Optic neuritis

• Optic neuritis:

  • Inflammatory optic neuropathy
  • Usually unilateral
  • Acute or subacute visual loss
  • Frequently occurs in associated with MS
• Causes:

  • Typically demyelinating optic neuritis associated with MS
  • Antibody mediation - neuromyelitis optica spectrum disorders
  • Non-infectious - neurosarcoidosis and systemic autoimmune conditions such as SLE
  • infectious - Syphilis, Lyme disease, cat-scratch disease, herpes zoster
  • Post infectious following an acute infection or immunisation
• Risk factors for ON include:

  • Known diagnosis of MS: up to 70% of patients with MS will have at least one episode. Optic neuritis can be the presenting feature of MS in up to 20% of cases.
  • Female sex: there is a female predominance by a ratio of 3:1
  • Young age: most patients are aged 20-50 years
  • Higher latitude: the incidence is higher for populations at higher or lower latitudes (the northern United States, northern and western Europe, southern Australia and New Zealand) compared with areas closer to the equator
• Symptoms of demyelinating ON:

  • Acute to subacute unilateral loss of vision
  • Retrobulbar and peri-ocular pain, exacerbated by movement
  • Photopsias - flashes exacerbated by eye movement
  • Visual field loss - can be any pattern of loss
  • Reduced contrast sensitivity and colour vision
• ophthalmic examination should include:

  • Visual acuity testing 
  • Colour vision assessment with an Ishihara test
  • Testing for a relative afferent pupillary defect (RAPD): this will be positive for the affected eye unless there is pre-existing disease in the contralateral eye.
  • Fundoscopy: swelling of the optic nerve may be visible in a third of patients. Over time, the optic nerve will develop pallor.
  • Testing extraocular muscle movements: expected to be normal in ON but may detect internuclear ophthalmoplegia (common in multiple sclerosis)
• Investigations:

  • Clinical diagnosis
  • MRI of the brain and orbits with gadolinium contrast will show enhancement of the optic nerve
  • MRI may also identify features suggestive of MS
  • A lumbar puncture may support diagnosis of MS
  • Patients with atypical features may require further tests to exclude other causes of optic neuritis
• Management:

  • IV methylprednisolone 1g OD for three days, followed by oral prednisolone taper
• Patients with ON have favourable outcomes with >90% recovering vision
• abnormalities such as contrast sensitivity, relative afferent pupil defect and abnormalities of colour perception may persist.
• The risk of recurrence in the affected or contralateral eye is about 30% at 5 years.