The effect of cataract surgery on neuropsychological test performance: A randomized controlled trial

Abstract

Recent cross-sectional studies have reported strong associations between visual and cognitive function, and longitudinal studies have shown relationships between visual and cognitive decline in late life. Improvement in cognitive performance after cataract surgery has been reported in patients with Mild Cognitive Impairment. We investigated whether improving visual function with cataract surgery would improve neuropsychological performance in healthy older adults. A randomized clinical trial of cataract surgery performed at acute hospitals was conducted on 56 patients (mean age 73) with bilateral cataract, after excluding a total of 54 patients at the screening stage, of whom 53 did not meet visual acuity criteria and one did not have cataract. In-home assessments included visual and neuropsychological function, computerized cognitive testing and health questionnaires. Results showed no cognitive benefits of cataract surgery in cognitively normal adults. We conclude that visual improvement following cataract surgery is not strongly associated with an improvement in neuropsychological test performance in otherwise healthy adults. Joint associations between visual and cognitive function in late life are likely to be due to central factors, and unlikely to be strongly related to eye disease. Short-term increased neural stimulation from improved visual function does not appear to affect cognitive performance.

Inappropriate use of covariate analysis renders meaningless results

“…In this journal, Anstey et al (2006) reported the results of a potentially important clinical study on the effect of cataract removal on the cognitive performance of older adults. Unfortunately, because of inappropriate data analyses, some reported results are meaningless.…”

Use of covariates in randomized controlled trials

“…The only significant baseline difference in Anstey et al (2006), that in visual acuity, had a p-value of .03, but this was one out of eight tests for baseline differences (see their Table 1). So the risk of a type I error caused by multiple testing was considerable.…”

“…We hope that our commentary will contribute to a further improvement in the use of advanced statistics in neuropsychology. Anstey et al (2006) reported the effects of cataract surgery on neuropsychological test performance in an RCT. They used repeated measures ANOVA to test for group by time interaction, adjusting for two covariates: age and baseline visual acuity.…”

Our correct use of ANCOVA yields acceptable results

“…argues that the use of ANCOVA in Anstey et al (2006) is invalid. Based on quotes in Winer (1971), he claims that covariates cannot be used to adjust interaction terms involving within-subject variables.…”

“…Based on quotes in Winer (1971), he claims that covariates cannot be used to adjust interaction terms involving within-subject variables. Because the withinsubject variable in Anstey et al (2006) is time, he concludes that the results involving Time 3 Group interaction coefficient are invalid and consequently all analyses need to be re-done.…”