Branch Retinal Vein Occlusion (BRVO) is a common vascular disorder affecting the retina, the light-sensitive tissue lining the back of the eye. This condition occurs when a clot or blockage forms in one of the smaller veins branching off the central retinal vein, preventing blood from draining properly. BRVO is typically an isolated event affecting only one eye and requires prompt attention from an eye care specialist to preserve vision.
Understanding Branch Retinal Vein Occlusion
The retina uses arteries for oxygenated blood and veins to carry deoxygenated blood away. When a branch vein becomes obstructed, blood flow is severely reduced or stopped entirely, leading to a backup of pressure in the vessels behind the blockage. This elevated pressure causes blood and fluid components to leak out of the compromised vein walls and into the surrounding retinal tissue.
Blockage most often occurs at an arteriovenous crossing, where a retinal artery passes over or under a retinal vein. If the adjacent artery has hardened or stiffened due to conditions like atherosclerosis, it compresses the softer vein beneath it. This compression causes turbulent blood flow that encourages a clot to form.
Leakage causes retinal hemorrhage and fluid accumulation (macular edema), especially if the blockage is near the macula, the central part of the retina responsible for sharp vision. Lack of proper blood flow creates oxygen deprivation (ischemia) in the affected retina.
Ischemia triggers the release of inflammatory substances and Vascular Endothelial Growth Factor (VEGF). VEGF breaks down the blood-retinal barrier, exacerbating fluid leakage and macular edema. This swelling in the macula is the primary mechanism by which BRVO reduces central visual acuity.
Key Symptoms and Risk Factors
The most common symptom of BRVO is a sudden, painless, and usually partial change in vision affecting only one eye. Patients typically describe blurring or distortion of their central vision if the macula is involved. If the blockage occurs away from the macula, the condition may initially go unnoticed until discovered during a routine eye examination.
New floaters (dark specks drifting across the field of view) may appear if blood leaks into the vitreous gel, causing a vitreous hemorrhage. The extent of vision loss correlates directly with the size of the blocked vein and whether the macula is affected by the resulting fluid.
BRVO risk is closely tied to systemic health conditions. Uncontrolled high blood pressure (hypertension) is the most common factor, leading to stiffening of retinal arteries that compress the veins. Diabetes and high cholesterol contribute to atherosclerosis (hardening of the arteries), increasing the risk of vessel compression and clot formation.
Glaucoma, characterized by elevated pressure within the eye, is also a recognized risk factor. In younger patients, BRVO may suggest an underlying hypercoagulable state, which is an abnormal tendency for the blood to clot. Managing these systemic conditions is fundamental to preventing BRVO and reducing recurrence risk.
Diagnosis and Treatment Options
Diagnosis begins with a comprehensive, dilated eye examination to visualize the retina. Specialists look for signs of occlusion, including sector-shaped retinal hemorrhage, swollen veins, and fluid accumulation. While physical findings establish the diagnosis, further imaging determines the extent of damage and guides treatment.
Diagnosis
Optical Coherence Tomography (OCT) is a non-invasive test providing high-resolution, cross-sectional views of the retina. OCT precisely measures macular edema (fluid accumulation). This allows the physician to quantify swelling and track the patient’s response to treatment.
Fluorescein Angiography (FA) involves injecting a fluorescent dye and photographing the retina as the dye circulates. FA highlights leakage from damaged vessels and reveals areas of capillary non-perfusion. Lack of blood flow in these areas signifies retinal ischemia and a risk of developing new, abnormal blood vessels.
Treatment
Treatment focuses on managing complications, primarily macular edema and vision loss. First-line therapy involves Intravitreal injections of medications directly into the eye.
These include anti-Vascular Endothelial Growth Factor (anti-VEGF) agents, such as ranibizumab and aflibercept. Anti-VEGF agents block the protein responsible for fluid leakage and abnormal blood vessel growth.
Corticosteroid implants, which release anti-inflammatory drugs like dexamethasone, are another option to reduce macular edema. They are often reserved for cases where anti-VEGF therapy is ineffective or as an alternative. While these injections do not remove the clot, they dry the retina and restore visual function.
Laser photocoagulation is a secondary option for specific complications. Focal laser treatment seals leaking microaneurysms to reduce persistent macular edema. Scatter or pan-retinal photocoagulation treats widespread retinal ischemia to prevent neovascularization (the growth of fragile, abnormal new blood vessels).
Managing Long-Term Visual Outcomes
Visual recovery following BRVO is favorable compared to Central Retinal Vein Occlusion (CRVO). However, long-term monitoring is necessary to manage secondary complications. The most common long-term issue is persistent or recurrent macular edema, requiring ongoing anti-VEGF or steroid injections.
Neovascularization, the growth of fragile new vessels stimulated by oxygen deprivation, is a serious complication that can occur months or years later. These abnormal vessels can easily rupture, causing a vitreous hemorrhage, which presents as a sudden increase in floaters and vision loss.
Untreated neovascularization can lead to Neovascular Glaucoma, where new vessels block the eye’s drainage system, causing a rapid rise in intraocular pressure. Regular follow-up with specialized imaging is the best defense. Proactive treatment, often using laser or additional injections, is initiated immediately if secondary issues are detected.