AIM:To evaluate the efficacy of diclofenac sodium ophthalmic solution and a steroidal ophthalmic solution administered prophylactically against macular edema after phacoemulsificaition and intraocular lens implantation and to assess macular thickness changes using optical coherence tomography(OCT).METHODS:In this prospective study,patients with diabetes mellitus but without diabetic retinopathy were randomized to either the A group(n=104) or the B group(n=113).Patients in the A group received either tobramycin and dexamethasone ophthalmic suspension 4 times daily(qid) for approximately one day preoperatively and four weeks postoperatively plus diclofenac 1% qid for four weeks postoperatively.Patients in the B group received topical tobramycin and dexamethasone qid for approximately four weeks postoperatively alone.Outcome measures included macular edema incidence,central field retinal thickness as measured by OCT,and best-corrected visual acuity.RESULTS:Four eyes in A group and ten eyes in B group had clinically apparent macular edema.Based on OCT,six eyes in A group had macular edema,twelve eyes in B group.The central subfield retinal thickness values were significantly lower in the A group at four weeks than those in the B group.CONCLUSION:This study suggests that adding preoperative diclofenac sodium ophthalmic solution to postoperative topical dexamethasone significantly reduces the incidences of macular edema and suppresses increasing retinal thickening after cataract surgery in patients with diabetes mellitus.