Walsh & Hoyt: Differences Between Physiologic and Pathologic Nystagmus

It is important to realize that not all nystagmus is pathologic. Physiologic nystagmus preserves clear vision during self-rotation. Under most circumstances, for example during locomotion, head movements are small and the vestibuloocular reflex is able to generate eye movements that compensate for them. Consequently, the line of sight remains pointed at the object of regard. In response to large head or body rotations, however, the vestibulo-ocular reflex alone cannot preserve clear vision because the eyes are limited in their range of rotation. Thus, during sustained rotations, quick phases occur to reset the eyes into their working range: vestibular nystagmus. If rotation is sustained for several seconds, the vestibular afferents no longer accurately signal head rotation, and visually driven or optokinetic nystagmus takes over to stop excessive slip of stationary retinal images. Additional examples of physiologic nystagmus are arthrokinetic and audiokinetic nystagmus (discussion following). In contrast to vestibular and optokinetic nystagmus, pathologic nystagmus causes excessive drift of stationary retinal images that degrades vision and may produce illusory motion of the seen world: oscillopsia. An exception is congenital nystagmus, which may be associated with normal visual acuity and which seldom causes oscillopsia.