1993 Volume 52 Issue 3 Pages 466-469
The characteristics of postrotatory nystagmus primary and second phase (PRN I and PRN II), and optokinetic after nystagmus (OKAN) were investigated. The slow phase velocity time course of both PRN I and OKAN were approximated by the exponential function : V = VIexp (-T/TC) where V is slow phase velocity time course, VI, initial velocity, T, time from the initiation of after nystagmus, and TC, a time constant. VI and TC were calculated by the least square method. The slow phase velocity time course of PRN I and OKAN were well approximated by the exponential function. Although the TC of both. PRN I and OKAN increased with the increase of stimulating velocity, the increase of TC reached a plateau in high velocity stimulation. From these results we concluded that PRN I and OKAN are similar responses involved in the velocity storage mechanism.
PRN II was observed in only 4 (38%) of 11 healthy subjects, but in 23 (78 %) of 28 patients with vertigo or dizziness. In 18 (78 %) of the 23, it was observed only in a unilateral direction. The duration of PRN II was in negative correlation with PRN I in the same stimulation. These results sugest that PRN II is a subliminal vestibular asymmetry developed by vestibular stimulation as head shaking nystagmus.
