Optic Neuritis

Definition & Causes - Optic Nerve Alarm

Inflammation of the optic nerve: acute, monocular vision loss, dyschromatopsia (red desat), pain with eye movements.

• Types & Comparison:
  • Typical: ~70% MS-related. Unilateral, retrobulbar pain, good steroid response & prognosis.
  • Atypical: Not MS. Often bilateral, severe vision loss, marked disc edema (papillitis), poor steroid response. Broader investigation needed.
• Key Causes:
  • Demyelinating: Multiple Sclerosis (MS), NMOSD, MOGAD.
  • Parainfectious: Post-viral (measles, mumps, varicella).
  • Infectious: Syphilis, TB, Lyme, Bartonella, viral (CMV).
  • Non-infectious Inflammatory: Sarcoidosis, SLE, Behcet's.
  • Idiopathic.

⭐ Most common cause of typical optic neuritis in adults is Multiple Sclerosis.

Clinical Picture - Vision Vanish

• Symptoms:
  • Acute unilateral vision loss (develops over hours-days).
  • Periocular pain, worse with eye movements (present in >90% of cases).
  • Dyschromatopsia (impaired color vision, especially red desaturation).
  • Photopsias (flashes of light).
• Signs:
  • Relative Afferent Pupillary Defect (RAPD).
  • Visual field defects: Central or centrocaecal scotoma most common.
  • Optic disc appearance:
    • Papillitis (swollen disc): ~1/3 of cases.
    • Retrobulbar neuritis (normal disc initially): ~2/3 of cases.
    • Neuroretinitis (optic disc swelling + macular star) - less common.
• Associated Phenomena:
  • Uhthoff's phenomenon: Transient visual blurring with ↑ body temperature.
  • Pulfrich phenomenon: Altered depth perception with moving objects.
• 📌 Mnemonic: 'ON Causes PAIN' (Optic Neuritis: Pain, Acuity ↓, Impaired color, Nerve signs).

⭐ Over 90% of typical optic neuritis cases experience pain on eye movement, often preceding visual loss.

Diagnosis - Nerve Detective

• MRI Brain & Orbits (with gadolinium): Key initial test.

  • Optic nerve: Enhancement, T2 hyperintensity.
  • Brain: T2 hyperintense lesions (periventricular, juxtacortical, infratentorial, spinal cord) predict MS.

  ⭐ An MRI of the brain showing characteristic demyelinating lesions at the time of a first episode of optic neuritis is the strongest predictor for developing clinically definite Multiple Sclerosis.

• Visual Evoked Potentials (VEP):

  • Delayed P100 latency with preserved waveform (confirms demyelination).

• Optical Coherence Tomography (OCT):

  • RNFL & GCIPL thinning (axonal loss in chronic stage).

• CSF Analysis (if MS suspected):

  • Oligoclonal bands (OCBs), ↑ IgG index.

• Serology (for atypical ON: bilateral, recurrent, severe):

  • AQP4-IgG (NMOSD).
  • MOG-IgG (MOGAD).

Diagnostic Workup Flow:

Treatment & Outlook - Visionary Ventures

• Acute Management (ONTT Guidelines):
  • Primary: IV Methylprednisolone (IVMP) 1g/day for 3 days.
  • Followed by: Oral prednisolone 1mg/kg/day for 11 days, then slow taper.
  • ⚠️ Oral prednisone alone contraindicated (↑ recurrence risk).
• Alternative/Adjunctive:
  • PLEX: For severe/atypical cases or no steroid response.
• Etiology-Specific Treatment:
  • NMOSD/MOGAD: Long-term immunosuppression (Rituximab, Azathioprine, MMF) to prevent relapses.
• Prognosis & Long-term Outlook:
  • Typical ON: Good visual recovery (weeks-months).
  • MS Risk: Stratify; high-risk may need early DMTs.

⭐ The ONTT demonstrated that while IV corticosteroids accelerate visual recovery in typical optic neuritis, they do not improve the final visual outcome at 6 months compared to placebo; however, oral prednisone alone was associated with an increased risk of new attacks.

High‑Yield Points - ⚡ Biggest Takeaways

• Strongly linked to Multiple Sclerosis (MS); often its first sign.
• Presents with acute painful monocular vision loss, RAPD, and impaired color vision (especially red).
• Uhthoff's phenomenon (worsening with heat) is common.
• Optic disc: Often normal (retrobulbar neuritis) or swollen (papillitis); optic atrophy develops later.
• VEP shows delayed P100 latency. MRI reveals demyelinating lesions.
• Treatment: IV methylprednisolone speeds recovery. Oral steroids alone are contraindicated.