nystagmus
Pronunciation: nih-STAG-mus
Involuntary rhythmic oscillation of the eyes, indicating vestibular or neurological dysfunction.
Full Definition
Nystagmus is an involuntary, rhythmic oscillation of the eyes that can occur in horizontal, vertical, or rotatory planes. The condition can be physiological (normal response to certain stimuli) or pathological (indicating disease of the vestibular system, cerebellum, or brainstem). Nystagmus is characterized by slow and fast phases, with the direction typically named for the fast phase. Common types include pendular nystagmus (equal velocity in both directions) and jerk nystagmus (slow drift followed by fast corrective movement). The finding provides important diagnostic information in neurological and otological evaluations.
Usage
Usage note: Direction is named for the fast phase of the oscillation.
In Context
- "Horizontal nystagmus on lateral gaze suggested a central vestibular lesion." — neuro-otological examination
- "The patient's downbeat nystagmus improved following cerebellar tumor resection." — post-operative assessment