The optokinetic test: interaction of the vestibular and optokinetic system in normal subjects and patients with vestibular disorders.

In 100 patients showing different lesions of the peripheral vestibular system and of the CNS, the influence of spontaneous vestibular nystagmus on optokinetic nystagmus was investigated. Considering the large interindividual differences in the results of vestibulo-visual interaction, the actual values of OKN slow-phase velocity obtained by visual stimulation are only of limited diagnostic value in a single case. However, by averaging the results obtained from various nosologic groups of patients very different but distinct patterns of vestibulo-visual interaction can be demonstrated: The diagnostic importance of quantitative assessment of optokinetic nystagmus is demonstrated by a statistical evaluation of test results obtained in normal subjects as well as in patients with peripheral and central vestibular disorders. The most important diagnostic parameters of a pathologic foveo-retinal optokinetic response are directional preponderance of slow phase velocity and gain of OKN. Increasing target velocity with decreasing gain clearly indicate the presence of a severe brainstem lesion involving the entire oculomotor control system which provides the coordination of head and eye movements.