The Food and Drug Administration has given its nod of approval for Regeneron's EYLEA to be used to treat macular edema following central retinal vein occlusion (CRVO). Currently, Eylea is being used as a treatment for wet age-related macular degeneration. Macular edema is the swelling or thickening of the eye's macula and develops when the blood vessels in the retina leak fluids. This build-up of fluid causes the macula to not function properly and can lead to vision loss.Central Retinal Vein Occlusion is caused by a blockage in the main blood vessel that transports deoxygentated blood away from the retina. 358 patients were involved in the Phase 3 studies. After six months of treatment, 56% of the patients in one study group receiving the EYLEA injections gained at least 15 letters of Best Corrected Visual Acuity compared to only 12% of patients receiving sham injections. 60% of patients in the second study group who received EYLEA injections gained at least 15 letters compared to 22% of patients receiving sham injections.