Ophthalmologymiddle twist
A 43-year-old woman has had two days of boring pain behind the right eye and, since this morning, double vision. Her right upper lid now covers the pupil and she cannot lift it. Held open, the right eye rests outwards and slightly downwards and will not turn up, in or down. The right pupil is 6 mm and does not constrict to light; the left is 3 mm and briskly reactive. There is no scalp or temple tenderness, and she has neither diabetes nor hypertension. The findings have not varied since they began. Which one of the following investigations should be arranged before she leaves the emergency department?