 Phase III study with intravitreal triamcinolone acetonide microspheresRETAACfor treatment of diffuse diabetic macular edema unresponsive to laser photocoagulation. Study hypothesis is that single intravitreal injection of RETAAC is safe and efficient compared to conventional treatment. Fifty patients will participate in this study and will be randomized into treatment and observation groups. Efficacy will be evaluated by best corrected visual acuity and macular thickness measured by optic coherence tomography OCT after 12 months of treatment. 