Context:The prevalence of visual impairment in the US public has not been surveyed nationally in several decades.Objective:To estimate the number of US individuals aged 12 years or older who have impaired distance vision due to uncorrected refractive error.Design,Setting,and Participants:The National Health and Nutrition Examination Survey(NHANES),using a multistage probability sampling design,included a vision evaluation in a mobile examination center.Visual acuity data were obtained from 13 265 of 14 203 participants(93.4%)-who visited the mobile examination center in 1999-2002.Visual impairment was defined as presenting distance visual acuity of 20/50 or worse in the better-seeing eye.Visual impairment due to uncorrected refractive error was defined as(presenting)visual impairment that improved,aided by automated refraction results,to 20/40 or better in the better-seeing eye.Main Outcome Measures:Presenting distance visual acuity(measured with usual corrective lenses,if any)and distance visual acuity after automated refraction.Results:Overall,1190 study participants had visual impairment(weighted prevalence,6.4% ;95% confidence interval CI,6.0%-6.8%),and of these,83.3% could achieve good visual acuity with correction(95% CI,80.9%-85.8%).Extrapolating these findings to the general US population,approximately 14 million individuals aged 12 years or older have visual impairment(defined as distance visual acuity of 20/50 or worse),and of these,more than 11 million individuals could have their vision improved to 20/40 or better with refractive correction.Conclusions:Visual impairment due to uncorrected refractive error is a common condition in the United States.Providing appropriate refractive correction to those individuals whose vision can be improved is an important public health endeavor with implications for safety and quality of life. Context: The prevalence of visual impairment in the US public has not been been surveyed nationally in several decades. Objective: To estimate the number of US persons aged 12 years or older who have impaired distance vision due to uncorrected refractive error. Design, Setting, and Participants: The National Health and Nutrition Examination Survey (NHANES), using a multistage probability sampling design, includes a vision evaluation in a mobile examination center. Visual acuity data were obtained from 13 265 of 14 203 participants (93.4%) - who visited the mobile examination center in 1999-2002. Visual impairment was defined as presenting distance visual acuity of 20/50 or worse in the better-seeing eye. Visual impairment due to uncorrected refractive error was defined as (presenting) visual impairment that improved, aided by automated refraction results, to 20/40 or better in the better-seeing eye. Main Outcome Measures: Presenting distance visual acuity (measured with usual corrective lenses, if any) and dist ance visual acuity after automated refraction. Results: Overall, 1190 study participants had visual impairment (weighted prevalence, 6.4%; 95% confidence interval CI, 6.0% -6.8%), and of these, 83.3% could achieve good visual acuity with correction (95% CI, 80.9% -85.8%). Extrapolating these findings to the general US population, approximately 14 million individuals aged 12 years or older with visual impairment (defined as distance visual acuity of 20/50 or worse), and of these , more than 11 million individuals could have their vision improved to 20/40 or better with refractive correction. Conclusions: Visual impairment due to uncorrected refractive error is a common condition in the United States. improved is an important public health endeavor with implications for safety and quality of life.