Visual impairment and dementia risk explained

Some types of visual impairment have been linked to a higher risk of dementia.

For example, vision problems caused by cataracts and diabetic retinopathy are linked to higher dementia risk.

Other conditions, like glaucoma and age-related macular degeneration, do not appear to have the same link.

Being long‑sighted or short‑sighted on its own is not the same as visual impairment. It can usually be corrected with glasses or contact lenses. Keeping vision as clear as possible may help people stay active and engaged in everyday life. It is important to visit the optician regularly.

Researchers are still working to understand this. There may be more than one reason, and different factors could affect different people.

1. Less stimulation and activity

Vision helps the brain understand what is happening around us.

When our sight is impaired, the brain receives less clear information. It can also make it harder to stay active and social.

Over time, this may mean the brain has fewer chances to keep active. This may make it harder for the brain to cope with conditions like Alzheimer’s.

2. Links with other health conditions

Some conditions that affect vision, such as diabetes, are also linked to a higher risk of dementia.

This means the increased risk may not be due to vision problems alone.

For every 100 cases of dementia worldwide, almost half (45%) could be prevented or delayed. Two of those 45 cases are linked to untreated visual impairment in later life. 

So, if nobody had an untreated visual impairment, there'd be two fewer cases of dementia for every 100 people who develop it now.

Find out more: Addressing 14 health and lifestyle factors could prevent nearly half of global dementia cases - Alzheimer's Research UK

Changes in the brain linked to dementia can start many years before symptoms are noticed.

These changes may also affect the eyes. This means visual problems could be an early sign of dementia, rather than a cause of dementia.

More research is needed to fully understand this two way relationship.

A rare condition called posterior cortical atrophy (PCA) mainly affects how the brain processes visual information. People with PCA often notice visual problems, such as difficulty judging distances or recognising objects, before they have memory problems.

Most of what we know about dementia risk comes from observational studies, which follow groups of people over time to look for patterns in health and lifestyle.

For example, studies like Insight 46 have followed people for decades to understand how health across life is linked to brain health and later on.

This is often the most practical way to study dementia risk. Many risk factors cannot be tested in trials in a fair or ethical way. Dementia also develops over many years, so studies can take a long time to show results.

Observational studies can show when something like our diet or occupation are linked to a higher or lower chance of dementia. But they cannot prove that something directly causes dementia, or that changing it will definitely reduce risk. These studies look at patterns across large groups, not what will happen to any one person.

Randomised controlled trials give stronger evidence because participants are assigned to different groups at random. This design makes it more likely that differences in outcomes, for example our risk of dementia, are caused by the intervention, for example a diet change, rather than by other factors.

But these studies are harder to do in dementia research. They often take many years and may test several changes at once, making results harder to interpret.

Newer trials are helping to build a clearer picture of what may support brain health. No single study can give a definite answer, but it is all research findings together that help us understand what is important for our brain health and risk of dementia.