Chewing oscillopsia. A case of voluntary visual illusions of movement.

A 60-year-old man had a history of frontal headaches and chewing-related oscillopsia. Examination disclosed a retro-orbital epidermoid cyst that had eroded through the lateral orbital wall and under the temporalis muscle. The illusion of movement was due to mechanical displacement of the tumor mass and eye by contraction of the temporalis muscle. Removal of the cyst produced complete remission of the oscillopsia.