A 21-year-old woman presented to the emergency department 1 day after a fall. On the day of presentation, she awoke with horizontal diplopia and posterior neck pain. Based on clinical findings, she was diagnosed with bilateral internuclear ophthalmoplegia. A conventional angiogram identified a left vertebral artery dissection. She was started on anticoagulant therapy, with gradual improvement of her diplopia over several months. Diplopia is frequently seen in the emergency department. Internuclear ophthalmoplegia is a cause of binocular diplopia and is important to recognize because it indicates a brainstem lesion requiring neurologic evaluation.
