Testing of my eye tracking library running in Flash 10. The red circle represents the perceived position of my eyes, and the green line is just a line that moves with a speed that is based on the circle position (when the circle is on top, the line moves up; when the circle is in the middle, the line stays; when the circle is at the bottom, the line moves down).
It uses a face tracking algorithm for initial face detection, then some other color-separating code to find where the eye is looking at in real-time. An initial calibration is necessary (the code must know when the eye is looking at the top and at the bottom of the screen; then it can find where you're looking at, in between those two).
The face detection used an AS3 port of OpenCV, based on the work of Ohtsuka Masakazu (maaash.jp/as3/as3marilena-object-detection-in-as3/) and Mario Klingemann (quasimondo.com/archives/000687.php) with a bunch of modifications for speed and varying levels of accuracy (nothing too crazy though, just better for our specific use case).
Part of my daily work at firstborn.com.