Optokinetic nystagmus in response to different stimulus modalities

Abstract

Eye movements were recorded in 42 patients with CNS and labyrinthine lesions during optokinetic (OK) stimulation with a small drum, a full field angular drum and a large linear screen. Gain (slow phase eye velocity/stimulus velocity) and symmetry of the response were measured. In the whole patient group the asymmetry of optokinetic nystagmus (OKN) with the small drum was larger than that elicited with the large field OK stimuli; this indicates that the small drum is a more sensitive stimulus for eliciting abnormal OKN asymmetry (directional preponderance). In some patients with parietal and cerebellar lesions, there was slow build-up of the nystagmic response which was selective to the full field angular OK stimulus. This finding suggests that the ‘old subcortical OKN system, responsible for slow build-up of the response, is specifically related to angular motion. Linear OKN may be coupled to otolith-ocular reflexes.

Key Words:

• optokinetic nystagmus
• vestibular system
• spatial orientation