nystagmus

Nystagmus is a rhythmic, biphasic oscillation of the eyes in which a slow drift of the eye initiates each cycle.¹ Nystagmus can be physiologic, as in optokinetic nystagmus or the vestibulo-ocular reflex during head rotation, or pathologic, signaling damage to the peripheral or central vestibular pathways or to the visual pathways.¹

In jerk nystagmus a slow, pathologic phase is followed by a fast corrective phase in the opposite direction, and the nystagmus is named for the direction of the fast phase.¹ In pendular nystagmus the two phases have equal velocity and there is no fast phase, so the oscillation is described by its vector as horizontal, vertical or torsional.¹ Combined horizontal and vertical components can produce a circular, elliptical or oblique waveform.¹

Acquired nystagmus commonly causes oscillopsia, an apparent jumping of the visual environment.¹ Congenital nystagmus typically reduces visual acuity without oscillopsia.¹ Drug-induced nystagmus is one of the most common forms, and anticonvulsants, sedatives, barbiturates and phenothiazines can produce it at therapeutic doses.¹ Patients with congenital nystagmus often see better with contact lenses than with spectacles, and the lenses seem to dampen the nystagmus through tactile feedback from the inner eyelids.²