Microvascular disease: what does the UKPDS tell us about diabetic retinopathy?

Background The UK Prospective Diabetes Study (UKPDS) was a randomised controlled clinical study which looked at the effect of improved blood glucose and blood pressure control on macro- and microvascular complications in Type 2 diabetes. Retinopathy was the commonest microvascular outcome and this paper looks at this complication. Methods Newly diagnosed diabetic patients were randomised to intensive or conventional glycaemic control and a subset of hypertensive patients to tight or less tight blood pressure control. Patients were seen every 3 months in study clinics and retinopathy was assessed by adjudicated grading of triennial colour retinal photographs. Photocoagulation treatment, vitreous haemorrhage and cataract extraction were predefined UKPDS endpoints. Observational analyses of the data were used to examine the relationship of updated mean glycated haemoglobin (HbA(1c)) and mean blood pressure levels to retinopathy outcomes. Results The UKPDS showed that both improved glucose control and improved blood pressure control reduced the risk of retinopathy, with a linear relationship between the log hazard ratio for retinopathy and both updated mean HbA(1c) and updated mean blood pressure. A 1% decrement in HbA(1c) equated to a 31% reduction in retinopathy and a 10 mmHg decrement in systolic blood pressure equated to an 11% reduction in photocoagulation or vitreous haemorrhage. Evidence of retinopathy at diagnosis, including the presence of microaneurysms only, increased significantly the risk of progression to photocoagulation. Conclusions The UKPDS stands out as a landmark study in Type 2 diabetes, emphasising the crucial importance of controlling both blood glucose and blood pressure in order to minimise the risk of developing sight-threatening retinopathy.