Radiation optic neuropathy (RON) is a devastating complication of radiotherapy to the anterior visual pathway resulting in acute, profound and sometimes irreversible visual loss. Cumulative doses of radiation that exceed 50 Gy or radiation fractions of greater than 2 Gy are usually required for RON to develop. Several factors, such as diabetes and pre-existing compression of the optic nerve, are associated with a higher risk for developing RON at lower doses of radiation. We report a case of presumed subacute RON following orbital irradiation for Graves' ophthalmopathy, successfully treated with megadoses of intravenous corticosteroids.