Lateral rectus dermoid cyst presenting as incomitant esotropia

A 24-year-old male presented with decreased vision associated with inward deviation of his left eye since childhood and gradually progressive prominence of left eye for 6 months. Left eye examination revealed visual acuity of 2/60, convergent squint with restricted abduction and medial dystopia. Computed tomography (CT) scan showed a well-circumscribed mass with fat fluid levels temporal to the optic nerve indistinguishable from the left lateral rectus. Intraoperatively, a well-encapsulated mass was identified within the lateral rectus muscle which was confirmed as dermoid cyst on histopathology. Patient subsequently underwent surgical correction of his esotropia and the final cosmetic outcome was satisfactory. Dermoid cysts are common orbital lesions usually found overlying suture lines. A dermoid cyst presenting within the ocular muscles is a rare entity. Deep dermoid cyst should be considered as one of the differentials for focal enlargement of extraocular muscles.