Retinal arterial occlusion (RAO)

Question 1

what is the etiology of RAO?

Answer 1

• embolism and thrombosis: atheromatous carotid plaque from bifurcation of the common carotid artery (CCA)
• Inflammation in or around the vessel wall/vasculitis (e.g. giant cell arteritis [GCA], systemic lupus erythematosus [SLE], Wegener granulomatosis, polyarteritis nodosa), vasospasm (e.g. migraine) and systemic hypotension contribute in a minority
• Thrombophilic disorders that may be associated with retinal artery occlusion (one-third of young patients) include hyperhomocysteinaemia, antiphospholipid antibody syndrome and inherited defects of various natural anticoagulants.

Question 2

what are the symptoms of CRAO?

Answer 2

visual loss over the entire field of vision

Question 3

what are the symptoms of BRAO?

Answer 3

hemifield defect (sectoral or altitudinal defect). If painful CRAO

Question 4

what is amaurosis fugax?

Answer 4

transient (usually a few minutes) monocular loss of vision, often described as a curtain coming down over the eye; the absence of pain may be included in the definition.

In clinical practice, it is typically used to refer to transient LOV of embolic origin.

Question 5

What are the signs for CRAO & BRAO?

Answer 5

• Reduced visual acuity
• **Profound RAPD
• the classic findings of retinal whitening and a cherry red spot are due to opacification of the nerve fibre layer as it becomes oedematous from ischaemia.
• Examination of the retinal blood vessels shows segmental blood flow, classically described as boxcarring.

Minutes to hours: evidence of vascular stasis

• **Attenuated retinal arteries
• **Cattle trucking/boxcarring – interrupted columns of blood within retinal vessels (due to sluggish blood flow)

Hours: evidence of ischaemia

• Pale retina due to oedema in ganglion cells, loss of normal transparency corresponding to area of ischaemia (due to infarction and tissue necrosis)
• **Cherry red spot at macula in CRAO: normal orange-red of fovea contrasts against pallor of perifoveal retina (no ganglion cells at fovea, allowing colour of choroid to be seen)

Question 6

What is management of CRAO/ BRAO?

Answer 6

Immediate management

• Ocular massage (attempt at dislodging embolus and moving it distally to restore proximal/central retinal blood flow)
• Carbogen therapy (induce vasodilation) (breathe through a paper bag; more porous than plastic bag (do NOT use plastic bag))
• Lower IOP

STAT high dose systemic steroids if arteritic anterior ischaemic optic neuropathy (AAION) is suspected, i.e. if GCA is suspected (consider in elderly w/o visible embolus)

Further management

• Investigate source of emboli (e.g. carotid U/S, 2D echocardiogram [2DE]) – risk of stroke (concurrent silent ischaemic stroke is not uncommon). Refer to cardiovascular medicine (CVM)
• Exclude thrombophilic disorders
• Exclude inflammatory vasculopathies
• Monitor for neovascularisation