Visual impairment appears to be a risk factor of cognitive impairment, but more research is necessary to confirm this, according to a study published in Ophthalmology. The study speculates that “it is possible that the additional cognitive resources allocated to sensory processing to overcome impaired visual input may end up depleting cognitive capacities for other tasks.”
The study, a systematic review and meta-analysis, looked at the bidirectional relationship between vision and cognition, both prevalent age-related conditions with real effects on society. The literature has shown a 60% risk of cognitive impairment. Researchers searched the Pubmed, Embase, and Cochrane Central registers for observational studies that were published from inception until April 2020 of adults aged 40 years and older that reported objectively measured visual impairment and cognitive impairment assessment with clinically validated cognitive screening tests or diagnostic evaluation. A total of 40 studies were included (N=47,913,570).
They looked at the meta-analyses on cross-sectional and longitudinal associations between visual impairment and cognitive impairment outcomes. Cognitive impairment was assessed using screening tests and clinically diagnosed dementia. They generated pooled odds ratios and 95% confidence interval with random effect models and examined publication bias and heterogeneity with Egger’s test, meta-regression, and trim-and-fill methods.
The meta-analysis found that participants with visual impairments were more likely to have cognitive impairment and had significantly higher odds [OR (95%CI)] of any cognitive impairment [cross-sectional: 2.38 (1.84-3.07); longitudinal: 1.66 (1.46-1.89)] and clinically diagnosed dementia [(cross-sectional: 2.43 (1.48-4.01); longitudinal: 2.09 (1.37-3.21)], compared to persons who did not have visual impairment. Differences in age, sex, and follow-up duration partially explained significant heterogeneity.
“There was also some evidence that individuals with [cognitive impairment], relative to cognitively intact persons, were more likely to have [visual impairment], with most papers (8/9, 89%) reporting significantly positive associations, however meta-analyses on this association could not be conducted due to insufficient data,” the study says.
And these findings were clinically relevant because “strategies for early detection and management of both visual and cognitive impairment in older people may minimize individual clinical and public health consequences,” according to the research.
The study did have limitations, including that the meta-analysis was conducted only in English-language publications, excluding any relevant findings in other language publications. Limited data also made some findings impossible, including determining the severity of visual impairment and the association between visual impairment and mild cognitive impairment. They also didn’t include studies looking at the association between different ocular pathologies and etiologies of cognitive impairment, so weren’t able to determine the mechanisms involved. They also didn’t consider other vision components that might contribute.
“Future prospective studies and randomized controlled trials are needed to investigate whether [cognitive impairment] predicts the risk of [visual impairment] and, whether in cognitively impaired patients, vision-saving interventions are effective in preventing the progression of cognitive decline,” researchers say.
Vu TA, Fenwick EK, Gan AT, et al. The bidirectional relationship between vision and cognition: a systematic review and meta-analysis. Ophthalmol. Published online December 14, 2020. doi:10.1016/j.ophtha.2020.12.010