Retinal Arterial Occlusion
Retinal arterial occlusion, including central retinal arterial occlusion (CRAO) and branch retinal arterial occlusion (BRAO), is an ophthalmic and stroke emergency caused by obstruction of the retinal arterial circulation.
This updated UKMLA guide to retinal arterial occlusion is based on the AHA scientific statement, which covers causes, risk factors, symptoms, diagnosis, and management.
Types and Anatomy
| Type | Implications |
|---|---|
| Central retinal arterial occlusion (CRAO) | Whole/near-whole retina affected |
| Branch retinal arterial occlusion (BRAO) (occlusion of a branch of the central retinal artery – distal to the central retinal artery) | Only part of the retina is affected |
Simplified (high-yield) blood supply to the eye:
The internal carotid artery gives off the ophthalmic artery, which then gives off the central retinal artery to supply the inner retina via multiple branch retinal arteries.
The retina has a dual blood supply:
- The central retinal artery supplies the inner retina
- The choroidal circulation supplies the outer retina (explains the cherry-red spot sign mentioned below)
Causes and Risk Factors
| Category | Description | Specific causes and risk factors |
|---|---|---|
| Thromboembolic occlusion (non-arteritic) | Most common form (~95% cases)
Blood flow is interrupted by embolism or thrombus formation |
Embolisation typically arises from:
Risk factors:
|
| Inflammatory occlusion (arteritic) | ~5% cases
Arteries occluded by an active inflammatory process |
Most common cause: giant cell arteritis (GCA) (temporal cell arteritis)
Suggestive factors:
|
| Rare causes |
|
|
Clinical Features
Typical presentation: sudden, painless, unilateral vision loss
| CRAO | BRAO |
|---|---|
|
|
Retinal arterial occlusion (CRAO and BRAO) is a form of acute ischaemic stroke (specifically a retinal infarction). Therefore, 30% cases of CRAO have concurrent ischaemic stroke.
Investigation and Diagnosis
CRAO can be diagnosed if there are typical clinical features (see above) + dilated fundoscopic examination
Typical fundoscopic findings of CRAO (suggestive of retinal hypoperfusion):
- Diffuse retinal whitening (due to inner retinal ischaemia and oedema)
- Cherry red spot at the fovea (due to the dual retinal blood supply)
- Retinal arterial attenuation (narrowed retinal artery – “boxcarring”)
- Optic disc is typically normal initially
In BRAO, the classic CRAO findings are localised / segmental rather than diffuse, because only one branch of the central retinal artery is occluded. In some cases, a visible embolus might be visible.
The classic fundoscopic findings of CRAO may take time to become fully evident as the ischaemia progresses. Initially, the fundus may appear relatively normal.
Given that, a clinical history of sudden, painless vision loss combined with the presence of a relative afferent pupillary defect strongly implicates CRAO. A normal fundoscopy should NOT exclude the diagnosis.
If the fundoscopy is inconclusive, consider:
- Optical coherence tomography (OCT) to detect retinal thickening and oedema secondary to retinal ischaemia
- Relatively quick and effective procedure, useful in the acute setting to confirm the diagnosis
- Fluorescein angiography to confirm delayed or absent retinal perfusion
- Time-consuming procedure and usually not necessary to establish a definitive diagnosis
Other Investigations
Perform the following for ALL patients:
- Visual acuity and visual field assessment
- Structured neurological assessment to assess for stroke (e.g. NIHSS )
- Non-contrast head CT to exclude haemorrhage
If CRAO is thought to be caused by underlying giant cell arteritis → check ESR and CRP immediately
Work up post-acute phase:
- Carotid artery imaging (ultrasound or CT/MR)
- Echo for structural heart disease or cardioembolic sources
- Ambulatory cardiac rhythm monitoring for AF
CRAO vs CRVO
Key differences in CRAO vs CRVO:
| Feature | CRAO (central retinal arterial occlusion) | CRVO (central retinal vein occlusion) |
|---|---|---|
| Underlying mechanism | Arterial occlusion → retinal ischaemia | Venous occlusion → retinal congestion and haemorrhage |
| Typical onset | Very acute | More subacute |
| Visual impairment | Usually severe and profound monocular blindness | Variable visual loss (may be mild to severe) |
| RAPD | Common | May occur |
| Fundoscopic findings | Diffuse pale / white retina + cherry-red spot | Blood-shot retina: widespread retinal haemorrhages and oedema |
Management
Acute Management
CRAO is a medical emergency equivalent to an acute ischemic stroke.
Definitive management: acute reperfusion therapies (for non-arteritic / thromboembolic CRAO):
- 1st line: consider IV thrombolysis (e.g. alteplase) if the patient presented <4.5 hours of symptom onset with NO contraindications
- If IV thrombolysis is contraindicated and the patient has visual deficits → consider intra-arterial thrombolysis (it remains an unproven therapy with procedural risks like arterial dissection, requires a specialised endovascular team)
Hyperbaric oxygen therapy can be used as a safe temporary measure to salvage retinal tissue and preserve viability while definitive reperfusion therapy is pursued (the retina can derive up to 97% of its oxygen from the underlying choroidal circulation under hyperbaric conditions).
Traditional “conservative” therapies aiming to lower IOP or dilating vessels to dislodge the embolus are no longer endorsed, including:
- Ocular massage
- Anterior chamber paracentesis
- Topical pressure-lowering drugs
- Haemodilution
Current evidence shows these are not effective (yielding worse visual recovery rates than the natural history of the disease), and some may even be harmful.
If CRAO secondary to giant cell arteritis is suspected, give high-dose IV methylprednisolone to preserve vision in the contralateral eye, followed by a temporal artery biopsy.
Chronic Management (Secondary Prevention)
If CRAO is caused by atherosclerosis of unknown origin:
- Long-term antiplatelet therapy (aspirin or clopidogrel)
- If an underlying cardioembolic source (e.g. AF) is found → long-term oral anticoagulation
Interventions:
- If severe, high-grade stenosis of the ipsilateral carotid artery is found → surgical revascularisation (carotid endarterectomy or stenting) is indicated to prevent recurrent strokes