What Is Branch Retinal Vein Occlusion?
The retina is a thin tissue in the back of the eye that consists of nerve cells. These nerve cells capture images that you see, much like the film of a camera. The center portion of the retina is called the macula and is where our best vision comes from. Our ability to do things like driving and reading comes from the function of the nerve cells in the macula. Blockage of one of the venous branches in the retina is called a branch retinal vein occlusion (BRVO), and may cause vision loss and other complications. Males and females are, in general, affected equally. Most retinal vein occlusions occur after the age of 50, although younger patients are sometimes seen with this disorder.
Risk Factors If BRVO Goes Untreated
A major risk factor for branch retinal vein occlusion is atherosclerosis. Other risk factors include a history of stroke, coronary artery disease, aging, hypertension, elevated blood lipids, smoking, and glaucoma. Furthermore, less common risk factors include blood clotting abnormalities, infectious diseases, and inflammatory disorders. Most patients with a retinal vein occlusion should see their internist for a thorough medical evaluation.
The symptoms of a branch retinal vein occlusion depend on the specific venous branch. Common symptoms include blurred vision or changes in a portion of the visual field (peripheral vision). Occasionally the branch retinal vein occlusion will affect a vein draining a portion of the retina away from the central vision and will not cause any symptoms.
As a result of a branch retinal vein occlusion, there is often a significant amount of blood within the retina that obscures complete visualization of the retina. The blood will often gradually absorb, but this may take several months. In addition, there are three other common complications of branch retinal vein occlusion that threaten vision: macular edema (swelling from leaking blood vessels), macular ischemia (loss of blood flow) and neovascularization (growth of new abnormal blood vessels in response to poor blood flow).
Branch Retinal Vein Occlusion Diagnosis
Several specialized tests may be necessary to confirm the diagnosis of BRVO. These include fluorescein angiography, ocular coherence tomography, and color fundus photographs of the retina.
Identifying and treating the risk factors for BRVO are the first steps in treatment. A multi-center study, the Branch Vein Occlusion Study, found that laser improved the visual prognosis after three years of follow-up. This study showed that eyes treated with laser were more likely to gain at least two lines of vision compared to untreated eyes. More than one laser treatment may sometimes be necessary. Other treatments are also available.
Intravitreal injection of medications that block the action of Vascular Endothelial Growth Factor (VEFG) such as bevacizumab (Avastin) can be helpful in treating macular edema and neovascularization. Also, intravitreal or periocular steroid injections may have a role. Some patients can develop a painless increase in their intraocular pressure as a result of steroids and need to be monitored for this. Patients with known glaucoma have a higher risk of steroid-related intraocular pressure elevation. Aspirin therapy is a common recommendation, in addition to a thorough systemic evaluation by a primary care provider.
Another serious potential problem in branch retinal vein occlusion is that of retinal neovascularization. In advanced cases, abnormal blood vessels grow from the retina into the vitreous gel of the eye. Since these vessels are very fragile, this can lead to major bleeding (vitreous hemorrhage) and scar tissue formation. Consequently, this will cause floaters and an immediate, painless loss of vision. Laser photocoagulation treatment to the peripheral retina (panretinal photocoagulation) is very helpful in this situation. Laser treatment usually results in stabilization or even regression of the blood vessel growth. The bleeding will sometimes clear on its own, but if it does not, then an operation to remove the blood and the vitreous gel, called a vitrectomy, is sometimes performed. In severe cases of abnormal blood vessel growth, the retina may be pulled away from the wall of the eye (tractional retinal detachment), and this may require surgical repair.