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Cataract surgery was linked to a nearly 30% lower risk of dementia in older adults, a prospective study showed.

Among 3,000 cataract patients, cataract extraction was associated with significantly reduced risk of dementia compared with people who did not have surgery (HR 0.71, 95% CI 0.62-0.83, P<0.001), reported Cecilia Lee, MD, MS, of the University of Washington in Seattle, and co-authors in .

The association between cataract surgery and dementia remained significant after controlling for multiple confounders and accounting for healthy patient bias. Decreased risk persisted for at least a decade after surgery, the researchers said.

"Sensory loss, such as vision loss due to untreated cataract, is of interest to the research community as a potentially modifiable risk factor for dementia," Lee told 番茄社区app.

"Cataract disease affects many older adults, and cataract surgery is a widely available intervention," she added. "To date, there are very few known measures, other than certain lifestyle factors such as diet and exercise, that are thought to be preventive against dementia."

The researchers tracked 3,038 people diagnosed with cataract or glaucoma in the Adult Changes in Thought () cohort, a Seattle-based study at Kaiser Permanente Washington. Participants were dementia-free at enrollment and did not have cataract surgery before they enrolled. Mean age of the group was 74.4; overall, 59% were women and 91% were white. Data were collected from 1994 through September 2018.

Participants in the ACT cohort were evaluated every 2 years with the Cognitive Abilities Screening Instrument (CASI). CASI scores range from 0-100, and participants with scores less than 85 underwent further diagnostic testing.

About 45% of the group (1,382 people) had cataract surgery during the study. Mean follow-up was 7.8 years. A total of 853 people developed dementia, mostly Alzheimer's disease (709 cases).

In contrast to cataract extraction, the researchers did not find lower dementia risk among people who had glaucoma surgery (HR 1.08, 95% CI 0.75-1.56, P=0.68).

Cataract extraction was more strongly linked to reduced dementia risk during the first 5 years after cataract surgery (HR 0.68, 95% CI 0.56-0.81, P<0.001) compared with later years (HR 0.76, 95% CI 0.63-0.92, P=0.02). Of several variables including additional education, race, smoking history, and sex, the only covariate more protective than cataract surgery was not carrying an APOE4 allele.

"One possible mechanism by which cataract surgery could decrease the risk of dementia or Alzheimer's disease is by enabling higher quality sensory input to the retina and therefore improving stimuli to the brain," Lee observed. "In addition, patients may be able to engage with the world more fully with improved vision, and this may have a protective effect against dementia development."

"Another potential explanation for the association between cataract surgery and decreased dementia risk centers around how cataract affects the type and quality of light that reaches the retina," Lee added.

Cataract causes the lens to develop a yellow tint that blocks blue light. Intrinsically photosensitive retinal ganglion cells in the retina are "exquisitely sensitive to blue light stimuli and are known to regulate circadian cycles," Lee pointed out.

"Degeneration and altered function of these cells has been shown to be associated with cognition and Alzheimer's disease," she said. "Because cataract affects the overall quality of light that reaches the retina including the blue light, cataract surgery may enable the reactivation of those cells in a way that is protective against cognitive decline."

The study has several limitations, the researchers acknowledged. Reverse causation was a possibility; people with early cognitive problems may be less conscious of vision issues, which might delay cataract surgery. Only a participant's first cataract surgery was evaluated, and whether subsequent surgeries influenced dementia risk was unknown. In addition, most participants were white, and results may not apply to other groups.

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