A Case of Nutritional Optic Neuropathy Caused by Vitamin B12 and Folate Deficiency Presenting With Bitemporal Hemianopia-Like Visual Field Defects.

Nutritional optic neuropathy is a rare condition caused by vitamin B12 or folate deficiency. It typically presents with subacute bilateral vision loss and central visual field defects, whereas a presentation resembling bitemporal hemianopia is uncommon. A 70-year-old man living alone presented with gradually worsening bilateral vision loss over four months. His best-corrected visual acuity (BCVA) had decreased to 20/400 in the right eye (OD) and 20/200 in the left eye (OS). Optical coherence tomography showed widespread thinning of the ganglion cell complex, with preservation of the peripapillary retinal nerve fiber layer. Humphrey 30-2 perimetry revealed bitemporal hemianopia-like defects, raising suspicion of a chiasmal lesion; however, contrast-enhanced MRI was normal. Serum vitamin B12 and folate levels were low (66 pg/mL and 3.4 ng/mL), leading to a diagnosis of nutritional optic neuropathy. The patient started oral methylcobalamin (1.5 mg/day) and folic acid (10 mg/day), along with smoking cessation counseling. After three weeks of treatment, vitamin levels normalized, and approximately 15 weeks later, BCVA improved to 20/30 in OD and 20/40 in OS, with significant recovery of visual fields. Nutritional optic neuropathy may rarely cause bitemporal hemianopia-like visual field defects. In patients with subacute bilateral vision loss, assessing diet and smoking history, along with measuring vitamin B12 and folate levels, is important.