TOXIC/METABOLIC OPTIC NEUROPATHY
Painless, progressive, bilateral loss of vision.
Bilateral cecocentral or central visual field defects, signs of alcoholism, tobacco/substance use, certain medication use, heavy metal exposure, or poor nutrition.
Visual acuity of 20/50 to 20/200, reduced color vision, temporal disc pallor, optic atrophy, or normal-appearing disc initially.
Pernicious anemia or other malabsorptive states (e.g., postgastric bypass surgery): Usually due to vitamin B12 malabsorption.
Toxic: Exposure to medications such as chloramphenicol, ethambutol, linezolid, isoniazid, digitalis, streptomycin, chlorpropamide, ethchlorvynol, disulfiram, amiodarone, and lead. Methanol can cause an acute optic neuropathy.
Complete ocular examination, including pupillary assessment, dyschromatopsia evaluation, and optic nerve examination.
Serum vitamin B1, B12, methylmalonic acid, and folate levels.
If disc is swollen, consider blood test for Leber hereditary optic neuropathy.
Coordinated care with an internist, including vitamin B12 1,000 mg intramuscularly every month for pernicious anemia.
Every month at first and then every 6 to 12 months.
COMPRESSIVE OPTIC NEUROPATHY
Slowly progressive visual loss, although occasionally acute or noticed acutely.
Central visual field defect, relative afferent pupillary defect.
The optic nerve can be normal, pale, or, occasionally, swollen; proptosis; optociliary (collateral) shunt vessels. Collateral vessels occur only with intrinsic lesions of the nerve (never with extrinsic lesions).
Optic nerve glioma: Age usually <20 years, often associated with neurofibromatosis.
Optic nerve meningioma: Usually adult women. Orbital imaging may show an optic nerve mass, diffuse optic nerve thickening, or a railroad-track sign (increased contrast of the periphery of the nerve).
Any intraorbital or intracranial mass (e.g., hemangioma, schwannoma).
All patients with progressive visual loss and optic nerve dysfunction should have an MRI of the orbit and brain.
Treatment for optic nerve glioma is controversial. These lesions are often monitored unless there is evidence of intracranial involvement, at which point surgical excision may be indicated. Most of these patients are young children, who are very susceptible to cognitive complications of radiotherapy. Chemotherapy may be considered if there is progressive visual loss.
For optic nerve sheath meningiomas, fractionated stereotactic radiotherapy treatment should be considered. Serial MRIs may be used to monitor tumor control.
LEBER HEREDITARY OPTIC NEUROPATHY
Painless progressive visual loss in one and then the other eye within days to months of each other. Visual loss is bilateral at onset in approximately 25% of cases.
Mild swelling of optic disc progressing over weeks to optic atrophy; small, telangiectatic blood vessels near the disc that do not leak on i.v. fluorescein angiography often present acutely; usually occurs in young men aged 15 to 30 years, and less commonly in women who are often older.
Visual acuity 20/200 to counting fingers, cecocentral visual field defect.
By mitochondrial DNA (transmitted by mothers to all offspring). However, 50% to 70% of sons and 10% to 15% of daughters manifest the disease. All daughters are carriers, and none of the sons can transmit the disease.
Genetic testing is available for the most frequent base-pair nucleotide substitutions at positions 11778, 3460, and 14484 in the mitochondrial gene for the NADH dehydrogenase protein.
Idebenone is used in Canada and the United Kingdom but is not available in the United States. Studies thus far have shown variable results regarding its effectiveness. Phase 3 clinical trials of gene replacement are ongoing.
Tobacco (or exposure to smoke) and alcohol avoidance are recommended to avoid mitochondrial stress.
Consider cardiology consult because of increased incidence of cardiac conduction defects.
DOMINANT OPTIC ATROPHY
Mild-to-moderate bilateral visual loss (20/40 to 20/200) usually presenting at approximately age 4 years old. Slow progression, temporal disc pallor, cecocentral visual field defect, tritanopic (blue-yellow) color defect on Farnsworth–Munsell 100-hue test, strong family history, and no nystagmus. OPA1 and other mutations are responsible.
COMPLICATED HEREDITARY OPTIC ATROPHY
Bilateral optic atrophy with spinocerebellar degenerations (e.g., Friedreich, Marie, Behr), polyneuropathy (e.g., Charcot–Marie–Tooth), or inborn errors of metabolism.
RADIATION OPTIC NEUROPATHY
Delayed effect (usually 1 to 5 years) after radiation therapy to the eye, orbit, sinus, nasopharynx, and brain with acute or gradual stepwise visual loss that is commonly severe. Disc swelling, radiation retinopathy, or both may be present. Enhancement of optic nerve or chiasm on MRI.