By Mark Steedman, PhD, Manager, Centre for Health Solutions
This week’s blog returns to our series on eye health, which we began in advance of the launch of a global report on eye health at the November 2018 World Innovation Summit for Health (WISH). Our first blog in the series focused on glaucoma, while our second blog examined new treatments for age-related macular degeneration (AMD). This blog focuses on diabetic retinopathy, a complication of diabetes that can damage the back of the eye and lead to blindness if left undiagnosed and untreated.
As we have previously mentioned, the retina is the light-sensitive area in the back of the eye. It contains multiple layers of cells and receives a constant supply of blood from an intricate network of small blood vessels. For people with diabetes mellitus, this blood supply often has a high blood sugar level that can damage these blood vessels, leading to a complication known as diabetic retinopathy (DR). In DR, lesions form on the retina, usually in patients who have had diabetes for several years. DR occurs in three stages:
- stage one – background retinopathy, characterised by microaneurysms (bulges) in retina blood vessels that may leak small amounts of blood. Sight is unaffected, but patients are at a higher risk of future vision problems
- stage two – pre-proliferative retinopathy, characterised by more severe microaneurysms and bleeding into the retina. Risk of sight loss is higher, and more frequent screening is advised
- stage three – proliferative retinopathy, characterised by the formation of new blood vessels and scar tissue on the retina, which increase the risk of retinal detachment and vision loss.1
Approximately one in three people with diabetes have some degree of DR, while one in ten will eventually develop stage three DR.2 Globally, DR is the leading cause of vision loss in adults aged 20-65 years, and in 2015, DR was responsible for blindness in an estimated 400,000 people and moderate to severe visual impairment (MSVI) in 2.6 million people.3 Public health experts expect these numbers to increase significantly in the future, in line with the predicted increase in the global incidence of diabetes. To put this into context, let’s first look at some background statistics on diabetes.
In 2016, the Non-Communicable Disease Risk Factor Collaboration published the results of their pooled analysis of 751 population-based studies aimed at calculating ‘Worldwide trends in diabetes since 1980’. They calculated that between 1980 and 2014, the age-standardised prevalence of diabetes in adults across 200 countries increased from 4.7 per cent to 8.5 per cent.4 Prevalence increased, or stayed the same, in every country, and due to population growth and ageing, the number of adults with diabetes nearly quadrupled over this timeframe. Prevalence grew most in low and middle-income countries (LMICs), which now account for approximately 75 per cent of the global diabetes burden.5 In 2015, an estimated 415 million people were living with diabetes, and by 2040 it is estimated this will rise to 642 million people, of which 70 million will have vision threatening DR (see Figure 1).
Here in the UK, prevalence between 1980 and 2014 increased at a slower rate than the global average, increasing from 4.4 per cent to 5.8 per cent.6 As of November 2017, nearly 3.7 million people have been diagnosed with diabetes (see Figure 2).7
Figure 2. Diabetes prevalence in the UK 2016-2017
Source: Diabetes UK
However, Diabetes UK estimates that almost 1 million people with Type 2 diabetes have not been diagnosed, and that an estimated 4.6 million people are actually living with the disease.8 This is important, not only because of the link between diabetes and DR, but because people with diabetes are one and a half times more likely to get glaucoma and three times more likely to get cataracts.9 Consequently, diabetes is the leading cause of preventable sight loss in the UK.10
Over the past decade our knowledge and understanding of the epidemiology of DR has grown with research evidence demonstrating that screening, early detection, and prompt treatment of stage three DR can prevent visual impairment by 57 per cent.11 In England, the NHS Diabetic Eye Screening Programme launched in 2003, and by 2008 all four UK countries provided annual screening for all diabetic patients over the age of 12. In 2011-2012, over 2.3 million people were invited to attend DR screening, with more than an 80 per cent acceptance rate.12 Consequently, a 2014 study found that for the first time in five decades inherited retinal disorders had overtaken DR as the leading cause of blindness in working age adults in England and Wales.13
Effective treatment options have also expanded. Treatments at stages one and two focus mainly on managing a patient’s underlying diabetes, combined with screening to determine if a person’s vision is at risk. At stage three, treatment options often mimic those for wet AMD. We discussed the most common of these treatments – intravitreal injections (injections directly into the eye) of anti-vascular endothelial growth factor (anti-VEGF) – in our earlier blog on AMD. Briefly, these injections are generally given monthly, and while complications are rare, side effects can include increased pressure in the eye, floaters, inflammation, bleeding, infection and vision loss.14 Other treatments, include laser treatment and surgical procedures to remove blood or scar tissue from the eye.
Despite the success of screening programmes and expanded treatment options in high-income countries like the UK, in many LMICs, screening services are patchy or non-existent, and access to treatment is severely limited. With the global burden of diabetes and DR shifting to LMICs, prioritising and improving screening programmes against DR could dramatically reduce the number of people that are predicted to be affected by DR in the coming years.