@gertsy
Actually, our eyes move constantly (or almost) and their movements can be divided between saccades and fixations, based on physiological thresholds. For most people, a saccades is an eye movements under 200 ms, above that threshold it is considered a fixation: the moment during which the light is captured by the eyes and a signal transfered to the brain. The Soviets even did funny experiments in their time, gluing micro-projectors on people eyes...
@Astral
Eye-tracking has many, many useful applications in lots of domains, regaring people with impairment, look at what it can do for Stephen Hawking:
http://iq.intel.com/iq/26909838/how-intel-helps-stephen-hawking-communicate-with-the-worldCheers!