Screening for diabetic retinopathy: new perspectives and challenges

Summary

Although the prevalence of all stages of diabetic retinopathy has been declining since 1980 in populations with improved diabetes control, the crude prevalence of visual impairment and blindness caused by diabetic retinopathy worldwide increased between 1990 and 2015, largely because of the increasing prevalence of type 2 diabetes, particularly in low-income and middle-income countries. Screening for diabetic retinopathy is essential to detect referable cases that need timely full ophthalmic examination and treatment to avoid permanent visual loss. In the past few years, personalised screening intervals that take into account several risk factors have been proposed, with good cost-effectiveness ratios. However, resources for nationwide screening programmes are scarce in many countries. New technologies, such as scanning confocal ophthalmology with ultrawide field imaging and handheld mobile devices, teleophthalmology for remote grading, and artificial intelligence for automated detection and classification of diabetic retinopathy, are changing screening strategies and improving cost-effectiveness. Additionally, emerging evidence suggests that retinal imaging could be useful for identifying individuals at risk of cardiovascular disease or cognitive impairment, which could expand the role of diabetic retinopathy screening beyond the prevention of sight-threatening disease.

Introduction

Diabetic retinopathy remains the leading cause of vision loss and preventable blindness in adults aged 20–74 years, particularly in middle-income and high-income countries.¹ In a meta-analysis of 35 studies done worldwide between 1980 and 2008, researchers estimated an overall prevalence of 34·6% (95% CI 34·5–34·8) for any diabetic retinopathy, 6·96% (6·87–7·04) for proliferative diabetic retinopathy, 6·81% (6·74–6·89) for diabetic macular oedema, and 10·2% (10·1–10·3) for vision-threatening diabetic retinopathy among people with diabetes.² Prevalence of any diabetic retinopathy and proliferative diabetic retinopathy was higher in people with type 1 diabetes than in people with type 2 diabetes.²

Although the proportion of people with diabetes developing proliferative diabetic retinopathy and severe visual loss has been declining between 1980 and 2008 in populations with improved diabetes control,³ the crude prevalence of visual impairment and blindness caused by diabetic retinopathy increased substantially between 1990 and 2015 according to the latest report of the Vision Loss Expert Group of the Global Burden of Disease Study,⁴ largely because of the increasing prevalence of type 2 diabetes in low-income and middle-income countries. Thus, the number of people affected by blindness due to diabetic retinopathy increased from 0·2 million to 0·4 million, and moderate to severe vision impairment increased from 1·4 million to 2·6 million.⁴ Furthermore, it has been estimated that the number of people with diabetes affected by any diabetic eye disease in Europe will increase from 6·4 million in 2019 to 8·6 million in 2050, and that 30% of affected individuals will require close monitoring or treatment.⁵

Few population-based studies examining the incidence of diabetic retinopathy have been done since 2000. The incidence of diabetic retinopathy was higher in studies from before 2000 than in those reported after 2000.⁶ However, contemporary studies that include more data from low-income and middle-income countries are needed.

Screening for diabetic retinopathy is necessary to detect referable cases that need timely full ophthalmic examination and treatment to avoid permanent visual loss. However, the resources for nationwide screening programmes are not sufficient in many countries. The new technologies based on artificial intelligence, which permit to implement personalised predictive models, the use of telemedicine, and portable imaging devices, are changing the screening strategies and are improving the cost-effectiveness of screening. In this Review, these new tools—which are changing the landscape of screening strategies—will be analysed. In addition, we will comment on the possibility of using retinal examination to identify patients at risk of cardiovascular disease and cognitive impairment, thus expanding the role of the screening of diabetic retinopathy.