Background The research of corneal thickness after pars plana vitrectomy in DM patient plays an important role not only theoretically but clinically. Objective Present study was to evaluate the change in corneal thickness after pars plana vitrectomy. Methods A prospective coherent study was designed.Seventy-five eyes of 70 consecutive diabetic retinopathy(DR) patients were collected in Tianjin Medical University Eye Center.Pentacam was used to assess the central and periphery corneal thickness by the same investigator preoperatively and 7 days,1 and 3 months postoperatively,respectively.The thickness values from five corneal zone were obtained,including cornea vertex,the thinnest point of the cornea,periphery cornea near the scleral incision of 4 mm away to vertex of cornea on vertical and 240°,120°,60° meridian ( right eye) or 300°,120°,60° meidian ( left eye ).These results were compared and analyzed with ANOVA of repeated measurement data.Subgroup analysis was performed to evaluate the influence of different corneal positions,the use of conventional 20g or 23g transconjunctival sutureless vitrectomy(TSV) groups,surgery duration,gas or fluid endotamponde on corneal thickness.This study was approved by Ethic Committee of this hospital.Written informed consent was obtained from the subjects before any relative medical procedure. Results The mean corneal thickness was ( 639.9 ± 103.1 ),( 689.5 ± 119.3 ),( 666.5 ±113.7),( 650.8 ± 108.6 ) μm before operation,postperative 7 days,1 and 3 months respectively.As covariates appearing in the model,the corneal thickness change rates were revised as the parameters as following: diabeitc duration =13.0 and age =57.2.The revised corneal thickness was significant different among various time points( F=210.928,P=0.000) and different corneal zones(F=24.843,P=0.000) with the size order in turn P4＞P3＞P1＞P2＞P5.The corneal thickness change rates were less in 23g TSV group compared with conventional 20-g group (F =53.843,P =0.000) and BSS tamponade group compared with gas tamponade group ( F =5.288,P =0.022).But no significant difference was found in the revised corneal thickness among surgery duration ＜ 1 hour group,1-2 hour group and ＞2 hour group( F=1.233,P =0.293). Conclusions Vitrectomy is a safe procedure on the ground of cornea,but TSV and fluid endotamponade appear to be more beneficial to the protection of cornea.Pentacam could offer the reliable data in not only central cornea but also periphery cornea.