Optokinetic nystagmus (OKN)

Physiologic — striate cortex + brainstem OKN pathway

Live animation

Fast-phase: → right-beating horizontal

Gaze directionprimary

← 40° LEFTPRIMARY40° RIGHT →

Slide to test Alexander's law (peripheral), gaze-evoked patterns, or the null zone (congenital).

Position-over-time tracing

Live strip-chart. Horizontal, vertical, and torsional channels.

In a sentence

Reflexive jerk nystagmus elicited by a moving full-field visual stimulus (e.g., striped drum). Slow phase tracks the stimulus, fast phase resets.

Clinical pearls

◆Tests cortico-subcortical visual-motor pathway integrity.
◆Asymmetric OKN (one direction reduced) localizes to deep parietal/occipital cortex.
◆Absent OKN with intact pursuit suggests cortical lesion; reversed OKN occurs in congenital nystagmus.
◆Useful for malingering screen (OKN is reflexive).

Common associations