Abstract
Purpose: :
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.
Methods: :
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.
Results: :
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.
Conclusions: :
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.
Keywords: nystagmus • eye movements: conjugate • aging