Monocular vertical nystagmus as an initial sign of chiasmal glioma.

A 5-year-old boy with monocular vertical nystagmus, initially believed to have spasmus nutans, subsequently developed optic atrophy and visual loss. Neuroradiologic investigation indicated probable chiasmal glioma. The case of this patient re-emphasizes the necessity of careful clinical and radiologic assessment before assuming acquired monocular nystagmus to be a benign and self-limited disorder.