Purpose of this study: Is to compare the macular thickness before and after modified grid laser photocoagulation treatment of clinically significant macular edema (CSME) in diabetic patients using optical coherence tomography (OCT) and to detect the effect of the change in the macular thickness on the visual prognosis. Patients &Methods: This is a single group, prospective interventional study that was performed on thirty eyes of 19 patients with clinically significant diabetic macular oedema undergoing OCT macular scanning before, 6 weeks and 3 months after receiving modified grid photocoagulation. Results: Showed that the mean BCVA showed no statistical significant change throughout the 3 months follow up period and also the mean central macular thickness showed no statistical significant change throughout the follow up period. Conclusion: Patients with DME have not good benefit from modified grid photocoagulation and will need alternative or adjunct treatments such as intravitreal triamcinolone acetonide (IVTA) and therapies using inhibitors of vascular endothelial growth factor (VEGF).