A 29-year-old woman comes to the physician for a 2-day history of visual loss in her left eye. Two years ago, she had an episode of vertigo, diplopia, and ataxic gait that resolved without treatment after one month. Physical examination shows reduced visual acuity and color vision on the left. The left eye does not react to direct light but demonstrates a normal consensual response. Babinski sign is present bilaterally. Which of the following is the most appropriate next step in diagnosis?
Carotid ultrasonography
Electromyography and nerve conduction studies
No diagnostic studies indicated
CT of the head with contrast
MRI of the brain with contrast
