To report a case of optic neuropathy from vitamin B₁₂ deficiency associated with chronic alcoholism and malnutrition.

A 51-year-old man with a complaint of declining visual acuity in both eyes without pain was found to have a temporal optic disc pallor in the left eye. The patient had a history of chronic alcoholism and malnutrition for the previous 7 months. Visual field examination showed central scotoma in both eyes. The vitamin B₁₂ level was undetectable by a blood biochemistry test. Blood dyscrasia such as anemia or thrombocytopenia was not found. The vitamin B₁₂ level became normal after intramuscular cobalamin injections, and visual acuity and visual field tests recovered after 3 months.

Optic neuropathy from vitamin B₁₂ deficiency can be solely present without other systemic manifestations in a patient with chronic alcoholism and malnutrition. Prompt diagnosis by thorough history taking and vitamin B₁₂ supplementation can reverse the disease.