Background
Sub-Saharan Africa (SSA) faces an epidemic of noncommunicable disease (NCD) driven by urbanization, lifestyle, poor diet, smoking, environmental factors and aging. Increased life expectancy and population growth (in part from successes in combating communicable diseases) add to the NCD burden to society, health services and the individual [
1].
The International Diabetes Federation has estimated that the number of adults with diabetes in Africa will double in 20 years, from 12 million in 2010 to 24 million in 2030 [
2]. Diabetes causes significant morbidity, disability and early mortality. The diabetes epidemic therefore poses significant health and socioeconomic challenges for a continent simultaneously facing other health challenges including infectious diseases (HIV, tuberculosis and malaria) and high levels of maternal and perinatal disorders and trauma.
Diabetes causes visual impairment (VI) through early-onset cataract and diabetic retinopathy (DR), a progressive disease of the retinal microvasculature. Cataract and DR are the second and sixth leading causes of global VI, respectively [
3]. Both are included in the list of nine target diseases of Vision 2020, a joint program of the World Health Organization (WHO) and the International Agency for the Prevention of Blindness. Diabetes damages retinal capillaries through prolonged exposure to hyperglycemia. This leads to loss of supporting pericyte cells and tight junctions between endothelial cells. In turn, this causes leakage from capillaries, resulting in retinal edema; capillary closure; and ischemia. An ischemic retina produces vascular endothelial growth factor (VEGF), which stimulates new vessel growth (proliferative diabetic retinopathy, PDR). An edematous or ischemic retina loses function, and this will reduce vision if the central retina or macular is involved. New vessels are prone to bleeding (vitreous hemorrhage) and the accompanying fibrosis leads to tractional retinal detachment. Thus the sight-threatening manifestations of DR are proliferative retinopathy and diabetic maculopathy, which are both preventable and treatable before vision is lost. The risk of development and progression of retinopathy has been shown in developed economies to be related to glycemic control or HbA1c [
4‐
7], blood pressure [
4,
8‐
11] and blood lipid levels [
12]. Laser photocoagulation has been shown to be effective at reducing visual loss in patients with PDR [
13] and macular edema [
14] if timely treatment is performed.
The epidemiology of DR in Africa has been systematically reviewed by our group [
15]. This review identified no community-based cross-sectional or cohort studies of DR from SSA on which to base incidence or prevalence estimates in the population with diabetes. A recent population-based survey (n = 4,414) in Nakuru, Kenya, identified a prevalence of ‘any DR’ of 35.9% (95% CI: 29.7, 42.6) and of ‘severe non proliferative DR or PDR’ of 13.9% (95% CI: 10.0, 18.8) in 277 people with diabetes [Bastawrous, personal communication]. Clinic-based studies report a wide range of prevalence, often with higher levels of sight-threatening disease, but these are subject to bias. The proportion of any VI in African populations due to DR is largely unknown. A recent population-based study from Cape Town, South Africa, of visual loss using WHO methods identified DR as the cause of 8% of blindness and 11% of severe visual loss in persons ≥50 years [
16]. Population-based surveys of VI usually underestimate DR as a cause. Retinal causes of VI are often recorded together as one category, and are not recorded if there is no fundal view (for example, due to cataract). Rectifiable causes of VI (for example, cataract) are recorded in preference to preventable or untreatable causes [
17].
In this article we first review the evidence on detection and management of DR in Africa. We discuss the potential costs and benefits of action on DR within an integrated strategy for diabetes care. Finally we propose that, drawing on experience and expertise from other continents, research into DR in Africa can drive the political agenda for service development.
Summary
Improvement of services for people with diabetes and its complications is an urgent priority for Africa. The cost of inaction for individuals, communities and countries is likely to be high. The first priorities for diabetes care delivery must be adequate disease detection and appropriate medical management: primary prevention of complications. However, detection and management of diabetes complications including DR within effective integrated diabetes services in an African setting is feasible. Expansion of clinical services requires a shift in national health priorities. A much better evidence base is needed to effect this change. Understanding the scale of the problem and areas where intervention is required will enable informed prioritization of available health funding at a national level.
There is a pressing need for high-quality research into the epidemiology of DR in Africa. The research agenda must also address strategies for disease detection and management and include health economic analyses. Models of care tailored to the local geographic and social context are most likely to be cost effective. Drawing on experience and expertise from other continents will aid design of clinical trials and, in turn, service development. We recognize the complex challenges inherent in health-care provision in SSA. However, effective interventions need to be implemented in the near future to avert a large burden of visual loss from DR on the continent.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
PB drafted the manuscript. GM critically revised manuscript. NB participated in the design of the article and critically revised the manuscript. All authors read and approved the final manuscript.