Using continuous vision metrics, researchers demonstrated that vision impairment was associated with increased risk of dementia. Photo: Getty Images.

There is increasing research that addresses the association between vision impairment and cognitive decline, with studies suggesting vision impairment increases the risk of dementia and accelerates cognitive decline. However, conclusions are restricted in generalizability and are limited by small sample sizes. Researchers at Johns Hopkins University analyzed a nationally representative sample of older US adults with a computerized cognitive assessment and found objective vision impairment of any type was associated with an increased likelihood of dementia.

The cohort was part of the National Health and Aging Trends Study, a nationally representative sample of Medicare beneficiaries aged ≥65. A total of 3,026 adults were included in this study, the majority of whom were female (55%) and Caucasian (82%). They were divided into groups by distance vision impairment (>20/40), near vision impairment (>20/40), contrast sensitivity impairment (<1.55), any objective vision impairment (distance/near visual acuity or contrast) and self-reported vision impairment. Dementia status was defined based on survey reports, interviews and cognitive tests.

The weighted prevalence rates were 10% for distance vision impairment, 22% for near impairment, 22% for contrast sensitivity impairment, 34% for any objective vision impairment and 7% for self-reported impairment. Across all measures of vision impairment, dementia was more than twice as prevalent in adults with vision impairment compared with their peers without. In adjusted models, all measures of vision impairment were associated with higher odds of dementia (distance OR: 1.74, near OR: 1.68, contrast sensitivity impairment OR: 1.95, any objective impairment OR: 1.83, self-reported impairment OR: 1.86).

When assessing the association between any objective vision impairment and cognitive performance, adults with any objective vision impairment performed slower (higher reaction times) and with lower accuracy across all cognitive domains (psychomotor function, visual attention and working memory) compared with those without. The worst performance was in the visual attention cognitive domain, which the researchers believe may be due to the impact of vision impairment on a person’s ability to attend to visual stimuli and execute cognitive tasks that necessitate visual attention.

“Our findings show that among a nationally representative cohort of older adults, poor visual acuity and contrast sensitivity are associated with an increased likelihood of dementia,” the researchers wrote in their paper. “These results suggest that maintaining good vision and eye health may be important for preserving cognitive function in older age.”