Gaze tracking system with contact lens fiducial

Abstract

A gaze tracking system includes a contact lens, a photodetector element, a light conditioning element and electronics. The contact lens includes a fiducial having a position. The photodetector element receives a light signal from the fiducial and provides a photodetector output signal. The light signal provides a light intensity pattern at the photodetector. The optical conditioning element receives the light signal and provides a variation in the light intensity pattern on the photodetector in response to changes in the position of the fiducial. And the electronics process the photodetector output signal to calculate the position of the fiducial. A method includes detecting a light signal from a fiducial included in a contact lens, and tracking the contact lens by analyzing the light signal.

1 . (canceled) 
     
     
         2 . A gaze tracking system comprising:
 a contact lens including a first fiducial having a first position and a second fiducial having a second position;   a photodetector element to receive a first light signal from the first fiducial and a second light signal from the second fiducial and to provide a photodetector output signal, the first light signal to provide a first light intensity pattern on the photodetector and the second light signal to provide a second light intensity pattern on the photodetector, the second light signal passing through a retarder;   an optical conditioning element to receive the first light signal and the second light signal, and the optical conditioning element to provide a first variation in the first light intensity pattern on the photodetector in response to changes in the first position of the first fiducial and a second variation in the second light intensity pattern on the photodetector in response to changes in the second position of the second fiducial; and   electronics to process the photodetector output signal to calculate the first fiducial position of the first fiducial and the second fiducial position of the second fiducial.   
     
     
         3 . The gaze tracking system of  claim 2 , wherein the retarder comprises a quarter-ave retarder. 
     
     
         4 . The gaze tracking system of  claim 2 , further comprising an emitter. 
     
     
         5 . The gaze tracking system of  claim 4 , wherein the emitter is centered on the photodetector element. 
     
     
         6 . The gaze tracking system of  claim 2 , wherein the first fiducial comprises a photoluminescent element. 
     
     
         7 . The gaze tracking system of  claim 2 , wherein the first fiducial comprises a light emitting element. 
     
     
         8 . The gaze tracking system of  claim 2 , wherein the first fiducial comprises titanium dioxide. 
     
     
         9 . The gaze tracking system of  claim 2 , wherein the first fiducial has a diameter of between about 0.25 mm to about 4.0 mm. 
     
     
         10 . The gaze tracking system of  claim 2 , wherein the first fiducial has a substantially rectangular shape. 
     
     
         11 . The gaze tracking system of  claim 2 , wherein the first fiducial is located to remain uncovered by upper and lower lids of a subject wearing the contact lens when the contact lens is inserted in an eye of the subject and the eye is in a normal open eye state. 
     
     
         12 . The gaze tracking system of  claim 2 , wherein the optical conditioning element has a two-layer structure. 
     
     
         13 . A gaze tracking system comprising:
 a transmitter to provide a cone of emitted light;   a contact lens including a fiducial having a position, the fiducial including a retroreflector, and the position of the fiducial located in the cone of emitted light;   a photodetector element to receive a light signal from the fiducial and to provide a photodetector output signal, the light signal to provide a light intensity pattern on the photodetector;   an optical conditioning element to receive the light signal and to provide a variation in the light intensity pattern on the photodetector in response to changes in the position of the fiducial; and   electronics to process the photodetector output signal to calculate the position of the fiducial.   
     
     
         14 . The gaze tracking system of  claim 13 , wherein the cone of emitted light comprises a cone of near-infrared light. 
     
     
         15 . The gaze tracking system of  claim 13 , wherein the fiducial reflects light that is substantially collimated and about the diameter of the retroreflector. 
     
     
         16 . A method for calibrating a gaze tracking system for a subject wearing a contact lens including a fiducial, the method comprising:
 instructing the subject to look in a first direction constituting a first gaze direction;   associating the first gaze direction with a first photodetector output;   instructing the subject to look in a second direction constituting a second gaze direction; and   associating the second gaze direction with the second photodetector output.   
     
     
         17 . The method of  claim 16 , wherein the first gaze direction and the second gaze direction cause the subject to exercise vision over a range of eye movement.