Understanding Central Retinal Artery Occlusion (CRAO)

What Is Central Retinal Artery Occlusion?

The central retinal artery is the primary arterial supply to the inner layers of the retina. When it is completely occluded — by an embolus, thrombosis or vasculitis — blood flow to virtually the entire retina ceases. The consequences are immediate and severe: retinal infarction begins within 90–100 minutes of complete ischaemia, and photoreceptors begin to die rapidly thereafter.

CRAO is rightly considered the ocular equivalent of a stroke. Like a cerebral stroke, time is the critical factor — the longer the occlusion persists, the more irreversible the ischaemic damage. Unlike many retinal conditions where treatment can be planned over days, CRAO demands an immediate response.

Causes

The most common cause of CRAO is an embolusoriginating from the carotid artery or heart, which lodges at the central retinal artery’s entry point into the optic nerve. Other causes include:

• • Atherothrombosis in situ — particularly in patients with severe hypertension or diabetes
• • Giant cell arteritis (GCA) — inflammatory occlusion; the most important to exclude because it is treatable and the fellow eye is at risk
• • Severe systemic hypotension — haemodynamic insufficiency reducing perfusion pressure below a critical threshold
• • Coagulation disorders — particularly in younger patients without conventional risk factors
• • Cardiac emboli — from atrial fibrillation, valvular disease or intracardiac thrombus

Symptoms and Signs

CRAO presents as sudden, painless, profound vision lossin one eye — typically down to counting fingers or hand motion only. The onset may be preceded by episodes of amaurosis fugax (transient monocular visual loss), which should be regarded as a warning sign of impending occlusion.

On fundoscopic examination, the classic findings are:

• • Pale, milky-white opacification of the retina from ischaemic oedema of the inner retinal layers
• • Cherry-red spot at the fovea — the fovea is supplied by the choroidal circulation (rather than the retinal artery), so it retains its red colour against the surrounding pale retina
• • Attenuated, thread-like retinal arteries with segmented “cattle-trucking” of blood column
• • A visible embolus may be seen at the optic disc or within the central retinal artery

Giant Cell Arteritis — Must Exclude

Giant cell arteritis (GCA) is a systemic granulomatous vasculitis affecting medium and large arteries, almost exclusively in patients over 60 years of age. In the eye, GCA can occlude the posterior ciliary arteries or the central retinal artery, producing sudden, complete visual loss.

GCA must be considered in every patient with CRAO, particularly those over 60. Suggestive symptoms include: new headache (often temporal), jaw claudication, scalp tenderness, shoulder or hip girdle aching, fever, weight loss and malaise. ESR and CRP should be checked immediately.

If GCA is suspected, high-dose intravenous methylprednisolone (500–1000 mg/day for 3 days)should be commenced immediately — before temporal artery biopsy results are available. Biopsy can be performed within 2 weeks of starting steroids without significantly affecting diagnostic yield. The priority is protecting the fellow eye.

Investigations

The systemic workup for CRAO is urgent and comprehensive:

• • ESR and CRP immediately — to assess for GCA; raised values in an older patient with CRAO should prompt urgent steroid treatment
• • Blood pressure — measured immediately
• • ECG — to identify atrial fibrillation or other arrhythmia
• • 24-hour Holter monitor — to detect paroxysmal AF
• • Echocardiography — transthoracic or transoesophageal to assess for cardiac embolic sources
• • Carotid Doppler — to detect ipsilateral carotid stenosis
• • Fasting glucose, HbA1c and lipid profile
• • Full blood examination and coagulation studies
• • Thrombophilia screen in younger patients without conventional risk factors

Treatment

GCA-related CRAO: immediate high-dose intravenous corticosteroids, as described above. This is the only CRAO scenario where a specific treatment reliably alters outcome (by protecting the fellow eye).

Non-arteritic CRAO (acute, within 24 hours):

• • Ocular massage — intermittent digital pressure to lower IOP transiently and potentially dislodge the embolus into a peripheral branch
• • Topical or systemic IOP-lowering agents — to increase the arterial perfusion pressure gradient
• • Anterior chamber paracentesis — rapid IOP reduction via drainage of aqueous humour; performed at the slit lamp by an ophthalmologist
• • Intravenous thrombolysis (tPA) — may be offered at specialist stroke centres within 4.5 hours of onset; evidence is limited but rationale is sound given the embolic mechanism

Systemic secondary prevention is initiated regardless of the acute scenario: antiplatelet therapy, statin, antihypertensives, anticoagulation if AF, and carotid endarterectomy if significant stenosis is identified.

Prognosis

The visual prognosis of CRAO is generally poor. Fewer than 10% of patients recover useful vision without treatment. Even with acute intervention, the narrow time window for potential benefit means that most patients present too late for meaningful vision restoration. Patients with a cilioretinal artery (a separate arterial supply to part of the macula in some individuals) may retain an island of central vision even after complete CRAO.

Beyond the eye, CRAO carries significant systemic implications: patients face elevated rates of stroke and myocardial infarction in the years following the occlusion, and long-term follow-up with a physician for cardiovascular risk management is essential.

Conclusion

CRAO is one of the most devastating and time-sensitive emergencies in all of ophthalmology. Immediate assessment, prompt exclusion of giant cell arteritis, and urgent cardiovascular investigation are the priorities. While visual recovery is often limited, identifying and treating the underlying cause can protect the fellow eye, prevent a cerebral stroke, and reduce long-term cardiovascular mortality. Any episode of sudden, complete vision loss in one eye must be treated as a medical emergency.

Frequently Asked Questions