Vision impairment ups risks for dementia, cognitive decline in older adults

Older adults with vision impairment are at higher risk of both dementia and cognitive impairment, according to a study.

“Vision impairment is an important modifiable contributor to dementia, and screening and treating vision impairment, especially in low- and middle-income countries, may help to alleviate the global burden of dementia,” the researchers said.

The databases of PubMed, Embase, Web of Science, and Google Scholar were searched for relevant studies on 15 September 2000. The researchers pooled relative risks (RRs) using random-effects models and stratified analyses for subgroups representing different study characteristics.

Funnel plots and the Egger test were used to assess publication bias. Finally, the global burden of dementia associated with vision impairment was estimated according to the Global Burden Disease Study data on the prevalence of dementia and vision impairment.

Fourteen prospective cohort studies, with a total of 6,204,827 participants and 171,888 dementia patients, were included in the first meta-analysis. The pooled RR associated with vision impairment was 1.47 (95 percent confidence interval [CI], 1.35–1.60). In the meta-analysis of 12 prospective cohort studies with 45,313 participants and 13,350 patients with cognitive impairment, the pooled RR was 1.35 (95 percent CI, 1.28–1.41). [Ophthalmology 2021;128:1135-1149]

In stratified analyses, the associations of vision impairment with incident dementia and cognitive impairment were found to be similar across methods of vision assessment, length of follow-up, and study quality.

In 2016, the global number of people with moderate or severe vision impairment-related dementia was 2.1 million (80 percent uncertainty interval, 1.0–3.3), representing 4.7 percent (95 percent CI, 2.3–7.5) of the global burden of dementia. Moreover, economic inequality was significant for the burden of vision impairment-related dementia.

“Only 40 percent of the risk of dementia has been attributable directly to modifiable factors globally; therefore, it is imperative to identify additional modifiable risk factors such as vision impairment because more than four-fifths of cases are preventable and treatable,” the researchers said. [Lancet 2020;396:413-446]

Certain mechanisms have been raised for the association between vision impairment and both dementia and cognitive impairment. For instance, older individuals with vision impairment have less participation in physical and social activities and are at higher risk of depression, which predispose them to cognitive decline. [Ophthalmic Epidemiol 2009;16:346-353; PLoS One 2019;14e0218540; Int J Geriatr Psychiatry 2020;35:358-364]

In addition, the association of vision impairment with dementia or cognitive impairment could be due to the positive correlation between vision and hearing impairment and between hearing impairment and dementia. [Sci Rep 2019;9:19660; Lancet 2020;396:413-446]

“Of note, cognitive decline and vision impairment share many risk factors, including smoking, poor diet quality, hypertension, diabetes, and obesity, which also may partly explain the positive association,” the researchers said. [Lancet 2020;396:413-446; Indian J Ophthalmol 2014;62:103-110; J Optom 2017;10:71-78; JAMA Ophthalmol 2018;136:473-481]

“However, the exact mechanism that underlies the association of dementia with vision impairment requires further exploration in future studies,” they added.