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
- 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
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