Objective:To observe the clinical efficacy of pars plana vitrectomy (PPV) combined with dexamethasone intravitreal implant (DEX) in the treatment of proliferative diabetic retinopathy (PDR).Methods:A prospective randomized controlled study. A total of 57 PDR patients with 79 eyes diagnosed by Department of Ophthalmology of The First Affiliated Hospital of Nanjing Medical University from May 2021 to February 2023 were included in the study. Best corrected visual acuity (BCVA) and optical coherence tomography (OCT) were performed in all affected eyes. Central macular thickness (CMT) was measured by OCT. The patients were randomly divided into control group and experimental group, with 27 cases and 35 eyes and 30 cases and 44 eyes, respectively. All eyes were treated with routine 25G PPV and intraoperative whole- retina laser photocoagulation. At the end of the operation, the experimental group was given 0.7 mg DEX intravitreal injection. At 1, 4, 12, and 24 weeks after operation, the same equipment and methods were used for relevant examinations. The improvement after surgery was assessed according to the diabetic retinopathy severity score (DRSS). Mixed analysis of variance was used to compare logarithm of the minimum angle of resolution BCVA and CMT between the two groups and within the two groups before and after operation.Results:At 1, 4, 12 and 24 weeks after surgery, BCVA was significantly improved at different time points after surgery, and the differences were statistically significant ( P<0.001). At different time after operation, BCVA and CMT in experimental groups were significantly better than that in control group, with statistical significance ( P<0.05). Compared with the CMT before surgery, the CMT at all time point after surgery in experimental group were significantly decreased, and the difference were statistically significant ( P<0.05). There was no significant difference one week after eye operation in control group ( P=0.315). At 4, 12 and 24 weeks after operation, CMT decreased in control group, and the differences were statistically significant ( P<0.05). Compared with before surgery, DRSS increased two steps higher at 1, 4, 12 and 24 weeks after surgery in 20 (45.45%, 20/44), 26 (59.10%, 26/44), 32 (72.73%, 32/44) and 31 (70.45%, 31/44) eyes in the experimental groups, respectively. The control group consisted of 15 (42.86%, 15/35), 15 (42.86%, 15/35), 16 (45.71%, 16/35) and 18 (51.43%, 18/35) eyes, respectively. There was no significant difference in DRSS at 1, 4 and 24 weeks after operation between the control group and the experimental group ( P=0.817, 0.178, 0.105). At 12 weeks after surgery, the difference was statistically significant ( P=0.020). Conclusion:PPV combined with intravitreal injection of DEX in the treatment of PDR can improve postoperative visual acuity, alleviate postoperative macular edema and improve the severity of DR.