Anterior Ischaemic Optic Neuropathy

Background

• Ischaemia of the optic nerve can have several causes with differing severity.  They can be classified by cause and location depending on the symptoms and presentation.
  • Non-arteritic AION (around 5/100,000)
  • Arteritic AION (rarer- almost always associated with Giant cell arteritis)
• Anterior ION affects the anterior 1mm segment of the optic nerve head- the optic disc. 
  • (Posterior ION can be due to any condition that causes ischaemia to any portion of the optic nerve posterior to the optic disc (i.e. will not cause disc oedema

Aetiology/Risk factory

• Arteritic AION is almost always secondary to Giant cell arteritis (see here)
• NAAION rarely occurs in isolation.  Risk factors include
  • Cardiovascular risk factors (hypertension, hyperlipidaemic, diabetes etc).  It is thought that inadequate perfusion of the optic disc is the main cause of ischaemia.  This could be made worse by
    • Small optic disc (increased vascular congestions
    • Dysregulation of blood flow to the optic disc (normally autoregulated but possibly altered by CVS risk factors)
      • Nocturnal hypotension- not uncommon in CVS patients- may worsen this
  • It is hypothesised that NAAION may not be caused (solely) by arterial factors, but by venous congestion, which would fit more with the symptoms and pathology (i.e. no haemorrhages etc)
  • Sleep apnoea syndrome has been linked with NAAION (? nocturnal increases in BP and subsequent optic disc vascular dysregulation)
  • Medications e.g. interferon alpha (? immune complex deposition in capillaries of the optic disc) NB No proven link

Presentation

• Acute (hours-days), painless unilateral visual loss
  • Blurring/clouding (rarely complete- if so consider alternative diagnosis)
  • Often central/inferiorly
  • Often on wakening
• Rarely accompanying pain but headache/periocular pain may be present in 10% (consider also optic neuritis)
• On examination
  • Most patients don’t have complete visual loss and on acuity examination, most will be between 20/64 and 20/200.
  • Colour loss can be present- often proportionate to visual acuity loss.
  • Pupils should be equal and round.  A relative afferent pupillary defect will be present (as long as other eye is normal)
  • Optic disc oedema is always present.  Often hyperaemic in NAAION and pallid in AAION; segmental (inferiorly more common)
  • Peripapillary splinter haemorrhages are common (cf uncommon in optic neuritis)
    • 
  • Retinal arterioles may show narrowings in the peripapillary region too

Investigations

• FBC, CRP and ESR/PV can be done to exclude/include GCA as a potential cause (this is very important as GCA can cause acute blindness- URGENT)
• Otherwise NAAION is a clinical diagnosis

Management

• If GCA is found, treat with steroids
• If NAAION is the diagnosis, unfortunately there is no treatment
  • Most patients’ vision will stabilise within several months, some will recover (20-40%, younger patients more likely), most will remain constant, others will deteriorate further