• sixth nerve palsy
• ipsilateral

A 73 year old man was evaluated for the sudden onset of binocular horizontal diplopia which was worse in left gaze and which began 1 day before initial examination. He also complained of a dull headache over his left brow. He had a medical history of hip and knee surgery and was taking no medications. He was a 50 pack a year smoker but had no other history of vascular disease, including hypertension and diabetes mellitus. He had no previous history of strabismus or eye muscle surgery. His referring ophthalmologist was concerned about giant cell arteritis (GCA) and ordered a Westergren erythrocyte sedimentation rate test, which was 15 mm in the first hour.

Additional history revealed that he had no jaw claudication, scalp tenderness, or other symptoms of GCA. Visual acuity was 20/25 in both eyes and his colour vision and confrontation visual fields were normal. His pupils were equal in size and briskly reactive without a relative afferent pupillary defect. A left abduction deficit was noted (fig 1) and, with alternate cover testing, …