Optic neuritis (ON)

Inflammation of the optic nerve.

• M/C optic neuropathy in persons < 50 years
• M/C cause of acute unilateral visual loss in young adults
• Earliest clinical symptom in about 20% of cases of MS

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Etiopathogenesis

• Idiopathic inflammatory demyelination (M/C)
• Multiple sclerosis (MS) (#2 M/C)
• Neuromyelitis optica (NMO) “Devic’s disease”: Demyelinating autoimmune disease that in contrast to MS primarily affects the optic nerve and spinal cord

Less commonly:

• Autoimmune diseases: Sarcoidosis, systemic lupus erythematosus (SLE)
• Infectious and para-infectious causes: Syphilis, tuberculosis
• Inflammatory and post vaccination immunological responses: Sinusitis, and vaccinations against measles and rubella

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Classification

Anatomical classification:

1. Retrobulbar neuritis (normal optic disc appearance) (M/C, ​²⁄3 cases)
2. Papillitis (with swollen disc)
3. Perineuritis (involves optic nerve sheath while optic disc may/may not be swollen)
4. Neuroretinitis (with optic disc oedema and macular star exudates) (least common)

Clinical classification:

Based on clinical features

• Typical ON: Acute, severe visual disturbance without any clear diagnostic findings on ocular examination. It is characterized by:
  • Age 18–50
  • Unilaterality
  • Pain on eye movement
  • Subsequent improvement
  • No evidence of any systemic disease other than multiple sclerosis.
• Atypical ON: The fewer of these criteria are met, the higher the likelihood that the patient is suffering from an atypical form of optic neuritis, or from another disease

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Clinical feature

Earliest sign:

• Marcus Gunn pupil (relative afferent pupillary defect)

Classic triad:

The onset is usually with pain on eye movement in one eye and subacute visual loss.

1. Visual loss (subacute onset)
2. Periocular pain (especially on eye movement)
3. Dyschromatopsia (impaired colour vision)

Classic phenomena:

• Pulfrich phenomenon: Object swinging back and forth in the plane of vision is perceived as moving in a circle
• Uhthoff phenomenon (MS specific): Vision worsens when the body temperature rises as a result of athletic activity, other sustained physical exertion, or a hot bath or shower.

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Diagnosis

Swinging flashlight test (for RAPD):

Direct pupillary light reaction and the accompanying consensual reaction of the opposite pupil are weaker on illumination of the affected eye than on illumination of the unaffected eye due to unilateral or asymmetrical disease of the retina or optic nerve

MRI (gadolinium enhanced):

Most important ancillary test; it can directly reveal inflammation of the optic nerve

Optical coherence tomography (OCT):

Reflects the severity of damage in optic neuritis and in related conditions such as neuromyelitis optica

• Thinning of the peripapillary retinal nerve fiber layer

Differential diagnosis:

Conditions which are thought to be non-inflammatory and most closely resemble the clinical profile of optic neuritis

• Anterior Ischemic Optic Neuropathy (AION): Unilateral sudden painless loss of vision, varying from visual acuity of better than 6/6 to no light perception with impairment of color vision and altitudinal visual field defect.
• Leber’s Hereditary Optic Neuropathy (LHON): Sub-acute and painless visual loss with central scotoma and poor color vision with sequential involvement of both eyes over a period of weeks to months

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Management

IV corticosteroids followed by oral taper

Treatment of choice which hastens recovery but does not recover lost vision. Only oral steroids increase risk of recurrence

• IV Methylpredisone (1g/day x 3 days), followed by
• Oral Methylprednisone (1mg/kg/day x 11 days)

Interferons

Long-term management

• β-interferon 1a: Reduces risk of MS after optic neuritis
• Glatiramir acetate (20mg) SC: Treatment of optic neuritis in MS