Hypertension and diabetic retinopathy---what's the story?

Abstract

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.

Hypertension and the eye: changing perspectives

“…87 UKPDS, EUCLID and other studies have shown retardation in the progression of diabetic retinopathy with improved control of blood pressure. 88 The HOPE study results showed that it was both safe and beneficial to lower BP already within the 'normal' range with angiotensin converting enzyme inhibitors in patients with known vascular risk factors including left ventricular dysfunction, hypertension or diabetic microalbuminuria. 89 …”

Is measurement of blood pressure worthwhile in the diabetic eye clinic?

“…Compared to UKPDS and HOT study drug treatment Blood pressure in the diabetic eye clinic S Al-Husainy et al 315 requirements to achieve target BP, it is clear that a large number of patients are not receiving sufficient combinations of two or three antihypertensive agents to achieve tight BP control (o140/85 mmHg). 3,13,14 With modern emphasis on evidence-based targets for other aspects of diabetes management, our data demonstrate that the majority of subjects with type II diabetic attending our diabetic eye clinic had not achieved a glycated haemoglobin target of o7%, and only a third of patients were on aspirin therapy; the latter has been recommended as appropriate for all patients with DR 430 years of age. 8 One-third of patients in our cohort were on statins.…”

“…12 The results of the recent large hypertension trials have led to national guidelines, defining targets and audit standards for optimal BP control, as well as lowering the threshold of BP formerly used in the definition of hypertension (BHS, 1999). 4,13 With such importance placed on the treatment of hypertension in the management of DR, several questions are raised:…”

Medical treatment of diabetic retinopathy

“…21 There have been a series of reports in the literature showing an association between systemic hypertension and retinal exudation, haemorrhage and maculopathy. [22][23][24] Retinal hyperperfusion is believed to be an important initial mode of injury to the retinal microcirculation in diabetes.…”