The effect of gravity on the stability of human eye orientation.
OBJECTIVE
The stabilization of both the horizontal (H) and vertical (V) eye movements during voluntary fixation is believed to depend upon the visual feedback system in the upright position. However, ocular stability in the tilted position has been less well investigated. Therefore, in the present study, we examined the gaze stability of healthy human subjects in the three dimensions in the tilted position using a video image analysis system (VIAS).


METHODS
In 10 healthy human subjects, the eye movements were recorded after fixating the eye on a target in an upright position and also in the tilted position. The standard deviations of the eye movements in the three dimensions were calculated to evaluate the stability of the movements.


RESULTS
In the tilted position, there were no significant changes in the horizontal and vertical eye movements as compared those in the upright position. However, the standard deviation of the torsional (T) segment was significantly larger in the tilted position, compared to that in the upright position.


CONCLUSIONS
From these results, we speculate that, a combination of otolith and somatosensory inputs play a major role in maintaining the stability of eye movements.
Aoyagi
Mio
M
Department of Otolaryngology, Nippon Medical School, 1-1-5 Sendagi, Bunkyo-ku, 113-8603, Tokyo, Japan.
Kimura
Maki
M
Yagi
Toshiaki
T
D000328:Adult; D005133:Eye Movements / Q000502:physiology*; D005246:Feedback; D005260:Female; D005403:Fixation, Ocular; D006112:Gravitation; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D009949:Orientation; D014741:Video Recording