Optic Neuritis

Optic neuritis is inflammation of the optic nerve causing acute or subacute visual loss. It is the commonest optic neuropathy in young adults (peak 20 to 45 years), more frequent in women (about 3 times) and in temperate latitudes.

• Causes:
  • Multiple sclerosis (MS) associated or isolated demyelinating optic neuritis (commonest, 40 to 50 percent develop MS over 15 years).
  • Neuromyelitis optica spectrum disorder (aquaporin-4 IgG positive): severe, often bilateral, optic neuritis with long optic nerve lesions and chiasm involvement.
  • Myelin oligodendrocyte glycoprotein antibody disease (MOGAD): often bilateral with marked disc swelling, children and adults, and good steroid response but relapsing.
  • Infection (syphilis, tuberculosis, Lyme disease, Bartonella neuroretinitis, herpes viruses, HIV, cryptococcosis), post-viral and post-vaccination, and sarcoidosis.
  • Systemic autoimmune disease (lupus, Sjögren, Behçet disease), chronic relapsing inflammatory optic neuropathy, and paraneoplastic disease.
• Pathology: demyelination and axonal injury with conduction block.

• Subacute unilateral visual loss over hours to days, worst at 1 to 2 weeks, with recovery beginning after 2 to 3 weeks.
• Pain on eye movement or behind the eye in about 90 percent, often preceding visual loss.
• Reduced colour vision (dyschromatopsia, red desaturation), reduced contrast sensitivity, central or arcuate visual field defect, and a relative afferent pupillary defect.
• Fundus: normal (retrobulbar neuritis, about two thirds) or hyperaemic swollen disc (papillitis); mild haemorrhages at the disc margin.
• Uhthoff phenomenon (worsening vision with heat or exercise) and Pulfrich phenomenon.
• Atypical features that point away from simple demyelination: painless onset, severe loss to no light perception, bilateral simultaneous disease, marked disc swelling with haemorrhages or exudates (neuroretinitis star), progression beyond 2 weeks, no recovery after 4 weeks, optic perineuritis, and systemic features.

• Visual acuity, colour plates, visual fields (central defect), pupil examination, and dilated fundus examination.
• MRI of the brain and orbits with gadolinium: optic nerve enhancement (T1 post-contrast) and T2 white matter lesions of the brain; one or more demyelinating lesions predicts MS risk (about 70 percent over 15 years versus 25 percent with a normal MRI).
• Serum aquaporin-4 IgG and MOG IgG by cell based assays in all patients with atypical features, bilateral disease, or severe loss.
• Further investigation as appropriate: ESR, CRP, ANA, ANCA, ACE, syphilis serology, tuberculosis testing, Lyme and Bartonella serology, HIV, vitamin B12; chest imaging; lumbar puncture for oligoclonal bands, cell count, and protein.
• Optical coherence tomography (retinal nerve fibre layer and ganglion cell layer thinning) for prognosis, and visual evoked potentials (delayed latency) in doubtful cases.
• Differential diagnosis: ischaemic optic neuropathy, compressive optic neuropathy, Leber hereditary optic neuropathy, toxic and nutritional neuropathy, and retinal disease.

• Typical demyelinating optic neuritis:
  • Methylprednisolone 1 g intravenously daily for 3 days (500 mg to 1 g daily for 3 to 5 days), with or without an oral taper (prednisolone 1 mg/kg for 11 days). This speeds recovery by 2 to 3 weeks but does not change the final visual outcome. Oral prednisolone alone at a low dose (1 mg/kg) is not recommended because it was associated with a higher recurrence rate.
  • Cover during steroids: proton pump inhibitor (omeprazole 20 mg daily), glucose monitoring, and mood and sleep warnings.
  • Observation without steroids is acceptable in mild disease with good vision.
• Severe or steroid refractory visual loss and NMOSD or MOGAD: plasma exchange (5 to 7 exchanges on alternate days) or immunoadsorption if no improvement within 5 to 7 days of steroids, or earlier in NMOSD; early intervention improves outcomes.
• NMOSD relapse prevention: eculizumab (900 mg weekly for 4 weeks then 1200 mg every 2 weeks), inebilizumab 300 mg intravenously on days 1 and 15 then every 6 months, satralizumab 120 mg subcutaneously at weeks 0, 2, and 4 then every 4 weeks, or rituximab 1 g twice 2 weeks apart then every 6 months; azathioprine 2 to 3 mg/kg daily or mycophenolate 1 g twice daily with prednisolone are alternatives. Avoid interferon beta and fingolimod.
• MOGAD: steroids with slow taper, and maintenance with rituximab, mycophenolate, azathioprine, or intravenous immunoglobulin 0.4 g/kg for relapses.
• Multiple sclerosis: after MRI evidence of dissemination in time or space, start a disease modifying therapy (for example ocrelizumab 600 mg intravenously every 6 months, ofatumumab 20 mg subcutaneously monthly, natalizumab 300 mg every 4 weeks, dimethyl fumarate 240 mg twice daily, or teriflunomide 14 mg daily) in consultation with a neurologist.
• Infectious optic neuritis: treat the cause (for neurosyphilis, benzylpenicillin 18 to 24 million units daily intravenously for 10 to 14 days; for tuberculosis, standard regimens with steroids), with steroids once antimicrobial cover is established.
• Rehabilitation, vitamin D optimisation, and avoidance of smoking.
• Follow up at 1 month, 3 months, and 6 months with acuity, colour, fields, and OCT. Most patients (over 90 percent) recover to 20/40 or better by 6 months, though some have persistent contrast and colour deficits.
• Complications: optic atrophy with persistent deficits, recurrence, and conversion to MS or NMOSD.