Retinal vein occlusion can lead to fluid buildup and swelling of the macula, a condition known as macular edema. LUCENTIS® (ranibizumab injection) is prescription medicine injected into the eye for the treatment of macular edema following retinal vein occlusion. A patient with macular edema can have increased amounts of a protein called VEGF-A, which can lead to leakage of small blood vessels in the affected eye. LUCENTIS blocks this protein, and has been found to significantly improve vision of the affected eye.