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How does a Branch Retinal Vein Occlusion happen?
Imagine what would happen if you stepped on a hose while watering your garden. As the hose narrows from being compressed, water flows through it more forcefully. There would be a build up of water and the hose would become swollen and perhaps begin to leak if the walls of the hose become damaged. That’s the basic principle of a vein occlusion.
Your eye has a main blood vessel, the central retinal artery, which delivers the blood supply to much of the retina. The central retinal artery enters the eye and branches out into smaller arteries upon reaching the retina like the branches of a tree. These branch retinal arteries tend to be thicker-walled and firm. Alongside these arteries are corresponding veins which deliver blood from the retina to the central retinal vein, the main vessel that takes blood away from the retina. The branch retinal veins are thinner walled and more collapsible. The branch retinal arteries and veins may cross over each other as they form a network of smaller and smaller vessels. Where an artery and vein crosses, there is a thickened sheath of connective tissue that binds the vessels together like a rubber band or “twist tie” that holds two adjacent electrical cables together.
In a BRVO, a blockage of a branch retinal vein can occur at this sheath, where a thicker and firmer branch retinal artery compresses the more collapsible branch retinal vein as they cross over each other. The narrowing of the vein results in more turbulent flow of blood through the vein, which can lead to the formation of a thrombus (or blot clot) that eventually blocks the opening of the branch retinal vein.
What are common symptoms of a BRVO?
You would typically experience a painless sudden loss of vision in one eye. Frequently, you may notice nothing at all, especially if the blockage occurs in the periphery of your retina and thus far away from the center of your field of vision. The amount of vision loss is different with each patient and often depends on the location of the blockage as well as the quality of the circulation in the retina and amount of swelling within the macula (the portion of your retina responsible for detailed vision).
How is BRVO diagnosed?
A BRVO is fairly easy to diagnose just by looking at the retina through the microscope. However, the extent and effects of a BRVO are best monitored by diagnostic tests such as fluorescein angiography and optical coherence tomography (please see the related pamphlets for more).
How common is this condition?
Branch retinal vein occlusions, together with central retinal vein occlusions, are the 2nd most common disorder of the retinal blood vessels after diabetic retinopathy.
Who gets Branch Retinal Vein Occlusions?
The large majority of people who gets BRVOs are over the age of 50. This condition can occur spontaneously without any associated systemic diseases. However, it is frequently associated with hypertension (or high blood pressure), atherosclerosis, and diabetes. It is debatable as to whether not glaucoma is an associated risk factor. More rarely, a BRVO can be associated with disorders of the blood that make it more likely for clotting to occur, which we sometimes see with younger patients.
What are the complications of a BRVO?
There are 3 complications that can occur as result of a BRVO:
Macular edema – Remember our comparison of a BRVO to stepping on a garden hose? Macular edema is swelling on the part of the retina responsible for your detailed vision due to leakage of fluid from the blood vessels which supply the retina.
Neovascularization – As you would expect, a BRVO can result in poor circulation to the retina, which becomes “starved” for oxygen. The eye responds to this by growing new blood vessels to help compensate for this deficit. The only problem is that these new blood vessels are prone to bleeding and scarring, which can lead to further loss of vision. This does not occur in all BRVOs, but is more likely to happen in eyes with very poor circulation. Your retina specialist will monitor you for any early signs of neovascularization.
Glaucoma – Glaucoma is a very rare complication of a branch retinal vein occlusion due to neovascularization at the eye where fluid is produced and drained. It occurs much less frequently than it may with the more extensive central retinal vein occlusion.
What are the treatments for a BRVO?
Methods of treatment can be divided into laser, medications, and surgery. The strategy of treatment is different from person to person as not all people benefit from all treatments. Your retinal specialist at Retina Associates of St. Louis, Inc. will determine a treatment plan specific to your condition.
One type of laser treatment, Focal Laser, can be used to close off areas of leakage from the blood vessels that cause macular edema. Another type of laser treatment, Panretinal photocoagulation, can cause neovascularization to regress by making the retina less “starved” for oxygen (please see the related pamphlets for more).
Frequently, medications are injected around or into the eye. The purpose of the medications is to decrease macular edema and perhaps block the substances that promote leakage and new vessel growth (please see the related pamphlets for more).
Can I expect my vision to improve?
As you would expect, different people respond differently. However, people with generally better vision after a BRVO tend to fare better that those with very poor vision. In either case, you will require close follow-up to monitor for any changes in the retina as well as eye pressure as complications are always easier to treat when addressed early.
What can I do to help myself?
Follow-up with your primary care physician can be helpful to monitor associated conditions like your blood pressure. With some younger patients, we may also recommend that your physician check your blood for any conditions that make it more likely for you to develop blood clots. There is little known at this time as to whether diet or exercise can help. However, proper diet, exercise, and abstaining from smoking can improve control of high blood pressure and diabetes, which are systemic conditions associated with BRVOs.