Prevalence of Diabetic Retinopathy in Various Ethnic Groups: A Worldwide Perspective

Abstract

The alarming rise in diabetes prevalence is a global public health and economic problem. Diabetic retinopathy is the most common complication of diabetes and the leading cause of blindness among working-age populations in the Western world. Screening and prompt treatment of diabetic retinopathy are not top priorities in many regions of the world, because the impacts of other causes of preventable blindness remain an issue. Ethnicity is a complex, independent risk factor for diabetic retinopathy. Observations from white populations cannot be extrapolated fully to other ethnic groups. The prevalence of diabetic retinopathy, sight-threatening diabetic retinopathy, and clinically significant macular edema are higher in people of South Asian, African, Latin American, and indigenous tribal descent compared to the white population. Although all ethnic groups are susceptible to the established risk factors of diabetic retinopathy—such as length of exposure and severity of hyperglycemia, hypertension, and hyperlipidemia—ethnic-specific risk factors also may influence these rates. Such risk factors may include differential susceptibility to conventional risk factors, insulin resistance, differences in anthropometric measurements, truncal obesity, urbanization, variations in access to healthcare systems, genetic susceptibility, and epigenetics. The rates of nonproliferative diabetic retinopathy appear to be declining in the United States, supporting the observation that better medical management of diabetes and prompt treatment of sight-threatening diabetic retinopathy substantially improve the long-term diabetic retinopathy incidence; studies from other parts of the world are limited and do not mirror this finding, however. We examine the ethnicity and region-based prevalence of diabetic retinopathy around the world and highlight the need to reinforce ethnicity-based screening and treatment thresholds in diabetic retinopathy.

Introduction

The total number of people with diabetes is projected to rise from 171 million in 2000 to 366 million in 2030.²⁷⁷ Race/ethnicity is a risk factor for both type 1 (T1D) and type 2 diabetes mellitus (T2D).21, 95 Hemoglobin A1c (HbA1c) is widely used as an index of mean glycemia, a measure of risk for the development of diabetic complications, and a measure of the quality of diabetes care.

Diabetic retinopathy (DR) is the most common microvascular complication of diabetes, and it remains a leading cause of legal blindness and visual impairment in the working-age population in the developed world.43, 72 Diabetic retinopathy involves damage to the microvasculature of the retina as a result of the prolonged exposure to the metabolic changes induced by diabetes. The two main types of DR are the less-severe form, nonproliferative DR, and the severe form, proliferative DR (PDR). Nonproliferative DR is associated with microaneurysms, superficial and deep retinal hemorrhages, hard exudates, and macular edema. Subsequent PDR involves the growth of new blood vessels in the retina that may cause scarification of the retina and vitreous. Methods of diagnosing DR clinically include ophthalmoscopy, optical coherence tomography, retinal photography, and fluorescein angiography.

Recent data suggest that the prevalence of DR may be decreasing in the United States.25, 127 The launch of the VISION 2020 initiative in 1999,73, 276 DR surveillance programs,²³¹ intensified risk-factor control in response to the results of randomized controlled trials,232, 256, 262 and continuing improvement in healthcare systems have been implicated in the decreasing rates of DR.¹⁰⁷ This transition is best reflected and reported in the United States²⁴¹ and is limited to a reduction in the prevalence of nonproliferative DR only.²⁵ Furthermore, these advantages may be masked by the alarming rate of increase in the global prevalence of T2D, especially in some areas.264, 277 The same situation applies to T1D, but the increase is not to the same degree.²¹ Although the decline in DR rates is encouraging, many developing countries are still struggling to cope with other preventable causes of blindness48, 270 and inequity in healthcare access.¹² Thus, visual impairment from diabetes is not a current priority for these countries.⁴⁸ Nevertheless, reliable estimates of regional and ethnic differences in DR rates should allow us to comprehend the healthcare need and aid in planning of resource allocations to provide patient-centered care to the high-risk groups. We shall address the regional and ethnic variations in DR and identify factors that may explain the differences.