Abstract
A 17-year-old girl presented with slowly progressive binocular horizontal diplopia, worse for distance viewing. She had distance esotropia (video), gaze-evoked nystagmus, broken smooth pursuit, reduced horizontal optokinetic nystagmus, and impaired vestibulo-ocular reflex suppression (VORS; video), in keeping with cerebellar dysfunction. The patient had full abduction during monocular viewing and head rotations, and normal saccadic velocities, excluding a bilateral sixth nerve palsy. An MRI scan confirmed a type 1 Chiari malformation (figure). A careful oculomotor assessment in patients with esotropia, including bedside VORS,1 may identify cerebellar signs that would suggest the tropia is cerebellar in origin.2 Cerebellar esotropia may arise from dorsal vermis impairment,2 or possibly from floccular and parafloccular dysfunction, explaining the associated abnormalities in smooth pursuit, optokinetic nystagmus, and VORS that share common neural pathways.
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