Impaired Vision an Overlooked Dementia Risk Factor

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Impaired vision in older adults is an underrecognized and modifiable dementia risk factor, new research suggests.

Investigators analyzed estimated population attributable fractions (PAFs) associated with dementia in more than 16,000 older adults. A PAF represents the number of dementia cases that could be prevented if a given risk factor were eliminated.

Results showed the PAF of vision impairment was 1.8%, suggesting that healthy vision had the potential to prevent more than 100,000 cases of dementia in the United States.

“Vision impairment and blindness disproportionately impacts older adults, yet vision impairment is often preventable or even correctable,” study investigator Joshua Ehrlich MD, assistant professor of ophthalmology and visual sciences, University of Michigan, Ann Arbor, told Medscape Medical News.

Poor vision affects not only how individuals see the world, but also their systemic health and well-being, Ehrlich said.

“Accordingly, ensuring that older adults receive appropriate eye care is vital to promoting health, independence, and optimal aging,” he added.

The findings were published online April 25 in JAMA Neurology.

A Surprising Omission

There is an “urgent need to identify modifiable risk factors for dementia that can be targeted with interventions to slow cognitive decline and prevent dementia,” the investigators write.

In 2020, the Lancet Commission report on dementia prevention, intervention, and care proposed a life-course model of 12 potentially modifiable dementia risk factors. This included lower educational level, hearing loss, traumatic brain injury, hypertension, excessive alcohol consumption, obesity, smoking, depression, social isolation, physical inactivity, diabetes, and air pollution.

Together, these factors are associated with about 40% of dementia cases worldwide, the report notes.

Vision impairment was not included in this model, “despite considerable evidence that it is associated with an elevated risk of incident dementia and that it may operate through the same pathways as hearing loss,” the current researchers write.

“We have known for some time that vision impairment is a risk factor for dementia [and] we also know that a very large fraction of vision impairment, possibly in excess of 80%, is avoidable or has simply yet to be addressed,” Ehrlich said.

He and his colleagues found it “surprising that vision impairment had been ignored in key models of modifiable dementia risk factors that are used to shape health policy and resource allocation.” They set out to demonstrate that, “in fact, vision impairment is just as influential as a number of other long accepted modifiable dementia risk factors.”

The investigators assessed data from the Health and Retirement Study (HRS), a panel study that surveys more than 20,000 US Adults aged 50 years or older every 2 years.

The investigators applied the same methods used by the Lancet Commission to the HRS dataset and added vision impairment to the Lancet life-course model. Air pollution was excluded in their model “because those data were not readily available in the HRS,” the researchers write.

They note the PAF is “based on the population prevalence and relative risk of dementia for each risk factor” and is “weighted, based on a principal components analysis, to account for communality (clustering of risk factors).”

A Missed Prevention Opportunity

The sample included 16,690 participants (54% women, 51.5% at least age 65, 80.2% White, 10.6% Black, 9.2% other).

In total, the 12 potentially modifiable risk factors used in the researchers’ model were associated with an estimated 62.4% of dementia cases in the United States, with hypertension as the most prevalent risk factor with the highest weighted PAF.

Risk Factor Dementia Risk Ratio (95% CI) Risk Factor Prevalence (%) Weighted PAF (%)
Hypertension 1.6 (1.2 – 2.2) 59.6 12.4
Obesity 1.6 (1.3 – 1.9) 40.3 9.2
Depression 1.9 (1.6 – 2.3 26.7 9.1
Hearing loss 1.9 (1.4 – 2.7 19.2 7.0
Traumatic brain injury 1.8 (1.5 – 2.2) 18.7 6.1
Diabetes 1.5 (1.3 – 1.8 24.4 5.1
Smoking 1.6 (1.2 – 2.2) 12.0 3.2
Less education 1.6 (1.3 – 2.0) 11.6 3.1
Physical inactivity 1.4 (1.2 – 1.7) 17.4 3.1
Social isolation 1.6 (1.3 – 1.9) 7.1 1.9
Vision Impairment 1.5 (1.4 – 1.6) 8.3 1.8
Excessive alcohol consumption 1.2 (1.1 – 1.3) 2.8 0.3
CI = confidence interval

Analyses stratified by race and ethnicity showed that the weighted PAF for vision impairment ranged from 1.8% among White non-Hispanic older adults to 2.2% among Hispanic older adults. The prevalence of vision impairment in Hispanic older adults was 11% vs 8.3% overall.

“Addressing preventable and treatable causes of vision impairment may…represent a novel avenue to slow cognitive decline and prevent dementia for a large number of older adults both in the US and globally,” the investigators write.

A New Focus for Prevention

Commenting for Medscape Medical News, Suzann Pershing, MD, associate professor of ophthalmology, Stanford University School of Medicine, California, called the study “particularly important because, despite growing recognition of its importance in relation to cognition, visual impairment is often an underrecognized risk factor.”

The current research “builds on increasingly robust medical literature linking visual impairment and dementia, applying analogous methods to those used for the life course model recently presented by the Lancet Commission to evaluate potentially modifiable dementia risk factors,” said Pershing, who was not involved with the study.

The investigators “make a compelling argument for inclusion of visual impairment as one of the potentially modifiable risk factors; practicing clinicians and healthcare systems may consider screening and targeted therapies to address visual impairment, with a goal of population health and contributing to a reduction in future dementia disease burden,” she added.

In an accompanying editorial, Jennifer Deal, PhD, Department of Epidemiology and Cochlear Center for Hearing and Public Health, Baltimore, Maryland, and Julio Rojas, MD, PhD, Memory and Aging Center, Department of Neurology, Weill Institute for Neurosciences, University of California, San Francisco, call the findings “an important reminder that dementia is a social problem in which potentially treatable risk factors, including visual impairment, are highly prevalent in disadvantaged populations.”

The editorialists note that 90% of cases of vision impairment are “preventable or have yet to be treated. The two “highly cost-effective interventions” of eyeglasses and/or cataract surgery “remain underused both in the US and globally, especially in disadvantaged communities,” they write.

They add that more research is needed to “test the effectiveness of interventions to preserve cognitive health by promoting healthy vision.”

JAMA Neurol. Published online April 25, 2022. Abstract, Editorial

The study was supported by grants from the National Institute on Aging, the National Institutes of Health, and Research to Prevent Blindness. The investigators report no relevant financial relationships. Deal reports having received grants from the National Institute on Aging. Rojas reports serving as site principal investigator on clinical trials for Eli Lilly and Eisai and receiving grants from the National Institute on Aging. Pershing is a consultant for Acumen, LLC, and Verana Health (as DigiSight Technologies).

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