Tobii Technology has an entire division dedicated to the use of eye tracking for medical
applications known as Tobii Dynavox.
The Tobii EyeX Tracker is designed primarily for gaming and basic interaction in conjunction with
traditional peripherals, not as keyboard/mouse replacement.
Please check out Tobii Dynavox site @ http://www.tobiidynavox.com/
I recommend that you get in touch with one of the sales representatives here who should
be able to provide your the correct hardware and software appropriate for your needs.