Neuro-ophthalmology: Optic Neuritis

Question 1

What are the causes of optic neuritis?

Answer 1

• Infection of optic nerve:
  o Caused by local infection to optic nerve e.g. sinus, syphilis, Lyme disease, Herpes zoster, cat-scratch disease
  o Following a viral infection e.g. chicken pox, whooping cough, glandular fever, measles, mumps
  o Following an immunisation – rare
• Inflammation of optic nerve (non-infectious):
  o Sarcoidosis
  o Autoimmune disease
• Demyelination of optic nerve (most common)

Question 2

What are the symptoms of optic neuritis?

Answer 2

• Monocular visual impairment – causes are more likely to be isolated
• Subacute: develops over several days to 2 weeks
• Discomfort, exacerbated by eye movements which precedes visual loss in majority of cases
• Globe tenderness

Question 3

What will are the signs of optic neuritis?

Answer 3

• VA 6/18 – 6/60 or worse
• RAPD – monocular, affects 1 eye, affects amount of light being transmitted by that one eye
• Reduced colour vision/ red desaturation
• Reduced contrast sensitivity
• Field Defects:
  o Generalised depression
  o Nerve fibre bundle defects – akin to those seen in glaucoma
  o Central loss
• Fundus Examination:
  o Normal in most cases (retrobulbar neuritis – inflammation behind ONH – inflammation of optic nerve but not affecting ONH itself)
  o Could get swollen disc

Question 4

Describe demyelination causing optic neuritis?

Answer 4

• Disrupts nerve conduction within brain, brainstem & spinal cord sparing peripheral nerves
• In general, spares the more peripheral nerves – more of central condition
• Causes:
  o Multiple sclerosis (most common) – most often unilateral optic neuritis
  o Isolated optic neuritis w/ no other demyelination, but that may subsequently develop
  o Devic disease or Schilder disease, both rare & produce bilateral optic neuritis

Question 5

Brainstem demyelinating lesions may also cause…?

Answer 5

• Cranial nerve palsies
• Gaze palsies
• Facial nerve palsies
• Nystagmus

Question 6

Describe multiple sclerosis?

Answer 6

• MS is an inflammatory, demyelinating disease of CNS
• Multiple exacerbations characterised by variable CNS involvement –> not just one incident, series of incidents
  o Exacerbations are separated in time & anatomical location
• Optic neuritis is presenting feature in 15-20% of those w/ MS
• 50% of those w/ MS will get optic neuritis at some point
• If have optic neuritis, overall 10 year risk of getting MS is 38%

Question 7

Describe neuro-retinitis?

Answer 7

• Feature of optic neuritis is neuro-retinitis
• Acute loss of vision (usually painless)
• Disc oedema – diffuse, spreads to involve around fovea at plexiform layer
• Star pattern of exudates at macula
• Tortuous BVs
• Causes:
  o Demyelination – rare
  o 66% secondary to cat-scratch disease
  o Syphilis
  o Lyme disease
  o Viruses

Question 8

What is the management of optic neuritis? (both in community and hospital)

Answer 8

• In community, difficult to differentiate from other causes of swollen disc – macular star, unilateral, slightly insidious onset can all help but need blood tests done
• Emergency referral to hospital
• Most need no medical tx, but may receive:
  o Intravenous steroids followed by oral course speed recovery by 1-2 weeks
  o Oral steroids alone associated w/ increased recurrence rate
  o Corticosteroids have no long-term effect on visual outcome
• To find out cause, speak to px about the various causes of optic neuritis & find out which applies
• If relapsing-emitting MS, immunomodulatory therapy for reducing morbidity
• If suspect MS, MRI scan:
  o Look for periventricular white matter lesions
  o Assesses risk of future MS:
   No lesions: 25% risk at 15 years – 1 in 4 chance
   >1 lesion: 72% at 15 years
   Overall risk if no scan: 50%
• Unresolving cases w/ other signs should raise suspicion of other underlying cause:
  o Blood tests – inflammatory markers, infective serum tests
  o CSF
  o Chest X-ray

Question 9

What is the prognosis of optic neuritis?

Answer 9

• Recovery within 1 month, lasting up to 6 months
• 75% recover to 6/9 or better
• May be permanent loss of colour perception & contrast sensitivity – even if VA improves
• Optic atrophy after optic neuritis – 4-6wks after optic neuritis
• Pseudo-Foster Kennedy syndrome:
  o If contralateral eye affected
  o Unilateral disc swelling in one eye with contralateral optic atrophy in absence of mass compressing nerve