Combination may be more than additive, national data show

The combination of self-reported visual impairment (VI) and dementia led to declines in mobility, self-care, and household activities greater than expected from their independent contributions, a cross-sectional analysis of data from the National Health and Aging Trends Study showed.

Expected decrease for self-reported VI, probable dementia, and the combination were:

  • Mobility score: 14.7%, 27.8%, and 50.1%, respectively.
  • Self-care score: 9.5%, 22.9%, and 42.4%, respectively.
  • Household activity score: 15.2%, 34.7%, and 52.4%, respectively.

“In this nationally representative study, participants with dementia and self-reported visual impairment reported greater limitations in mobility, self-care, and household activities than would be expected based on the individual associations of each of these health conditions,” wrote Joshua Ehrlich, MD, MPH, of the University of Michigan and coauthors in JAMA Ophthalmology. “Findings from this study may be relevant to designing and implementing clinical and public health interventions to promote independence and optimal aging for a rapidly growing population of older US adults.”

The paper makes an important point about patients’ disabilities, noted David Friedman, MD, PhD, of Harvard University and Pradeep Ramulu, MD, PhD, of Johns Hopkins University, in an accompanying editorial. “Many patients with VI may continue to maintain the skills and abilities necessary for independence, but when other abilities (which may have allowed them to compensate for VI) are also lost, they lose these skills and abilities,” they wrote.

“Many will likely need caretakers or be forced to leave the home in which they currently live,” they added. “Understanding this, we not only ought to make greater efforts both to preserve and restore vision in these individuals but also need to identify ways in which we can ease the burden that the combination of VI and dementia can create.”

VI in the elderly increases the risk of falls, loss of independence, and isolation, and occurs with dementia in about 4% of elderly US adults. People with both are known to be at greater risk for disability than those with only one of these conditions, though prior research has not consistently suggested an effect beyond the merely additive.

For example, a 2007 prospective cohort study included a mental status questionnaire, self-reported visual acuity, and evaluations of mobility, self-care, and household activities, and concluded that VI and cognitive impairment were additive, with no significant interactions observed between them as predictors of disability. Another study in an Asian population found similar results and suggested that sex differences in self-reported health and tasks performed could affect results. Both assessments used a binary definition of disability (yes/no).

“The detailed assessments of disability in the National Health and Aging Trends Study (NHATS) allow for a nuanced analysis of the functional outcomes of vision and dementia on mobility, self-care (corresponding to activities of daily living), and household activities (corresponding to instrumental activities of daily living), while accounting for behavioral adaptations to changes in capacity,” the authors noted.

To explore whether coexisting dementia worsens the functionality of people with visual impairment in a nationally representative population, researchers included 7,124 participants from NHATS, an ongoing cohort study of Medicare beneficiaries 65 and older. Participants from the 2015 survey update with complete data on outcomes and covariates were included (55.3% were female, and about 56% of the study population was 65 to 74 years old).

Participants reported whether they used any assistive devices or environmental modifications for various functions in the past month, rating each activity on a four-level scale (fully able; successful accommodation; with difficulty; and assistance required). Categorical scores were derived from these responses, with lower scores implying more limitation.

NHATS functional categories included:

  • Mobility: going outside, getting around inside, and getting out of bed (range 3-12).
  • Self-care: eating, dressing, toileting, and bathing (range 4-16).
  • Household activities: laundry, shopping, making hot meals, paying bills, and keeping track of medications (range 5-20).

Self-reported VI was present in 8.6% (95% CI 7.8%-9.3%) of participants, while 8.3% (95% CI 7.8%-8.9%) had possible dementia and 6.3% (95% CI 5.7%-6.9%) had probable dementia.

A dose-response association with dementia diagnosis was also seen: given VI, people with probable dementia had worse functionality compared with people with possible dementia.

Limitations include possible recall bias with survey data, and self-reports of VI may be less reliable among those with cognitive impairment. Self-report also does not differentiate VI due to eye disease from correctable refractive error. Causality cannot be concluded from this analysis.

“Those with dementia in the NHATS had substantially higher rates of self-reported VI, which raises the possibility that greater severity of cognitive impairment in the population with VI may have led to greater functional impairment,” the editorialists observed.

  1. The combination of self-reported visual impairment (VI) and dementia led to declines in mobility, self-care, and household activities greater than expected from their independent contributions, an analysis of the National Health and Aging Trends Study showed.

  2. Findings are based on a cross-sectional analysis of self-reported visual impairment data and do not show causality.

Paul Smyth, MD, Contributing Writer, BreakingMED™

This research was supported by grants from the National Eye Institute and unrestricted grants from Research to Prevent Blindness to the Department of Ophthalmology and Visual Sciences at the University of Michigan and the Department of Ophthalmology and Visual Sciences at the University of Utah.

Ehrlich is a co-investigator of the National Health and Aging Trends Study and reported grants from National Institutes of Health during the conduct of the study.

Friedman was a mentor to study authors Joshua Ehrlich, MD, MPH, and Bonnelin Swenor, PhD, in the past. Ramulu collaborated on research with Swenor at Johns Hopkins University.

Cat ID: 240

Topic ID: 92,240,404,485,730,33,361,192,255,925,240