Clinical evaluation of dysrhythmia of postrotatory nystagmus.

Postrotatory responses of nystagmus were analysed in an exponential model by utilizing linear regression analysis. Four nystagmus qualities (velocity and duration of slow and fast phases) were studied in 10 patients with vestibular peripheral lesions, 10 patients with frontal lobe lesions and 10 patients with brain-stem lesions, together with 10 control subjects. In addition, pauses during the responses were quantified. Patients with frontal lobe lesions differed from other groups by scoring higher values of slow phase velocity and by exhibiting more pauses. The time constant was significantly shorter in patients with brain-stem lesion than in any other group. As regards other qualities, e.g. slow phase duration and fast phase velocity, or duration, no differences were observed. The pathological dysrhythmia may therefore be presented as changes in the gain and time constant of slow phase velocity as well as in pauses during nystagmus. Since all these changes may be encountered in normal subjects, one should be cautious in interpreting these changes as being pathological in each individual case.