Clinical significance of step stimulus-induced optokinetic nystagmus.

The optokinetic nystagmus (OKN) test has diagnostic values in that it can detect lesioned sites in patients with infratentorial lesions. The test has so far been performed by using angular acceleration to the final velocity over 100 degrees/s, which is time-consuming and inconvenient for patients. In the present study, we tried to modify and simplify the OKN test used previously to give step stimulus of constant stimulus and compared the results in 20 normal subjects. Slow-phase velocity versus stimulus velocity, and fast phase amplitude and peak velocity versus stimulus velocity of OKN were compared between step-stimulus OKN and linear-stimulus OKN. As a result, each parameter showed significantly higher values in step-stimulus OKN than in linear-stimulus OKN. Averaged slow-phase OKN velocity during the first 5 s is sufficient to calculate OKN velocity, and it requires only short time to perform.