 Central and branch retinal vein occlusions are major causes of visual loss. Hemorrhage and capillary nonperfusion, when they involve the macula, can contribute to visual loss, but the major cause is macular edema. Focal and grid laser photocoagulation can sometimes provide benefit in patients with macular edema due to branch vein occlusions, but several laser treatments are often needed and recovery of vision can be very slow and incomplete 1. Laser photocoagulation does not provide benefit for macular edema due to central vein occlusions 2. Therefore, new treatments are needed.The objective of this study is to assess the bioactivity of 3 intravitreous injections 0.5 mg or 0.3 mg of ranibizumab in patients with macular edema due to central and branch retinal vein occlusions and correlate activity with peak and trough aqueous levels. The purpose of this research protocol is pilot study to determine if a randomized placebo controlled trial is warranted. 