The eye position detector monitors {HEAD ~ light} reflected from the users eye to identify {TAIL ~ the pupil position} 
The eye position detector monitors { HEAD ~ light } reflected from the users eye to identify { TAIL ~ the pupil position }
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL