Early postoperative retinal thickness changes and complications after vitrectomy for diabetic macular edema

PURPOSE: To determine the early postoperative changes in retinal thickness and complications after pars plana vitrectomy for diabetic macular edema. DESIGN: Consecutive interventional case series. METHODS: Studied retrospectively, pars plana vitrectomy was performed on 65 consecutive eyes of 63 patients with diabetic macular edema. The follow-up interval ranged from 6 to 36 months (12.6 +/- 7.4 months [mean +/- standard deviation (SD)]). The indications of pars plana vitrectomy in this study were (1) diffuse diabetic macular edema, (2) preoperative visual acuity less than 20/40, and (3) noneffective macular photocoagulation therapy. Preoperative and postoperative examinations by stereoscopic biomicroscopy, color fundus photography of the macula and optical coherence tomography (OCT) were performed on all eyes. Preoperatively, direct photocoagulation to microaneurysms in the macula had been performed in 48 eyes, and focal/grid photocoagulation had been performed in five eyes. Preoperative examination showed that epiretinal membranes were observed in 20 eyes, cystoid macular edema in 40 eyes, and 23 eyes had a complete posterior vitreous detachment (PVD). Epimacular membranes, removed during surgery, were examined histopathologically. RESULTS: The postoperative mean best,corrected visual acuity (logarithm of the minimum angle of resolution [logMAR] = 0.696 +/- 0.491 [mean +/- SD]) was significantly better than the preoperative mean best. corrected visual acuity (0.827 +/- 0.361; P < .0001; Wilcoxon signed,rank test). The final visual acuity improved by 2 or more lines in 32 of 65 eyes (45%), remained unchanged in 32 of 65 eyes (49%), and exacerbated after the surgery in 4 of 65 eyes (6%) due to neovascular glaucoma (2 eyes) and residual cystoid macular edema (2 eyes). The postoperative foveal retinal thickness (224.9 +/- 116.9 μm) at the last visit was significantly thinner than the preoperative foveal retinal thickness (463.7 +/- 177.3 μm; P < .0001; Wilcoxon signed rank test). The foveal retinal thickness did not decrease linealy but fluctuated: The mean postoperative retinal thickness had decreased significantly 7 days after surgery, then remained unchanged for approximately 1 month, and thereafter gradually decreased until 4 months. The intraoperative and postoperative complications included peripheral retinal tear in 3 of 65 (4.6%) eyes, postoperative rhegmatogenous retinal detachment in 1 of 65 (1.5%) eyes, neovascular glaucoma in 3 of 65 (5%) eyes, recurrent vitreous hemorrage in 1 of 65 ( 1.5%) eyes, hard exudates in the center of the macula in 3 of 56 (4.6%) eyes, postoperative epiretinal membrane formation in 9 of 65 (13.8%) eyes, and a lamellar macular hole in 1 of 65 (1.5%) eyes. CONCLUSIONS: Vitrectomy for diabetic macular edema is an effective procedure for reducing the edema and improving visual acuity. Because the postoperative reduction in retinal thickness is not complete until 4 months, the assessment of vitrectomy on foveal thickness should not be made until this time. In addition, there are severe complications from vitrectomy for diabetic macular edema, and careful preoperative and postoperative examinations and surgical methods arc required.