Clinical Reasoning: A woman with monocular vision loss

A 48-year-old woman presented to her primary care physician (PCP) with right eye vision loss. She began noticing changes in her vision earlier in the year while at work. Over the ensuing months, her vision progressively declined such that she was no longer able to read with the right eye but could appreciate movement. Her past medical history included iron deficiency anemia for which she received iron infusions, depression, and anxiety. She denied fevers, sweats, chills, anorexia, weight loss, cough, shortness of breath, swollen lymph nodes, or any other systemic symptoms. She had traveled to Mexico, South America, the Caribbean, and Europe. She never had penetrating trauma to the head, although she did have a concussion as a toddler. She had spent time in Arizona and in the northern United States/southern Canada. She has several pets including dogs, small mammals, and birds; none was ill. She had no history of diabetes, immunosuppression, or HIV.