Improved understanding of the role of hypertension in the pathogenesis of diabetic retinopathy presents both a challenge and an opportunity for ophthalmologists and other diabetic healthcare professionals to improve patient care. Around 40% of patients with type 2 diabetes are hypertensive, the proportion increasing to 60% by the age of 75.1 Recent reports from the United Kingdom Prospective Diabetes Study (UKPDS) have focused attention on the links between hypertension and sight loss in diabetes. These reports in type 2 diabetes accord with previous observational studies in type 1 diabetes 3 4 and demonstrate both hypertension as a risk factor for diabetic retinopathy and the beneficial eVects of tight blood pressure control. This review summarises recent papers, including the UKPDS reports, and discusses the implications for management of people with diabetes.
Prevalence of hypertension in diabetesDiabetes and hypertension are among the commonest diseases in developed countries, and the frequency of both diseases rises with age. In the Wisconsin study examining patients with type 1 diabetes, hypertension was defined by current antihypertensive treatment or a mean blood pressure >160/95 (or >140/90 in those under 25 years). The prevalence of hypertension at baseline was 17.3%, and the 10 year incidence was 25.9%.5 Hypertension is more common in type 2 diabetes, and in the UKPDS 38% of newly diagnosed patients with type 2 diabetes had hypertension defined as repeated blood pressure >160/90 (or >150/85 in those on antihypertensive medication). 6 In the years after diagnosis of type 2 diabetes the incidence of hypertension is higher than in the age matched general population.In type 1 diabetes the development of diabetic nephropathy may play a major role in the subsequent development of hypertension since microalbuminuria is present in about 80% of type 1 diabetic subjects before the onset of hypertension. 7 The pathogenesis of hypertension in type 2 diabetes is not so clear, with a lesser significance for nephropathy, with microalbuminuria predating hypertension in approximately 25% of type 2 diabetic subjects with hypertension.7 Other relevant factors in type 2 diabetes are decreased baroceptor sensitivity, increased peripheral vascular resistance from enhanced smooth muscle contractility, and vascular structural changes including protein glycosylation and increased type IV collagen. Additionally, hyperglycaemia causes increased function of the sodium/glucose proximal convoluted tubule cotransporter leading to sodium retention. Over and above the action of hyperglycaemia, other factors including insulin resistance and hyperinsulinaemia may be aetiologically important in the development of hypertension in type 2 diabetes as insulin itself has sodium retaining properties. Reaven's syndrome (also known as the metabolic syndrome or syndrome X) describes this association of hyperinsulinaemia, insulin resistance, obesity, hypertension, and hyperlipidaemia in type 2 diabetes.
Non-arteritic anterior ischaemic optic neuropathy (AION) is thought to be due to occlusion of the posterior ciliary circulation. Raised lipid and fibrinogen concentrations are recognised risk factors for vessel occlusion in cardiovascular disease and stroke but, although suspected as risk factors in non-arteritic AION, they have not been studied in this condition. We therefore performed a case-control study on 41 patients with non-arteritic AION, looking at these and other atherosclerotic risk factors. The odds ratio of cholesterol being > 6.5 mmol/l in non-arteritic AION was 2.7 (95% confidence interval 1.09 to 6.65; p < 0.05) and of fibrinogen being > 3.6 g/l was 5 (2.66 to 9.39; p < 0.05). Smoking was also found to be significantly associated with non-arteritic AION, the odds ratio being 16 (3.23 to 79.23; p < 0.001). These were the only risk factors found to be significantly associated with non-arteritic AION. This raises the possibility that appropriate medical management of these factors could be given to prevent recurrence in the fellow eye.
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