Bigus Dickus
Regular
Some of the more precise implementations use laser, but inexpensive IR led works pretty well too. And a new method called electro-occulography sounds promising.Unless you want lasers bounced off your eyeballs to determine where you're looking, I don't see that happening.
It isn't like this hasn't been done for years or anything. Getting the level of precision required for game control/aiming in an inexpensive package is the hard part.