Optic Neuritis ๐๏ธ: 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 ~โ
(retrobulbar neuritis) but shows swollen disc in ~โ
.
๐ About
- Optic neuritis: Inflammatory/demyelinating optic neuropathy with visual loss.
- Retrobulbar neuritis: Posterior nerve inflammation โ normal disc at presentation (โthe patient sees nothing, and the doctor sees nothingโ).
๐งฌ Aetiology
- Demyelinating: Multiple sclerosis (MS), neuromyelitis optica (NMO), ADEM.
- Inflammatory: Sarcoidosis, SLE, Behรงetโs, 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, Pagetโs.
๐ฉบ Clinical Features
- Subacute visual loss over hoursโdays (often unilateral).
- ๐ฅ 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 โ pale disc.
๐ Differentials
- Anterior ischaemic optic neuropathy (AION).
- Compressive optic neuropathies (tumour, thyroid eye disease).
- Vascular: CRAO/CRVO.
- Inherited: LHON.
- Other autoimmune/infective optic neuropathies.
๐งช 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.
๐ Management
- Refer urgently to neurology/ophthalmology.
- IV methylprednisolone (1 g ร 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 โ ~50% risk at 15 years if MRI lesions present.
๐ก 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 โ needs different management (avoid interferon-ฮฒ, use immunosuppressants).
๐ก Mnemonic: โPORCโ = Pain on movement, Optic disc may be normal, Red desaturation, Central scotoma.
