Occlusion of the central retinal artery – the principal blood supply to the retina – may be caused by diverse mechanisms, of which embolism from the carotid arteries or heart is the most common. Other rarer causes include inflammatory conditions (e.g. giant cell arteritis (GCA), collagen vascular diseases) and coagulation disorders (e.g. polycythemia and antiphospholipid syndrome). When a diagnosis of central retinal artery occlusion (CRAO) is suspected, two urgent considerations are of paramount importance:
- The duration of symptoms – determines the urgency of treatment
- Exclusion of inflammatory conditions that require prompt treatment with corticosteroids.
The typical symptoms are severe, sudden, unilateral, painless loss of vision. Amaurosis fugax may have occurred previously. Other symptoms may give a clue to a potentially treatable cause (e.g. jaw claudication with GCA).
Acuity is typically reduced to light perception or worse. Central vision may be preserved in about 20 per cent of cases, when a portion of macular nerve fibres is supplied by one or more cilioretinal arterioles. There is usually a marked relative afferent pupillary defect. Emboli may be visible in the retinal circulation. On systemic examination, a carotid bruit, irregular heart beat or signs of an inflammatory disorder may suggest a cause.
Within a few hours of CRAO, swelling of the retinal nerve fibre layer causes retinal pallor. A cherry-red spot appears in 42 foveola (where the nerve fibre layer is
thinnest, allowing visualization of the vascular choroid beneath). The cherry-red spot recedes after approximately 6 weeks. Optic disc pallor develops as nerve fibres degenerate.
Very rare (approximately 1 per 100,000 per year).
CRAO must always be considered in the differential diagnosis of sudden, painless loss of vision. When a patient presents within around 2 hours of onset of symptoms, rapid treatment may possibly provide some benefit.
Acute ophthalmic artery occlusion; arteritic ischemic optic neuropathy; macular hemorrhage; retinal detachment; retinal vein occlusion; vitreous hemorrhage.
Urgent treatment Unfortunately, treatment of this condition is unsatisfactory, with minimal evidence to suggest that it improves prognosis. The goal of therapy is to increase the effective perfusion pressure of the retinal circulation as soon as possible; the principal strategy is to lower intraocular pressure. Urgent treatment is generally considered appropriate within around 2 hours of symptom onset, because retinal tissue appears unable to tolerate complete ischemia for more than a few hours. However, as absolute arterial occlusion is rare, some clinicians advocate treatment within 48 hours of symptom onset. Common emergency measures include:
Recent central artery occlusion. Look for the blurring of the retinal vessels, particularly inferiorly, from the swollen retinal axons. Note the cherry-red spot, multiple emboli and stagnation of blood flow in surrounding arterioles.
- Ocular massage – to lower intraocular pressure, increase blood flow and dislodge emboli
- Medications – acetazolamide and/or topical p blockers
- Anterior chamber paracentesis – a needle is passed through the corneal limbus and used to withdraw fluid until the anterior chamber shallows slightly.
Blood tests Urgent erythrocyte sedimentation rate and C-reactive protein levels are measured in patients over 60 years of age, when a diagnosis of GCA cannot be excluded. Coagulation studies, full blood examination and screening tests for vasculitis are usually performed. In the longer term, cardiovascular risk
assessment includes measurement of fasting blood sugar levels and lipid profile.
Ocular investigations Fluorescein delayed arterial filling and masking of background fluorescence by retinal edema.
Surgery Carotid endarterectomy is generally indicated for incomplete stenotic lesions of the carotid artery greater than 70 per cent. Lesser degrees of stenosis are treated non-surgically (i.e. medications and lifestyle adjustments).
Review Initial review is often conducted after an interval of several weeks. Evidence of iris or disc neovascularization is treated with panretinal photocoagulation.