 Topical insulin application has been proved recently to increase corneal reepithelization rate over diabetic animals. However, its effectiveness on corneal epithelial wound healing in patients who received pars planar vitrectomy PPV for diabetic retinopathy and penetrating keratoplasty has not been reported. In this study, we plan to perform a prospective randomized study to determine the effectiveness of topical insulin as a primary treatment for corneal epithelial defect in patients undergoing vitrectomy for diabetic retinopathy and penetrating keratoplasty. All patients enrolled in this study have received corneal epithelial debridement at the end of the ocular surgeries, namely PPV for diabetic retinopathy and penetrating keratoplasty. The patients were randomized into two treatment groups. In the control group, the patients receive conventional postoperative eye drops including topical steroid, antibiotic and mydriatics. In the experimental group, the patients receive topical insulin eye drops in addition to conventional postoperative eye drops. The duration for the corneal surface to completely re-epithelize, the incidence of corneal complications due to delayed surface re-epithelization e.g. infectious corneal ulcer, corneal melting, sterile corneal ulcer, corneal neovascularization, and the incidence of recurrent epithelial break down after initial epithelization will be compared between these two groups. Patients undergoing PPV for diabetic retinopathy and penetrating keratoplasty will be compared separately. 