Public Health and the EyePrevalence of Diabetic Retinopathy in Various Ethnic Groups: A Worldwide Perspective
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.
Section snippets
Characteristics of Type 1 Diabetes
T1D is characterized by an absolute deficiency of insulin secondary to immune-mediated destruction of the pancreatic β cells. The development of T1D is thought to be triggered by environmental factors in genetically susceptible patients. Several lines of evidence indicate rather complex genetics for T1D, with the strongest risk associated within the human leukocyte antigen (HLA) region15 that has both susceptible and protective haplotypes. The relative contribution of these haplotypes and their
Characteristics of Type 2 Diabetes
T2D is a growing worldwide problem, with WHO estimates suggesting that 300 million people will be affected by 2025. T2D is characterized by peripheral insulin resistance, impaired regulation of hepatic glucose production, and declining ß-cell function, eventually leading to ß-cell failure. There has been a surge in the reports of T2D-related DR in the last 2 decades, especially from Asia. More multiethnic comparative studies are now available to elucidate the variations in DR between racial
Conclusions
Race- and ethnicity-related differences in the prevalence of DR, CSME, and visual impairment are an important public health issue. Understanding the epidemiology of DR in different ethnic groups is essential for more effective screening and treatment of DR. Although these differences are usually explained by health-seeking behaviors and access to healthcare, we have also highlighted interethnic variations in the susceptibility to known risk factors of diabetes complications. In particular, the
Method of Literature Search
The literature search for our review article was performed on the online electronic Medline Ovid database dated 1950 to January 2011. The keywords searched included: diabetic macular edema, clinically significant macular edema, diabetic retinopathy, prevalence, incidence, laser photocoagulation, risk factors,visual impairment, blindness, type 1 diabetes, type 2 diabetes, ethinicity, screening, microvascular complications, burden of diabetes, demographics, genetics, insulin-dependent diabetes.
Disclosure
The authors reported no proprietary or commercial interest in any product mentioned or concept discussed in this article. The review was funded by Guide Dogs for the Blind Association.
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