Posterior capsule opacification (PCO) is a serious complication after cataract surgery. Diabetes could increase the occurrence of PCO, but the mechanism is still unclear. The purpose of this study is to investigate the role of small extracellular vesicles (sEVs) derived from diabetic aqueous humor in PCO process. Intraoperatively-derived aqueous humor sEVs from patients with diabetic related cataract (DRC) promoted the epithelial-mesenchymal transition (EMT) and metastasis of human lens epithelial cells (LECs). Via mouse PCO surgical model and DiI labeled fluorescence detection of sEVs, the sEVs derived from vascular endothelium were discovered directly contacting with LECs. Furthermore, we demonstrated that high-glucose-cultured human umbilical vein endothelial cells (HUVEC) -derived sEVs facilitated EMT process of HLE-B3 using co-culture model in vitro. miRNA-seq data and GEO datasets analysis revealed that miR-1246 was essential in EMT process with diabetes. The miR-1246 was highly expressed in diabetic aqueous humor sEVs and high-glucose-treated vascular-endothelial-cell-derived sEVs. Moreover, miR-1246 promoted the metastasis and EMT process of HLE-B3 cells by directly targeting GSK-3β. Inhibiting miR-1246 could negatively regulated EMT. This finding might serve as a potential therapy for diabetic PCO. • The exosomes of aqueous humor in diabetic patients can promote EMT. • Vascular endothelial cell-exosomes participates the LECs pathological process induced by diabetes. • Vascular endothelial cell-exosomes regulate the EMT via miR-1246/GSK-3β axis. [ABSTRACT FROM AUTHOR]