Intravitreal Bevacizumab (Avastin®) Versus Intravitreal Dexamethasone (Ozurdex™) for Persistent Diabetic Macular Oedema

The specific aims of the study are to test the following hypotheses: * That there is a difference in change in visual acuity resulting from treatment with intravitreal bevacizumab compared with dexamethasone implant in eyes with advanced macular oedema * That there is a difference in degree of resolution of macular oedema resulting from treatment with intravitreal bevacizumab compared with dexamethasone implant in eyes with advanced macular oedema * That both intravitreal bevacizumab and dexamethasone implants have a manageable and acceptable safety profile in eyes with diabetic macular oedema