by Dr. Walter Moscoso, MD.
Fellowship-trained retina specialist

BRANCH RETINAL VEIN OCCLUSION
Branch retinal vein occlusion occurs when one of the veins of the retina becomes occluded (or plugged up). Arteries bring blood to your eye and veins drain blood away from your eye. When a retinal vein is occluded, blood is able to enter the eye, but has difficulty exiting. This causes an increase in pressure in the capillaries, which are the very small blood vessels that exist in between the retinal arteries and occluded vein. As a result of this increased pressure, these capillaries may rupture and cause retinal bleeding. Other capillaries may just become very sick and die or allow a clear liquid, which is inside of your blood stream, to exit into the retina. This clear liquid is called serum. The serum can cause a significant amount of edema (or swelling) of the retina. The combination of the swelling and hemorrhaging, in addition to decreased blood flow to a given section of the retina, can result in a decrease in the vision. You will need to be examined periodically as this condition can at times cause other problems in your eye. Most of the time the condition improves and although the vision will unlikely return to perfect vision, you may experience a significant restoration of vision in the affected eye. Laser treatment is indicated in those with significant swelling that does not improve and those who develop abnormal blood vessel growth of the retina.

Some patients experiencing a branch retinal vein occlusion are otherwise healthy patients that were born with an unusual "kink" (or bend) in a retinal vein. Other causes of branch retinal vein occlusions are hypertension (high blood pressure) and arteriosclerosis (hardening of the arteries). Physical activity, control of blood pressure and lowering elevated cholesterol levels may prevent this disease from recurring.

CENTRAL RETINAL VEIN OCCLUSION
This condition occurs when the main vein that drains the retinal circulation becomes occluded. Arteries bring blood to your eye and veins drain blood away from your eye. When the central retinal vein is occluded there is a build-up in the pressure in the capillaries, which are the very small blood vessels that connect the arteries and the veins of your eye. Since blood is able to get into your eye through the central retinal artery and has difficulty getting out of your eye through the central retinal vein, the increased pressure causes the small capillaries to rupture and consequently hemorrhaging occurs in the eye. In addition, the capillaries may also just become very sick and allow a clear liquid, which exists in the blood stream, called serum, to seep into the retina. This can accumulate in the retina and cause edema. Finally, the decrease in blood flow or circulation into the retina can cause damage to the retina, as the retina needs a constant flow of fresh blood in order for it to function properly. The vision in the eye affected by this condition is usually worse for the first month or so after the initial disease onset. Most patients have mild restoration of vision and, on occasion, a few patients experience a significant improvement in the vision. Those with this condition require regular follow-up to check for complications that can arise. These possible complications include new blood vessels growing in the retina, which are abnormal and can cause bleeding and scarring of the retina, or new blood vessels growing in the iris (the blue or brown part of the eye) which can cause a very severe form of glaucoma called neovascular glaucoma. If these complications occur prompt laser treatment is needed.