Of the more than 3,000 elderly people with eye The researchers found that those who had surgery were about 30% less likely to be diagnosed with Alzheimer’s disease in the coming years.
Findings cannot prove that cataract surgery helps protect against Alzheimer’s disease, said lead researcher Dr Cecilia Lee. However, it provides strong evidence that this could be the case.
Lee and her colleagues were able to explain a number of other factors that could explain the finding. Even after that, cataract surgery was still associated with a reduced risk of Alzheimer’s.
“This evidence could be as good as we can get,” said Lee, chairman of ophthalmology at the University of Washington School of Medicine.
Cataract is a clouding of the lens of the eye that can cause symptoms such as blurred vision, difficulty seeing at night and noticing “halos” around lights. Cataracts are very common among the elderly – it affects more than half of Americans under the age of 80, according to the U.S. National Eye Institute.
Cataract removal and artificial lens replacement surgery can improve vision problems.
Past studies have linked cataracts, as well as other visual impairments, to an increased risk of dementia, including Alzheimer’s disease. That, Lee said, raised an obvious question: can cataract treatment reduce that risk?
However, this is a tricky issue to address.
“There are so many confusing variables,” Lee said, “especially for older people who have other health conditions.”
Even if older adults who have had cataract surgery show a lower risk of dementia, it could be because healthier people are more likely to opt for surgery – or because those people have better access to health care.
Lee’s team solved these problems using data from a large group of patients in the Kaiser Permanente healthcare system. All had access to health care, and the researchers had detailed information about their health history.
They focused on 3,038 adults aged 65 and older who had cataracts and did not have dementia at baseline. Just under half underwent cataract surgery.
Over an average of eight years, 853 patients were diagnosed with dementia, most commonly Alzheimer’s disease. But the risk was 29% lower among those who underwent cataract surgery, compared with those who did not.
This reduction is visible after Lee and her team considered all other variables they could – including whether people had physical disabilities or medical conditions such as heart disease, stroke or diabetes. They also counted body weight, training habits, level of education and smoking history – everything is associated with the risk of dementia.
Why would cataract surgery and subsequent vision improvement affect the risk of dementia? Lee said this is partly convincing because vision problems limit the engagement of older people in the world.
“If you don’t see well, you may not want to go out and hang out,” she said. “Or maybe you don’t want to exercise because you’re worried about safety.”
Like physical exercise, social and mental stimulation is thought to support healthy brain aging.
Another theory, Lee said, concerns blue light. Over time, the cataract may turn yellow, and this especially blocks the blue light. Certain specialized cells in the retina of the eye are very sensitive to blue light, Lee noted, and are associated with both sleep cycles and cognition (memory and thinking skills).
Claire Sexton, director of scientific programs and departments at the Alzheimer’s Association, agreed that these theories are compelling.
Because cataracts are so common, she said, there is great potential in targeting this condition as a risk factor for Alzheimer’s disease.
However, Sexton pointed to a limitation of the study: most of the patients were white. She said the findings should be replicated in a diverse group of older adults, to confirm that the connection also applies to colored people.
An even bigger message, Sexton said, is that people need to be aware that their general health – including heart, vision and hearing health – can affect their chances of dementia.
Lee encouraged seniors with vision problems to visit an ophthalmologist, a doctor who diagnoses and treats eye diseases.
The study was published on December 6th JAMA Internal Medicine.
The Alzheimer’s Association has more on that supports brain health.
SOURCES: Cecilia Lee, MD, MS, Associate Professor and Chair, Ophthalmology, University of Washington School of Medicine, Seattle; Claire Sexton, DPhil, Director, Scientific Programs and Approach, Alzheimer’s Association, Chicago; JAMA Internal Medicine, online, December. 6, 2021