Diabetic retinopathy (DR) is the most common complication of diabetes, and proliferative DR (PDR) remains the leading cause of blindness among working-age individuals in developed countries. Diabetic macular edema (DME), another important event that occurs in DR, is more frequent in type 2 than in type 1 diabetes [1]. Whereas PDR is the most common sight-threatening lesion in type 1 diabetes, DME is the primary cause of poor visual acuity in type 2 diabetes. Owing to the high prevalence of type 2 diabetes, DME is the main cause of visual impairment for diabetic patients overall [1]. In addition, DME is almost invariably present when PDR is detected in type 2 diabetes. Neovascularization caused by severe hypoxia is the hallmark of PDR, whereas vascular leakage caused by the breakdown of the blood–retinal barrier (BRB) is the main event involved in the pathogenesis of DME [2].