Cataract surgery may reduce dementia risk, research shows

Surgery to remove cataracts, a condition that causes the eye’s normally clear lens to become opaque, can restore vision almost instantly. Recent research suggests that the procedure may have another benefit as well: reducing the risk of Alzheimer’s and other forms of dementia.

For the study, scientists examined 3,038 men and women with cataracts who were 65 years of age or older, and did not have dementia at the time of diagnosis. Among them, 1,382 had had cataract surgery and the others had not. All were participants in a memory study that spanned decades and followed them over the years.

The researchers found that the overall risk of dementia was 29% lower among participants who had cataract surgery compared with those who had not.

The researchers also looked at glaucoma surgery, another type of eye surgery that doesn’t restore vision but can help prevent vision loss. It had no effect on the risk of dementia.

Published in the journal Jama Internal Medicine, the study took into account the age of participants at first diagnosis of cataract and also several risk factors for dementia, including few years of education, smoking, hypertension and high body mass index. The only factor that had a greater effect than cataract surgery on the risk of dementia was not carrying the APOE-e4 gene, which is linked to an increased risk of Alzheimer’s disease.

“The authors were extremely careful in approaching the data and in considering other variables,” commented Nathaniel A. Chin, an assistant professor of medicine at the University of Wisconsin who was not involved in the study. “They compared cataract surgery to surgery that doesn’t improve vision — glaucoma surgery — and controls to account for many important variables that could cause confusion.” Chin is medical director of the Wisconsin Center for Alzheimer’s Research.

“We were amazed at the significance of the effect,” said the study’s lead author, Cecilia S. Lee, an assistant professor of ophthalmology at the University of Washington.

The authors emphasize that this is an observation-based study that does not prove cause and effect. But they suggest that this may be the best kind of evidence one can get, as a randomized trial in which only a few people were allowed to have cataract surgery would be practically and ethically impossible.

“Perhaps you could say that people healthy enough to have the surgery are healthier overall and therefore less likely to develop dementia anyway,” Lee said. “But when we don’t see any association between glaucoma surgery and risk of dementia, this reinforces the idea that it is not simply eye surgery [que ajudam a reduzir o risco de demência], nor that a person is healthy enough to undergo surgery, but rather that the effect is specific to cataract surgery.”

The results reinforce previous research that has indicated that vision loss — as well as hearing loss — are important risk factors for cognitive decline. For example, people who have difficulty seeing or hearing may withdraw from activities such as exercise, social interactions, reading or intellectual pursuits, all of which are linked to a lower risk of dementia.

But the researchers also suggested a possible physiological mechanism. The visual cortex changes with vision loss, they wrote in the paper, and impaired vision can reduce the arrival of information to the brain, leading to brain shrinkage, another risk factor for dementia. At least one previous study found an increase in brain gray matter volume after cataract surgery.

While the exact mechanism of cataract surgery’s benefits is still unknown, Lee said it’s not surprising that some of the changes we see in the eyes may reflect processes in the brain. “The eye is very strongly linked to the brain,” he said. “The eye develops in utero from the brain, with which it shares the same neural tissue. The developing eye comes from the forebrain.”

Chin said that for him, the most important question to look at now is what this means for doctors and patients. Doctors in primary care clinics or those treating memory need to do more accurate tests to look for visual decline, he said. “We can talk to people about potential brain health improvements from cataract surgery, and the need to care for vision throughout life as a way to protect cognition.”

Translation by Clara Allain

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