Cataract surgery is often undertaken to reverse the natural decline in vision as we get older. Now, a new association study underscores the wider benefits such a procedure can have on one's health – especially when it comes to reducing dementia risk.

Cataracts are cloudy areas that develop in the lens of the eye as we get older, causing colors to fade and vision to become more blurry. A cataract surgery replaces this cloudy lens with an artificial one to improve sight again.

On first glance, it may seem strange that this could have anything to do with the risk of developing dementia, but sensory impairment and loss of vision in particular is known to affect cognitive functioning in older adults.

Thus, the team behind this study, led by ophthalmologist Cecilia Lee from the University of Washington, hypothesized that "older adults with cataract who undergo cataract extraction may have a lower risk of developing dementia" compared to people who don't receive such procedures.

To test their hypothesis, the researchers analyzed data gathered as part of the ongoing Adult Changes in Thought study, a long-term, prospective cohort study started back in 1994 designed to study the development of dementia.

Their data pool included 3,038 dementia-free participants over 65 years of age diagnosed with either cataracts or glaucoma. Of those participants, 853 developed dementia, with 709 of those cases being Alzheimer's disease.

Those who underwent cataract surgery were almost 30 percent less likely to develop dementia for the next 10 years at least, with a similar reduction in risk when it came to Alzheimer's disease specifically.

However, there was no change in risk for developing dementia amongst those who did or did not undergo glaucoma surgery across the same period – a procedure that can help halt further vision impairment, but does not improve it in the same way that cataract surgery does.

"These results are consistent with the notion that sensory input to the brain is important to brain health," says study co-author Eric Larson, a senior investigator at the Kaiser Permanente Washington Health Research Institute.

The results were adjusted for a variety of health-related factors, including smoking habits, diabetes, a history of heart disease, and hypertension – but the strong association between cataract surgery and a reduced risk of developing dementia remained.

There's a swathe of potential reasons why this may be the case. Dealing with visual impairment in old age may lead to social difficulties, and the person can withdraw from life and friends, reducing their activity and exercise, "all of which are associated with cognitive decline", the team writes.

Alternatively, the way cataracts impair vision could lead to specific changes in the brain, speeding up some of the mechanisms that cause the neurons to work less efficiently and lead to increased cognitive issues in old age.

Furthermore, the team also hypothesizes that it may have something to do with better quality sensory input traveling from the eyes to the brain after surgery has been carried out.

"Some special cells in the retina are associated with cognition and regulate sleep cycles, and these cells respond well to blue light," says Lee. "Cataracts specifically block blue light, and cataract surgery could reactivate those cells."

While the connection between poor vision and an increased risk of dementia is already on the research radar, this is the first study to assess dementia risk while comparing cataract surgery to another surgical eye procedure.

With dementia affecting some 50 million people worldwide, and no effective treatment or cure available, anything we can learn about prevention is a truly valuable avenue of inquiry.

The researchers are hoping their work can prompt more investigations into the link between vision impairment in old age and dementia risk.

"This kind of evidence is as good as it gets in epidemiology," says Lee. "This is really exciting because no other medical intervention has shown such a strong association with lessening dementia risk in older individuals."

The research has been published in JAMA Internal Medicine.