 Each study eye is required to complete a 12-week run-in phase. The run-in phase will identify study eyes that truly have persistent DME despite anti-VEGF therapy by requiring an additional 3 injections while also collecting standardized visual acuity and OCT measurements. At the enrollment, 4-week and 8-week visits of the run-in phase, enrolled eyes will receive an intravitreal injection of ranibizumab 3mg. Then at the 12-week run-in visit, if the eye still has persistent DME, it will be randomized to receive either intravitreal shamintravitreal ranibizumab 0.3 or intravitreal dexamethasoneintravitreal ranibizumab 0.3 injections. The randomized study duration is 24 week, during which a protocol visit takes place every month. The combination injections of shamranibizumab or dexamethasone ranibizumab will be given at the randomization visit baseline and at the 12-week visit after randomization. In between, an intravitreal injection of ranibizumab only will be given to study eyes at the 4, 8, 16 and 20 week visits. 