Neuro-ophthalmology: Ischaemic Optic Neuropathy

Question 1

List the types of ischaemic optic neuropathy?

Answer 1

• Anterior Ischaemic Optic Neuropathy (AION)
  o Arteritic Anterior Ischaemic Optic Neuropathy (AAION)
  o Non-arteritic Anterior Ischaemic Optic Neuropathy (NAION)
• Posterior Ischaemic optic neuropathy

Question 2

Describe anterior ischaemic optic neuropathy (AION)?

Answer 2

• Most common optic neuropathy over 50 years
• Represents ischaemic damage to ONH – something has happened to the BVs & supply of oxygen to ONH
  o Anterior  affects arteries placed anterior
• Visual loss (both types):
  o Painless, monocular visual loss over hours to days – blood supply just going in one eye
  o Altitudinal defects most common – because arteries branch into inferior & superior divisions, tends to innervate one or other half of retina
  o Reduced central vision – most of blood supply is going to macula area & if get blockage then get reduced blood supply to this area
• Relative afferent pupillary defect – as affects one eye  D+C responses may be fine
• Optic disc oedema present from onset of the loss of blood supply

Question 3

Describe arteritic anterior ischaemic optic neuropathy (AAION)?

Answer 3

• More severe & less common
• 5-10% of AION cases
• Occurs in older pxs – 70/80 year olds
• Caused by Giant Cell Arteritis (GCA)
  o Inflammatory & thrombotic occlusion (blockage) of short posterior ciliary arteries causing optic nerve head infarction (reduced blood supply to ONH)
   Blockage in blood supply due to inflammation & thrombosis of PCAs
• Systemic Symptoms:
  o Variable
  o No systemic symptoms in 20% (1 in 5)

Question 4

Describe giant cell arteritis including symptoms and visual examination?

Answer 4

• Granulomatous necrotising arteritis
• Affects large & medium sized arteries, especially:
  o Superficial temporal artery
  o Ophthalmic artery – central retinal artery branches from this
  o Posterior ciliary artery
  o Proximal vertebral artery
  o 5-10% of GCA have AAION
• Usually 60-80 years old
• Tender, hardened, non-pulsatile temporal artery
  o Scalp tenderness, especially on brushing hair
• Jaw claudication – pain on speaking or chewing, almost pathognomonic – v indicative of GCA
• Proximal muscle weakness – typically shoulders, same side as eye affected – may occur 1st
• Reduced appetite
• Unexplained weight loss
• Unexplained lethargy, malaise, depression – feels like having flue/cold
• Visual Symptoms:
  o Sudden, profound, visual loss – blockage in blood supply – happens suddenly
  o Usually unilateral (initially) – usually affects one artery
  o May be proceeded by transient visual obscurations, flashing lights – lost vision & it came back
  o Periocular pain – strong, stabbing pain
• Visual Examination:
  o Severe visual loss – likely to be <6/60
  o Pale, swollen disc – loss of blood supply
  o Cotton wool spots – retinal ischaemia – RNFL losing its function
  o Over 1-2 months, swelling resolves leaving optic atrophy

Question 5

What is the management of AAION?

Answer 5

• If in community, immediate (same day) referral to ophthalmologist
  o Possible that other eye can be affected or blockage can occur elsewhere causing a stroke
• Treatment aimed at preventing blindness of 2nd eye  aimed at preventing stroke also
  o Px’s vision in their affected eye will not come back

Question 6

What is the management by ophthalmologist of AAION?

Answer 6

• Immediate therapy is essential
• Confirmed w/ immediate blood results (Erythrocyte Sedimentation Rate (ESR)/CRP/Platelets)
• Temporal artery biopsy confirms diagnosis
• Usually overnight stay in hospital
• High dose systemic steroid (IV or oral (less likely)) – to reduce inflammation/damage
• Blood tests aid in tapering of steroids which is done in response to serial blood tests & symptoms
• Pxs may remain on oral steroids for years (average 1-2 years) – to try & prevent another attack happening in future

Question 7

What is the prognosis of AAION?

Answer 7

• Visual loss usually permanent
• Prompt administration of steroids may allow partial visual recovery
• In 25% of causes, 2nd eye affected despite tx, this could be within days

Question 8

Describe non-arteritic anterior ischaemic optic neuropathy (NAION)?

Answer 8

• More common, least sever & more easily treated
• 90% of AION cases
• Occlusion of short posterior ciliary arteries causing infarction of ONH
• Typically in 55-70yrs (average 60yrs) – younger compared to AAION
• Structural “crowding” of disc when cup is small/absent – predisposes these pxs to having an occlusion of the arteries

Question 9

What are the common risk factors of NAION?

Answer 9

• Diabetes
• Hypertension
• High cholesterol
• Smoking

Question 10

What are the symptoms of NAION?

Answer 10

• Sudden, painless loss of vision
• Unilateral
• Visual impairment on wakening (nocturnal hypotension (BP reduces overnight as sleep) on top of the other problems)
• Lack of systemic symptoms that are present in GCA

Question 11

Describe the examination of NAION?

Answer 11

• VA:
  o Moderate to severe reduction in VA in most px – 6/24, 6/36
  o 30% have normal or slightly reduced VA
• Visual Fields:
  o Commonly inferior altitudinal defect – superior retina
  o Often respect horizontal midline
• Dyschromatopsia:
  o Colour vision is affected
  o Proportional to amount of VA loss
• After initial loss of vision, most pxs have no further visual loss although in a small number, visual loss continues for about 6 weeks
• Fundus Examination:
  o Disc oedema diffuse or segmental (in just one section if one artery or smaller artery is affected)
  o Disc hyperaemic w/ focal telangiectasia (general dilation of capillaries causing them to appear as small red/purple clusters – spidery in appearance) on disc surface
   Dilating up to supply more blood to the area
  o Often a few peripapillary splinter-shaped haemorrhages
  o Atrophy within 3 to 8 weeks of onset of blockage
  o Contralateral usually small with absent cup – “disc at risk” – at risk of occlusion – BVs are crowded and pressurised together

Question 12

What is the management of NAION?

Answer 12

• In community, difficult to differentiate from other causes of swollen disc & AAION
• Refer emergency same-day
• Hospital does tests – treat underlying cause
• Prophylaxis? Aspirin is frequently given but does not appear to reduce risk in fellow eye

Question 13

What is the prognosis of NAION?

Answer 13

• Most px have no further visual loss although in a small number, visual loss continues for about 6wks
• Some recovery (e.g. 2 lines) in 31% at 2yrs
• Chance of other eye being affected is 15% over 5yrs
• Risk factors for other eye are:
  o Poor VA in 1st eye
  o Diabetes
• Pseudo-Foster Kennedy syndrome if contralateral eye affected
  o Unilateral disc swelling w/ contralateral optic atrophy in absence of mass compressing nerve

Question 14

Describe posterior ischaemic optic neuropathy?

Answer 14

• Much rarer than AION
• Obstruction of plial artery/capillary plexus leading to ischaemia to retrolaminar part of optic nerve
  o Compared to AION which was obstruction of PCA
• All systemic symptoms and risk factors for AAION & NAION are same here
• After surgical procedure of spine:
  o Arteritic (similar to AAION)
  o Non-arteritic (similar to NAION)
• Diagnosis after ruling out other causes (compression, inflammation)