Radiation-induced Optic Neuropathy

    • Sudden, irreversible visual loss from radiation-induced infarction of the intracranial optic nerve
    • Occurs months to years after radiation therapy of paranasal sinus or cranial base tumors
    • More likely if the total radiation dose exceeds 6000 cGy, the daily dose fraction exceeds 200 cGy, or there was faulty delivery technique
    • Patients with arteriolar sclerosis, diabetes, neurofibromatosis Type 1 are at higher risk
    • Afferent pupil defect is often the only objective clinical sign
    • MRI brain abnormalities are often distinctive
    • No effective treatment, although corticosteroids and hyperbaric oxygen are often proposed
    • Acute painless visual loss, usually monocular, but step-wise visual decline is common
    • Subnormal visual acuity
    • Nerve fiber bundle or hemianopic visual field defects
    • Eyes and surrounding tissues appear structurally normal
    • Afferent pupil defect
    • Brain MRI shows sharp-margined enhancement and thickening of the intracranial optic nerve near the optic chiasm
    • Optic neuritis
    • Infiltrative optic neuropathy
    • Compressive optic neuropathy
    • Hypotensive optic neuropathy
    • Order brain MRI to exclude compressive, inflammatory, and infiltrative causes and to confirm the classic imaging sign of radiation optic neuropathy
    • Consider lumbar puncture if the diagnosis remains uncertain
    • Trap: high-dose corticosteroid, anticoagulation, and hyperbaric oxygen treatments are often prescribed but support for their benefit is very weak
    • No effective treatment
    • Vision loss is irreversible, and further visual loss may occur from repeated infarction over weeks to months

    Optic Nerve And Chiasm Disorders

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