Inflammatory optic neuropathy usually affecting one eye at a time and typically presents with acute or subacute visual loss

Aetiology

• Typical (demyelinating) ON is strongly associated with MS
• Other atypical causes include:
  • Antibody-mediated: neuromyelitis optica spectrum disorders (NMOSD) and myelin oligodendrocyte glycoprotein antibody disease (MOGAD)
  • Non-infectious: neurosarcoidosis and systemic autoimmune conditions such as SLE
  • Infectious: syphilis, Lyme disease, cat-scratch disease, herpes zoster, sinus disease
  • Post-infectious: following an acute infection or immunisation

Clinical features

Symptoms

• Acute to subacute unilateral loss of vision
• Retrobulbar and peri-ocular pain
• Photopsias (flashes) exacerbated by eye movements
• Visual field loss: any pattern of field loss may be seen including diffuse, altitudinal, central and sectoral losses
• Reduced contrast sensitivity and colour vision

Signs

• Reduced visual acuity on testing with Snellen chart
• Changes in colour vision on testing with Ischihara test
• RAPD positive in affected eye (unless there is pre-existing disease in the contralateral eye)
• Testing extraocular movements: expected to be normal but may detect internuclear ophthalmoplegia (common in multiple sclerosis)

Investigations and management

• See multiple sclerosis