 Background: During PPV for diabetic retinopathy retinopathy and penetrating keratoplasty, removal of the edematous corneal epithelial layer was usually required in order to obtain a better surgical view1 or enhance the postoperative epithelial wound healing process. However, delayed epithelial healing was frequently found in these patients after surgeries. In addition, corneal epithelial defect is also frequent found in diabetic patients after PPV even corneal epithelial debridement is not performed during the operation. Topical insulin application has been known to increase corneal reepithelization rate over diabetic animals, has is known to have no influence on systemic glucose level in humans and animals. In this study, we plan to perform a prospective randomized study to determine the effectiveness of topical insulin eye drops as a primary treatment in corneal epithelial defect following vitrectomy in diabetic patients and penetrating keratoplasty. 