Mechanisms underlying nystagmus

Abstract

In health, there are three main control mechanisms for maintaining steady gaze—fixation; the vestibulo-ocular reflex; and a gaze-holding system (the neural integrator), which operates whenever the eyes are required to hold an eccentric gaze position1,2,3. Failure of any of these control systems will bring about a disruption of steady fixation. Two types of abnormal fixation can result—nystagmus and saccadic intrusions/oscillations. The essential difference between them lies in the initial movement that takes the line of sight off the object of regard. In the case of nystagmus, it is a slow drift or ‘slow phase’ often due to a disturbance of one of the three mechanisms for gaze stability. On the other hand, with either saccadic intrusions or saccadic oscillations, it is an inappropriate fast movement that moves the eyes off target4,5. This paper will concern itself only with the clinical aspects of nystagmus and cover the possible reasons for its presence.