Acquired monocular nystagmus in chiasmal glioma-a video-oculographic study.

We report the case of a 9-year-old girl with chiasmal glioma and longstanding monocular nystagmus, in whom video-oculography showed a disconjugate binocular nystagmus indistinguishable from spasmus nutans. The "acquired monocular nystagmus" associated with chiasmal glioma is actually a binocular nystagmus that is indistinguishable from spasmus nutans, except that it lacks the associated head nodding and torticollis. Superimposed visual loss in one eye predisposes to acquired monocular nystagmus and explains the absence of the other components of the spasmus nutans triad.