| Management |
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| Diabetic Retinopathy |
| - Annie Mathai, Nihal Thomas |
Vellore, India
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| Diabetic retinopathy is one of the leading causes of blindness in persons aged 20-74 years. Ninety percent of patients with diabetes mellitus have type 2 diabetes. Because of disproportionately large number of patients with type 2 diabetes, this group comprises a substantial proportion of patients with visual impairment secondary to diabetic retinopathy, even though type 1 diabetes mellitus is associated with more frequent and severe ocular complications. |
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| Prevalence of diabetic retinopathy |
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| The prevalence of diabetic retinopathy according to the Wisconsin Epidemiologic Study of Diabetic Retinopathy (WESDR)are:1.2 |
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| Type 1 diabetes - 71% |
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| Type 2 diabetes (not requiring insulin) - 39% |
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| Type 2 diabetes (requiring insulin) - 70% |
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| Risk factor for development of diabetic retinopathy |
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- Duration of diabetes: The duration of diabetes is a major risk factor for the onset of retinopathy. After a 15-year duration, 80% of type 1 diabetes, 84% of type 1 diabetes on insulin and 53% of type 2 patients not on insulin have some form of retinopathy.
- Hyperglycaemia: The severity of hyperglycaemia is a key alterable risk factor associated with the development with the development and progression of diabetic retinopathy. The Diabetes Control and Complications Trial (DCCT)3 examined as to whether intensive treatment with the goal of maintaining glucose levels within the normal range could decrease the frequency of long-term microvascular and neurological complications in type 1 diabetic patients. Intensive therapy was compared with conventional therapy and the study showed that though intensive therapy resulted in transient worsening of retinopathy during the first year there was are reduction in subsequent progression of retinopathy.
- Hypertension: WESDR data revealed that blood pressure had a slight association with retinopathy in younger-onset patients, but no relation in older- onset patients4. A recent study showed blood pressure and glycosylated haemoglobin levels as important factors in the development of retinopathy5.
- Hyperlipidemia: A relationship between the development of retinal hard exudates with elevated triglycerides and low-density lipoprotein cholesterol (LDL) has been documented6.
- Nephropathy: Micro-albuminuria is associated with the prevalence of severe retinopathy in both insulin-dependent8and non-insulin- dependent diabetes8.
The WESDR also observed that in type 1 diabetic patients gross proteinuria was a predictor for the development of proliferative retinopathy.
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Hormonal
- Pregnancy: A two-fold increase in progression of retinopathy among pregnant women with type 1 diabetes has been shown in a prospective controlled study9. The progression of retinopathy was greater for women who had a longer duration of diabetes and who presented with diabetic retinopathy at conception10. However, women with gestational diabetes are not at increased risk for retinopathy.
- Post-menarche: In the WESDR, the postmenearcheal had a relative risk of developing diabetic retinopathy of 3.2 times that of the premenearcheal diabetes population. This can be explained by the rise in IGF-I, growth hormone, sex hormone, blood pressure and poorer glycaemic control at puberty.
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Genetic factors: After controlling for all risk factors, some races have a greater propensity for proliferative retinopathy than others. In particular are the Pima Indians and the Mexican-Americans11.
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| Pathogenesis of diabetic retinopathy |
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| Diabetic retinopathy is a microangiopathy affecting retinal capillary arterioles, capillaries and venules. The larger vessels also get involved. The microangiopathy has features of both microvascular leakage and occlusion. |
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| Microvascular leakage |
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| The cellular elements of retinal capillaries are the endothelial cells and pericytes (mural cells). The tight junctions of the endothelial cells from the inner blood-retinal barrier. The pericytes are wrapped around capillaries and give structural integrity to the vessel wall. The normal pericyte: Endothelial cell ratio is 1:1. However, in diabetic patients, there is a reduction in the number of pericytes resulting in capillary wall distention producing microaneurysms. There is also breakdown of blood- retinal barrier with leakage of plasma constituents into the retina. |
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| Microvascular occlusion |
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| The changes leading to microvascular occlusion are: |
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- Basement membrane thickening, endothelial cell damage and endothelial cell proliferation of the capillaries.
- Deformation of red blood corpuscles resulting in decrease oxygen transport.
- Changes in platelets leading to increased stickiness and aggregation.
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