Adults who have undergone cataract surgery have a lower chance of developing dementia, findings that could open the door to understanding further connections between eye and brain health, a new University of Washington study reported last week.

The study was published in JAMA Internal Medicine. It says that seniors who've had cataract surgery had a nearly 30% lower risk of developing dementia for at least 10 years after the operation, compared to those who didn't.

The Seattle Times' recent article entitled “Cataract surgery associated with lower risk of dementia, University of Washington study finds” reports that lead researcher Dr. Cecilia Lee said the findings could be important in learning more about the memory loss disorder that doesn't have known treatment options or preventive methods.

Researchers understand that there's a strong genetic risk factor that increases the risk of developing Alzheimer's disease. However, Lee found in an earlier study that for people with certain eye diseases — like age-related macular degeneration or diabetic retinopathy — their risk of developing memory loss is “as significant” as someone with the genetic risk factor.

“It wasn't a subtle or small risk,” she said. “That gave us the foundation to really go after the connection between the aging eye and the aging brain.”

This research is part of longer-term program that the university is conducting with Kaiser Permanente Washington, which contributed data from more than 5,500 patients who volunteered to participate. The patients were evaluated every two years for cognitive ability. Of more than 3,000 adults over 65 years old with cataracts or glaucoma, 853 developed dementia. Of those, 504 cases happened before or without cataract surgery, and just 320 occurred after surgery. Researchers also evaluated seniors with glaucoma surgery (which doesn't restore vision). They saw that it didn't have a significant link to dementia risk.

“That gave us more reassurance that the result we found is not something we picked up because people were healthy enough to have eye surgery,” Lee said. “It was more likely more specific to cataract surgery, which improves visual function.”

The researchers have some hypotheses as to why that might be. When a person develops cataracts — a clouding of the lens that's common in people as they age — their brains are receiving lower quality sensory input.

“We're born with a crystal-clear lens,” Lee said. “As we age, the lens becomes yellow and cloudy. Because the lens becomes yellow, it's almost like you're wearing yellow sunglasses all the time.”

Those with cataracts often experience blurry vision, have difficulty seeing sharp colors, see halos around bright lights and are unable to drive at night.

“So, a brain that's not getting enough visual stimuli might be at a higher risk of developing dementia because it's losing those neuronic connections,” Lee said. Another hypothesis, Lee said, is that after cataract surgery, people are getting more blue light, or a “better quality light that enters retinas.”

“Some special cells in the retina regulate sleep cycles and have been shown to be associated with cognition, and these cells respond well to blue light,” she said. “Cataracts specifically block blue light, and cataract surgery could reactivate those cells.”

When cataracts are gone, a person's vision immediately improves. He or she is then able to interact with this world better. However, it's unclear if cataract surgery could have an impact on a person who has already developed dementia or memory loss.

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Reference: Seattle Times (Dec. 13, 2021) “Cataract surgery associated with lower risk of dementia, University of Washington study finds”