Cataract Surgery, Hearing Aids May Curb Cognitive Decline

Hearing aids and cataract surgery may protect against age-related cognitive decline in older adults with hearing and visual impairments, new research suggests.

Two studies conducted by the same group of researchers investigated the impact of correcting vision through cataract surgery and improving hearing through the use of hearing aids on cognitive decline in older adults.

The study on vision, which drew on participants in the English Longitudinal Study of Ageing (ELSA) study, compared 2000 older individuals who underwent cataract surgery with 3600 who did not have surgery and found that the rate of cognitive declined was halved in those whose vision had been corrected through surgery.

The study on hearing, which used the American Health and Retirement Survey (HRS), involved 2000 participants and found that cognitive decline was 75% lower after they adopted the use of hearing aids than before use.

"Our studies show a less steep decrease in episodic memory performance after cataract surgery and the use of hearing aids," lead author Asri Maharani, PhD, Division of Neuroscience and Experimental Psychology, Cathie Marsh Institute for Social Research, University of Manchester, United Kingdom, told Medscape Medical News.

"Cataract surgery and hearing aids may allow better sensory input and delay cognitive decline by preventing the adverse effects of sensory deprivation or facilitating lower levels of depression symptoms, greater social engagement, and higher self-efficacy, which protect cognitive function," she added.

The study on cataract surgery was published online October 11 in PLoS ONE, and the study on hearing aids was published in the Journal of the American Geriatrics Society (2018;66:1130-1136).

Strongest Midlife Risk Factor

"We were motivated to conduct these studies because maintaining cognitive function in later life has become a public health priority, as the burden imposed by dementia in the aging population has increased more rapidly than that of most other diseases," said Maharani.

"Hearing and vision sensory impairments among older people may contribute to the risk of cognitive decline and dementia; however, the effect of interventions [to address] sensory functions — that is, hearing aids and cataract surgery — on cognitive function is poorly understood," she said.

The researchers used an 18-year follow-up of the HRS cohort to "assess the consequences of hearing aid use on long-term age-related decline in episodic memory."

The study forms part of the SENSE-Cog multiphase research program that "aims to promote mental well-being in older adults with sensory and cognitive impairments."

The researchers studied a cohort of participants in Waves 3 to 12 (1996-1997 and 2014-2015, respectively) of the HRS study — an ongoing biennial investigation of US adults aged ≥ 20 years that started in 1992.

Respondents were aged ≥ 50 years, responded to at least 3 waves of the HRS, had no dementia at baseline, and used hearing aids for the first time between Waves 4 and 11 (n = 2040).

Cognitive ability was measured using episodic memory as the cognitive domain, with the task consisting of recall of 10 words immediately and at the end of the cognitive function module.

Covariates included age, sex, education, marital status/cohabiting, wealth, smoking, drinking, and physical activity.

On average, participants used hearing aids for the first time at age 62 years. Of the respondents, 61% were men, 45% had completed college or higher, and 815 were married.

Slower Decline

Episodic memory declined significantly as participants aged, but the rate of decline slowed down after, compared with before, they started to use hearing aids (β = –0.03, P < .001 vs β = –0.11, P < .001).

The difference in the coefficient between those two slopes was 0.08 (P < .001).

Hearing aid use was associated with higher memory scores (β = 2.13, P < .001), an association that remained significant even when the risk factors used as covariates were included in a second model (β = 1.53, P < .001).

In the second model, slopes for the decline of episodic memory scores were steeper before than after beginning hearing aid use (β = –0.1 and β = 0.02, respectively, both P < .001).

Confounders in the second model included being female, having attained a higher education level, having a higher income, drinking alcohol, and engaging in regular physical exercise, which were positively associated with episodic memory scores.

On the other hand, depression and chronic diseases were associated with lower memory scores.

Nevertheless, "for all individuals, there was a decline in episodic memory leading up to hearing aid use; and although the episodic memory scores continued to decline, even after beginning use of hearing aids, the rate of decline was less steep," the authors comment.

Similar to hearing impairment, visual impairment is "one of the risk factors for cognitive decline and dementia," the authors write.

Although associations between visual impairment and cognitive performance/dementia among the older population have previously been described, little evidence exists regarding the potential impact of interventions for visual impairment on cognition, they state.

The researchers set out to "test the possibility that treating visual impairment could reduce the rate of cognitive decline" and to "test hypotheses that posit a causal impact of vision impairment on cognitive decline."

The study of the impact of cataract surgery on cognitive decline drew participants from ELSA Wave 1 (2002-2003) until Wave 7 (2014-2015).

Participants who underwent cataract surgery between Waves 2 and 6 were considered the treatment group (n = 2068), and individuals with no cataract disease constituted the control group (n = 3636).

The episodic memory test used was the same as that employed in the study on hearing aids.

The researchers used a "dummy variable" for cataract surgery (one for a treated respondent and zero for a nontreated, cataract-free respondent) and created an "artificial" intervention point for the control point at which the matched no-cataract person had his or her "surgery."

At baseline, respondents in the treatment group scored, on average, slightly lower on the cognitive task than the control group (nine of 20 words vs 10 of 20 words, respectively).

Additional differences at baseline between the treatment and control groups included higher average age (68.4 vs 60.1 years), less physical activity, and slightly higher levels of depression.

In both groups, the majority of participants were married.

Increased Self-Efficacy

Cataract surgery was associated with improved memory (β = 4.23, P < .001), with a slower decline in episodic memory score after than before the surgery (β = –0.05, P < .001 and β = –0.1, P < .001, respectively) when social determinants, behavioral risk factors, depression score, and chronic conditions were included.

In the control group, the slope of cognitive decline pre-intervention was "gentler" than that of the treatment group (β = –0.08 and β = –0.1, both P < .001).

However, the rate of memory decline post-intervention was similar in both groups (both β = –0.05, P < .001).

"These findings indicate that the cognitive trajectory of respondents with cataract disease after having cataract surgery decreased at a similar rate with those free from cataract disease," the authors comment.

Female sex, higher educational attainment, higher income, and moderate physical exercise were associated with higher memory scores, and depression and the presence of chronic diseases were negatively associated with memory scores.

The authors suggest that their findings support the "cascade hypothesis, according to which cataract surgery may allow better visual input and thus result in a slower rate of cognitive decline."

Mechanisms posited by this hypothesis include reduction in the adverse impacts of sensory deprivation on brain function and facilitating increased physical activity, richer social networks, better mood, and higher self-efficacy.

The impact of improved vision on self-efficacy in slowing cognitive decline would apply to improved hearing as well, the authors note.

"We found that hearing and vision interventions may slow down cognitive decline and perhaps prevent some cases of dementia, which is exciting — although we can't say yet that this is a causal relationship," Maharani said.

Protective Effect?

Commenting on the study for Medscape Medical News, Heather Elizabeth Whitson, MD, MHS, associate professor of medicine and ophthalmology, Duke University School of Medicine, and deputy director, Duke Aging Center, Durham, North Carolina, who was not involved in either study, described the findings as "exciting."

She noted that although "there is little debate that sensory impairments are a risk factor for cognitive decline in older adults," these studies go beyond looking merely at risk factors.

"The studies suggest that perhaps correcting hearing and visual impairments can potentially protect cognitive health," she said.

Although the findings are "not definitive" they suggest that "fixing or improving sensory health actually protects cognition."

The "most important take-home message is to pay attention to sensory health," she said.

"Vision and hearing loss in old age are so common that sometimes they get ignored and are seen as nuisances rather than risk factors for other aspects of health," she continued.

"For psychiatrists, it's even more important to think about sensory health as a potentially modifiable risk factor for cognitive outcomes as well as affective outcomes," Whitson said.

Maharani added, "Preventing sensory loss, screening individuals for hearing and visual function, and providing interventions to improve sensory function, such as cataract surgery and hearing aids, may preserve cognitive function in old age."

This research was supported by the SENSE-Cog project, which received funding from the European Union Horizon 2020 research and innovation Program. The authors and Whitson have reported no relevant financial relationships.

PLoS ONE. Published online October 11, 2018. Full text

J Am Geriatr Soc. 2018;66:1130-1136. Abstract

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