CRVO, or central retinal vein occlusion, is a blockage of the main vein that drains blood from your retina. When this vein becomes blocked, blood and fluid back up into the retina, causing swelling and vision loss. It typically affects one eye, and the vision loss is sudden and painless. Nearly half of all cases are linked to high blood pressure.
How the Blockage Happens
The retina has its own blood supply: a central artery brings blood in, and a central retinal vein carries it out. These two vessels share a tight space as they pass through the optic nerve at the back of your eye, wrapped together in a common outer sheath. Over time, if the artery stiffens and thickens from atherosclerosis (the same process that narrows heart arteries), it can physically compress the vein next to it.
That compression slows blood flow in the vein, which sets the stage for a blood clot (thrombus) to form. Three factors drive clot formation here: sluggish blood flow, damage to the vein wall, and blood that clots too easily. Any condition that worsens one or more of these factors raises the risk of CRVO. Once the clot blocks the vein, blood has nowhere to go and leaks into the surrounding retinal tissue, causing hemorrhages and swelling, particularly at the macula (the central part of the retina responsible for sharp, detailed vision).
What It Feels Like
The hallmark symptom is blurry or suddenly reduced vision in one eye. There’s usually no pain. In very mild cases, you might not notice any change at all. More severe blockages can cause noticeable redness or a dull ache in the affected eye, though this is less common. The vision loss can range from mild blurriness to a dramatic drop where you can only see large shapes or hand movements.
Two Types With Very Different Outlooks
Not all CRVOs are equally serious. Doctors classify them into two types based on how much blood flow is cut off to the retina’s tiny capillaries.
Non-ischemic CRVO is the milder form. Blood flow is reduced but not severely disrupted. Vision at diagnosis is often better than 20/400, and the long-term outlook is considerably better. In natural history studies, 83% of people with non-ischemic CRVO eventually reached a visual acuity of 20/100 or better once the swelling resolved. About 47% showed meaningful vision improvement over two to five years of follow-up.
Ischemic CRVO is more severe. Large areas of the retina are starved of blood supply, and vision at diagnosis is typically 20/400 or worse. Only about 12% of people with ischemic CRVO reached 20/100 or better after the swelling resolved. This form also carries a higher risk of serious complications, including abnormal new blood vessel growth that can lead to a dangerous type of glaucoma.
The distinction between these two types matters enormously for treatment planning and what you can realistically expect for recovery.
Major Risk Factors
High blood pressure is by far the strongest risk factor. Research published in JAMA Ophthalmology estimated that hypertension accounts for roughly 48% of all retinal vein occlusion cases. High cholesterol is the second most common contributor, since it accelerates the arterial stiffening that compresses the vein. Diabetes plays a role as well, though it’s a less frequent cause than the other two.
Glaucoma and elevated eye pressure also increase the risk. The American Academy of Ophthalmology’s 2024 guidelines emphasize controlling blood pressure, blood sugar, and cholesterol as key modifiable risk factors, ideally in partnership with your primary care doctor. Because these are the same cardiovascular risk factors behind heart attacks and strokes, a CRVO diagnosis often prompts broader health screening.
How It’s Diagnosed
An eye doctor can usually identify CRVO during a dilated eye exam. The retina has a characteristic appearance: widespread hemorrhages fanning out from the optic nerve, swollen veins, and fluid accumulation.
Two imaging tests help determine the severity. One is a dye-based test called fluorescein angiography, where a special dye is injected into your arm and photographs are taken as it flows through the retinal blood vessels. This reveals exactly how much of the retina has lost its blood supply, which is the key measurement for distinguishing ischemic from non-ischemic CRVO. The other is optical coherence tomography (OCT), a quick, non-invasive scan that creates cross-sectional images of the retina. OCT measures macular swelling with high precision and tracks how well treatment is working over time. A newer version of this technology, called OCT angiography, can map blood flow in the retina’s tiny vessels without needing a dye injection at all, providing another way to assess how ischemic the retina is.
Treatment for Macular Swelling
The main cause of vision loss in CRVO is swelling at the macula, and the primary treatment targets this directly. The standard first-line therapy is a series of injections into the eye (intravitreal injections) using medications that block a protein called VEGF. When the retina is starved of oxygen, it overproduces VEGF, which causes blood vessels to leak and drives the swelling. Blocking this protein reduces fluid buildup and can improve vision.
Treatment typically starts with monthly injections for six months. Several large clinical trials, including studies known as COPERNICUS, GALILEO, SCORE2, and LEAVO, have confirmed that this approach is safe and effective. After the initial loading phase, the frequency of injections is adjusted based on how your eye responds, with some people needing ongoing treatment and others able to taper off.
For people who don’t respond well to anti-VEGF therapy, a steroid implant placed inside the eye is an alternative. This small device slowly releases medication over several months. Research suggests that some patients whose eyes don’t improve with anti-VEGF drugs have higher levels of inflammatory signals in the eye rather than just VEGF, which may explain why steroids work better for them.
Recovery Timeline and Long-Term Outlook
Recovery from CRVO is slow. For the non-ischemic type, macular swelling takes a median of about 23 months to resolve on its own without treatment (anti-VEGF injections can speed this up considerably). For ischemic CRVO, the median resolution time is even longer, around 29 months. These numbers reflect natural history before modern anti-VEGF therapy became standard, so treated patients generally see faster improvement.
Among people with non-ischemic CRVO and poor initial vision (20/70 or worse), 59% improved once the macular swelling resolved, compared to only 26% of those whose swelling persisted. This underscores why treating the swelling early and aggressively matters.
The biggest threats to long-term vision in non-ischemic cases are changes that develop from chronic, prolonged swelling: pigmentary damage at the center of the retina and scar-like membrane formation on the retinal surface. One study found that developing pigmentary changes at the fovea made poor visual outcomes roughly 21 times more likely, while membrane formation made them about 10 times more likely. This is why regular monitoring and consistent treatment are so important, even when the condition seems mild.
For ischemic CRVO, the prognosis is more guarded. Vision recovery is limited because the retinal tissue itself has been damaged by lack of blood flow, not just by swelling. These patients also need close monitoring for the growth of abnormal new blood vessels, which can develop in the weeks and months following the initial blockage and lead to further complications if left untreated.