nystagmus /nīstag″məs/ [Gk, nystagmos, nodding] , involuntary, rhythmic movements of the eyes. The oscillations may be horizontal, vertical, rotary, or mixed. Jerking nystagmus, characterized by faster movements in one direction than in the opposite direction, is more common than pendular nystagmus, in which the oscillations are approximately equal in rate in both directions. Jerking nystagmus occurs normally when an individual observes a moving object, but on other occasions it may be a sign of barbiturate intoxication or of labyrinthine vestibular, vascular, or neurological disease. Labyrinthine vestibular nystagmus, most frequently rotary, is usually accompanied by vertigo and nausea. Vertical nystagmus is considered pathognomonic of disease of the tegmentum of the brainstem; nystagmus occurring only in the abducting eye is said to be a sign of multiple sclerosis. Seesaw nystagmus, in which one eye moves up and the other down, may be observed in bilateral hemianopia. Pendular nystagmus occurs in albinism, in various diseases of the retina and refractive media, and in miners after many years of working in darkness. In miners the eye movements are very rapid, increase on upward gaze, and are often associated with vertigo, head tremor, and photophobia. Electronystagmography, used in testing for vestibular disease and evaluating patients with vertigo, hearing loss, or tinnitus, records changes in the electrical field around the eyes. Nystagmus is measured as the person gazes at various objects and is placed in various positions and when cold or warm water or air is introduced into the external auditory canal. This final test causes nystagmus of equal intensity in normal individuals. In patients with an inner ear or neural disorder, nystagmus may be more intense, diminished, or absent. Also called nystaxis. −nystagmic, adj.
