What is Central Retinal Artery Occlusion (CRAO)?
CRAO is an interruption of blood flow through the central retinal artery caused by thromboembolism or vasospasm, resulting in retinal infarction—it is a form of acute ischemic stroke affecting the eye. 1
Definition and Classification
CRAO represents retinal cell death due to ischemia, formally classified as part of the central nervous system infarction spectrum, making it a true stroke equivalent rather than merely an ophthalmologic condition. 1, 2
The condition has several important subtypes:
- Nonarteritic CRAO: Results from local thrombus formation or thromboembolism (most common form) 1
- Arteritic CRAO: Occurs in the context of systemic inflammatory conditions like giant cell arteritis 1
- CRAO with cilioretinal artery sparing: When a patent cilioretinal artery preserves central vision while peripheral vision is lost 1
- CRAO without cilioretinal artery sparing: Complete loss of central retinal artery perfusion 1
Anatomic and Pathophysiologic Basis
The central retinal artery originates from the ophthalmic artery (the first branch of the internal carotid artery) and supplies the inner retina, including the retinal nerve fiber layer, ganglion cell layer, and inner plexiform layer. 1
The critical window for irreversible retinal damage is approximately 97 minutes of complete occlusion, with severe permanent damage occurring after 240 minutes. 3 This narrow therapeutic window makes CRAO a true medical emergency requiring immediate intervention. 2, 4
Epidemiology and Risk Profile
The incidence is 1.9 per 100,000 person-years in the United States, rising dramatically to 10.1 per 100,000 in those over 80 years of age. 1 Men have slightly higher incidence than women, and patients with CRAO are typically younger (mean age 66.8 years) than those with cerebral ischemic stroke. 1
Embolic Sources and Associated Conditions
CRAO is most strongly associated with ipsilateral internal carotid artery stenosis, found in 37-40% of patients with ≥70% stenosis. 1
Additional embolic sources include:
- Cardiac sources (aortic and mitral valves, atrial fibrillation) 1
- Aortic arch atherosclerosis 1
- Great vessel disease 1
The cardiovascular risk factor burden is substantial: 82% have obesity, 73% hypertension, 49% tobacco use, 49% hypercholesterolemia, and 14% diabetes. 1 Additionally, 20% have cardiac arrhythmias, 17% have valvular disease, and 5% have heart failure. 1
Clinical Presentation
Patients experience sudden, painless, severe monocular vision loss occurring over seconds. 2 Fewer than 20% of affected patients regain functional visual acuity in the affected eye without intervention. 1, 2
Critical Clinical Pitfall
Giant cell arteritis must be immediately ruled out in any patient over 50 years presenting with CRAO, as it can cause irreversible bilateral blindness and requires immediate high-dose corticosteroids before biopsy confirmation. 4, 3 ESR >60 mm/h and jaw claudication are highly specific findings. 4
Stroke Risk and Systemic Implications
CRAO portends high risk of recurrent stroke and cardiovascular events. 2, 4 Up to 25% of patients have concurrent silent brain infarctions on MRI. 4 Patients with CRAO and atrial fibrillation face particularly elevated stroke risk. 1
CRAO should be treated as a medical emergency requiring immediate triage to an emergency department or stroke center without delay for additional ophthalmologic testing. 2, 4, 3