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S.I. Benskin, S.J. Farooq, F.A. Proudlock, R.J. Mc lean, U.K. Bhatt, S. Banerjee, I. Gottlob; The Effect of Aging on Torsional Optokinetic Nystagmus . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2500.
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Horizontal and vertical optokinetic nystagmus (OKN) is mildly affected by senescence with only a small reduction in gain with age, however, the effect of aging on torsional OKN (tOKN) is unknown. We compared tOKN in older volunteers to younger controls.
Torsional OKN was elicited in 8 older volunteers (mean age=68.0, SD=3.0) and 8 healthy controls (mean age=33.5, SD=6.5) using a rear projected sinusoidal stimulus applied monocularly (cycle size 90º, diameter 50.8º). 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.
Torsional OKN responses were absent in all eight older volunteers but only one of the eight younger volunteers. The mean torsional velocity for the younger volunteers was 1.2°/s (SD=1.0) and 2.1°/s (SD=1.3) for stimulus velocities of 40º/s and 400º/s, respectively.
These data indicate that aging causes tOKN responses to be significantly reduced or absent. This is in contrast to horizontal and vertical OKN responses that show only a mild deterioration with age. This is the first reported finding of reduced tOKN with age.
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