Vision as a risk factor for dementia

As the science of dementia risk reduction has firmed up in recent years, it has been fascinating that many risk factors relate to the sensory inputs into the brain. Loss of sensory input to the brain such as via hearing impairment has been identified as an important risk factor, but also pain, particularly at multiple sites, is emerging as a potential risk factor.

In the most recent Lancet Commission report on dementia risk, untreated visual loss in older age has been proposed to be a small but important contributor to the impacts of potentially modifiable risk factors. In a similar fashion to other risk factors, most of what we know about vision loss and dementia risk comes from large scale retrospective epidemiological studies, and there are some differences in research outcomes. There is broad consistency that cataracts are a particular risk factor, and that surgery for cataracts to correct visual impairment may reduce this risk. Diabetic retinopathy may also be a risk factor, irrespective of the other impacts of diabetes on the brain. However, whether this risk extends to other major eye conditions, such as age-related macular degeneration and glaucoma is less clear.

What may be the basis for this risk relationship?

It may be that some eye conditions share some pathological underpinnings with causes of dementia, such as with problems with the vascular system and supply of blood. An alternative view, shared with interpretations of the impacts of hearing impairment, is that vision loss may lead to higher levels of social isolation, perhaps also reduced physical activity, and that these latter consequences may reduce resilience to dementia. Alternatively, there may be direct negative effects of visual loss on brain function and plasticity. Human brain function is very visual and loss of a major input may be expected to alter how the brain normally operates which may lead to less resilience to the diseases of dementia.

 It is important to recognise that alterations in visual function may be an uncommon indicator of specific forms of dementia, such as Posterior Cortical Atrophy. Also, there is evidence that Alzheimer’s disease pathology can occur in the retina, which may be an early indicator of this condition.  While vision loss may impact risk, not everyone who experiences vision loss will develop dementia. Given that some of these areas of vision loss are amenable to correction to some degree, awareness of this risk link should enable a broad public health approach to monitor for and address this risk factor if possible.