Walsh & Hoyt: Common Features of Saccadic Intrusions

Several types of inappropriate saccadic eye movements may intrude upon steady fixation. Saccadic intrusions must be differentiated from nystagmus, in which a drift of the eyes from the desired position of gaze is the primary abnormality, and from saccadic dysmetria, in which the eye over- or under- shoots a target, sometimes several times, before achieving stable fixation. Because all of these movements are often rapid and brief, it may be necessary to measure eye and target position, as well as eye velocity, in order to identify accurately the saccadic abnormality. In this section, we first describe the characteristics of each type of saccadic intrusion and then review possible mechanisms of pathogenesis.