Makindo Medical Notes

Optic Neuritis 👁️: Autoimmune inflammation and demyelination of the optic nerve. Classically presents with pain on eye movement, colour desaturation (esp. red), and subacute visual loss. Fundoscopy is normal in ~⅔ (retrobulbar neuritis) but shows swollen disc in ~⅓.

📖 About

• Optic neuritis: Inflammatory/demyelinating optic neuropathy with visual loss.
• Retrobulbar neuritis: Posterior nerve inflammation → normal disc at presentation (“the patient sees nothing, and the doctor sees nothing”).

🧬 Aetiology

• Demyelinating: Multiple sclerosis (MS), neuromyelitis optica (NMO), ADEM.
• Inflammatory: Sarcoidosis, SLE, Behçet’s, post-infectious, paraneoplastic.
• Infectious: Syphilis, TB, Lyme, HIV, CMV, herpes viruses.
• Ischaemic mimics: AION, diabetic papillopathy.
• Toxic: Methanol, ethambutol, alcohol, tobacco.
• Mitochondrial: Leber hereditary optic neuropathy (LHON).
• Compression: Tumours, thyroid eye disease, Paget’s.

🩺 Clinical Features

• Subacute visual loss over hours–days (often unilateral).
• 🔥 Pain with eye movement (highly characteristic).
• Colour desaturation (esp. red).
• Relative afferent pupillary defect (RAPD).
• Field defects (commonly central scotoma).
• Photopsia (flashes of light).
• Chronic/late: optic atrophy → pale disc.

🔍 Differentials

• Anterior ischaemic optic neuropathy (AION).
• Compressive optic neuropathies (tumour, thyroid eye disease).
• Vascular: CRAO/CRVO.
• Inherited: LHON.
• Other autoimmune/infective optic neuropathies.

🧪 Investigations

• Bloods: FBC, ESR/CRP, ANA, ACE; syphilis & HIV serology.
• MRI brain & orbits: Demyelinating plaques; rule out compressive lesion.
• Specialist: Aquaporin-4 (NMO) & MOG antibodies; visual evoked potentials.

💊 Management

• Refer urgently to neurology/ophthalmology.
• IV methylprednisolone (1 g × 3 days) speeds recovery in acute demyelinating ON but does not improve long-term vision.
• Treat underlying cause: antimicrobials (infective), immunosuppression (autoimmune), toxin avoidance.
• Monitor for conversion to MS → ~50% risk at 15 years if MRI lesions present.

💡 Clinical Pearls

• Young woman + painful eye movements + red colour desaturation = classic MS-associated optic neuritis.
• ONTT trial: IV steroids help recovery speed, not long-term vision or MS risk.
• NMOSD: consider if bilateral, severe, or poor recovery — needs different management (avoid interferon-β, use immunosuppressants).

💡 Mnemonic: “PORC” = Pain on movement, Optic disc may be normal, Red desaturation, Central scotoma.