Useful notes for medical students
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Risk factors for developing diabetic retinopathy
The risk of macular exudation, edema, and ischemia increases with:
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Duration of diabetes
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Blood glucose levels and poor control of diabetes
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Blood pressure
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High cholesterol and Triglyceride levels
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Anemia
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Diabetic kidney disease
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Smoking
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Excessive alcohol consumption
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Lack of exercise
A) Role of Blood glucose control
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Prolonged exposure to hyperglycemia causes microvascular complications, such as retinopathy, nephropathy, and neuropathy.
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Two important studies to remember:
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Diabetes Control and Complications Trial:
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Intensive insulin therapy effectively delays the onset and slows the progression of diabetic retinopathy in patients with type 1 diabetes. In the primary prevention cohort (those with no retinopathy at baseline), intensive therapy reduced the adjusted mean risk for the development of retinopathy by 76% compared with conventional therapy. In the secondary intervention cohort (those with mild retinopathy at baseline), intensive therapy slowed the progression of retinopathy by 54% and reduced the development of proliferative or severe nonproliferative retinopathy by 47%.
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UK Prospective Diabetes Study:
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Improved control in patients with type 2 diabetes not only led to a reduction in retinopathy but also reduced overall microvascular complications by 25%. A one-point decrease in hemoglobin A1c (HbA1c) was associated with a 35% reduction in risk of microvascular complications. The American Diabetes Association advocates an HbA1c goal of less than 7%.
B) Diet and exercise
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Exercise alone reduces the concentration of HbA1c by about 0.65 point and should be strongly encouraged.
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Risks of progressive nephropathy and neuropathy are also reduced with tight glucose control.
C) Blood pressure control
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Wisconsin Epidemiologic Study of Diabetic Retinopathy and the UK Prospective Diabetes Study: Diabetic retinopathy progressed significantly more slowly with more tightly controlled blood pressure Risks of progressive nephropathy and neuropathy are also reduced with good blood pressure control. EURODIAB Controlled Trial of Lisinopril in Insulin-Dependent Diabetes Mellitus: Showed that an angiotensin-converting enzyme (ACE) inhibitor (lisinopril) reduced progression of retinopathy in nonhypertensive patients with type 1 diabetes by 50% in 2 years. This finding needs to be confirmed on a larger scale, much evidence supports the use of ACE inhibitors in both hypertensive and nonhypertensive patients with diabetes to prevent microvascular and macrovascular diabetic complications.
D) Lipid control
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Evidence suggests that hyperlipidemia contributes to the progression and morbidity of diabetic retinopathy. Wisconsin Epidemiologic Study of Diabetic Retinopathy, The presence of retinal hard exudates was significantly associated with increased serum cholesterol levels in patients taking insulin. Early Treatment Diabetic Retinopathy Study Subjects who had an elevated total cholesterol or low-density lipoprotein cholesterol level were significantly more likely than those with normal levels to have retinal hard exudates.
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Accumulation of retinal hard exudates can lead to vision loss either from a foveal lipid plaque or from the development of fibrosis. Risks of progressive nephropathy and neuropathy also are reduced with lipid control.
E) Diabetic nephropathy:
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This condition may exacerbate diabetic retinopathy in a number of ways:
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Erythropoietin-sensitive anemia exacerbates retinopathy if not effectively treated. Erythropoietin (Epogen, Procrit) treatment of nephropathy-associated anemia has been shown to result in resolution of diabetic macular edema. Two factors--hypoalbuminemia associated with diabetic nephropathy-induced microalbuminuria and the hypertension that often accompanies diabetic nephropathy--shift the Starling forces toward the extravascular compartment, which exacerbates edema.
References Michael Colucciello, MD Diabetic retinopathy Control of systemic factors preserves vision VOL 116 / NO 1 / JULY 2004 / POSTGRADUATE MEDICINE
