Metastasis to the optic nerve is very rare. We report a case of metastatic breast cancer to the optic nerve without the involvement of other ocular or orbital structures.

The patient, a 39-year-old female who had been previously treated for breast cancer, reported a gradually progressive decrement in visual acuity of the right eye during the past two months.

Fundus examination of the affected eye revealed swelling of the optic disc which was infiltrated by a yellowish mass. Further evaluation using optical coherence tomography and fluorescein angiography showed the optic disc swelling. B-scan ultrasonography revealed abnormal increasing of the optic nerve sheath diameter. Magnetic resonance imaging revealed no pathologic findings. With a diagnosis of unilateral infiltrative optic neuropathy, we referred the patient to an oncologist for further evaluation.

Most patients with optic nerve metastatic tumors exhibit a known diagnosis of a primary malignancy along with other evidence of metastases. Thus, when a known cancer patient develops an optic neuropathy, metastases and infiltration should be suspected as the cause; unless proven otherwise.