Effects of a fixation target on torsional optokinetic nystagmus.
OBJECTIVE
To investigate the effects of an imaginary and a visual target on torsional optokinetic nystagmus (tOKN) and directional symmetry of tOKN.


METHODS
Torsional OKN was induced by a rotating random dot pattern (52 degrees in diameter, constant angular velocity: +/-30 deg/sec to +/-52 deg/sec) with an imaginary or a visual target in 11 eyes of 10 healthy humans by dual-search coil methods.


RESULTS
Intorsional OKN and extorsional OKN were symmetrical in their slow-phase gain. The mean slow-phase gain (0. 037/0.041, intorsion/extorsion) of tOKN during fixation on a visual target at the center of the rotating random dot pattern was significantly (P: < 0.002) smaller than that (0.051/0.052, intorsion/extorsion) during fixation on an imaginary target at the center of the rotating random dot pattern. The mean tOKN slow-phase beat duration (840 msec/724 msec, intorsion/extorsion) during fixation on the visual target was significantly (P: < 0.002) longer than that (585 msec/543 msec, intorsion/extorsion) during fixation on the imaginary target. In seven eyes of six subjects, the mean slow-phase gain and beat duration (0.034 and 812 msec) of tOKN during fixation on a visual target 6.5 degrees left or right from the center of the rotating random dot pattern were not significantly different from those (0.037 and 825 msec) with a visual target at the center of the rotating random dot pattern (P: > 0.3).


CONCLUSIONS
A visual target spot suppresses tOKN by a nonpursuit visual system. Intorsional and extorsional OKNs were symmetrical.
Suzuki
Y
Y
Department of Physiology, School of Medicine, Hokkaido University, Sapporo, Japan.
Shinmei
Y
Y
Nara
H
H
Ifukube
T
T
D000328:Adult; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology*; D006801:Humans; D008297:Male; D017120:Nystagmus, Optokinetic / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology