Branch retinal vein occlusion (BRVO) is a vascular disorder of the eye’s circulatory system. The retina is the light-sensitive tissue at the back of the eye, serviced by a network of arteries and veins. Veins in this network function to drain blood away after it has delivered oxygen.
An occlusion is a blockage. In BRVO, this blockage occurs in one of the smaller “branch” veins that feed into the main central retinal vein. When a branch vein is obstructed, it cannot drain blood properly. This causes pressure to build, leading to leakage of blood and fluid into the retinal tissue, which can interfere with its function and impact vision.
Symptoms and Diagnosis
The onset of BRVO often manifests as a sudden, painless change in vision in one eye. A person may experience blurriness or a loss of sight confined to a specific part of their visual field, corresponding to the area served by the blocked vein. This visual disturbance can develop abruptly or worsen over several hours or days.
Another symptom is the appearance of floaters, perceived as dark spots or lines drifting in the field of vision. These are caused by small clumps of blood that have leaked from retinal vessels into the vitreous, the gel-like substance filling the eye. In some instances, if the affected area does not involve the center of the retina, the condition may not produce noticeable symptoms.
Diagnosing BRVO requires a comprehensive eye examination by an ophthalmologist. The process includes a dilated eye exam, where drops widen the pupils, allowing a clear view of the retina to check for hemorrhages and swelling. An imaging test called optical coherence tomography (OCT) is also used to create a detailed image of the retina. This scan allows the doctor to measure any swelling of the macula, a common consequence of fluid leakage.
To assess blood flow and identify the blockage, a fluorescein angiography may be performed. This procedure involves injecting a dye into an arm vein, which travels to the retinal vessels. A special camera then takes photographs as the dye passes through the retina, highlighting areas of leakage or poor blood flow and confirming the occlusion’s location.
Underlying Causes and Risk Factors
The development of BRVO is linked to systemic health conditions that affect the vascular system. The most common cause is the compression of a retinal vein by an adjacent retinal artery where they cross. If an artery hardens and becomes less flexible due to atherosclerosis, it can press on the vein, narrowing it and leading to a clot.
High blood pressure (hypertension) is a significant risk factor because it contributes to the hardening of arterial walls. Conditions like diabetes and high cholesterol can also lead to abnormalities in blood vessels, increasing the likelihood of an occlusion. The risk of developing BRVO increases with age, with most cases occurring in individuals over 50.
Other contributing factors include glaucoma, an eye condition with increased pressure that can compress retinal veins. Obesity is also associated with a greater risk. In some patients, particularly younger individuals, an abnormal tendency for blood to clot may be investigated as a potential cause.
Available Treatment Options
Treatment for BRVO is not aimed at removing the blockage but at managing the complications that cause vision loss. The primary objective is to resolve macular edema, which is swelling in the central retina from fluid leakage. Addressing this swelling can help stabilize and, in many cases, improve vision.
A leading treatment involves injecting medication into the eye’s vitreous gel. The most common drugs are anti-vascular endothelial growth factor (anti-VEGF) agents, such as Avastin, Lucentis, and Eylea. These drugs block a protein that promotes leaky blood vessels and swelling, and injections may need to be administered regularly.
Corticosteroid injections are another option for reducing macular edema. These anti-inflammatory agents can be delivered as an implant or injection to decrease swelling within the retina. They are carefully considered due to potential side effects.
Laser photocoagulation may also be used in specific situations. This procedure uses a focused beam of light to seal leaking blood vessels in the retina, which helps reduce macular edema. This approach is often considered a second-line treatment.
Potential Complications and Outlook
Following a BRVO, several secondary issues can develop that may further impact vision. The most persistent complication is chronic macular edema, the long-term swelling of the macula. This sustained fluid accumulation is the primary reason for vision impairment, as it affects the part of the retina responsible for sharp, central vision.
Another complication is the development of neovascularization. In response to poor circulation, the retina may grow new, abnormal blood vessels. These vessels are fragile and can rupture and bleed into the vitreous humor, an event known as a vitreous hemorrhage, which can cause a sudden reduction in vision.
The long-term outlook for BRVO varies and depends on the severity of the blockage and how the eye responds to therapy. With timely treatment to manage complications like macular edema and neovascularization, many individuals can recover a substantial amount of their vision. Regular follow-up visits are necessary to monitor the condition and apply treatments to preserve sight.