CNA/THE NEW YORK TIMES – Surgery to remove cataracts, which cause the eye’s normally clear lens to become cloudy, can restore vision almost instantaneously. New research suggests cataract surgery may have another benefit as well: A reduced risk for Alzheimer’s disease and other forms of dementia.
For the study, scientists looked at 3,038 men and women with cataracts who were 65 or older and free of dementia at the time of their diagnosis. Of these, 1,382 had cataract surgery, and the rest did not. The subjects were part of a decades-long memory study that followed them over decades.
The researchers found that the overall risk for dementia was 29 per cent lower in those who had cataract surgery compared with those who did not.
The study, in JAMA Internal Medicine, adjusted for age at first diagnosis of cataracts as well as various risk factors for dementia, including few years of education, smoking, a high body mass index and hypertension.
The only trait that had a bigger impact on dementia risk than cataract surgery was not carrying a gene called APOE-e4 linked to increased risk of Alzheimer’s disease.
“The authors were thoughtful in how they approached the data and considered other variables,” University of Wisconsin assistant professor of medicine Dr Nathaniel Chin said, who was not involved in the study.
“They compared cataract surgery to non-vision-improving surgery – glaucoma surgery – and controlled for many important confounding variables.” Dr Chin is the medical director of the Wisconsin Alzheimer’s Disease Research Centre.
“We were astounded by the magnitude of the effect,” said the lead author, Dr Cecilia Lee, an associate professor of ophthalmology at the University of Washington.
The authors noted that this is an observational study that does not prove cause and effect.
But they suggested that this may be the best kind of evidence attainable, since a randomised trial in which only some people are allowed to get cataract surgery would be both practically and ethically impossible.
The findings bolster earlier research showing that vision loss – as well as hearing loss – are important risk factors for cognitive decline. People who have trouble seeing or hearing, for example, may withdraw from activities like exercise, social interactions, reading or intellectual pursuits, all of which are tied to a lower risk of dementia.
But the researchers also suggested a possible physiological mechanism. The visual cortex undergoes changes with vision loss, they wrote in the paper, and impaired vision may lessen input to the brain, leading to brain shrinkage, also a risk factor for dementia. At least one previous study found an increase in the brain’s grey matter volume after cataract surgery.
While the exact mechanism for the benefits of cataract surgery remains unknown, Dr Lee said it’s not surprising that some of the changes we see in the eye might reflect processes in the brain.
“The eye is very strongly connected to the brain,” he said. “The eye develops in utero from the brain and shares the same neural tissue. The eye in development comes out of the forebrain.”