The association between dual sensory impairment and dementia: A meta-analysis and systematic review of the literature

In recent years, a growing body of evidence has suggested that sensory impairment represents a modifiable risk factor for dementia. While previous reviews have considered the role of hearing impairment or visual impairment separately, no systematic review to date has considered the literature exploring the association between cognitive decline and having both visual and hearing impairment. Thus, the aim of this systematic review was to synthesise the published literature on the association between dual sensory impairment (DSI) and dementia by comparing individuals with DSI to those without sensory impairment and/or those with a single sensory impairment. A total of 22 papers were included in the narrative review, and 13 were included in the meta-analysis, which aimed to statistically assess whether DSI poses an additional risk of developing dementia compared to those with no sensory impairment and relative to individuals with hearing or vision impairment alone. Overall, we found a consistent link between dementia prevalence and incidence with DSI. Specifically, our results indicate that participants with DSI are at an approximately 50% greater risk of developing dementia compared to those without sensory impairments. Moreover, DSI was found to be a potentially greater risk factor for dementia than isolated hearing and visual impairment, with the risk for dementia in the DSI group exceeding the combined risk of the individual sensory impairments. While the review highlights substantial evidence supporting DSI as a significant risk factor for dementia and cognitive decline, it also acknowledges several limitations in the existing literature, including an absence of measurement validation, failure to consider sensory aids use and onset of sensory impairment, and the potential influence of sensory difficulties on cognitive test performance. We recommend that future studies should address those concerns, while also beginning to explore the effect of interventions targeting DSI on cognition.