To describe an uncommon presentation of malignant melanoma metastasizing to the optic nerve, leading to progressive vision loss.

Cutaneous malignant melanoma has the brain as the most common metastatic site. Optic nerve involvement is rare and may manifest with a reduction in visual acuity. We report a case of cutaneous malignant melanoma with metastasis to the optic pathway and cerebral cortex.

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A 67-year-old man with a history of malignant melanoma presented with one week of painless progressive vision loss in the left eye. Examination revealed a left relative afferent pupillary defect and visual acuity limited to hand movements without optic disc edema. MRI showed expansile T2/FLAIR hyperintensity and peripheral nodular enhancement of the left intracranial optic nerve, left > right optic chiasm, and left optic tract, along with a hemorrhagic left temporal lobe lesion. Ophthalmology noted a peripheral retinal mass suspicious for choroidal melanoma. A biopsy was not feasible, and he was started on dexamethasone and was advised to follow up with neuro-oncology, oncology, neurosurgery, and ophthalmology for further management.

One month later, he developed worsening aphasia, no light perception in the left eye, a right temporal field defect, and bilateral optic disc pallor. Repeat MRI demonstrated progression of the optic pathway lesion into both intracranial optic nerves and enlargement of the temporal hemorrhagic lesion. Given the imaging findings and oncologic history, the presentation was most consistent with metastatic melanoma. He was continued on dexamethasone and referred for systemic immunotherapy.

This case highlights that metastatic melanoma can cause rapidly progressive optic neuropathy from optic nerve infiltration. Prompt recognition of light perception loss and early imaging studies are essential when a biopsy is not feasible. Early multidisciplinary team management is a crucial part of management.