Complete unilateral vision loss and optic nerve cupping from metastatic prostate cancer to the optic canal.

A 71-year-old man, living with metastatic castrate-resistant prostate cancer to the lymph nodes, spine and skull, presented with acute on chronic left eye vision loss. Examination revealed no-light-perception vision, a relative afferent pupillary defect and optic disc cupping. MRI brain revealed optic canal narrowing from metastatic sphenoid bone expansion and extraosseous tumour compressing the intracanalicular optic nerve. The optic disc cupping and excavation without significant pallor of the remaining neuroretinal rim was likely secondary to chronic compression of the optic nerve. The patient was treated with radiation therapy, but did not regain vision and was referred to palliative care as his condition continued to worsen. As patients live longer with advanced cancer, there is a greater risk of metastasis to atypical areas of the body including the optic nerve. This case demonstrates the unique combination of optic disc cupping from optic canal metastasis due to prostate cancer.