Most current eye-trackers are camera-based and rely on image processing. To improve gaze tracking accuracy, this paper presents a new approach based on a camera-less gaze tracking system using a smart contact lens. A scleral lens is fitted with photodetectors illuminated by specific spectacles. Photo-currents vary with eye movements as the light photodetectors received varies. The gaze direction is obtained then by computing a barycenter from the photo-currents by means of an integrated circuit implemented on the lens and powered using an inductive link. Experimental measurements with a prototype lens fitted with four infrared photodiodes and mounted on an artificial eyeball validate the method. Designed for the AMS 0.35-µm CMOS process, a 170 µW integrated circuit is proposed, including a subthreshold analog barycenter computation unit and an analog-to-digital converter. Monte Carlo analysis based on the circuit layout and measured photo-currents shows an accuracy of 0.2° can be achieved. This is 2.5 times better than current camera-based eye-trackers.
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