Vision Health May Be a Modifiable Risk Factor for Dementia, Study Finds

Between 4.9% and 19% of dementia prevalence could be prevented through the treatment of vision impairments that are able to be corrected, a new study in JAMA Ophthalmology¹ found. Multiple objective measurements of vision impairments should be used in the future to assess the effect vision health has on dementia.

Dementia prevention strategies should involve going over risk factors that are adjustable and can be treated. Vision impairment has been found to be a risk factor for dementia in the past, including estimates that 100,000 dementia cases could have been prevented by adults having healthy vision.² Previous studies that attempted to calculate the population attributable fraction (PAF) of dementia from vision impairment likely underestimated the proportion due to limited definitions of vision impairment. The new study aimed to quantify the PAFs of dementia through near visual acuity, distance visual acuity, and contrast sensitivity impairment in adults aged 71 years and older.

Preventing vision impairment could improve dementia outcomes in adults aged 71 and older | Image credit: LIGHTFIELD STUDIOS - stock.adobe.com

The study used data from the National health and Aging Trends Study (NHATS) in its eleventh round from 2021 as this was the round wherein objective visual function assessments were first done in the population. The population consisted of older adults who were living in communities who had both cognitive and visual assessments. All data were assessed between April and August 2023.

All participants were evaluated for dementia using either the doctor’s diagnosis, neurocognitive battery scores that measured memory and executive function, and through a questionnaire. Patients were separated by possible dementia and probable dementia. NHATS also conducts vision assessment using a tablet by collecting data on near visual acuity, distance visual acuity, and contrast sensitivity. A vision impairment was defined as having at least 1 impairment between these 3 measurements. Demographic characteristics, including age, sex, and ethnicity, were also collected.

There were 2767 adults included in this study, of which 54.7% were women and 81.7% were non-Hispanic White. The cohort also consisted of 7.1% Hispanic participants, 8.0% non-Hispanic Black participants, and 3.3% non-Hispanic other participants. The prevalence of at least 1 visual impairment was 32.2% (95% CI, 29.7-34.6), with participants with a visual impairment being older, non-Hispanic Black, and lower levels of education. Contrast sensitivity impairment (63.1%; 95% CI, 59.0-67.3) and near acuity impairment (65.3%; 95% CI, 60.9-69.7) were more prevalent than distance acuity impairment (30.1%; 95% CI, 26.0-34.3).

The presence of at least 1 visual impairment had a PAF of dementia of 19.0% (95% CI, 8.2-29.7). Contrast sensitivity (15.0%; 95% CI, 6.6-23.6) had the strongest PAF of dementia followed by near acuity (9.7; 95% CI, 2.6-17.0) and distance acuity (4.9%; 95% CI, 0.1-9.9). There was a high PAF for dementia when looking at any visual impairment (11.6%; 95% CI, 3.7-19.7). PAFs for vision impairment decreased from 24% to 8% from age 71 to 79 to 90 years and older, respectively, even as the prevalence of at least 1 vision impairment increased.

PAF from a vision impairment was higher in women compared with men (27% vs 7%); contrast sensitivity was also higher in women compared with men (19% vs 9%). Non-Hispanic White participants had a higher PAF from at least 1 vision impairment compared with non-Hispanic Black participants (22% vs 16%). Non-Hispanic White participants also had higher PAFs for contrast sensitivity compared with non-Hispanic Black participants (20% vs 6%). Participants who had at least 1 vision impairment had a higher PAF if they did not have diabetes (25.0%; 95% CI, 11.4-38.0) compared with those living with diabetes (8.4%; 95% Ci, –10.2 to 27.3).

There were some limitations to this study. There were a limited number of American Indian, Alaska Native, Asian, and Hispanic participants, which could prevent adequate calculations of PAFs in these groups. The temporality of vision impairment could not be accounted for due to the cross-sectional design of the study. Other associations with measures of visual function could not be evaluated in this study. Institutionalized older adults are not covered by this study.

The researchers concluded that dementia prevalence could have been avoided in up to 19% of participants by preventing and treating vision impairment in these adults. Distance visual acuity is not the only method by which this can be measured, as contrast sensitivity had the largest association with PAF. Reducing these risk factors could help in preventing dementia and other visual impairments.

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 5, 2024. doi:10.1001/jamaophthalmol.2024.3131
2. Ehrlich J, Goldstein J, Swenor BK, Whitson H, Langa KM, Veliz P. Addition of vision impairment to a life-course model of potentially modifiable dementia risk factors in the US. JAMA Neurol. 2022;79(6):623-626. doi:10.1001/jamaneurol.2022.0723