An occlusion is a blockage that occurs in a blood vessel as a result of debris in the bloodstream, inflammation, or high blood pressure. Within the veins of the retina, occlusions most often occur due to high blood pressure or high intra-ocular pressure and at a point where arteries and veins cross over each other. A blockage may occur in the main vein of the retina or in any of the smaller veins that branch off from it.
When an occlusion occurs, the veins of the retina cannot drain properly. This prevents the retinal cells in the area from receiving a fresh supply of oxygen- and nutrient-rich blood. Deprived of oxygen and nutrients, the affected cells cannot function properly and may even die. Perhaps more destructive is the hemorrhage of vessels that occurs because the backed-up blood has nowhere to go. The surrounding retinal tissue then succumbs to edema and swelling.
Occlusions occur suddenly, causing decreased vision in one eye that will vary from mild to severe. In most cases, complete vision cannot be restored, but lasers can treat any persisting edema and the related bleeding from burst blood vessels. Laser treatment can improve vision significantly. In addition, the FDA is expected to approve Lucentis, an anti-vegf injectable medication used for the treatment of wet AMD, for use in treating branch retinal vein occlusions sometime in late 2010. Anti-vegf agents inhibit the growth of new blood vessels from damaged tissue and play a role in preventing vessels from leaking.