RVO, or retinal vein occlusion, is a common eye condition where a blood clot blocks one of the veins that drains blood from the retina, the light-sensitive tissue at the back of your eye. When blood can’t flow out properly, it backs up, causing swelling, bleeding, and vision loss in the affected eye. It’s one of the most frequent causes of sudden, painless vision changes in adults, particularly those over 50 with high blood pressure or diabetes.
How RVO Happens
Your retina needs a constant supply of blood to function. Small arteries bring blood in, and small veins carry it back out. In certain spots, these arteries and veins cross over each other. Over time, conditions like high blood pressure cause the arteries to stiffen and thicken. When a rigid artery presses against a softer vein at one of these crossing points, it disrupts normal blood flow, damages the vein wall, and can trigger a clot that blocks the vein entirely.
Once a vein is blocked, blood backs up behind the clot. Pressure builds inside the tiny blood vessels of the retina, forcing fluid and blood to leak into the surrounding tissue. The retina, starved of proper circulation and waterlogged with fluid, can’t send clear visual signals to the brain. The body also responds to the oxygen shortage by releasing inflammatory signals that make the blood vessels even leakier, compounding the problem.
Two Types of RVO
RVO comes in two forms, depending on where the blockage occurs:
- Branch retinal vein occlusion (BRVO) is the more common type. The clot forms where an artery crosses over a smaller branch vein, so only part of the retina is affected. Vision loss is often limited to one area of your visual field.
- Central retinal vein occlusion (CRVO) is more serious. The clot blocks the main vein that drains the entire retina, near the point where it exits the eye through the optic nerve. Because the whole retina is involved, vision loss tends to be more widespread and severe.
On examination, CRVO produces a dramatic appearance sometimes called a “blood and thunder” fundus, with swollen optic disc, dilated veins, and widespread hemorrhages across the retina in all four quadrants.
Symptoms to Recognize
RVO typically affects only one eye. The hallmark symptom is blurry vision or outright vision loss that can appear suddenly or develop gradually over hours to days. You may also notice floaters, those dark spots or squiggly lines drifting across your vision, caused by blood leaking into the eye. Pain or pressure in the eye can occur but is generally only present in more severe cases. Many people describe waking up one morning and realizing one eye isn’t seeing clearly.
Who Is Most at Risk
The biggest risk factors for RVO are conditions that damage blood vessels throughout the body. Hypertension is the strongest single risk factor, followed by diabetes and high cholesterol. These conditions promote the stiffening and narrowing of arteries that leads to vein compression in the retina. Chronic kidney disease and elevated levels of homocysteine (an amino acid linked to blood clot formation) also increase risk.
On the eye side, glaucoma and elevated eye pressure contribute by mechanically impeding the outflow of blood from the retina, creating the kind of sluggish circulation where clots are more likely to form. Age is another major factor. RVO can happen to younger people, but the risk climbs significantly after 50 as years of wear on the blood vessels accumulate.
How Doctors Diagnose RVO
A dilated eye exam is the first step. Your eye doctor can see the telltale signs directly: swollen veins, scattered hemorrhages, and fluid buildup in the retina. From there, two imaging tests help determine how severe the blockage is and guide treatment decisions.
Optical coherence tomography (OCT) uses light waves to create a cross-sectional image of the retina, showing exactly how much fluid has accumulated in the macula (the central area responsible for sharp, detailed vision) and whether the deeper layers of light-sensing cells are still intact. This scan is quick, painless, and repeated at follow-up visits to track whether treatment is working.
Fluorescein angiography involves injecting a fluorescent dye into a vein in your arm and photographing it as it travels through the retinal blood vessels. This reveals areas where blood flow has been cut off entirely. In CRVO, doctors look for more than 10 disc-sized areas of lost blood flow, extensive deep hemorrhages, and multiple cotton-wool spots (white patches indicating tissue damage) as markers of severe, ischemic disease. These markers matter because they predict whether the eye is at risk for serious complications.
The Main Cause of Vision Loss: Macular Edema
The primary reason people lose vision from RVO is macular edema, swelling in the central retina caused by fluid leaking from damaged blood vessels. When the vein is blocked, oxygen-deprived retinal cells release a protein called VEGF (vascular endothelial growth factor) along with a cascade of inflammatory signals. VEGF makes blood vessel walls more permeable, allowing even more fluid to seep into the macula. The waterlogged tissue distorts and blurs central vision.
If the oxygen deprivation is severe enough, the eye may respond by growing entirely new blood vessels, a process called neovascularization. These new vessels sound helpful but are actually fragile and abnormal. They can bleed into the vitreous (the gel filling the eye), block the eye’s internal drainage system and cause a dangerous spike in eye pressure known as neovascular glaucoma, or pull on the retina and cause a detachment. These complications represent the most vision-threatening consequences of untreated RVO.
Treatment With Eye Injections
The standard treatment for RVO-related vision loss is a series of injections directly into the eye. This sounds intimidating, but the procedure is done in the office with numbing drops and takes only a few minutes. The injections deliver drugs that block VEGF, reducing the leakiness of blood vessels and allowing the macular swelling to resolve.
Clinical trials show these injections make a meaningful difference. In the landmark BRAVO trial for branch RVO, about 61% of patients treated with the anti-VEGF drug ranibizumab gained significant vision improvement (15 or more letters on a standard eye chart) at six months, compared to 29% with no treatment. Results for central RVO are slightly lower but still substantial: in the CRUISE trial, about 48% of treated patients achieved the same level of improvement versus 17% without treatment. The drug aflibercept showed comparable results, with roughly 53% of branch RVO patients and 56% of central RVO patients gaining significant vision at six months.
Most patients need repeated injections, especially in the first year. The frequency varies, but monthly injections for the first several months are common before spacing out based on how the eye responds. Newer drugs are being developed that may last longer between doses.
Steroid Implants and Laser Options
For patients who don’t respond well to anti-VEGF injections, or who have difficulty keeping up with frequent injection schedules, steroid implants are an alternative. A tiny slow-release device is placed inside the eye to deliver anti-inflammatory medication over weeks to months. The trade-off is a higher risk of developing cataracts and increased eye pressure that may need its own treatment. In clinical comparisons, patients receiving steroid injections for branch RVO were significantly more likely to develop cataracts or need pressure-lowering eye drops than those treated with laser.
Laser treatment was the standard approach before anti-VEGF drugs became available. It’s still used in certain situations, particularly for branch RVO, where it can seal leaking vessels and reduce swelling. For most patients today, anti-VEGF injections produce better visual outcomes, but laser remains a useful tool in combination therapy or when injections aren’t an option.
What Recovery Looks Like
The trajectory of recovery differs between the two types of RVO. With branch RVO, vision tends to improve relatively quickly once the macular swelling resolves, with meaningful gains often appearing within the first few months of treatment. Central RVO is slower to recover. Studies show that while patients with CRVO do see significant improvement, the visual gains may lag behind the reduction in swelling, with the clearest improvements emerging between six and twelve months after starting treatment.
The single strongest predictor of your long-term outcome is how good your vision was when treatment began. Patients who start treatment with relatively preserved vision tend to end up with better final results, likely because less damage has occurred to the deeper, light-sensing layers of the retina. This is one of the strongest arguments for seeking care promptly if you notice sudden changes in your vision. Early treatment gives the retina the best chance of recovering before irreversible damage sets in.
Managing the underlying health conditions that caused the RVO in the first place is equally important. Controlling blood pressure, blood sugar, and cholesterol reduces the risk of RVO recurring in the same or opposite eye and protects against the broader cardiovascular problems that share the same root causes.