Suppression of vestibular nystagmus by forced convergence in normal human subjects.

Abstract

It has been suggested that the principal mechanism of nystagmus suppression in the nystagmus blockage syndrome is either adduction of the eye or convergence. We examined this issue using the nystagmus of the vestibulo-ocular reflex (VOR) as a model. A motorized, computer-controlled rotary chair was used to produce VOR in darkness, using either sinusoidal or velocity step stimulation. Left eye position was monitored and horizontal slow-phase eye velocity was calculated. Subjects were cued to converge or perform other gaze tasks. Convergence suppressed nystagmus. With sinusoidal stimulation, nystagmus was nearly extinguished in extreme lateroversion, probably due to mechanical tethering of the eye. However, VOR gain suppression of 47% during convergence was observed even when the monitored eye was close to primary position. With velocity step stimulation, nystagmus was nearly extinguished at moderate angles of adduction. Convergence is sufficient to suppress nystagmus, without vision and without regard to whether the eye is adducted.