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A.Z. Zivotofsky, A. Caspi, R. Raz; Voluntary Nystagmus and Slow Eye Movements are Independently Controlled . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2502.
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The ability of an individual to generate volitional, rapid, to–and–fro eye movements has been reported in 5–8% of the population, but the etiology of this "voluntary nystagmus" is unknown. Previous studies (Ciuffreda, 1980) have shown that subjects are capable of superimposing voluntary nystagmus on slow eye movements that track a smoothly moving target. We investigated the superposition of voluntary nystagmus on different eye movements for clues about its etiology.
Using a search coil we recorded the horizontal and vertical movements of one eye in a subject capable of generating voluntary nystagmus. The subject attempted to generate nystagmus during fixation at four different depths as well as during smooth pursuit, VOR, and VOR suppression. Tracking was done in both horizontal and vertical planes.
Voluntary nystagmus was present in both the horizontal and vertical planes. Its amplitude increased with convergence. In the horizontal plane there was a high frequency peak in the power spectrum above 20 Hz, but in the vertical plane predominant frequencies were less than 10 Hz, without a clear peak. In all tasks (SP, VOR, VOR suppression both horizontally and vertically) the subject successfully stayed on target without a significant change in the frequency components of the power spectrum of his voluntary nystagmus.
We infer that voluntary nystagmus is not due to an oscillation of the slow eye movement system, because it is unaffected by concurrent activation of either smooth pursuit or VOR systems. We propose that the oscillations occur in the rapid eye movement system, and are triggered when the fixation system is voluntary disengaged.
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