Dave Pope views a visual target through the lenses of the eye-tracker. His eye position is measured according to the reflections of infrared light off the front of his cornea (forming the first Purkinje image) and the back of his lens (forming the fourth Purkinje image).
Another view of Dave Pope in the eye-tracker.
Jim Maxwell models the El-mar eye-tracking apparatus. The system uses two video cameras to track the two pupils and reflections of infrared light off the cornea. Head position is based on the pulsed magnetic field that is emitted from a transmitter located at the top of the headpiece.