INS and diabetic retinopathy: DM is a lifelong endocrine disease caused by defects in insulin secretion (i.e., deficient or insufficient synthesis of insulin from the pancreas), insulin action (i.e., insulin resistance and hyperinsulinemia), or both [6–8], leading to hyperglycemia and severe irreversible microvascular and macrovascular complications [9] that affect the eyes (diabetic retinopathy), feet (diabetic foot), nerves (diabetic neuropathy), kidneys (diabetic nephropathy), blood vessels (atherosclerosis), and heart (cardiovascular disease).