Correcting Vision Impairment May Prevent Dementia in Older Adults

Jason R. Smith, ScM

Credit: Johns Hopkins University

A new investigation reported approximately 1 in 5 cases of dementia among community-dwelling US adults aged 71 years and older may have been avoided with the prevention and treatment of largely-correctable vision impairment.¹

These data from 2021 revealed the largest population attributable fraction (PAF) of dementia within contrast sensitivity (15%), rather than distance (9.7%) or near visual acuity (4.9%). According to investigators at Johns Hopkins University, the total impact of vision impairment on dementia may be underestimated if defined using only distance VA.

“Overall, while not establishing a cause-and-effect relationship, these findings support considering vision health in dementia prevention strategies aimed at reducing modifiable risk factors,” wrote the investigative team, led by Jason R. Smith, ScM, department of epidemiology, Johns Hopkins University Bloomberg School of Public Health.

With an increasing prevalence in the US and globally, reducing modifiable risk factors for dementia is critical for preventive strategies.² Available literature has consistently pointed to vision impairment as a notable risk factor for dementia, believed to impact risk with similar mechanisms as hearing loss.³

Although up to 28% of adults older than 70 years are impacted by vision impairment, more than 90% of vision impairments are hypothesized to be preventable or correctable.⁴ Smith and colleagues indicated a determination of the PAF of dementia from vision impairment in a relevant sample of older adults could influence primary prevention strategies for public health.¹

In this analysis, the team sought to determine PAFs of dementia from 3 types of vision impairments (near, distance, and contrast sensitivity impairment), with stratification by age, self-reported race and ethnicity, and educational attainment.

Overall, 2767 community-dwelling adults aged ≥65 years eligible for vision and cognitive testing in 2021 were enrolled for analysis from the nationally representative National Health and Aging Trends Study (NHATS).

Dementia status was classified using the standardized algorithm developed in NHATS, including possible dementia (≥1.5 SDs below the sample mean on 1 cognitive domain) and probable dementia (≥1.5 SDs below the sample mean on ≥2 cognitive domains, a physical diagnosis of dementia, or Ascertain Dementia-8 Dementia Screening Interview Score). Near and distance visual acuity impairments were defined as >0.30 logMar, while contrast sensitivity impairment was defined as <1.55 logCS.

More than half (54.7%) of participants were female – 8.0% were non-Hispanic Black, 7.1% were Hispanic, 81.7% were non-Hispanic White, and 3.3% were non-Hispanic Other, including American Indian or Alaska Native and Asian. Upon analysis, the prevalence of ≥1 vision impairment was 32.2% (95% CI, 29.7–34.6).

After further analysis, Smith and colleagues found the PAF of dementia from ≥1 vision impairment was 19.0% (95% CI, 8.2–29.7). Vision impairment linked to the strongest PAF of dementia was contrast sensitivity (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).

The PAFs from ≥1 vision impairment were largest among those aged 71–79 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 remaining consistent across education level.

In their conclusion, Smith and colleagues called for further randomized clinical trials to allow for stronger evidence on the preventative potential of addressing vision impairments on incident dementia and analyses on the combined effect of co-occurring hearing and vision loss.

“It is believed that hearing and vision impairment increases the risk of dementia through similar pathways: increased social isolation and loneliness, increased cognitive load from poor sensory encoding, and neurodegeneration and cortical reorganization from sensory deprivation,” they added.

References

1. _{Smith JR, Huang AR, Zhou Y, et al. Vision Impairment and the Population Attributable Fraction of Dementia in Older Adults. JAMA Ophthalmol. Published online September 05, 2024. doi:10.1001/jamaophthalmol.2024.3131}
2. _{Livingston G, Huntley J, Sommerlad A, et al. Dementia prevention, intervention, and care: 2020 report of the Lancet Commission [published correction appears in Lancet. 2023 Sep 30;402(10408):1132. doi: 10.1016/S0140-6736(23)02043-3]. Lancet. 2020;396(10248):413-446. doi:10.1016/S0140-6736(20)30367-6}
3. _{Burton MJ, Ramke J, Marques AP, et al. The Lancet Global Health Commission on Global Eye Health: vision beyond 2020. Lancet Glob Health. 2021;9(4):e489-e551. doi:10.1016/S2214-109X(20)30488-5}
4. _{Killeen OJ, De Lott LB, Zhou Y, et al. Population Prevalence of Vision Impairment in US Adults 71 Years and Older: The National Health and Aging Trends Study. JAMA Ophthalmol. 2023;141(2):197-204. doi:10.1001/jamaophthalmol.2022.5840}