Central Retinal Artery Occlusion: An Eye Emergency
Understanding Central Retinal Artery Occlusion
The central retinal artery is the primary blood vessel that delivers oxygen and nutrients to the inner layers of the retina. When this artery becomes blocked, the retinal cells are starved of oxygen. This oxygen deprivation is called ischemia.
The retina is extremely sensitive to a lack of blood flow. Research using animal models has shown that irreversible damage to retinal cells can occur after as little as 105 minutes of blocked blood flow. This is why CRAO is treated as an emergency. The longer the retina goes without blood, the greater the risk of lasting vision loss.
The most common cause of CRAO is an embolus. An embolus is a small piece of material that travels through the bloodstream and lodges in a blood vessel. It often originates from plaque buildup in the carotid artery (the major artery in the neck), the aortic arch, or the heart.
Studies of embolus composition reveal important details about their origin. Approximately 74% are made of cholesterol, about 10.5% are composed of calcific material, and roughly 15.5% are platelet-fibrin complexes (AAO). The blockage most commonly occurs at the narrowest point of the artery, where it pierces the outer sheath of the optic nerve.
Medical guidelines now classify CRAO as a form of acute ischemic stroke. The American Heart Association defines ischemic stroke as an episode of neurological dysfunction caused by focal cerebral, spinal, or retinal infarction. This classification is important because it means CRAO shares the same underlying causes and risk factors as a brain stroke. A diagnosis of CRAO signals that a person may be at higher risk for future cardiovascular and cerebrovascular events.
Who Is Affected and Risk Factors
CRAO is uncommon but serious. The incidence is approximately 1 to 2 per 100,000 people. It has a slightly higher rate among men and a mean age of onset between 60 and 65 years (AAO). Age-adjusted and sex-adjusted incidence rates vary somewhat by country. Rates are approximately 1.9 per 100,000 person-years in the United States, 1.8 in South Korea, and 2.5 in Japan (American Heart Association, Stroke: Vascular and Interventional Neurology, 2023).
Most patients are in their 60s, and the condition is more commonly diagnosed in men than in women. Only 1% to 2% of cases involve both eyes (ASRS).
The risk factors for CRAO are the same as those for stroke and heart disease. These include conditions and habits that promote atherosclerosis, which is the buildup of plaque inside artery walls.
Key risk factors include:
- High blood pressure (hypertension)
- High cholesterol and elevated serum lipid levels
- Cigarette smoking
- Diabetes
- Cardiac disease, including atrial fibrillation (an irregular heart rhythm)
- Elevated body mass index
- Blood clotting disorders (coagulopathies)
Atherosclerosis of the carotid artery on the same side as the affected eye is the most common source of retinal artery blockages. Studies report that carotid artery disease is present in as many as 70% of patients diagnosed with CRAO or branch retinal artery occlusion (AAO).
A diagnosis of CRAO is a warning sign for future stroke. Analysis from a Korean national health claims database found that patients with CRAO carry a 1.78-fold increased risk of developing a cerebral stroke within four years (American Heart Association, Stroke: Vascular and Interventional Neurology, 2023). This elevated stroke risk makes prompt systemic evaluation essential after a CRAO diagnosis.
Signs and Symptoms
The hallmark symptom of CRAO is sudden, severe, and painless loss of vision in one eye. Patients typically describe the vision loss as occurring over seconds, not gradually over hours or days. The vision loss is usually profound. Research shows that more than three-quarters of patients experience acute visual acuity of 20/400 or worse at presentation (AAO).
Sudden vision loss in one eye is a medical emergency. If you experience a rapid, painless loss of vision, see a retina specialist or go to the emergency room immediately. Do not wait to see if your vision improves on its own. Every minute of delay increases the risk of irreversible damage to the retina.
For patients older than 50, sudden vision loss should also raise suspicion for giant cell arteritis (GCA). GCA is a condition involving inflammation of blood vessels. It may require urgent treatment with systemic steroids to protect vision in both eyes (AAO Preferred Practice Pattern). A retina specialist or emergency physician can help determine whether GCA testing is needed.
Diagnosis and Testing
A retina specialist can often diagnose CRAO based on a dilated eye examination. The classic finding is a pale, swollen retina with a characteristic 'cherry-red spot' at the center of the macula. This appearance occurs because the retina turns white from lack of blood flow. The thin tissue over the central fovea allows the underlying red choroidal blood supply to show through.
The specialist will also look for visible emboli within the retinal blood vessels. These small, bright or whitish deposits can sometimes be seen lodged at branch points in the retinal arteries.
Several imaging tests help confirm the diagnosis and evaluate blood flow in the retina. Fluorescein angiography (a test that uses a special dye and camera to photograph retinal blood flow) may show delayed or absent filling of the central retinal artery. Optical coherence tomography, or OCT (a non-invasive scan that creates detailed cross-section images of the retina), may reveal swelling in the inner retinal layers caused by ischemia.
Because CRAO is linked to systemic vascular disease, additional testing is typically recommended. This may include carotid artery ultrasound, echocardiography (an ultrasound of the heart), and blood tests. Blood work evaluates cholesterol levels, blood sugar, clotting factors, and inflammatory markers.
Persons with acute CRAO should be referred promptly to the emergency room or their primary care doctor for a stroke risk evaluation (AAO Preferred Practice Pattern). Because CRAO is now classified as a form of stroke, a comprehensive workup similar to what is performed after a brain stroke is considered appropriate. This workup helps identify treatable conditions that could lead to a future cerebrovascular event.
Treatment Options
Unfortunately, there is no clinically proven treatment for CRAO that has been shown to reliably restore vision. For any treatment to have potential benefit, it must be started within a very short time window. This window is probably within 4 to 6 hours after symptoms begin. Because the retina suffers irreversible damage so quickly, most patients present too late for acute intervention to be effective.
A number of therapies have been tried over the years in an effort to restore blood flow to the retina. These have included:
- Ocular massage (applying pressure to the eye to try to dislodge the embolus)
- Anterior chamber paracentesis (removing a small amount of fluid from the front of the eye to lower eye pressure)
- Carbogen inhalation (breathing a mixture of carbon dioxide and oxygen)
- Acetazolamide infusion (a medication to reduce eye pressure)
- Various vasodilators such as intravenous glyceryl trinitrate
None of these standard therapies have been shown to definitively alter the natural course of the disease (AAO).
The use of tissue plasminogen activator (tPA), a clot-dissolving medication used in brain strokes, has been investigated for CRAO. Two randomized controlled trials have studied intravenous tPA. However, there are no current guideline-endorsed treatments based on this approach.
Several major clinical trials are evaluating intravenous tPA for acute CRAO. The THEIA trial is a phase III study assessing the efficacy and safety of intravenous alteplase (a form of tPA). The TenCRAOS trial in Norway is evaluating tenecteplase (another form of tPA) in CRAO patients. Results from these trials may provide the evidence needed to establish a guideline-endorsed treatment in the future.
Treatment for CRAO has also evolved with advances in microsurgical instruments and surgical robotics. Some researchers have explored direct surgical approaches to remove or bypass the blockage. However, surgical treatment for CRAO is not widely available or recognized as a standard option at this time.
What to Expect
The visual prognosis after CRAO is generally poor. Over three-quarters of patients experience profound vision loss with visual acuity of 20/400 or worse (AAO). Some patients may retain limited peripheral vision depending on whether a cilioretinal artery is present. This small branch artery, found in some individuals, provides an alternate blood supply to a portion of the central retina. It may help preserve some central vision.
Because CRAO indicates underlying vascular disease, ongoing management of cardiovascular risk factors becomes a priority. A retina specialist will often coordinate with a primary care doctor, cardiologist, or neurologist. Together they address conditions like high blood pressure, high cholesterol, diabetes, or heart rhythm problems. Managing these conditions is critical for reducing the risk of future stroke or heart attack.
Living with Central Retinal Artery Occlusion
Significant vision loss in one eye can affect daily activities such as driving, reading, and depth perception. Low vision rehabilitation services can help patients learn strategies and use assistive devices to maximize their remaining vision. A retina specialist can provide referrals to these services.
Patients diagnosed with CRAO can take important steps to lower their risk of another vascular event. Working closely with a primary care doctor or cardiologist to manage blood pressure, cholesterol, blood sugar, and heart conditions is essential. Quitting smoking, maintaining a healthy weight, eating a heart-healthy diet, and exercising regularly are all beneficial. Medications such as blood thinners or cholesterol-lowering drugs may be recommended based on the results of the stroke workup.
While only 1% to 2% of CRAO cases affect both eyes (ASRS), protecting the health of the unaffected eye remains a priority. Regular eye examinations allow a retina specialist to monitor for any changes and address risk factors that could affect the other eye.
When to See a Retina Specialist
Sudden, painless loss of vision in one eye requires immediate medical attention. See a retina specialist or go to the emergency room right away. Do not wait for the vision to return on its own. Time is critical because the retina can suffer irreversible damage within minutes to hours of a blocked artery.
After a CRAO diagnosis, regular follow-up visits with a retina specialist are important. These appointments allow the specialist to monitor the health of both eyes. The specialist also watches for complications such as abnormal new blood vessel growth. This can develop weeks to months after the initial event. Ongoing communication between the retina specialist and the primary care doctor or cardiologist helps ensure that systemic risk factors are being managed effectively.
Questions and Answers
In most cases, the vision loss from CRAO is severe and lasting. The retina is extremely sensitive to oxygen deprivation, and irreversible damage can occur within about two hours of the blockage. A small number of patients may retain some vision if a cilioretinal artery provides an alternate blood supply to part of the central retina. Currently, no treatment has been proven to reliably restore vision after CRAO.
CRAO is now classified as a form of acute ischemic stroke affecting the retina. It shares the same underlying mechanisms and risk factors as a stroke in the brain. This means a diagnosis of CRAO should prompt a full cardiovascular and cerebrovascular workup, just as a brain stroke would. Patients with CRAO have a significantly higher risk of experiencing a brain stroke in the years that follow.
Any treatment for CRAO is most likely to have potential benefit only if started within 4 to 6 hours of symptom onset. Because of this extremely narrow window, immediate action is essential. If you experience sudden vision loss in one eye, go to an emergency room or see a retina specialist as quickly as possible. Even though current treatments have limited effectiveness, a prompt evaluation is critical. It helps diagnose the condition, rule out giant cell arteritis, and begin a stroke risk assessment.
In addition to a comprehensive eye examination, a retina specialist will typically recommend systemic testing. This often includes a carotid artery ultrasound to check for plaque buildup and an echocardiogram to evaluate heart function. Blood tests for cholesterol, blood sugar levels, and blood clotting disorders are also common. For patients over 50, blood tests to check for giant cell arteritis may be performed as well. These tests help identify the source of the blockage and guide treatment to reduce future stroke risk.
CRAO affects both eyes in only about 1% to 2% of cases (ASRS). However, having CRAO in one eye signals significant underlying vascular disease. Managing cardiovascular risk factors is essential to protect the unaffected eye and reduce the risk of stroke or other vascular events. Regular follow-up with both a retina specialist and a primary care doctor or cardiologist is recommended.