Prologue

Peter H. Scanlon

The scope of the problem of the epidemic of diabetes

There is currently an epidemic of diabetes in the world, principally type 2 diabetes, that is linked to changing lifestyle, obesity and increasing age of the population. The International Diabetes Federation (IDF) publishes the Diabetes Atlas1 and has forecast a rise from the current level of 387 million people worldwide in 2014 to 592 million by 2035. The current level in 2014 is equivalent to 1 in 12 people in the world having diabetes, and 48.3% of these people are believed to be undiagnosed.

In 2000, Karvonen et al.2 reported a global variation in the incidence in different populations; the overall age-adjusted incidence of type 1 diabetes varied from 0.1/100,000 per year in China and Venezuela to 36.8/100,000 per year in Sardinia and 36.5/100,000 per year in Finland. The 2014 estimates1 for the prevalence of type 1 diabetes are 500,000 children aged under 15 years with type 1 diabetes worldwide, the largest numbers3 being in Europe (129,000) and North America (108,700), with the numbers have increased in most of the IDF regions.

The International Diabetes Federation has estimated1 the prevalence of diabetes in 2014 in 20-79 age groups and projected this to an estimate in 2035 (Fig. 1).

Fig 1 World map showing rising incidence and prevalence of diabetes.

Table 1

Individual publications4-10 from each region have described how these figures were arrived at. The report from the Western Pacific region was noteworthy because this region is home to one-quarter of the world's population, and includes China with the largest number of people with diabetes (98.41 million) as well as the Pacific Islands countries with the highest prevalence rates (Tokelau 37.49%, Federated States of Micronesia 35.03%, Marshall Islands 34.89%).

The prevalence of sight-threatening diabetic retinopathy worldwide

It is difficult to compare the many studies that have recorded the incidence and prevalence of diabetic retinopathy (DR) or sight-threatening or vision-threatening diabetic retinopathy (STDR or VTDR) because of the difference in examination techniques and the different definitions, particularly of STDR and VTDR (see Fig. 2).

Fig. 2 World map showing high prevalence of diabetic retinopathy (DR) and proliferative DR.

Table 2

The map in Fig. 2 uses data from the following studies.

1. 1. In 2012, Yau et al.11 reviewed a total of 35 studies (1980-2008) which provided data from 22,896 individuals with diabetes, and found that the overall prevalence was 34.6% (95% CI 34.5-34.8) for any DR, 6.96% (6.87-7.04) for proliferative DR, 6.81% (6.74-6.89) for diabetic macular oedema and 10.2% (10.1-10.3) for VTDR.
2. 2. In the USA, Zhang et al.12 reported that the estimated prevalence of diabetic retinopathy and vision-threatening diabetic retinopathy was 28.5% (95% CI, 24.9-32.5%) and 4.4% (95% CI, 3.5-5.7%) among US adults with diabetes, respectively.
3. 3. In Saudi Arabia, Ghamdi et al.13 reported that the prevalence of any DR was 34.6% but what was noticeable was the high level of STDR of 17.5%, which was mostly due to high levels of referable maculopathy (15.9%) and may be related to the high number with poor glycaemic control.
4. 4. Burgess et al.14 reported a systematic literature review of studies of diabetic retinopathy and maculopathy in Africa. A total of 62 studies from 21 countries were included. In population-based studies, the reported prevalence range in patients with diabetes was 30-31.6% for any DR, 0.9-1.3% for PDR and 1.2-4.5% for any maculopathy.
5. 5. Thomas et al.15 reported results from the Welsh Screening Programme in the UK. The prevalence of any DR and sight-threatening DR in those with type 1 diabetes was 56.0% and 11.2%, respectively, and in type 2 diabetes was 30.3% and 2.9%, respectively.
6. 6. Wu et al.16 reported on the prevalence of diabetic retinopathy in mainland China. The prevalence of DR, non-proliferative diabetic retinopathy (NPDR) and proliferative diabetic retinopathy (PDR) was 23% (95% CI: 17.8-29.2%), 19.1% (95% CI: 13.6-26.3%), and 2.8% (95% CI: 1.9-4.2%) in people with diabetes.
7. 7. Wong et al.17 reported from the Singapore Malay Eye Study that the overall prevalence of any retinopathy was 35.0% (95% CI, 28.2-43.4%), the overall prevalence of macular oedema was 5.7% (95% CI, 3.2-9.9%), PDR 4.9% (95% CI, 2.7-8.8%) and the overall prevalence of vision-threatening retinopathy was 9.0% (95% CI, 5.8-13.8%).
8. 8. Rema et al.18 reported that the overall prevalence of DR in the population of known diabetic subjects in Chennai, India was 20.8% (95% CI: 18.7-23.1%) and 5.1% (95% CI: 3.1-8.0%) in subjects with newly detected diabetes.
9. 9. Villena et al.19 reported from a hospital-based photographic screening programme in Peru that DR was detected in 282 patients (23.1%) (95% CI: 20.71-25.44%); 249 patients (20.4%) (95% CI: 18.1-22.6%) had non-proliferative DR and 33 (2.7%) (95% CI: 1.8-3.6%) had proliferative DR.
10. 10. In the Australian Diabetes, Obesity and Lifestyle study (AusDiab) of 11,247 adults > 25 years in 42 randomly selected areas of Australia, Tapp et al.20 showed a prevalence of any DR of 21.9% in those with known type 2 diabetes (KDM) and 6.2% in those newly diagnosed (NDM). The prevalence of PDR was 2.1% in those with known DM.

Of note, three studies21-23 have demonstrated that, if one screens for type 2 diabetes in different populations, the prevalence of diabetic retinopathy in screen-positive patients (7.6%, 6.8% and 9%) is much lower than the prevalence in the known population of people with diabetes.

In 1997, Kernell et al.24 reported the youngest child in the literature (11.8 years) at that time with pre-proliferative DR from Sweden.

In 1999, Donaghue et al.25 described the youngest child reported in the literature to have background diabetic retinopathy at that time (1999): 7.9 years (duration 5.6 years, HbA1c 8.9%) from Australia.

Incidence of DR

In 2008 and 2009, Klein et al.26,27 reported on the 25-year cumulative progression and regression of diabetic retinopathy and cumulative incidence of macular oedema (MO) and clinically significant macular oedema (CSMO) in type 1 patients in the Wisconsin Epidemiologic Study of Diabetic Retinopathy. The 25-year cumulative rate of progression of DR was 83%, progression to proliferative DR was 42%, and improvement of DR was 18%; the 25-year cumulative incidence was 29% for ME and 17% for CSME.

In 2009, Wong et al.28 conducted a systematic review of rates of progression of diabetic retinopathy in people with both type 1 and type 2 diabetes during different time periods. The article concluded that,...