Bilateral Blindness Due to Radiation-Induced Optic Neuropathy in a Patient with Nasal Mucosal Melanoma

Radiation-induced optic neuropathy is an uncommon but devastating complication of radiotherapy for head and neck tumors, characterized by subacute, painless, irreversible visual loss. Nasal mucosal melanoma, although rare, carries a high risk of visual pathway toxicity due to its proximity to anterior optic structures. We report the case of a 73-year-old woman with right nasal mucosal melanoma treated with adjuvant radiotherapy (66 Gy) and anti-PD1 immunotherapy, who developed progressive bilateral vision loss. Neuro-ophthalmological examination revealed severe visual acuity reduction, bilateral mydriasis, and optic disc pallor. Optical coherence tomography showed retinal nerve fiber layer thinning. Brain MRI demonstrated contrast enhancement of the optic chiasm and prechiasmatic optic nerves. Despite intensive treatment, the patient progressed to bilateral blindness. This case underscores the importance of early recognition of radiation-induced optic neuropathy, particularly in high-risk anatomical sites and in patients receiving radiotherapy combined with immunotherapy.