While the current focus in HCI is sensor-based interaction (à la Kinect), recent developments could foster interaction with the eyes. The Danish company EyeTribe (formerly Senseye) is building a very nice tracking system with $2.3 million support from the Danish government. Partnering companies include the IT University of Copenhagen, DTU Informatics, LEGO and Serious Games Interactive.
EyeTribe plans to release an SDK for app development next year.