 2 wherein said means for processing includes means for calculating the radii of curvature of the object along two perpendicular directions.

4. The apparatus of claim 1 wherein said means for processing includes means for calculating the Gaussian curvature on different points on the object.

5. The apparatus of claim 1 wherein a real image of the diagnostic pattern is formed in front of the object from light reflected therefrom.

6. The apparatus of claim 1 wherein said object is a patient'"'"'s cornea.

7. The apparatus of claim 1 wherein said diagnostic pattern includes a keratoscope pattern.

8. The apparatus of claim 1 wherein said diagnostic pattern includes a circular checkerboard pattern consisting of concentric circles cut across with radial lines having alternating regions of light and dark.

9. The apparatus of claim 1 wherein said diagnostic pattern is a virtual image.

10. The apparatus of claim 1 further including an aperture stop imaged approximately at the center of curvature of the object.

11. The apparatus of claim 1 further including an exit pupil approximately satisfying the following condition:

##EQU2## wherein L is the location of the exit pupil from the nominal image plane of the diagnostic pattern;

C₁ and R_o are positive constants, and r is the radius of curvature of the object.

12. The apparatus of claim 1 wherein said means for processing includes an imaging sensor.

13. The apparatus of claim 12 wherein said imaging sensor is a CMOS type imaging sensor.

14. The apparatus of claim 12 wherein said imaging sensor is a charge coupled device (CCD).

15. An optical instrument for measuring the topography of a patient'"'"'s cornea, comprising:

an optical system for projecting a distance behind the cornea a virtual object of a diagnostic pattern;

means for forming an image of said diagnostic pattern from light reflected from the cornea, wherein abnormalities in the shape of the cornea are observed in distortions in the reflected image of the diagnostic pattern; and

means for processing said distorted image of the diagnostic pattern.

16. The optical instrument of claim 15 wherein said means for processing includes means for calculating the radii of curvature of the cornea along two perpendicular directions.

17. The optical instrument of claim 15 wherein said means for processing includes means for calculating the Gaussian curvature on different points on the cornea.

18. The optical instrument of claim 15 wherein a real image of the diagnostic pattern is formed in front of the cornea from light reflected therefrom.

19. The optical instrument of claim 15 wherein said diagnostic pattern includes a keratoscope pattern.

20. The optical instrument of claim 15 wherein said diagnostic pattern includes a circular checkerboard pattern consisting of concentric circles cut across with radial lines having alternating regions of light and dark.

21. The optical instrument of claim 15 wherein said diagnostic pattern is a virtual image.

22. The optical instrument of claim 15 wherein said optical system includes a lens refracting light rays of said virtual image to strike substantially perpendicular to the surface of the cornea.

23. The optical instrument of claim 15 further including an exit pupil approximately satisfying the following condition:

##EQU3## wherein L is the location of the exit pupil from the nominal image plane of the diagnostic pattern;

C₁ and R_o are positive constants, and r is the base radius of curvature of the cornea.

24. The optical instrument of claim 15 wherein said means for processing includes an imaging sensor.

25. The optical instrument of claim 15 wherein said imaging sensor is a CMOS imaging sensor.

26. The optical instrument of claim 23 wherein said imaging sensor is a charge coupled device (CCD).

27. An apparatus for measuring the topography of a patient'"'"'s cornea, comprising:

an optical system for projecting at a distance behind the cornea a virtual object of a diagnostic pattern, such that light rays from said diagnostic pattern are directed substantially normal to the surface of the cornea; and

means for forming an image of said diagnostic pattern from light rays reflected from the cornea, wherein abnormalities in the shape of the cornea are observed in distortions in the reflected image of the diagnostic pattern.

28. The apparatus of claim 27 further comprising means for processing said reflected image of the diagnostic pattern.

29. The apparatus of claim 27 wherein a real image of the diagnostic pattern is formed in front of the cornea from light reflected therefrom.

30. The apparatus of claim 27 wherein said diagnostic pattern includes a keratoscope pattern.

31. The apparatus of claim 27 wherein said diagnostic pattern includes a circular checkerboard pattern consisting of concentric circles cut across with radial lines having alternating regions of light and dark.

32. The apparatus of claim 27 wherein said diagnostic pattern is a virtual image.

33. The apparatus of claim 27 wherein said optical system includes an exit pupil satisfying approximately the following condition:

##EQU4## wherein L is the location of the exit pupil from the nominal image plane of the diagnostic pattern;

C₁ and R_o are positive constants, and r is the base radius of curvature of the cornea.

34. An apparatus for measuring the topography of a patient'"'"'s cornea, comprising:

an optical system for projecting at a distance behind the cornea a virtual object of a diagnostic pattern, said optical system having an exit pupil, wherein abnormalities in the shape of the cornea are observed in distortions in a reflected image of the diagnostic pattern; and

means for forming an image of said diagnostic pattern from light rays reflected from the cornea, said image located at a first plane for a cornea having a normal base radius of curvature, wherein for radii of curvature deviating from the normal base radius of curvature the location of the exit pupil does not pass through said first plane even though the location thereof shifts from one side of said first plane to the other with variations in the radius of curvature of the cornea.

35. The apparatus of claim 34 further comprising means for processing said distorted image of the diagnostic pattern.

36. The apparatus of claim 34 wherein a real image of the diagnostic pattern is formed in front of the cornea from light reflected therefrom.

37. The apparatus of claim 34 wherein said diagnostic pattern includes a keratoscope pattern.

38. The apparatus of claim 34 wherein said diagnostic pattern includes a circular checkerboard pattern consisting of concentric circles cut across with radial lines having alternating regions of light and dark.

39. The apparatus of claim 34 wherein said diagnostic pattern is a virtual image.

40. A method of obtaining the topography of a patient'"'"'s cornea comprising the steps of:

diffusely illuminating the cornea with a first illumination source;

imaging said first illumination source from light rays reflected from the cornea;

imaging the pupil and iris of the cornea from light rays passing through the cornea and thereafter reflecting off the iris;

capturing a composite image of the iris with said first illumination source for outlining the pupil; and

then

illuminating the cornea with a second illumination source for projecting a virtual object of a keratoscope pattern at a distance behind the cornea;

capturing an image of the keratoscope pattern from light rays reflected from the cornea; and

processing the image of the keratoscope pattern for obtaining the topography of the surface of the cornea.

41. The method of claim 40 further comprising the steps of storing said composite image on a first video frame and storing said image of the keratoscope pattern on a second video frame.

42. An apparatus for measuring the topography of a patient'"'"'s cornea, comprising:

an optical system for projecting at a distance behind the cornea a virtual object of a diagnostic pattern of light and dark regions;

means for forming an image of said diagnostic pattern from light rays reflected from the cornea, wherein abnormalities in the shape of the cornea are observed in distortions in the reflected image of the diagnostic pattern; and

means for processing the reflected image of said diagnostic pattern so as to obtain the topography of the surface of the cornea, said optical system having a sufficiently high f-number such that each of the light regions of said diagnostic pattern substantially illuminates only a corresponding region on the cornea.

43. The apparatus of claim 42 wherein a real image of the diagnostic pattern is formed in front of the cornea from light reflected therefrom.

44. The apparatus of claim 42 wherein said diagnostic pattern includes a keratoscope pattern.

45. The apparatus of claim 42 wherein said diagnostic pattern includes a circular checkerboard pattern consisting of concentric circles cut across with radial lines having alternating regions of light and dark.

46. The apparatus of claim 42 wherein said diagnostic pattern is a virtual image.

47. The apparatus of claim 42 further including an aperture stop imaged approximately at the nominal center of curvature of the cornea.

48. The apparatus of claim 42 further including an exit pupil approximately satisfying the following condition:

##EQU5## wherein L is the location of the exit pupil from the nominal image plane of the diagnostic pattern;

C₁ and R_o are positive constants, and r is the base radius of curvature of the cornea.

49. An apparatus for measuring the topography of a patient'"'"'s cornea, comprising:

an optical system for projecting at a distance behind the cornea a virtual object of a diagnostic pattern of light and dark regions;

means for forming an image of said diagnostic pattern from light rays reflected from the cornea, wherein abnormalities in the shape of the cornea are observed in distortions in the reflected image of the diagnostic pattern;

means for illuminating the cornea with a focusing beam;

a position detector;

means for imaging onto said position detector a portion of the focusing beam reflected off the cornea, said position detector generating a signal proportional to the position of the reflected focusing beam; and

means for processing the reflected image of said diagnostic pattern so as to obtain the topography of the surface of the cornea.

50. The apparatus of claim 49 wherein said position detector is a linear position detector.

51. The apparatus of claim 49 wherein a real image of the diagnostic pattern is formed in front of the cornea from light reflected therefrom.

52. The apparatus of claim 49 wherein said diagnostic pattern includes a keratoscope pattern.

53. The apparatus of claim 49 wherein said diagnostic pattern includes a circular checkerboard pattern consisting of concentric circles cut across with radial lines having alternating regions of light and dark.

54. The apparatus of claim 49 wherein said diagnostic pattern is a virtual image.

55. The apparatus of claim 49 wherein said optical system includes an aperture stop imaged approximately at the nominal center of curvature of the cornea.

56. The apparatus of claim 49 further wherein said optical system includes an exit pupil approximately satisfying the following condition:

##EQU6## wherein L is the location of the exit pupil from the nominal image plane of the diagnostic pattern;

C₁ and R_o are positive constants, and r is the base radius of curvature of the cornea.