DPP4 and diabetic retinopathy: The individual members or classes of these drugs (OHAs) are sometimes able to regulate the elevated glucose levels to optimal level via various mechanisms and/ or involving the inhibition of specific protein targets such as alpha-glucosidase, dipeptidyl peptidase -IV (DPP-IV), protein tyrosine phosphatase-1 B (PTP-1B) implicated in the emergence of T2DM and aldose reductase as a consequent of diabetes retinopathy.