Branch retinal vein occlusion (BRVO) happens when a small vein in the retina becomes blocked, almost always at a spot where a retinal artery crosses over and physically compresses the vein beneath it. It is the most common type of retinal vein occlusion, affecting an estimated 23 million people worldwide, and high blood pressure is present in roughly two-thirds of all cases.
How the Blockage Forms
Inside your eye, retinal arteries and veins cross over each other at dozens of points. At most of these crossings, the thin-walled vein sits sandwiched between the thicker, more rigid artery above it and the dense retinal tissue below. The artery and vein also share a common outer sheath of connective tissue, so they’re bound tightly together. Even in healthy eyes, the vein narrows slightly at these crossing points.
That anatomy becomes a problem when the artery stiffens. Conditions like high blood pressure and high cholesterol cause the artery wall to thicken and lose flexibility, a process called arteriosclerosis. As the artery hardens, it presses down more forcefully on the vein beneath it. The shared connective sheath contracts, squeezing the vein further. Blood flow through the compressed vein becomes turbulent, damaging the inner lining of the vein wall. That damage triggers clot formation, and the vein occludes.
Once the vein is blocked, blood backs up behind the obstruction. Pressure builds in the smaller vessels upstream, causing them to leak fluid and blood into the retina. This is what produces the sudden blurred vision or blind spots that most people notice first.
High Blood Pressure Is the Leading Cause
A large meta-analysis across multiple studies found that 67.7% of people diagnosed with BRVO had systemic hypertension. That makes it by far the strongest single risk factor. High blood pressure accelerates the arterial stiffening that compresses retinal veins, so managing blood pressure is the most important thing you can do to reduce your risk.
Hyperlipidemia (high cholesterol and triglycerides) was present in about 40% of BRVO cases, and diabetes in about 16%. Both conditions contribute to arterial wall damage throughout the body, including in the tiny vessels of the retina. The combination of two or more of these conditions compounds the risk substantially.
Who Gets BRVO
BRVO becomes steadily more common with age. Prevalence ranges from about 0.23% in people in their 30s to 2.64% in those in their 80s. The age group that contributes the most total cases is 60 to 69, since that’s where a large population overlaps with meaningfully elevated risk. That said, BRVO does occur in younger adults, particularly when clotting disorders or inflammatory diseases are involved.
Clotting Disorders in Younger Patients
When BRVO occurs in someone under 50 without high blood pressure or other obvious vascular risk factors, inherited or acquired blood clotting problems become a more likely explanation. The conditions most commonly screened for include Factor V Leiden mutation, protein C or S deficiency, antithrombin deficiency, elevated homocysteine levels, and antiphospholipid antibody syndrome.
These disorders make blood more prone to clotting throughout the body, not just in the eye. A retinal vein occlusion in a young person can sometimes be the first sign of one of these conditions. Screening typically involves a panel of blood tests. The results matter because they can affect treatment decisions and flag risk for clots in other parts of the body, like the legs or lungs.
Inflammatory and Autoimmune Diseases
Certain inflammatory conditions can cause the walls of retinal veins to swell and narrow from the inside, a process distinct from the mechanical compression at arterial crossings. Sarcoidosis, Behçet’s disease, and systemic lupus erythematosus are among the better-documented causes of retinal vein inflammation (phlebitis) that can progress to branch vein occlusion. Tuberculosis, multiple sclerosis, and some forms of inflammatory bowel disease like Crohn’s disease have also been linked to retinal vasculitis affecting veins.
In these cases, the occlusion results from immune-driven inflammation rather than arterial hardening. The treatment approach differs because controlling the underlying inflammatory disease is essential to preventing recurrence.
Glaucoma and Eye Pressure
People with glaucoma or elevated intraocular pressure have a higher prevalence of retinal vein occlusion than the general population. The connection likely involves shared vascular pathways: both conditions involve compromised blood flow in the retina’s small vessels. High pressure inside the eye may also directly reduce blood flow through retinal veins, making them more vulnerable to clot formation at crossing points that are already compressed. A population-based study from South Korea confirmed glaucoma as a significant independent risk factor for BRVO.
Smoking, Weight, and Lifestyle
Smoking roughly doubles the risk of BRVO. In a large Korean population study, people with a lifetime history of 100 or more cigarettes had about 2.3 times the odds of developing BRVO compared to non-smokers, even after adjusting for other risk factors. Smoking damages blood vessel linings throughout the body and accelerates arteriosclerosis, the same process that drives compression at arterial-venous crossings in the retina.
Body weight matters too. Being overweight (pre-obese by BMI classification) was associated with a 1.6-fold increased risk of BRVO. At the highest obesity levels, risk appeared to climb further, though the numbers were less statistically certain due to smaller sample sizes. Interestingly, being underweight also carried elevated risk in that study, with a 4.1-fold increase, possibly reflecting underlying illness or nutritional factors that affect blood vessel health.
What Happens After the Blockage
The occlusion itself is the initial event, but the complications that follow are what determine long-term vision outcomes. The most common problem is macular edema, where fluid leaks into the central retina and blurs vision. This develops in the majority of BRVO cases and is the primary reason people lose visual sharpness.
A less common but more serious complication is the growth of abnormal new blood vessels (neovascularization). Over 36 months, about 7.6% of BRVO eyes developed neovascularization or bleeding from new vessel growth. The risk was dramatically higher in eyes with poor blood flow: 17.8% of eyes classified as “nonperfused” developed these complications, compared to just 3.6% of eyes with adequate blood flow. This is why your eye doctor monitors perfusion status closely after a diagnosis.
The distinction between a well-perfused and poorly perfused BRVO shapes the follow-up plan. Eyes with good blood flow tend to have better visual recovery and lower complication rates. Eyes with significant areas of retinal ischemia need more frequent monitoring and may need treatment to prevent abnormal vessel growth that can lead to bleeding inside the eye.