Studies on voluntary and reflexive optokinetic nystagmus in cerebellar disturbances

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Voluntary and reflexive optokinetic nystagmus (Schau-and Stier-Nystagmus by Ter Braak) was examined in patients with cerebellar disorders.An Ohm type rotating cylinder was rotated electrically with an angular acceleration of 2°/s2 for 90s. Optokinetic nystagmus (OKN) was analyzed with a computer and specially designed program. In the qualitative test, stripe movements and nystagmus waves were displayed in superimposition on a cathode ray tube. From the relationship between the two, the ocular ability to catch and follow the stripes was evaluated. In the quantitative test, the number of nystagmus beats, average eye speed of slow and rapid phases and average amplitude for 10s were calculated. These values were compared with those of normal subjects.The tests were performed on 2 patients with lesions in the cerebellar hemisphere, 11 with lesions in the vermis and flocculus, and 7 with lesions in the cerebellum and brain stem.1. No abnormalities were noted in voluntary and reflexive OKN, or the voluntary OKN was slightly impared in the patients with lesions in the cerebellar hemisphere.2. In patients with lesions in the flocculus, voluntary OKN was decreased at high cylinder speed and reflexive OKN was decreased at all cylinder speeds, but there were no abnormalities of wave form.3. In patients with lesions in the posterior vermis, voluntary OKN showed saccadic movements in stripe pursuit and ocular dysmetria for the target catch. No abnormalities were noted in reflexive OKN.4. In patients with lesions in the cerebellum and brain stem, voluntary OKN showed irregular pursuit and was markedly decreased. Reflexive OKN showed disorders of wave form, or was markedly decreased.