EYE TRACKER AND METHOD

• US 3,724,932 A
• Filed: 04/09/1971
• Issued: 04/03/1973
• Est. Priority Date: 04/09/1971
• Status: Expired due to Term

• Current Assignee: Hewitt D. Crane, Tom N. Cornsweet
• Original Assignee: Hewitt D. Crane, Tom N. Cornsweet
• Inventors: Cornsweet, Tom N., Crane, Hewitt D.
• Primary Examiner(s): Schonberg, David
• Assistant Examiner(s): Sacher, Paul A.
• Application Number:
  US05/132,747
• Time in Patent Office: 725 Days
• Field of Search: 351/1,6,7,9,14,16,39 250/206,221 340/279
• US Class Current: 351/210
• CPC Class Codes: A61B 3/10 Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
• CPC Class Codes: A61B 3/113 for determining or recording eye movement

Abstract

A technique and apparatus for two dimensional tracking of eye position. An infrared pattern is projected into the eye and measurements taken of the spatial separation of the first and fourth Purkinje reflections, the reflections from the cornea and the back of the eye lens, respectively. Because the centers of curvature of the surfaces of the cornea and lens lie at different distances from the center of rotation of the eye, these reflections move in opposite directions under eye rotation, in either the vertical or the horizontal direction. During translation of the eye in either the vertical or the horizontal direction the spacing or separation between the two Purkinje images does not change. In one embodiment, a rotating scanning disc having a plurality of spaced orthogonal slits is provided and imaging means are provided for imaging the first and fourth Purkinje images of the light source through the orthogonal slits of the scanning disc onto a photomultiplier tube. The time period between pulse outputs of the photomultiplier tube is proportional to the separation of the first and fourth Purkinje images. In another embodiment the two Purkinje images are deflected so as to be incident on photodetectors. The photodetectors and deflecting means are movable so that the two Purkinje images are kept centered on their respective photodetectors. By monitoring the position of the photodetectors and deflecting means an indication is obtained of the separation of the Purkinje images which gives an indication of the orientation of the optic axis of the eye.

Claims

1. A method of tracking rotational movement of an eye having a lens and a cornea where the eye is capable of rotational and translational movements comprising the steps of directing collimated light into the eye whereby first and fourth Purkinje images are formed by reflection from the eye cornea and lens respectively, imaging the first and fourth Purkinje images on detecting means and continuously measuring the spatial separation between the first and fourth Purkinje images whereby changes in such spatial separation are proportional to rotational movements of the eye.

2. A method in accordance with claim 1 wherein collimated infrared light is directed into the eye whereby the eye is not aware of the presence of such light.

3. an eye tracker for tracking rotational movements of an eye of the type having a pupil, a cornea and a lens where the eye is capable of both rotational and translational movements comprising light source means for generating a light beam, light source imaging means for coupling said light beam into the eye whereby first and fourth Purkinje images are formed by reflections of said light beam from the cornea and eye lens, respectively, detecting means, means for imaging said first and fourth Purkinje images on said detecting means, said detecting means generating signals proportional to the spatial separation of said first and said fourth Purkinje images.

4. An eye tracker in accordance with claim 3 wherein said light beam generated by said lights source means comprises an infrared light beam whereby said light beam does not interfere with normal visual functions of the eye.

5. An eye tracker in accordance with claim 3 wherein said light source imaging means includes a stop having orthogonal slits whereby said first and fourth Purkinje images comprise images of an orthogonal slit.

6. An eye tracker in accordance with claim 5 wherein said detecting means comprises a rotating disc having a plurality of pairs of orthogonal slits and adapted to scan said first and fourth Purkinje images while rotating, and a photo detector spaced from said rotating disc whereby portions of said first and said fourth Purkinje images are passed through said plurality of pairs of orthogonal slits and fall on said photo detector.

7. An eye tracker in accordance with claim 6 wherein one slit in each of the pairs of orthogonal slits scans a portion of both the first and fourth Purkinje images and whereby the time between said one slit scanning the one portion of the fourth Purkinje image and the one portion of the first Purkinje image is proportional to the spatial horizontal separation of said first and fourth Purkinje images and wherein said second slit of each of said pairs of orthogonal slits scans a second portion of said fourth Purkinje image and a second portion of said first Purkinje image whereby the time between said second slit scanning said second portion of said fourth Purkinje image and said second portion of said first Purkinje image is proportional to the spatial vertical separation of said first and fourth Purkinje image.

8. An eye tracker for continuously tracking orientation of an optic axis of an eye having a cornea and a lens where the eye is adapted to translate in a horizontal and a vertical direction and also adapted to rotate in a horizontal and a vertical direction comprising light source means for forming a light beam, optical means for directing said light beam into the eye whereby light reflected by the cornea forms a first Purkinje image and light reflected by the rear of the eye lens forms a fourth Purkinje image, photodetecting means for generating electrical signals in response to said first and fourth Purkinje light images falling thereon, centering means responsive to said electrical signals for centering the first and fourth Purkinje images on said photodetecting means, said centering means developing position signals indicative of the orientation of the optic axis of the eye.

9. An eye tracker in accordance with claim 8 wherein said centering means includes at least one pivoted mirror.

10. An eye tracker in accordance with claim 8 wherein said centering means includes means for moving said photodetecting means with respect to the eye.

11. An eye tracker for continously tracking orientation of an optic axis of an eye having a cornea and a lens where the eye can translate in a horizontal and a vertical direction and also rotate in a horizontal and a vertical direction comprising light source means for flooding the eye with light whereby light reflected by the cornea forms a first Purkinje image and light reflected by the rear of the eye lens forms a fourth Purkinje image, a first Purkinje image detector having an electrical output and a fourth Purkinje image detector having an electrical output, positioning means responsive to said electrical output of one of said first and fourth Purkinje image detectors for adjusting the horizontal position of said one of said first and fourth Purkinje image detectors so as to horizontally center one of said first and fourth Purkinje images thereon, additional positioning means responsive to said electrical output of said other of said first and fourth Purkinje image detectors for adjusting the vertical position of said other of said first and fourth Purkinje image detectors so as to vertically center the other of said first and fourth Purkinje images thereon, said positioning means and said additional positioning means generating electrical position signals indicative of the position of said first and fourth Purkinje image detectors, which electrical position signals contain information about the orientation of the optic axis of the eye.

12. An eye tracker in accordance with claim 11 wherein said light source means comprises an infrared light source.

13. An eye tracker in accordance with claim 11 wherein said first and fourth Purkinje image detectors comprise multiple field photodetectors.

14. An eye tracker in accordance with claim 11 wherein said positioning means and said additional positioning means comprise servosystems.

15. An eye tracker in accordance with claim 11 including a pivoted reflecting surface for reflecting the first and fourth Purkinje images to said first and fourth Purkinje image detectors and including reflecting surface servo means responsive to said electrical outputs of said first and fourth Purkinje image detectors for adjusting the position of said reflecting surface, said servo means generating electrical position signals indicative of the position of said reflecting surface, which electrical position signals contain information about the orientation of the optic axis of the eye.

16. An eye tracker in accordance with claim 15 wherein said reflecting surface servo means adjust the position of said pivoted reflecting surface in one direction so that one of said first and fourth Purkinje images is horizontally centered on one of said first and fourth Purkinje image detectors and wherein said reflecting surface servo means adjusts the position of said pivoted reflecting surface in another direction so that the other of said first and fourth Purkinje images is vertically centered on the other of said first and fourth Purkinje image detectors.