Gain of human torsional optokinetic nystagmus depends on horizontal disparity.
OBJECTIVE
To investigate the effects of horizontal disparity on torsional optokinetic nystagmus (tOKN) in humans.


METHODS
Ten healthy human subjects were selected for this experiment. Monocular eye movements were recorded three-dimensionally using dual-search coil methods. Torsional OKN was induced by a rotating random-dot pattern (22 degrees in diameter, constant angular velocity: +/-54 deg/s) projected on the virtual screen of the optical see-through, head-mounted display (HMD). The optical distance of the HMD's virtual screen was 2 m. A red LED that could be fixated through the virtual screen of the HMD was located near the center of the rotating random-dot pattern. Horizontal disparity was induced by changing the distance between the fixated target and the subject systematically (1, 1.5, 2, or 3 m; five subjects) or by the prism (+1.5, +0.5, 0, or -0.5 prism-diopter [PD] in each eye; five subjects) in front of the HMD.


RESULTS
The average gain with zero horizontal disparity (0.022 +/- 0.008/0.025 +/- 0.014, fixated target at 2 m/fixated target with the plain glass) was significantly higher than the gain with crossed disparity (0.017 +/- 0.003/0.019 +/- 0.008, target at 3 m/with the prism of -0.5 PD) and uncrossed disparity (0.017 +/- 0.002, target at 1 m/with the prism of +1.5 PD; one-way ANOVA, P <0.05).


CONCLUSIONS
The horizontal disparity of optokinetic stimulus affects tOKN. Nonzero horizontal disparity decreases the gain of tOKN.
Washio
Noriaki
N
Department of Ophthalmology, Sapporo Medical University, School of Medicine, Sapporo, Japan.
Suzuki
Yasuo
Y
Sawa
Masahiro
M
Ohtsuka
Kenji
K
D000328:Adult; D003290:Convergence, Ocular / Q000502:physiology; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D008297:Male; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D014102:Torsion Abnormality; D015357:Vision Disparity / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology