Is the risk of diabetic retinopathy greater in non-Hispanic blacks and Mexican Americans than in non-Hispanic whites with type 2 diabetes? A US population study

OBJECTIVE - To compare the risk for diabetic retinopathy in non-Hispanic white, non-Hispanic black, and Mexican-American adults with type 2 diabetes in the U.S, population. RESEARCH DESIGN AND METHODS - Representative population-based samples of people aged greater than or equal to 40 years in each of the three racial/ethnic groups were studied in the 1988-1994 Third National Health and Nutrition Examination Survey (NHANES III). Diagnosed diabetes was ascertained by medical history interview and undiagnosed diabetes by measurement of fasting plasma glucose. A fundus photograph of a single eye was taken with a nonmydriatic camera, and a standardized protocol was used to grade diabetic retinopathy. Information on risk factors for retinopathy was obtained by interview and standard laboratory procedures. RESULTS - Prevalence of any lesions of diabetic retinopathy in people with diagnosed diabetes was 46% higher in non-Hispanic blacks and 84% higher in Mexican Americans, compared with non-Hispanic whites. Blacks and Mexican Americans also had higher rates of moderate and severe retinopathy and higher levels of many putative risk factors for retinopathy. Blacks had lower retinopathy prevalence among those with undiagnosed diabetes. In logistic regression, retinopathy in people with diagnosed diabetes was associated only with measures of diabetes severity (duration of diabetes, HbA(1c) level, treatment with insulin and oral agents) and systolic blood pressure. After adjustment for these factors, the risk of retinopathy in Mexican Americans was twice that of non-Hispanic whites, but non-Hispanic blacks were not at higher risk for retinopathy. These risks were similar when people with undiagnosed diabetes were included in the logistic regression models. CONCLUSIONS - The prevalence and severity of diabetic retinopathy is greater in non-Hispanic blacks and Mexican Americans with type 2 diabetes in the U.S. population than in non-Hispanic whites. For blacks, this can be attributed to their higher levels of risk factors for retinopathy, but the excess risk in Mexican Americans is unexplained.