EYE TRACKER

• US 3,712,716 A
• Filed: 04/09/1971
• Issued: 01/23/1973
• 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:
  US05/132,678
• Time in Patent Office: 655 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 3/113 for determining or recording eye movement

Abstract

An eye tracker for continuously tracking orientation of the optic axis of an eye in which the eye is flooded with light so that Purkinje images are formed. Two of the Purkinje images are deflected so as to be incident on photodetectors. In one embodiment the detectors and the light source are moved so that the light sources move to keep the Purkinje images centered on the two photodetectors with a fixed distance between the images. The positions of the light source in order to obtain the predetermined distance between the Purkinje images is monitored and gives an indication of the orientation of the optic axis of the eye. In another embodiment only one photodetector is used with two alternating light sources and means are provided to form the two Purkinje images respectively from the two light sources. Further means are provided with the photodetector for differentiating between the two Purkinje images.

Claims

1. 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 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 including means for moving both said photodetecting means and said light source means, and said centering means developing position signals indicative of the orientation of the optic axis of the eye.

2. 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 a first moveable platform having a horizontal servo for causing movement in a horizontal plane and having a vertical servo for causing movement in a vertical plane, a second moveable platform mounted on said first moveable platform and moveable with respect thereto, said second moveable platform having a horizontal servo for causing movement in a horizontal plane and having a vertical servo for causing movement in a vertical plane, light source means mounted on said second movable platform 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, said first and fourth Purkinje image detectors mounted on said second movable platform, means responsive to said electrical output of one of said first and fourth Purkinje image detectors for controlling one of said horizontal servos for moving one of said first and second movable platforms whereby the Purkinje image associated with said one of said first and fourth Purkinje image detectors is horizontally centered thereon and means responsive to said electrical output of said one of said first and fourth Purkinje image detectors for controlling one of said vertical servos for moving one of said first and second movable platforms whereby the Purkinje image associated with said one of said first and fourth Purkinje image detectors is vertically centered thereon, means responsive to said electrical output of said other of said first and fourth Purkinje image detectoRs for controlling the other of said horizontal servos for moving the other of said first and second movable platforms whereby the Purkinje image associated with said other of said first and fourth Purkinje image detectors is horizontally centered thereon and means responsive to said electrical output of said other of said first and fourth Purkinje image detectors for controlling the other of said vertical servos for moving the other of said first and second movable platform whereby the Purkinje image associated with said other of said first and fourth Purkinje image detectors is vertically centered thereon, said horizontal and vertical servos generating position signals indicative of the vertical and horizontal positions of said first and second movable platforms, which position signals contain information about the orientation of the optic axis of the eye.

3. An eye tracker in accordance with claim 2 wherein said light source means comprises an infrared light source.

4. An eye tracker in accordance with claim 2 wherein said first and fourth Purkinje image detectors comprise multiple field photodetectors.

5. An eye tracker in accordance with claim 4 wherein said multiple field photodetectors each have an upper left, an upper right, a lower left and a lower right field, each of said fields having an electrical output proportional to the light image falling thereon.

6. An eye tracker in accordance with claim 5 wherein said means responsive to said electrical output of one of said multiple field photodetectors for controlling one of said horizontal servos comprises first summer means for summing the electrical output signals of said upper left and lower left fields of said one multiple field photodetector to form a first sum signal, second summer means for summing the electrical output signals of said upper right and said lower right fields of said one multiple field photodetector to form a second sum signal, and first subtractor means for subtracting said first sum signal from said second sum signal to form a first difference signal for controlling said one of said horizontal servos.

7. An eye tracker in accordance with claim 6 wherein said means responsive to said electrical output of one of said multiple field photodetectors for controlling one of said vertical servos comprises third summer means for summing the electrical output signals of said upper left and upper right fields of said one multiple field photodetector to form a third sum signal, fourth summer means for summing the electrical output signals of said lower right and lower left fields of said one multiple field photodetector to form a fourth sum signal, second subtractor means for subtracting said third sum signal from said fourth sum signal to form a second difference signal for controlling said one of said vertical servos.

8. An eye tracker for continuously 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 alternately excited first and second light sources, said first light source adapted to generate an infrared light beam and said second light source adapted to generate an ultraviolet light beam, means for directing said infrared and ultraviolet beams into the eye whereby first Purkinje images are formed by reflections of said infrared and ultraviolet light beams by the cornea and wherein a fourth Purkinje image is formed only by reflection of said infrared light beam from the rear of the eye lens, the eye lens strongly absorbing the ultraviolet light beam, photodetecting means for generating electrical signals in response to light images falling thereon, centering means responsive to said electrical signals centering the first and fourth Purkinje images on said photodetecting means, said centering means generating position signals indicative of the orientation of the optic axis of the eye.

9. An eye tracker iN accordance with claim 8 wherein said photodetecting means comprises a multiple field photodetector and wherein the electrical signals generated thereby include DC signals corresponding to the first Purkinje image and AC signals corresponding to said fourth Purkinje image.

10. An eye tracker in accordance with claim 9 including filter means for separating said AC signals and said DC signals.

11. An eye tracker in accordance with claim 10 wherein said centering means comprises apparatus for moving said first and second light sources and said photodetecting means so that the infrared and ultraviolet light beams are directed into the eye along its optic axis whereby the first and fourth Purkinje images are coincident and centered on said photodetecting means.

12. An eye tracker in accordance with claim 10 wherein said centering means comprises apparatus for changing the orientation of said infrared and ultraviolet light beams with respect to the optic axis of the eye until the first and fourth Purkinje images are coincident and centered on said photodetecting means.