Improved sensory input may benefit cataract patients.

A recent study, published in JAMA Internal Medicine, indicated that cataract surgery was associated with a nearly 30% lower risk of dementia in older adults. In the study of 3,000 cataract patients, cataract extraction was linked with significantly reduced risk of dementia compared with individuals who had not undergone the surgery, according to Cecilia S. Lee, MD, MS, an ophthalmologist and associate professor at the University of Washington in Seattle and a study co-author. The decreased risk remained for at least a decade after surgery, the study indicated.

“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 said. “Cataract disease affects many older adults, and cataract surgery is a widely available intervention. 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.”

Researchers followed 3,038 individuals diagnosed with cataract or glaucoma in the Adult Changes in Thought (ACT) cohort, a Seattle-based study at Kaiser Permanente Washington. At enrollment participants were dementia-free and had not had cataract surgery. The mean age of the participants was 74.4, with 59% women and 91% white. Researchers collected data from 1994 through September 2018.

Researchers evaluated participants in the ACT cohort every two years with the Cognitive Abilities Screening Instrument (CASI). CASI scores range from 0 to 100; participants with scores under 85 underwent further diagnostic testing. About 45% of participants (1,382) underwent cataract surgery over the course of the study. Overall, a total of 853 study participants developed dementia, with Alzheimer’s disease most prevalent (709). By contrast to cataract extraction, researchers found no lower dementia risk among people who had undergone glaucoma surgery.

The strongest link between cataract extraction and reduced dementia risk was found to occur during the first five years following cataract surgery compared with later years. Although several variables factored into risk calculation, including additional education, smoking history, gender and race, the only covariate more protective than cataract surgery was the absence of an APOE4 allele in participants.

“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 said. “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 explained. Cataract causes the lens to develop a yellow tint that blocks blue light.

The retina’s intrinsically photosensitive retinal ganglion cells are “exquisitely sensitive to blue light stimuli and are known to regulate circadian cycles,” she said. “Degeneration and altered function of these cells has been shown to be associated with cognition and Alzheimer’s disease. 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.”