“This is the first evidence, to our knowledge, of a strong, clear association between self-reported [visual impairment] and cognitive impairment in a large-scale, broadly representative sample of the U.S. population,” senior author Suzann Pershing, M.D., M.S., of the Stanford University School of Medicine and colleagues wrote. This association remained after adjusting for demographics as well as age-related predictors of cognitive decline including hearing and physical function impairments, the authors noted.
To examine the relationship between visual impairment and cognition in older U.S. adults, the researchers analyzed two national data sets, the National Health and Nutrition Examination Survey (NHANES), 1999-2002, and the National Health and Aging Trends Study (NHATS), 2011-2015. Vision was measured at distance and near and by self-report in the NHANES and by self-report alone in the NHATS. The NHANES measured Digit Symbol Substitution Test (DSST) score and relative DSST impairment (DSST score ≤28, lowest quartile in study cohort), and the NHATS measured possible or probable dementia (based on self-report and performance on cognitive tests).
The NHANES included 2,975 respondents aged 60 years and older who completed the DSST measuring cognitive performance. The NHATS included 30,202 respondents aged 65 years and older with dementia status assessment. In the NHANES, distance visual impairment (odds ratio [OR], 2.8) and subjective visual impairment (OR, 2.7) were both associated with lower DSST scores and higher odds of DSST impairment. The NHATS data corroborated these results, with all vision variables associated with higher odds of dementia (distance visual impairment: OR, 1.9; near visual impairment: OR, 2.6).
The authors cautioned that “the results presented in this cross-sectional analysis are purely observational. A causative relationship between [visual impairment] and cognitive dysfunction cannot be established without longitudinal studies.”
Nonetheless, they concluded that “should causality be established, this may contribute to the value of vision screening, not only to identify patients who may benefit from treatment of correctable eye diseases but also to suspect broader limitations in function from cognitive and directly visual tasks.”
Numerous questions remain, wrote Jennifer Evans, Ph.D., of the London School of Hygiene and Tropical Medicine in a related editorial. “If the results of this investigation are not a measurement artifact and not confounding, and visual impairment and cognition are indeed associated, then the next question is: which came first? … Would successful intervention for visual impairment (where possible) reduce the risk of cognitive impairment? Or is sensory impairment an early marker of decline?”
For related information, see the Psychiatric News article “Dual-Task Gait Testing Identifies MCI Patients Likely to Develop Dementia.”