Retinal artery occlusion is a blockage of blood flow to the retina, the light-sensitive tissue at the back of your eye. It causes sudden, painless vision loss in one eye and is considered a medical emergency, similar in mechanism to a stroke. In fact, the retinal nerve cells that die from this blockage are part of the central nervous system, and irreversible damage can begin within 12 to 15 minutes of complete blood flow loss.
Types of Retinal Artery Occlusion
The retina receives its blood supply through the central retinal artery, which enters the eye and branches into smaller vessels. A blockage can happen at different points along this network, and where the blockage occurs determines how much vision is affected.
In central retinal artery occlusion (CRAO), the main artery itself is blocked. This cuts off blood to the entire retina, typically causing severe, widespread vision loss in the affected eye. In branch retinal artery occlusion (BRAO), only one of the smaller branch vessels is blocked. Vision loss is limited to the section of retina that branch supplies, so you may lose part of your visual field rather than all of it. A third, less common type involves the cilioretinal artery, a small supplemental vessel that some people have, which supplies a portion of the central retina.
What It Feels Like
The hallmark symptom is sudden, painless vision loss in one eye. There is no warning pain, no redness, no gradual blurring over days. Vision simply drops, sometimes to the point where you can only perceive light or hand movements. With CRAO, the loss is usually severe and affects the entire visual field of that eye. With BRAO, you may notice a dark or missing area in part of your vision while other areas remain relatively clear.
Some people experience a brief episode of temporary vision loss (lasting seconds to minutes) in the days or weeks before a full occlusion. These transient episodes are warning signs that a blockage is forming.
Who Is at Risk
Retinal artery occlusion shares the same risk factors as heart attack and stroke, because the underlying problem is the same: damaged or narrowed blood vessels. In the EAGLE study, which evaluated 77 patients with CRAO, 82% were obese, 73% had high blood pressure, 49% used tobacco, 49% had high cholesterol, and 14% had diabetes.
Carotid artery disease is especially common. About 37% to 40% of CRAO patients have significant narrowing (70% or more) of the carotid artery on the same side as the affected eye. A clot or cholesterol fragment breaks loose from the narrowed carotid, travels into the smaller retinal artery, and lodges there.
In patients over 50, a condition called giant cell arteritis (GCA) needs to be ruled out. GCA is an inflammatory disease of blood vessel walls that can cause retinal artery occlusion in both eyes, sometimes within weeks of each other. Bilateral or sequential vision loss from retinal artery occlusion raises strong suspicion for GCA, which has been reported in 28% to 31% of GCA patients presenting with visual symptoms.
How It’s Diagnosed
An eye doctor can often identify retinal artery occlusion during a dilated eye exam. In CRAO, the retina appears pale and swollen because the oxygen-starved tissue becomes opaque and whitish. The center of the retina, called the fovea, stays its normal reddish color because it gets some blood supply from a deeper layer of vessels. This creates the classic “cherry-red spot,” a small red circle surrounded by pale, swollen retina.
Other visible signs include fragmented columns of blood in the retinal vessels (sometimes called boxcarring, because the blood looks like separated train cars) and sometimes a visible clot or cholesterol deposit lodged in a vessel.
Optical coherence tomography (OCT), a scan that creates cross-sectional images of the retina, shows characteristic swelling of the inner retinal layers in 100% of acute cases. Fluorescein angiography, where dye is injected into a vein and photographed as it flows through the retinal vessels, reveals delayed blood flow in about 60% of cases. OCT tends to give the more definitive picture and is often the most useful imaging tool in confirming the diagnosis.
Blood tests for inflammation markers are typically ordered to check for giant cell arteritis, particularly in patients over 50. Elevated results prompt further evaluation, often including a biopsy of the temporal artery to confirm the diagnosis.
The Treatment Challenge
Retinal artery occlusion is difficult to treat effectively, largely because the window for saving retinal tissue is extremely short. Research suggests that complete blockage of the central retinal artery causes significant, irreversible nerve cell death after just 12 to 15 minutes, similar to how brain cells die during a stroke. By the time most patients reach an emergency room, the damage is already done.
Several treatments have been tried over the years. Ocular massage involves pressing on the eye to create fluctuations in pressure inside the eyeball, with the hope of dislodging a clot into a smaller, less damaging location. Anterior chamber paracentesis removes a tiny amount of fluid from the front of the eye to rapidly lower eye pressure and improve blood flow. Medications to lower eye pressure and inhaled gas mixtures to dilate blood vessels have also been used. None of these approaches have been proven to change the natural course of the disease in rigorous studies.
Intravenous clot-dissolving drugs, the same type used for brain strokes, are being studied for CRAO when given within 4.5 hours of symptom onset. Systematic reviews of the existing clinical trials are underway, but there is not yet a clear consensus on whether this treatment improves visual outcomes. The extremely narrow time window for retinal survival makes any treatment a race against the clock.
Visual Recovery
The outlook depends heavily on which type of occlusion you have. BRAO carries a much better prognosis than CRAO. In studies of permanent BRAO, 89% of patients eventually achieved visual acuity of 20/40 or better (good enough to drive in most states). Among those who started with poor vision, 79% improved during follow-up. Patients with cilioretinal artery occlusion also tend to recover well, with all studied patients reaching 20/40 or better over time.
CRAO outcomes are considerably worse. Because the entire retinal blood supply is cut off, severe and permanent vision loss is the typical result. Some patients retain limited peripheral vision or light perception, but meaningful recovery of central vision is uncommon.
In the late phase after any retinal artery occlusion, the retina thins, the optic nerve can atrophy, and pigment changes may develop at the center of the retina. These are permanent structural changes.
The Stroke Connection
One of the most important things to understand about retinal artery occlusion is that it signals elevated risk for a brain stroke. The retinal arteries are, anatomically, branches of the brain’s blood supply. A blockage in the retinal artery means the same process (clot formation, plaque buildup, vessel inflammation) could affect the brain.
The numbers are striking. Within two weeks of a retinal artery occlusion, the risk of stroke is roughly 1.7%, compared to 0.08% in the general population. At one year, stroke risk reaches about 5.9%. At ten years, nearly 15% of retinal artery occlusion patients will have had a stroke.
This is why the American Academy of Ophthalmology recommends that all patients with retinal artery occlusion receive an immediate referral to a stroke center or emergency department. The priority shifts from trying to restore vision (which may already be beyond salvage) to preventing a potentially life-threatening brain stroke. That evaluation typically includes imaging of the carotid arteries, heart rhythm monitoring to check for atrial fibrillation, and optimization of blood pressure, cholesterol, and blood sugar management.