Methods and Limitations
We estimated the prevalence of self–reported visual impairment among the U.S. diabetic adult population aged 18 years or older using data from the CDC's National Health Interview Survey (NHIS) of the National Center for Health Statistics (NCHS). Conducted continuously since 1957, NHIS is a health survey of the civilian, noninstitutionalized, household population of the United States. The survey provides information on the health of the U.S. population, including information on the prevalence and incidence of disease, the extent of disability, and the use of health care services. The design of the survey has been described elsewhere.1,2
Adult respondents are asked whether a health professional had ever told them they had diabetes. To exclude gestational diabetes, women are asked whether they had been told they had diabetes other than during pregnancy. Adult respondents are asked whether they have any trouble seeing even when wearing glasses or contact lenses. For our analyses visual impairment was defined as a positive response to the question.
The prevalence estimates of self-reported visual impairment in the diabetic population are presented by age, race/ethnicity, and sex. Persons of Hispanic origin may be of any race. The race groups include persons of both Hispanic and non-Hispanic origin. Three-year averages were used to improve the precision of the annual estimates. Estimates were age-adjusted using estimates of the 2000 U.S. population as the standard.
Approximately 25% of persons with diabetes are unaware they have diabetes because their diabetes has not been diagnosed.3 Therefore, the NHIS may underestimate the true prevalence of visual impairment in adults with diabetes. In addition, NHIS data on history of diabetes and visual impairment are self-reported; however, studies have found self-reported visual impairment to be high in accuracy,4,5 and the validity of self-reported diabetes is high for those with diagnosed diabetes.6-9
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- U.S. Department of Health and Human Services. National Diabetes Fact Sheet: General Information and National Estimates on Diabetes in the United States. Atlanta, GA: Centers for Disease Control and Prevention; 2008.
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- Saydah SH, Geiss LS, Tierney E, Benjamin SM, Engelgau M, Brancati F. Review of the performance of methods to identify diabetes cases among vital statistics, administrative, and survey data. Ann Epidemiol. 2004;14(7):507–516.