Is there an association between cognitive and visual decline?

Cognitive and visual abilities decline with age. Recently, it has been suggested that the risk to suffer from dementia is associated with decreased visual acuity. Two theories, the sensory deprivation theory (stating that visual impairments cause cognitive decline) and the common cause theory (stating that cognitive and visual decline are caused by a general age-related decline of the system) have been proposed to explain the relationship between cognitive and visual changes. There is currently no consensus on which theory is valid. However, both agree that visual factors could act as biomarkers for cognitive decline. Given the limited research studying the link between vision and cognition using multiple measures of vision, we tested a battery of 19 visual tasks on 39 older adults with mild cognitive impairment (i.e., MCI group, age = 67 ± 5, 26 females) and 91 without evidence of cognitive decline (i.e., healthy group, age = 66 ± 5, 60 females), as measured by the Montreal Cognitive Assessment (MoCa). Our results revealed a strong association between visual and cognitive decline. The tasks showing the largest effect sizes were orientation discrimination, biological motion, motion detection and visual search. However, mirroring previous results in young adults, there were only weak correlations between the performance levels of the visual functions in both the healthy and the MCI groups, arguing against a common factor. Our results suggest that visual and cognitive abilities decline simultaneously, but they do so independently across visual and cognitive functions and participants.