EDITORIAL Editorials represent the opinions of the authors and JAMA and not those of the American Medical Association. Diabetes and Nonrefractive Visual Impairment The Young Have It David C. Musch, PhD, MPH Thomas W. Gardner, MD, MS T YPE 2 DIABETES MELLITUS, A DISEASE MOST COM- monly encountered in older obese persons, has be- come endemic in teenagers and young adults. Evi- dence for the increasing incidence of type 2 diabetes in youth and adolescents has been well documented. 1 Given the known risk of complications from diabetes, an increase in the prevalence of these complications over time would be expected among younger diabetics. In this issue of JAMA, Ko and colleagues 2 provide evidence that this is likely hap- pening in the US population. In a 2006 article, Vitale et al 3 reported on the prevalence of visual impairment in the United States, based on the 1999- 2002 data from the National Health and Nutrition Exami- nation Survey (NHANES). The authors estimated that 14 million individuals aged 12 years or older in the general popu- lation had visual impairment and suggested that approxi- mately 75% of visual impairment was due to a readily re- mediable cause—uncorrected refractive error. In the current report, Ko et al 2 use data from 2 cycles of NHANES to de- termine if the prevalence of nonrefractive (not due to need for glasses and presumably organic in nature) causes of vi- sual impairment—the other 25% of visual impairment in the report by Vitale et al—has increased between the sur- veys conducted in 1999-2002 and 2005-2008. Ko et al 2 found that the prevalence of nonrefractive vi- sual impairment increased from 1.4% to 1.7% (by 21%) be- tween the 2 surveys among adults aged 20 years or older. Although a 0.3% absolute increase in prevalence may seem small, extrapolating this to the US population suggests that the number of individuals who have this visual deficit has increased substantially. With about 230 million people aged 20 years or older in the US population, a 0.3% increase could potentially represent an increase of almost 700 000 indi- viduals with nonrefractive visual impairment over a rela- tively short time. While this increase may be thought to be driven by visual impairment in the elderly, inspection of changes over time by age and race/ethnicity found the larg- est absolute change among those aged 20 to 39 years (from 0.6% to 1.0%; P = .09), and within that age group, increases in nonrefractive visual impairment prevalence were ob- served in all 3 race/ethnicity groups. The substantial in- crease of nonrefractive visual impairment prevalence among Mexican Americans aged 60 years and older (from 4.6% to 8.9%; P  .001) warrants notice as well. Several factors associated with nonrefractive visual im- pairment were consistent in the 2 survey time periods. In multivariable analyses, older age was associated with an in- creased odds of nonrefractive visual impairment by 5% to 7% per year, and both poverty and having diabetes for 10 years or more (vs no diabetes) were associated with an ap- proximate 2-fold increased odds. Since the prevalence of pov- erty did not change between surveys, the authors explored associations of diabetes with the 2 surveys’ findings and ob- served that the prevalence of diabetes, both overall and within the youngest age group (20-39 years), significantly in- creased from the 1999-2002 survey to the 2005-2008 sur- vey. They note the potential interplay of several factors— increasing childhood obesity, increasing type 2 diabetes in younger age groups, and that diabetes increases the risk of nonrefractive visual impairment—as likely contributors to their findings. The results of these studies generate several relevant ques- tions. Among these are whether the results are based on sound data, do they make sense, and whether they are mean- ingful. The data source for this study is the NHANES, a long- standing program of government-supported studies de- signed to assess the health and nutritional status of US adults and children. Although others have estimated the preva- lence of visual impairment based on self-report, 4,5 the preva- lence data from NHANES are based on both interviews and examinations. Periodic surveys and examinations use a mul- tistage probability sample design that includes over- sampling to obtain sufficient numbers of respondents from various subgroups (such as Hispanics and low-income white individuals) that would otherwise yield insufficient sample sizes for estimating prevalence. This results in obtaining data on a relatively large number of respondents from relatively few primary sampling units, which can adversely affect the precision and generalizability of overall and subgroup preva- See also p 2361. Author Affiliations: Departments of Ophthalmology and Visual Sciences (Drs Musch and Gardner), Epidemiology (Dr Musch), and Molecular and Integrative Physiol- ogy (Dr Gardner), University of Michigan, Ann Arbor. Corresponding Author: David C. Musch, PhD, MPH, University of Michigan, Kel- logg Eye Center, 1000 Wall St, Ann Arbor, MI 48105 (dmusch@med.umich.edu). ©2012 American Medical Association. All rights reserved. JAMA, December 12, 2012—Vol 308, No. 22 2403 Downloaded From: http://jama.jamanetwork.com/ by a University of Michigan User on 01/08/2013