Highlights Vision decline is associated with increased risks of cognitive decline and dementia in older adults, according to a systematic review and meta-analysis recently published in Aging and Mental Health . Gui-Ying Cao, Ph.D., of Peking University in Beijing, and colleagues conducted a systematic review of the literature to identify studies evaluating the relationship between visual impairment and cognitive outcomes in older adults. Based on 16 included studies (76,373 participants), researchers observed increased risks of adverse cognitive outcomes associated with visual impairment identified by subjective measures (odds ratio, 1.63) and objective measures (odds ratio, 1.59). . For older adults with visual impairment, the odds of baseline cognitive decline were higher (odds ratio, 2.37), as were the risks of incident cognitive decline (relative risk, 1.41) and dementia (relative risk, 1.44). ), compared to those without vision impairment at baseline. "Finding ways to prevent or delay the onset of dementia could help reduce its devastating impact on the lives of affected people and their families, especially in light of the growing burden of the disease. Identifying modifiable risk factors is the critical first step in developing interventions to achieve this goal," a co-author said in a statement. "Our new results highlight the importance of regular eye exams for older adults, allowing any potential problems with their vision to be detected and treated early." |
Cognitive impairment has become a growing public health problem, especially among older adults. Approximately 50 million people live with severe cognitive problems worldwide and, as a consequence of global aging, this number is expected to almost triple by 2050 ( Alzheimer’s Disease International , 2019).
Cognitive impairment is associated with increased risks of functional decline and mortality among older people and creates a large burden on society and families. Identifying risk factors for cognitive decline is essential for developing interventions to prevent or delay the onset of cognitive decline.
Goals
To provide a quantitative synthesis of studies on the relationship between visual impairment (VI) and cognitive outcomes in older adults.
Method
A systematic search of relevant databases was conducted for original articles published before April 2020. Random effects models were used to obtain pooled estimates of the associations between visual impairment (VI) and cognitive outcomes (cognitive impairment and dementia) with analyzes of subgroups of VI measures, cross-sectional associations of VI with cognitive decline, and longitudinal associations of baseline VI with incident cognitive decline and dementia. Possible sources of heterogeneity were explored using meta-regression. Publication bias was assessed with Egger’s test.
Results
Sixteen studies with 76,373 participants, five cross-sectional studies and eleven longitudinal studies, were included in this meta-analysis . There was a significantly increased risk of cognitive outcomes with IV identified by subjective measures (odds ratio (OR) = 1.63; 95% confidence interval (CI): 1.26–1.99) and objective measures (OR = 1 .59; 95% CI: 1.40– 1.78).
The odds of baseline cognitive impairment were 137% higher in older adults with VI compared to those without VI (OR = 2.37, 95% CI: 1.84–3.03) at baseline.
Compared with older adults without VI at baseline, those with LV at baseline had a higher relative risk (RR) of incident cognitive decline (RR = 1.41, 95% CI: 1.31–1.51) and dementia (RR = 1.44, 95% CI: 1.19). –1.75).
Conclusions
This meta-analysis of population-based studies indicates that visual impairment (VI) is significantly associated with cognitive decline and dementia.
Given the severe outcomes of cognitive impairment and dementia and the high prevalence of VI, these findings could have significant clinical implications. These findings suggested that treatment of VI, such as optical correction or cataract surgery , could be beneficial in maintaining cognitive function.
Therefore, future research and randomized clinical trials are warranted to examine the implications of VI treatment, such as glasses use and cataract surgery, to prevent cognitive decline and dementia.
Discussion
To our knowledge, this study is among the first to evaluate the association between visual impairment (VI) and cognitive outcomes among older adults through a comprehensive systematic review and quantitative synthesis of population-based studies.
In this meta-analysis, we found that VI was significantly associated with cognitive decline and dementia in older adults.
This study found that VI was associated with an increased risk of cognitive outcomes (cognitive impairment and dementia) regardless of subjective or objective measures of VI in cross-sectional and longitudinal studies. Although VI is an objective measure of vision function and is widely accepted by researchers, the function of self-reported vision should not be overlooked. Previous studies indicated that self-reported visual function incorporates individuals’ perceptions of their health status and is a multidimensional measure that could reflect visual function in daily life.
In this meta-analysis, we found significant associations between VI and cognitive impairment and dementia in cross-sectional and longitudinal studies. Although the mechanisms of VI with cognitive impairment and dementia remain unclear, sensory deprivation, information degradation, cognitive load on perception, and common cause hypotheses have been reported to be related between VI and cognitive decline. (cognitive impairment and dementia). Furthermore, previous studies generated evidence to support a significant association between cognitive impairment and eye diseases such as glaucoma and cataracts, which are common causes of VI.
Finally, cardiovascular risk factors have been proposed as a third factor that negatively affects both cognition and perception and contributes to the decline of these two domains. It is worth noting that people may need time to notice their sensory impairment due to progressive adaptation in performing tasks of daily living in the presence of an insidious decline in visual function. Therefore, regular vision examinations are important for older adults to maintain visual and cognitive function, especially for older adults with VI perception in daily life.
The main strengths of this meta-analysis are the comprehensive literature search, as well as the careful study selection and quality assessment, which provide a reliable overview of the evidence in the field. However, some limitations must be taken into account .
First, the limited number of studies, as well as considerable heterogeneity between studies, may have reduced the precision of the pooled effect size estimates.
Second, this meta-analysis included cross-sectional and longitudinal observational studies and reported significant associations between VI and cognitive decline and dementia; however, these associations are still warranted to be explored in the future. Finally, as is the case with any meta-analysis of aggregate data, there is the possibility of an ecological fallacy .
