Toxic Optic Neuropathy

    • Subacute or chronic binocularly symmetrical optic neuropathy caused by systemic medications or toxins
    • Common causes: ethambutol treatment, alcohol ingestion (See Nutritional Deficiency Optic Neuropathy )
    • Uncommon causes: methanol ingestion, linezolid treatment
    • Core clinical features
      • Slowly progressive painless binocular visual loss (faster in methanol toxicity)
      • Bilateral symmetrical visual acuity loss
      • Bilateral central or centrocecal scotomas
      • Acquired color vision loss
      • Pupil size and constriction are normal (no afferent pupil defect)
      • Optic discs appear normal, slightly swollen, or show temporal pallor
      • Peripapillary nerve fiber layer edema in methanol toxicity
      • Causative agent is often evident
    • Possible accompanying clinical features
      • Peripheral neuropathy
    • Imaging features
      • Brain imaging is normal or shows reduced optic nerve caliber bilaterally
    • Nutritional deficiency optic neuropathy
    • Maculopathy
    • Hereditary optic neuropathy (dominantly-inherited or Leber hereditary optic neuropathy)
    • Optic neuritis
    • Compressive optic neuropathy
    • Chiasmal or bilateral retrogeniculate vision loss
    • Psychogenic visual loss
    • Exclude maculopathy with ophthalmoscopy and retinal imaging
    • Exclude nutritional and hereditary optic neuropathies
    • Look for exposure to the following toxins: ethambutol, alcohol, methanol, linezolid, thallium, toluene, vincristine, desferrioxamine, ethylene glycol, halogenated hydroxyquinolones, disulfiram
    • Promptly discontinue exposure to potential toxins
    • In suspected methanol toxicity, obtain blood chemistry for acidosis and order brain MRI, which often discloses high T2/FLAIR signal abnormalities in basal ganglia and parieto-occipital white matter
    • Treat methanol toxicity with base solutions to correct acidosis and facilitate excretion of formic acid, which causes the damage; in severe intoxications with reduced vision, may also need to treat with alcohol dehydrogenase inhibitors like fomepizole or, if not available, with ethanol, which competes with methanol for alcohol dehydrogenase; hemodialysis may also be necessary
    • Tip: if a toxic agent is not definitely identified, brain imaging and other evaluation for alternative causes of optic neuropathy is necessary
    • Tip: the causative toxin may not initially be recognized
    • Visual recovery depends on the type of toxin and the extent of damage at discovery
    • Trap: a standard ethambutol dose (< 25mg/kg/day) may cause optic neuropathy, especially in underweight patients, those with renal disease, and those being dialyzed (because ethambutol is not eliminated in the dialysate)
    • Tip: early diagnosis of ethambutol toxicity is critical because it is minimally reversible; therefore, patients should undergo pre-treatment visual screening and monitoring of visual acuity and color vision at regular intervals while on treatment
    • Tip: novel anti-neoplastic agents may have toxic effects with still-undefined frequency

    Optic Nerve And Chiasm Disorders

    Drusen Optic Neuropathy Colobomatous Optic Neuropathy Optic Pit Neuropathy Morning Glory Optic Neuropathy Hypoplastic Optic Neuropathy Typical Optic Neuritis Atypical Optic Neuritis Papillitis (Neuroretinitis) Non-arteritic Ischemic Optic Neuropathy Arteritic Ischemic Optic Neuropathy Posterior Ischemic Optic Neuropathy Hypotensive Ischemic Optic Neuropathy Radiation-induced Optic Neuropathy Diabetic Papillopathy Hypertensive Optic Disc Edema Papilledema Idiopathic Intracranial Hypertension (Pseudotumor Cerebri) Compressive Optic Neuropathy: Overview Optic Neuropathy of Graves Disease Optic Nerve Sheath Meningioma Sphenoid Meningioma Craniopharyngioma Pituitary Adenoma Pilocytic Astrocytoma (Optic Glioma) Carotid Aneurysm Suprasellar Germinoma Infiltrative (Neoplastic) Optic Neuropathy Paraneoplastic Optic Neuropathy Traumatic Optic Neuropathy Toxic Optic Neuropathy Nutritional Deficiency Optic Neuropathy Dominantly-Inherited Optic Neuropathy Leber Hereditary Optic Neuropathy Primary Open Angle Glaucoma