Clinical Reasoning: A 58-year-old woman with loss of vision in her left eye.

A 58-year-old woman developed painless visual loss in her left eye over several days. She described the vision in her left eye as “similar to looking through a dirty screen door.” She denied double vision and eye pain but reported frontal throbbing headaches associated with nausea over the preceding months. Two weeks before presentation, she had several days of nausea and vomiting that had been attributed to viral gastroenteritis.