Acquired esotropia as initial manifestation of Arnold-Chiari malformation.

A 13-year-old patient originally presented with a divergence palsy and gaze-evoked nystagmus. Over a short period of time, the esotropia became increasingly comitant and was successfully treated with strabismus surgery. Three years later, she developed downbeat nystagmus. An Arnold-Chiari Malformation could only be demonstrated using nuclear magnetic resonance imaging (MRI). Subsequent neurosurgical decompression resulted in resolution of the downbeat nystagmus with maintenance of single binocularity.