Written by Corrie Pelc — Fact checked by Jessica Beake, Ph.D.
More than 55 million people worldwide live with dementia — a syndrome that causes a decline in cognitive functions such as memory, language, and comprehension.
Alzheimer’s disease is the most common form of dementia, accounting for 60–80% of all people who have dementia. Scientists have carried out much research over the years examining the causes of Alzheimer’s; however, they remain unclear.
Researchers from the University of Washington School of Medicine in Seattle now say they have uncovered a link between cataract surgery and a lowered risk for developing dementia in older adults, including Alzheimer’s disease.
The study’s authors believe the heightened sensory input and increased exposure to blue light after cataract surgery may help explain why. There is hope that this information might lead to potential new therapies to either slow down or prevent age-related dementia.
The results from this observational study appear in the journal JAMA Internal Medicine.
What are cataracts?
A cataract occurs when proteins in the naturally clear lens of the eye break down, causing it to become “cloudy.”
Vision becomes foggy, and objects may appear blurry or less colorful. Cataracts generally start small, but over time if left untreated, they can grow and impair vision, making it difficult to read and drive.
An estimated 94 million people, globally, have cataracts.
Aging is the most common cause of cataracts. Certain risk factors, including smoking, diabetes, excessive sun exposure throughout a lifetime, and previous eye injuries, can increase the risk of developing cataracts.
The only way to remove a cataract is through cataract surgery. The procedure involves an eye surgeon removing the eye’s natural lens and replacing it with an artificial lens called an intraocular lens (IOL).
The aging eye and the aging brain
Medical News Today spoke with lead researcher Dr. Cecilia S. Lee, associate professor and Klorfine Family Endowed Chair in ophthalmology at the University of Washington School of Medicine.
She explained that previous research has found an association between several eye diseases, such as age-related macular degeneration (AMD) and diabetic retinopathy, and an increased risk of Alzheimer’s disease and dementia.
“A cataract is a natural aging process of the eye and affects the majority of older adults who are at risk for dementia,” Dr. Lee explained.
“Sensory loss, including vision and hearing, is of interest to the research community as a possible modifiable risk factor for dementia. Because cataract surgery improves visual function, we hypothesized that older people who undergo cataract surgery might have a decreased risk of developing Alzheimer’s disease and dementia.”
For their study, Dr. Lee and her team analyzed data from over 3,000 participants in the ongoing Adult Changes in Thought Study.
When participants in the Adult Changes in Thought Study enrolled, they were aged 65 years or older and did not have dementia. The researchers followed up with them every 2 years until dementia symptoms or Alzheimer’s disease presented themselves.
Kaiser Permanente Washington collected data for this study from 1994–2018 and analyzed them between 2019–2021.
The analysis only included participants who had received a diagnosis of cataract or glaucoma before enrollment or during follow-up.
Upon extracting information on cataract surgeries from the study participants’ medical records, researchers found of the 3,038 study participants, 853 developed dementia, including 709 with Alzheimer’s disease. Additionally, 1,382 of the participants — or 45% of the total — underwent cataract surgery.
During further investigation, Dr. Lee and her team found the participants who underwent cataract surgery had an almost 30% less risk of developing dementia after their surgery.
The researchers also reported that glaucoma surgery did not affect dementia risk.
Dr. Claire Sexton, director of scientific programs and outreach for the Alzheimer’s Association who was not involved in the study, explained to MNT the importance of this finding:
“We’ve seen in previous research that sensory impairments, such as vision loss, are associated with a higher risk for dementia. But this research tells us that improving vision — in this case, extracting cataracts — may reduce risk of dementia.”
“There is a strong message here for doctors that they need to assess and treat sensory impairment in their patients who are older adults and those with Alzheimer’s disease and other dementias,” Dr. Sexton continued.
“Assessment of sensory function should also play a role in assessing cognitive changes and diagnosing Alzheimer’s. People with sensory impairments such as vision or hearing loss should track them and discuss them with their doctor. Family members can play an important role in paying attention to sensory changes and encouraging assessment and follow up.”
Dr. Lee hopes these results will inform doctors about the importance of eye health in their older patients who are at risk for dementia.
“To date, there are few known measures, other than certain lifestyle factors, such as diet and exercise, that are thought to be preventive against dementia,” she explained.
“Older adults who are experiencing symptoms of cataracts, such as night driving difficulty or seeing halos around bright lights are to be evaluated by ophthalmologists […] who specialize in eye surgeries. If ophthalmologists recommend someone undergoes cataract surgery and the patient is on the fence about proceeding, our study results suggest that cataract surgery would not hurt, and there may be an added benefit.”
A role for blue light?
Cataracts block blue light. Following surgery, more blue light can enter the eye. According to the authors, this might play a part in reducing dementia risk.
Dr. Lee explained that special cells in the retina called intrinsically photosensitive retinal ganglion cells (ipRGCs) are particularly sensitive to blue light stimuli and help regulate circadian cycles.
“Degeneration and altered function of these cells has been shown to be associated with cognition and Alzheimer’s disease,” she added. “Because cataract surgery restores the passage of blue light through the lens and to the ipRGCs, it may enable the reactivation of those cells in a way that is protective against cognitive decline.”
Additionally, Dr. Lee said the retina might provide a non-invasive way to diagnose Alzheimer’s disease and other dementias before clinical symptoms develop.
“Sensitive retinal biomarkers of preclinical Alzheimer’s disease would be very useful for clinical trials of potential treatment approaches,” she explained.
“We are currently conducting research where we collect a number of non-invasive, highly sensitive retinal imaging in people with and without cognitive problems and use artificial intelligence (AI) techniques to interpret and analyze the data. Our ultimate goal in the future is to develop AI algorithms that can identify features in the eye that can predict someone’s risks of developing dementia, such as Alzheimer’s disease.”