Friendly fire: neurogenic visual loss from radiation therapy.

The author's experience and review of the medical literature suggest that radiation-induced neurogenic visual loss presents on average 18 months after treatment and usually after cumulative doses of radiation that exceed 50 Gy or single doses to the visual apparatus of greater than 10 Gy. Visual loss may result from lesions of the disc, retrobulbar segment of the optic nerve, optic chiasm, or retrogeniculate pathways. Magnetic resonance imaging, the best means of demonstrating radiation injury to the visual pathway, may show abnormalities before the loss of vision. The second eye may show clinical manifestations of optic neuropathy many months after the diagnosis in the first involved eye. Spontaneous improvement in visual function may rarely occur. Treatment has been disappointing, but if visual dysfunction is detected early, hyperbaric oxygen might be beneficial. The risk of neurogenic visual loss must be factored into the decision to irradiate the brain.