Poor eyesight may signal worsening cognitive function

Poor vision may be an indicator of deteriorating cognition in elderly adults, according to a recent Singapore study.

“In this study, we observed a 6-year longitudinal association between presenting visual impairment (VI) and poorer visual acuity (VA) at baseline and decline in cognitive function,” said researchers. “To our knowledge, this was the first longitudinal, population-based study of a multiethnic Asian population that prospectively evaluated this association.”

Of the 2,478 participants (mean age, 67.6±5.6 years; 50.7 percent male), almost 20 percent (n=489) saw drops in scores in the Abbreviated Mental Test (AMT) over the 6-year follow-up. These participants were 66.3-percent more likely to have VI at baseline on their worse eye (p<0.001). They were also 37.6 percent more likely to have VI at baseline on their better eye. [JAMA Netw Open 2020;3:e203560]

Multivariable linear regression validated these findings. For each 1-logMAR unit decrease in VA in the better eye at presentation, AMT scores over 6 years dropped significantly (β, –0.07, 95 percent confidence interval [CI], –0.09 to –0.05; p<0.001).

Better-eye VI at baseline also correlated with a significant and larger decrease in AMT scores over the following 6 years (β, –0.27, 95 percent CI, –0.37 to –0.17; p<0.001). Stratifying according to severity, both low vision (β, –0.25, 95 percent CI, –0.35 to –0.14; p<0.01) and being blind (β, –1.07, 95 percent CI, –1.50 to –0.64) significantly negatively impacted long-term AMT scores.

VA, VI and VI severity in the worse eye upon presentation were all also significantly correlated with lower AMT scores over time, but at weaker magnitudes.

Longitudinal changes in vision also affected AMT scores over 6 years. In both the better (β, –0.29, 95 percent CI, –0.40 to –0.18; p<0.001) and worse (β, –0.20, 95 percent CI, –0.29 to –0.10; p<0.001) eyes, participants whose vision status remained constant or worsened saw significantly greater drops in AMT scores. Those whose vision remained or improved were used as a reference group.

These findings were robust to sensitivity analyses accounting for educational attainment and hearing loss.

“Several mechanisms have been postulated to potentially explain the association between VI and decline in cognitive function,” the researchers said, pointing out that VI may promote the nonengagement in daily activities that may help stimulate the brain. They also acknowledged that both vision and cognitive factors assessed in the study are associated with ageing.

“[I]t remains unclear whether the observed association is a direct causal effect or one that is mediated by intermediate factors, such as reduced involvement in social and cognitively stimulating activities owing to VI. Thus, further studies are still required to investigate the potential mediation pathways in this association,” they added.

Participants in the present study were recruited from the Singapore Epidemiology of Eye Diseases Study, excluding those with incomplete baseline data and with severe illness or mobility impairments. Any VI was defined as having a presenting VA worse than 20/40.

“Most of these VI cases were attributable to undercorrected refractive error and cataract, which are highly preventable or treatable, therefore further emphasizing the importance of prompt interventions for VI,” the researcher said.

“Holistic measures appear to be needed to manage preventable VI and to reduce the collective burden of both visual and cognitive decline,” they added.