Why are diabetics still going blind?

Diabetic retinopathy is not an old disease. It was recognized just over a century ago and was still a rare disease in the early part of the twentieth century. With the breakthrough discovery of insulin, the accompanying increase in survival of type I diabetics and with the epidemic of type II diabetes in recent times, diabetic retinopathy has become a major public health hazard and remains the main cause of blindness in working-aged people in many developed countries. Today, there are around 200 million people with diabetes in the world¹ and this number is increasing by approximately 10 million people per year; equating to around 3% of the global population. However, if we consider the incidence of diabetes mellitus in adult Latinos in Los Angeles, where the condition affects almost one-quarter (23%) of this population, it seems probable that we will see an escalation in the worldwide epidemic of obesity and type II diabetes mellitus in the coming years.

It is known that the majority of diabetic patients eventually develop diabetic retinopathy, with more than three out of every four type I diabetic patients and over half of all type II patients going on to develop retinopathy after 20 years.

The risk of diabetic retinopathy and the rapidity of its development depends predominantly on blood glucose control and blood pressure. For example, a 1% difference in glycosylated haemoglobin levels changes the rate of development of retinopathy by one-third, whilst diabetic retinopathy is less likely to progress in one-third of patients in whom arterial blood pressure is well-controlled, in comparison with those whose arterial blood pressure is poorly controlled.

Although several factors contribute to the rate of retinopathy development, it is these factors, along with the duration and type of diabetes that are the main determinants of the rate of development of the disease. There are significant variations in the statistics quoted in published epidemiological studies of diabetic retinopathy and this, in part, can be owed to the variability of blood glucose control and the different duration of diabetes between populations around the world. Hence, a general consensus on prevalence has yet to be achieved in published literature.

Screen early and prevent blindness

Retinal laser coagulation is the fundamental ophthalmologic treatment approach to diabetic retinopathy. Extensive clinical studies have demonstrated the benefit of laser treatment in reducing the risk of vision loss in proliferative diabetic retinopathy and diabetic macular oedema. The timing of laser treatment is very important and the treatment is most effective if it is applied in the early phases of sight-threatening retinopathy. It is much less effective in dealing with chronic diabetic macular oedema or advanced proliferative diabetic retinopathy with extensive fibrovascular proliferations and haemorrhages.

Since the early stages of sight-threatening retinopathy are virtually asymptomatic, the only way of detecting the disease at the optimal treatment stage is by screening diabetic patients regularly and looking for the first signs of diabetic macular oedema or proliferative diabetic retinopathy. This has been practiced in several regions, mostly in Northern Europe. The first program was established in Iceland in 1980 and now several programmes exist in other Nordic countries. In all cases, regular screening and preventive treatment has resulted in a significant decrease in the prevalence of blindness among diabetic patients. In Iceland, for example, the prevalence of blindness amongst diabetic patients has decreased from 2.4% in 1980 to 0.5% today. Similar and even better outcomes have been shown in certain regions of Denmark and Sweden. Screening programs are already established or are being planned in several areas, including a national system in the UK.