The word nystagmus comes from a Greek word meaning “to nod off” and refers to eye movements with a phase in one direction and a another phase in the opposite direction. The movements may be horizontal, vertical or torsional. Movements in either direction can have a slow and a fast phase, but may also have the same speed.
Normal physiologic nystagmus
Observed with head rotations that are too large for the vestibuloocular reflex to compensate for. Spontaneous or exaggerated nystagmus, however, may be characteristic of some kinds of neuropathology.
The differential diagnosis for nystagmus includes:
- vision loss early in life
- ocular infarction
- toxic or metabolic encephalopathy
- alcohol intoxication
- thiamine deficiency
- cerebellar degeneration
- vascular brainstem lesions
- Arnold–Chiari malformation
- nonpathologic (extreme lateral gaze)
- opticokinetic nystagmus
Nystagmus can be induce by instilling cool or warm water into a subjects ear, causing endolymphatic convection currents that simulate rotation. This is called caloric nystagmus.
Optokinetic nystagmus is induced by moving visual stimuli.