Pathological injury to the optic nerves or the blood supply to them. Usually, only one eye is affected. Several forms have been described, including ischemic optic neuropathy (which if prolonged leads to blindness in the affected eye); optic neuritis due to acute demyelination of optic nerve fibers; infiltrative optic neuropathy (in which the optic nerve is compressed by a tumor or aneurysm); and optic neuropathy due to toxic nutritional factors (e.g., methanol or a combined nutritional and vitamin deficiency).