開眼正中固視時に消失する交代性眼振症例

DISAPPEARANCE OF NYSTAGMUS ALTERNANS IN THE STRAIGHT AHEAD GAZE POSITION: REPORT OF A CASE

　I．緒言

　交代性眼振についてはRuttin^1）の最初の報告以来，現在まで100例近くの症例報告がなされている。しかし今だにその発生機序は不明である。今回我々は第四脳室腫瘍例において，閉眼時，暗所開眼時，Frenzel眼鏡時に出現し，開眼正中固視時に消失する交代性眼振症例を経験した。このような症例はToglia^2），Baloh^3）の報告があるのみである。この数少ない1例をここに報告し，その発生機序に関して神経学的考察を加えた。

　Nystagmus alternans in one hundred cases reported previously by many investigations was observed in patients who were looking straight ahead. But in a case descrived here, nystagmus alternans was disappeared when the patient's eyes were carried to the straight ahead gaze position and it appeared when the patient closed his eyes or opened them in the dark. The similar cases as above were reported by Toglia (1968) and by Baloh (1976).

　In this case, eye tracking function and optokinetic function and visual suppression of caloric nystagmus were normal. Therefore, it seemed probable that those function were not always necessary for the etiology of nystagmus alternans.