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S.J. Farooq, F.A. Proudlock, I. Gottlob; Torsional Optokinetic Nystgamus in Congenital Nystagmus . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2501.
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There is no previous research on the torsional optokinetic response (tOKN) in patients with congenital nystagmus. We investigated the tOKN response in patients with congenital nystagmus (CN)
Torsional OKN was elicited using a rear projected sinusoidal stimulus of cycle size 90º subtending 50.8 º in diameter. Eye movements were recorded using a three dimensional pupil and iris tracking video oculography technique (Strabs system, Sensomotoric instruments GmbH, Teltow, Germany) while subjects viewed the rotating stimulus at velocities of 40º/s and 400º/s in the clockwise and anticlockwise directions.
A total of 14 patients were tested whom either had a diagnosis of CN that was idiopathic n=7 or secondary to other pathology n=7. All patients had manifest nystagmus in the primary position with 7/14 patients displaying a jerk waveform and the remaining seven a pendular waveform. 11/14 subjects displayed no tOKN response to stimuli rotating at clockwise and anticlockwise directions at either stimulus velocity. The remaining three subjects (2 idiopathic, 1 secondary) that demonstrated a tOKN response displayed a clear waveform that was consistent with the direction of rotation of the stimulus. 2/3 of these subjects displayed a response to only 400º/s stimulation in either direction. Slow phase velocities of this group varied from 2.5º/s to 6.2º/s (gain: 0.0063, 0.015) at 400º/s (normal gain: 0.008).
In patients with CN there was an absence of tOKN in most patients and in those that showed a response a higher than normal stimulus velocity was required to elicit the response. There was no reversal of the response noted as has been noted by previous studies investigating the horizontal OKN response in CN.
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