Date Published: October 11, 2018
Publisher: Public Library of Science
Author(s): Asri Maharani, Piers Dawes, James Nazroo, Gindo Tampubolon, Neil Pendleton, Antony Bayer.
Visual impairment has been associated with lower cognitive ability among older adults, yet little is known about whether improving visual function with cataract surgery would be associated with slower cognitive decline. This study aimed to assess whether trajectories of cognitive decline differed before and after cataract surgery and compare those trajectories between older adults with cataract surgery and without cataract.
Data were drawn from the English Longitudinal Study of Ageing (ELSA) Wave 1 (2002/03) until Wave 7 (2014/15). The study population consisted of 2,068 individuals who underwent cataract surgery between Wave 2 and Wave 6 as the treatment group and 3,636 individuals with no cataract as the control group. We included only respondents who took part in a minimum three waves. Propensity score matching method was used to match the individuals in the treatment group with those in the control group. After we put an “artificial” intervention point for the individuals in the control group at the point that the matched person has cataract surgery, spline method was used to identify differences in cognitive trajectories pre- and post-cataract surgery. In the treatment group, we found that cataract surgery was positively associated with episodic memory scores after controlling for the potential covariates (β = 4.23, p<0.001). Episodic memory scores declined with older age, but the decline in episodic memory scores was slower after cataract surgery (β = -0.05, p<0.001) than before cataract surgery (β = -0.1, p<0.001). Although the episodic memory among respondents in the control group before intervention (β = -0.08, p<0.001) declined slower than those in the intervention group (β = -0.1, p<0.001), the declines in episodic memory scores were similar in both groups after the intervention (control: β = -0.05, p<0.001; intervention: β = -0.05, p<0.001). Cataract surgery may have a positive impact on trajectories of cognitive decline in later life. Further research is required to identify the mechanism to explain the association between cataract surgery and cognitive ageing, and whether early intervention towards vision correction results in a reduction in dementia risk.
Visual impairment—a condition affecting one in three adults 50 years or older –is one of the risk factors for cognitive decline and dementia. The presence of visual and hearing impairment is associated with lower cognitive function among older adults in Europe and the United States (US) . A retrospective study examining 625 older adults in the US found that those with untreated poor vision had a ninefold risk of developing Alzheimer’s disease and a fivefold risk of developing cognitive impairment no dementia (CIND) .
This study forms part of the SENSE-Cog multi-phase research programme, funded by the European Union Horizon 2020 programme. SENSE-Cog aims to promote mental well-being in older adults with sensory and cognitive impairments (http://www.sense-cog.eu/). The first work package of this project aims to better understand the links between sensory, cognitive and mental ill-health in older Europeans.
A total of 2,068 individuals from the ELSA sample who underwent cataract surgery between Waves 2 and 6 and 3,636 individuals with no cataract were initially included in this study. The descriptive statistics (see Table 1) show that the respondents in the treatment group achieved an average score of nine words out of 20 in the first wave, while those in the control group were able to memorise 10 words on average. The average age of the respondents in the treatment and control groups at baseline was 68.54 and 60.12, respectively. The majority of respondents were married in both groups. More than half of the respondents in the treatment group engaged in moderate physical activity, and 14.79% of them engaged in vigorous physical activity more than once a week. The proportions of respondents in the control group who did moderate and vigorous physical activities were higher than those in the treatment groups. The average CES-D score of the respondents in the treatment and control groups at baseline were 1.62 and 1.34 on a scale of 0 to 8, with 0 representing the lowest level of depression.
We found cataract surgery to be associated with a reduction in the rate of cognitive decline over 13 years of follow-up. The rate of cognitive decline among individuals with cataract was gentler after than before the surgery and had become similar with that among individuals with no cataract. Our finding supports the cascade hypothesis [4, 5], according to which cataract surgery may allow better visual input and thus result in a slower rate of cognitive decline by means of several potential mechanisms. One possible mechanism is neurobiological. Better visual acuity may reduce the adverse impacts of sensory deprivation on brain function via diaschisis . Neuroimaging study suggests that sensory impairment may affect brain regions distant from those in which the impairment has occurred . The Baltimore Study of Aging reported that individuals with hearing impairment showed accelerated atrophy in the whole brain, particularly in the right temporal lobe . Other mechanisms that may account for the positive impact of visual function on cognition include visual function’s facilitating of increased physical activity, richer social networks, better mood and higher self-efficacy. Better vision may facilitate physical activity , which in turn improves cognitive function . Better visual function may also improve social networks and facilitate cognitive stimulation. Sensory impairment may lead to social isolation ; prior study has demonstrated associations between poor social networks and cognitive decline and dementia . Better visual function may also lead to better mood, reducing dementia risk. Gray et al. found lower depression and anxiety levels in 92 patients at two and six months after cataract surgery . Depression has been reported to be associated with cognitive impairment, including executive function and memory .
Cataract surgery was positively associated with a lower rate of cognitive decline among older adults in England, independent of risk factors for cognitive impairment including those related to age, gender, education, wealth, chronic diseases, depressive symptoms, and physical inactivity. Due to the high prevalence of both cataracts and cognitive disorders in later life, the association between cataract surgery and cognitive longevity has important public health implication for targeting people at risk of cognitive decline and as a potential means to improve cognitive health and prevent dementia. A recent study using ELSA showed that the odds ratio for future pathological cognitive impairment was more than five times lower among respondents with the most advantaged trajectory of episodic memory than among those in the most disadvantaged trajectory . A positive impact of cataract surgery on cognitive decline would support the presence of a direct or indirect causal impact of visual impairment on cognitive ageing. Further research may test the potential for treatment and/or prevention of vision impairment to lower the risk of dementia.