When the blood glucose persistently increases, the activity of aldose reductase in pericytes of retinal capillaries increases too, resulting in enhanced level of metabolites (sorbitol and fructose) in intracellular pericytes leading to an elevation of intracellular osmotic pressure, cell swelling and metabolic disorders, eventually bringing about the loss of pericytes and damage of their primary function (autoregulation of retinal capillaries; Hammes, 2005). Here, AKR1B1 is linked to metabolic disease.