okn

OKN, or optokinetic nystagmus, is a reflexive eye movement triggered when the entire visual scene moves relative to the viewer. It consists of a slow tracking movement of the eyes in the direction of the moving scene, followed by a rapid corrective saccade back to the starting position. This pattern repeats as long as the visual field continues to move, producing a characteristic alternating slow and fast phase.

The reflex helps stabilize the retinal image during sustained movement and supports motion perception by integrating visual input with vestibular signals. In clinical contexts, OKN is used to assess the integrity of the visual pathways and binocular function. Methods to elicit OKN include rotating striped drums or videos (the OKN drum test) and recording eye movements with infrared video or electro-oculography.

A normal, symmetrical OKN response suggests intact afferent pathways from the retina through the optic nerve and brainstem to cortical areas involved in motion processing. Absent or diminished OKN can indicate monocular visual loss, amblyopia, strabismus, optic neuropathy, or intracranial lesions affecting the brainstem or occipital cortex. Asymmetries between the two eyes may point to unilateral impairments.

In research, OKN is used to study motion perception and the development of binocular vision, particularly in infants and nonverbal subjects. The optokinetic response is related to, but distinct from, the vestibulo-ocular reflex, which stabilizes vision during head movement. The term OKN is most commonly encountered in ophthalmology, neurology, and vision science contexts.