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Optic Neuritis (ON)

BASICS

Description

  • Inflammation of the optic nerve (CN II)
  • Most common: acute demyelinating optic neuritis
  • Can also be infectious or autoimmune
  • Key features:
  • Abrupt, usually monocular visual loss
  • Periorbital pain (especially with eye movement, ~90%)
  • Dyschromatopsia (color vision deficits, especially red desaturation)
  • Relative afferent pupillary defect (RAPD)
  • Optic disc: normal (retrobulbar ON, 67%) or swollen (papillitis, 33%)
  • Associated with Multiple Sclerosis (MS) (ON is a presenting complaint in 25% of MS)
  • Children: more likely bilateral, with headaches

EPIDEMIOLOGY

  • Incidence: 5/100,000/year; more common in whites, females (3:1)
  • Mean age: 30 years (range: 18–45)

ETIOLOGY & PATHOPHYSIOLOGY

  • Autoimmune demyelination (MS or isolated)
  • Antibody-associated (NMO-IgG [aquaporin-4], MOG)
  • Infectious (viral: measles, mumps, VZV, coxsackie, adenovirus, hepatitis, HIV, HSV, CMV, SARS-CoV-2; nonviral: syphilis, TB, etc.)
  • Systemic inflammatory: SLE, sarcoidosis, vasculitis
  • Local inflammation: intraocular/orbital disease
  • Toxic (lead, methanol, ethambutol, etc.), medications
  • Genetics: some association with immune-mediated diseases and MS

COMMONLY ASSOCIATED CONDITIONS

  • Multiple Sclerosis (MS)
  • Other demyelinating diseases (NMO, MOG-AD, ADEM)
  • Guillain-Barré syndrome

DIAGNOSIS

Clinical Criteria

  • Monocular, subacute visual loss with orbital pain on eye movement
  • Reduced contrast and color vision
  • RAPD on exam

Paraclinical Criteria

  • OCT: optic disc swelling or RNFL thinning
  • MRI: contrast enhancement of optic nerve; can show MS lesions
  • Serology: AQP4, MOG, or CRMP5 antibodies; CSF IgG oligoclonal bands

History

  • Vision loss: deteriorates over hours–days, peaks at 1 week
  • Pain: periorbital, worse with eye movement
  • Dyschromatopsia: especially red desaturation
  • Uhthoff phenomenon: symptoms worsen with heat/exercise
  • Pulfrich phenomenon, phosphenes
  • May follow viral illness

Physical Exam

  • ↓ Visual acuity & color
  • Visual field defects (central, cecocentral, arcuate)
  • Optic disc: swollen or normal (temporal pallor develops later)
  • RAPD unless bilateral

Differential Diagnosis

  • MS/NMO/MOG-AD
  • Papilledema, tumor/abscess, temporal arteritis, diabetic papillopathy, infectious/systemic inflammatory disease

Diagnostic Tests

  • MRI (brain & orbits with contrast): for MS lesions, optic nerve enhancement
  • OCT: for RNFL thickness
  • Serology: NMO/MOG antibodies, only if indicated (recurrent/atypical ON)
  • LP: CSF for OCBs if MS suspected (not always necessary)
  • Labs (atypical cases): CBC, ANA, RPR, SARS-CoV-2 PCR

TREATMENT

Most recover spontaneously.

First Line

  • IV methylprednisolone: 250 mg q6h x3 days, then oral corticosteroids (1 mg/kg/day PO x11 days, taper 1–2 weeks)
  • Speeds visual recovery, but no long-term benefit
  • Avoid oral prednisone alone: increases recurrence risk

Second Line

  • Disease-modifying agents: IFN-β1a, IFN-β1b for MS prevention in high-risk (≥2 brain lesions on MRI)
  • Eculizumab: FDA-approved for NMOSD with AQP4 antibody
  • Vitamin D: supplement if deficient (may delay MS conversion)

Pediatrics

  • Bilateral disease & disc swelling more common
  • Consensus: 3–5 days IV methylprednisolone (4–30 mg/kg/day) → 2–4 week oral taper
  • Screen for MOG antibodies

Referral

  • Ophthalmology and neurology

Admission

  • For acute visual loss to expedite workup if needed

ONGOING CARE

  • Monthly follow-up for vision changes and steroid side effects

PROGNOSIS

  • Pain resolves in 1 week
  • Vision improvement: 2–4 weeks (most recover to 20/40 or better in 1 year)
  • Recurrence risk: 35% at 10 yrs; higher with MS
  • ON → MS: 35% risk at 7 years, 58% at 15 years
  • Poor prognosis: absence of pain, low initial vision, intracanalicular involvement

COMPLICATIONS

  • Permanent visual loss

ICD-10 Codes

  • H46.9: Unspecified optic neuritis
  • H46.00: Optic papillitis, unspecified eye
  • H46.10: Retrobulbar neuritis, unspecified eye

Clinical Pearls

  • Key features: abrupt monocular visual loss, pain with eye movement, RAPD, color vision deficits
  • MRI is essential for risk stratification and MS diagnosis
  • High-dose IV steroids accelerate recovery; oral prednisone alone should not be used
  • Recurrence and MS risk are high—counsel patients accordingly