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Yasuo Suzuki, Yasuhiro Shinmei, Hiroyuki Nara, Tohru Ifukube; Effects of a Fixation Target on Torsional Optokinetic Nystagmus. Invest. Ophthalmol. Vis. Sci. 2000;41(10):2954-2959.
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purpose. To investigate the effects of an imaginary and a visual target on
torsional optokinetic nystagmus (tOKN) and directional symmetry of
methods. Torsional OKN was induced by a rotating random dot pattern (52° 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° 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
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