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.
Early diabetic retinopathy does not significantly impact a patient's quality of life; however, it is when this condition develops
into sight-threatening retinopathy that it reaches clinical significance for the patient.
Einar Stefansson MD, PhD
Diabetic macular oedema and proliferative diabetic retinopathy are the sight-threatening stages of diabetic retinopathy. A
patient with type I diabetes has almost a 50/50 chance of developing sight-threatening retinopathy, either proliferative diabetic
retinopathy or diabetic macular oedema, in his or her lifetime. With type II diabetes mellitus, the lifetime risk of sight-threatening
retinopathy is approximately one in three. This high lifetime risk and subsequent loss of vision creates the need for a preventative
public health approach to this serious disease.
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.