Key PointsQuestion
What proportion of dementia cases in the US is potentially attributable to objectively measured vision impairments?
Findings
This cross-sectional study of a nationally representative longitudinal study of 2767 adults in the US found population attributable fractions up to 19.0% of prevalent dementia cases attributed to at least 1 vision impairment. These fractions varied across contrast sensitivity, near visual acuity, and distance visual acuity.
Meaning
The findings support stronger contributions to dementia from vision impairment than from midlife vascular risk factors and consideration of vision health in dementia prevention strategies.
Importance
Vision impairment is a potentially modifiable risk factor for dementia. Although few prior studies have estimated the contribution of vision impairments to dementia, none have reported on multiple objectively measured vision impairments (eg, distance and near visual acuity and contrast sensitivity) in a nationally representative sample of older adults.
Objective
To quantify population attributable fractions of dementia from objective vision impairments in older adults, stratified by age, self-reported sex, self-reported race and ethnicity, and educational attainment.
Design, Setting, and Participants
This was a population-based cross-sectional analysis in the National Health and Aging Trends Study, which gathers nationally representative information on Medicare beneficiaries aged 65 years and older in the US. A total of 2767 community-dwelling adults eligible for vision and cognitive testing in 2021 were included. Data were analyzed from April to August 2023.
Exposures
Near and distance visual acuity impairments were each defined as >0.30 logMAR. Contrast sensitivity impairment was defined as <1.55 logCS. At least 1 vision impairment was defined as impairment to either near acuity, distance acuity, or contrast sensitivity.
Main Outcomes and Measures
Adjusted population attributable fractions of prevalent dementia, defined using a standardized algorithmic diagnosis (≥1.5 SDs below mean on 1 or more cognitive domains, self- or proxy-reported dementia diagnosis, or the Ascertain Dementia-8 Dementia Screening Interview Score of probable dementia).
Results
The survey-weighted prevalence of vision impairment among participants aged 71 and older (1575 [54.7%] female and 1192 [45.3%] male; 570 [8.0%] non-Hispanic Black, 132 [81.7%] Hispanic, 2004 [81.7%] non-Hispanic White, and 61 [3.3%] non-Hispanic other) was 32.2% (95% CI, 29.7-34.6). The population attributable fraction of prevalent dementia from at least 1 vision impairment was 19.0% (95% CI, 8.2-29.7). Contrast sensitivity impairment yielded the strongest attributable fraction among all impairments (15.0%; 95% CI, 6.6-23.6), followed by near acuity (9.7%; 95% CI, 2.6-17.0) and distance acuity (4.9%; 95% CI, 0.1-9.9). Population attributable fractions from at least 1 impairment were highest among participants aged 71 to 79 years (24.3%; 95% CI, 6.6-41.8), female (26.8%; 95% CI, 12.2-39.9), and non-Hispanic White (22.3%; 95% CI, 9.6-34.5) subpopulations, with estimates consistent across educational strata.
Conclusions and Relevance
The population attributable fraction of dementia from vision impairments ranged from 4.9%-19.0%. While not proving a cause-and-effect relationship, these findings support inclusion of multiple objective measures of vision impairments, including contrast sensitivity and visual acuity, to capture the total potential impact of addressing vision impairment on dementia.