Optic neuropathy from folic acid deficiency without alcohol abuse

A 47-year-old woman with a 2-month history of bilateral progressive visual loss was found to have a bilateral retrobulbar optic neuropathy. Her serum vitamin B₁₂ concentration and hemoglobin level were normal, but her serum folic acid concentration was decreased. The patient had a minimal alcohol intake and moderate tobacco use that had been unchanged for over 20 years; however, she had markedly altered her diet 4 years earlier in the setting of clinical depression. After treatment with oral folic acid and diet modification without change in her tobacco or alcohol use, the patient's visual function returned to normal. This case supports the role of folic acid deficiency as an important cause of some cases of nutritional optic neuropathy.