Optic Neuritis

Inflammation of the optic nerve — usually caused by multiple sclerosis (MS), of which it is often the presenting symptom. See neurology/multiple-sclerosis.md for current disease- modifying therapy (anti-CD20 agents now first-line for high-efficacy treatment).

Other causes

Category	Causes
Infectious	Viral encephalitis (especially children), sinusitis, meningitis, TB, syphilis, HIV
Neoplastic	Metastasis to the optic nerve
Drugs/toxins	Lead, methanol, quinine, arsenic, certain antibiotics
Rare	Neuromyelitis optica, MOG-IgG disease, diabetes, pernicious anaemia, autoimmune disease, thyroid eye disease (Graves’ ophthalmopathy — see thyroid-eye-disease.md), bee stings, trauma

Presentation

Demographics: typically age 20–40. Classic triad: vision loss, eye discomfort, reduced colour vision, ± RAPD.

• Vision loss, maximal over 1–2 days, usually a small central or paracentral scotoma; may progress to complete blindness
• Mild eye pain, worse with eye movement
• Only one eye affected

Examination

• Fundoscopy: optic disc may be swollen (papilloedema)
• Reduced visual acuity
• Disturbed colour vision — characteristically out of proportion to the reduction in visual acuity
• Relative afferent pupillary defect (RAPD)

Investigations

Gadolinium-enhanced MRI — to identify demyelinating disease (MS, MOG-IgG, neuromyelitis optica).

Management

• IV methylprednisolone 500–1000 mg, as for an MS flare. This hasn’t been shown to change the long-term visual outcome compared with observation alone, but may speed recovery and delay onset of further MS symptoms — treat if MS is suspected
• Discuss with neurology or ophthalmology
• Most cases resolve spontaneously over 2–3 months