The eye tracker, provided by Tobii Technology, uses infrared light to track Fink's eye movements. Those movements are then translated into lines on a screen.
Interesting concept. Still, no word if Graham is aware he has perfectly functional arms and hands.
Keep going for a couple examples of his portraits and a video of the process. SPOILER: Lots of little eye movements.
Thanks to thatguyfrommathclass, who, wait -- the one that used to kick my desk all the time?!