Nystagmus and Other Ocular Motor Oscillations and Intrusions

If one is to understand the pathophysiology of ocular oscillations it is imperative to distinguish between those involving only the slow system and those that are purely saccadic. Oscillations containing both saccades and slow phases require identification of the causative phase (i.e., that which takes the eyes away from their intended direction) and the corrective phase. Modem methods of recording have enabled us to make these determinations and thereby clarify the ocular motor mechanisms responsible for the particular oscillation in question. Table 1 lists 43 types of nystagmus along with many other terms found in the literature to describe them; similarly, Table 2 lists 16 saccadic oscillations and intrusions with other descriptive terms. The Tables evolved from those that appeared in previous chap­ ters on the subject. 1-4 The definitions and categorizations used herein are a result of the systematic application of criteria derived from accurate ocular motility recordings. Such cri­ teria clearly differentiate between nystagmus and other ocular motor oscillations and, as a result, some eye movements described by the word "nystagmus," were found to be saccadic oscillations. Most oscillations were named without the ben­ efit of accurate ocular motor recordings. Quotation marks are used for those os-