The objective of this study is to investigate the relation between the otolith organ and nystagmus. The observation of eye movement on linear acceleration which was induced by parallel swing were performed in twenty normal subjects and in forty-nine cases with peripheral vestibular disorders.
The parallel swing was performed under the conditions of 3.3 seconds in one cycle, 70cm in amplitude, and 114cm/sec
2 in the maximum acceleration. Vestibular nystagmus in the parallel swing was observed in the opened eyes in the dark, and optokinetic nystagmus was observed in the opened eyes in the light. The following results were obtained.
1. Paralled swing in normal subjects.
a) The parallel swing for the opened eyes in the dark induced nystagmus in seven out of twenty subjects. However, these seven cases showed no abnormality on caloric test and on spontaneous nystagmus test. Therefore, it is most possible that nystagmus was induced by the parallel swing because of the presence of latent differences between the functions of right and left labyrinth even in normal individuals. b) Compensatory eye deviation induced by parallel swing was more easily observed in the closed eyes in the dark than in the opened eyes in the dark. c) The parallel swing performed on the opened eyes in the light induced optokinetic nystagmus accompanied by vestibular stimulation.
2. Parallel swing in cases with peripheral vestibular disorders.
a) Nystagmus was newly induced by parallel swing in seventeen out of twenty-six cases with the absence of spontaneous nystagmus. On the other hand, sixteen out of twenty-three cases with the presence of spontaneous nystagmus showed an increase in the amplitude or the frequency of nystagmus. There were two types of the nystagmus observed during parallel swing, unidirectional and bidirectional, and the former was more frequ ently observed than the latter during the stage when central compensation was insuf ficient. b) Abnormal optokinetic nystagmus was more frequently seen in optokinetic nystagmus accompanied by vestibular stimulation which was caused by parallel swing than in optokinetic nystagmus not accompanied by vestibular stimulation. It was conclud ed to be the result of the promoted imbalance of oculomotor system. c) The directions of spontaneous nystagmus, DP of optokinetic nystagmus and nystagmus during parallel swing agreed in a number of cases. d) There were no differences in the results of the parallel swing test between four cases with disorder of the otolith organ and the group showing a 100% CP in caloric test. e) In view of the fact that the spontaneous nysta gmus which evidently originated in the semicircular canals was influenced by parallel swing, it was concluded that the nystagmus observed during parallel swing was caused not only by the otolith organ alone but by the semicircular canals.
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