A quantitative analysis of head-shaking nystagmus of peripheral vestibular origin

A quantitative analysis of horizontal head-shaking nystagmus (HSN) was made on 48 patients with unilateral peripheral vestibular lesions in conjunction with stimulus intensity. Each patient underwent three head-shaking tests with 10, 30 and 50 horizontal head-excursions at a frequency of approximately 2 Hz, and HSN was recorded on ENG with eyes open in total darkness. i) HSN appeared in a biphasic or monophasic pattern. ii) The maximal slow-phase eye velocity (MSV) of the 1st phase (PI) of biphasic HSN increased significantly in proportion to stimulus intensity, and was significantly greater than that of monophasic HSN. iii) The duration of HSN was greater in the 2nd phase (PII) of biphasic HSN than in PI and increased markedly in proportion to stimulus intensity. iv) As the stimulus intensity rose to a high level, the interval between PI and PII (2nd phase latency) shortened, and the PII tended to appear more quickly after head-shaking. It was especially noteworthy that in response to an increase in stimulus intensity, both the MSV in PI and the duration of PII of biphasic HSN increased, but the duration of PI was reversely suppressed by the PII.