To demonstrate the characteristic difference between "irrtative nystagmus" and "paralytic nystagmus", electronystagmographs of 72 cases of unilateral peripherel vestibular disorder were analyzed by Signal Processor 7T17 (NEC-Sanei). The patients could be divided into 3 groups
i) Group(1), 24 patients with irritative nystagmus.
ii) Group (Pi), 24 patients with early paralytic nyst-agmus occurring within 6 day after an attck of vertigo.
iii) Group( P2), 24 patients with late paralytic nystagmus occurring 7 days or more after an attach of vertigo.
1) Irritative nystagmus, directed to the affected side, had a large amplitude, wide amplitude variation, high frequency and high velocity of the slow phase. This type of nystagmus was increased when the patients lay with the normal side down.
2) Paralytic nystagmus, directed to the normal side in the early stage the same as irritative nystagmus. However, this type of nystagmus decreased when the patient lay with the normal side down.
On the other hand, late stage paralytic nystagmus showed a lower frequency and amplitude than early stage paralytic nystagmus, and the interval varied widely.
3) It was concluded that the analysis of irritative nystagmus and paralytic nystagmus is very important in monitoring the changing process of labyrinthine pathophysiology during and after attacks.
