Diabetic Retinopathy — It Affects Over 25% of All Diabetes Sufferers

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EXECUTIVE SUMMARYDiabetes is a disease that affects not only the blood glucose levels, but also the blood vessels. Small blood vessels (capillaries) throughout the retina become damaged or blocked, resulting in lack of blood supply to small patches of the retina. The damaged blood vessels also tend to leak, producing swelling within the retina. This disease of the retinal blood vessels is known as diabetic retinopathy. Approximately 25% of diabetics have some degree of diabetic retinopathy.While diabetic retinopathy can occur in both Type I diabetics and Type II diabetics, it tends to be more common and more severe in Type I patients. Because Type II diabetes is often not diagnosed until the patient has had the disease for many years, diabetic retinopathy may be present in a Type II patient at the time diabetes is discovered. In fact, many patients first learn that they have diabetes when their ophthalmologist finds diabetic retinopathy on a routine eye exam.The duration of diabetes is important in the development of diabetic retinopathy. The longer a patient has had diabetes, the more likely they are to have diabetic retinopathy. Diabetic retinopathy does not usually occur for at least three years after the onset of Type I diabetes. After having diabetes for 15 years, however, about 80% of Type I diabetics will have some degree of diabetic retinopathy, and 50% will have proliferative retinopathy.Retinal blood vessels are different from vessels elsewhere in the body. Most blood vessels are fenestrated, meaning that they have tiny openings that allow fluid to pass through the vessel wall. The openings are small enough to prevent the egress of larger blood elements, such as blood cells and large proteins, but large enough to allow water and small molecules, such as ions, to pass. Retinal blood vessels, on the other hand, have tight junctions between the cells of the blood vessel wall, so all fluid and molecules exiting the vessel have to pass through the cells. This lack of fenestration helps keep the retina relatively dehydrated, which is necessary for proper function.Whereas the multiple physiological perturbations of diabetes mellitus result from lowered availability and/or cellular recognition of insulin, the complications of diabetes such as diabetic retinopathy are caused by the chronic hyperglycemia. Although insulin therapy lowers the blood glucose levels enough to preserve life, prudent administration of insulin does not permit complete euglycemia nor prevent the long-term complications of chronic supernormal levels of blood glucose. The earliest effect of elevated glucose levels is a substrate-driven increased flux through the polyol pathway expressed as an increased activity of aldose reductase and concomitant intracellular accumulation of sorbitol, the polyol of glucose.The polyol pathway has been the most widely studied and is the most firmly established as a cause of diabetic microvascular complication. Sorbitol is found in numerous organ systems, suggesting that it may also play a major role in microvascular complications.Source: Diabetes — Managing Markets and Technology — Genesis 1998

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