Does renin-angiotensin system blockade have a role in preventing diabetic retinopathy? A clinical review.

Diabetes management has increasingly focused on the prevention of macrovascular disease, in particular for type 2 diabetes. Diabetic retinopathy, one of the main microvascular complications of diabetes, is also an important public health problem. Much of the care invested in retinopathy relates to treatment rather than prevention of disease. Tight glycaemic and blood pressure control helps to reduce the risk of retinopathy, but this is not easy to achieve in practice and additional treatments are needed for both primary and secondary prevention of retinopathy. A renin-angiotensin system (RAS) has been identified in the eye and found to be upregulated in retinopathy. This has led to specific interest in the role of RAS blockade in retinopathy prevention. The recent DIRECT programme assessed use of the angiotensin receptor blocker (ARB) candesartan in type 1 and type 2 diabetes. Although the primary trial end-points were not met, there was a clear trend to less severe retinopathy with RAS blockade. A smaller trial, RASS, reported reduced retinopathy progression in type 1 diabetes from RAS blockade with both the ARB losartan and the angiotensin converting enzyme (ACE) inhibitor enalapril. The clinical implications of these new data are discussed.