Grandparents chauffeuring back-to-schoolers to eye exam appointments might want to see if the doctor can squeeze them in, too. Treating vision problems not only helps ward off blindness in old age; it can also reduce chances of Alzheimer’s disease and other dementias.
Researchers exploring links between dementia and sight-stealing ocular disorders such as cataracts and age-related macular degeneration have been stacking up the studies for a few years. Last year, after a meta-analysis of many of those studies, the Lancet Commission added untreated vision loss in later life to its list of modifiable risk factors for dementia.
“It had been bubbling up for a while, so the Lancet report wasn't a big surprise to anybody who was aware of these association studies,” said Victoria Pelak, MD, a CU Anschutz neurologist and neuro-ophthalmologist, who sees the toll of both losses – eyesight and memory – in her work.
Yet the doctor and researcher at the CU Anschutz Alzheimer's and Cognition Center does view the heightened awareness about the importance of vision on brain health as a call to action for the public, medical scientists and health policymakers.
“I think knowing that 2% of your risk for dementia is related to vision really tells you that, with very little effort in high-income countries, you can lower your risk by making sure that you're going to your eye doctors, you're getting your regular eye visits, you're taking care of your eye diseases.”
An estimated 93 million adults in the United States have a high risk for serious vision loss, but only half visited an eye doctor in the past 12 months (Centers for Disease Control and Prevention).
Report spurs more research
The commission found benefits particularly pronounced with care of cataracts and diabetic retinopathy, citing one study that showed a 30% drop in dementia risk for people who underwent cataract surgery compared with patients who did not.
Cataracts are a leading cause of blindness worldwide and result in total vision loss for an estimated 20 million of the more than 35 million people affected.
Pelak said the Lancet report leaves unanswered questions that call for researchers to dig deeper into the individual degenerative eye diseases and the ways treating vision loss specifically impacts the brain, decreasing dementia risk.
“How, if people with cataracts get their cataracts out, does that change brain function? Does that change cognition over time? Does that change potential biomarkers that bring you closer to dementia?” Pelak and her fellow researchers on campus have begun organizing teams to answer these and other questions.
The Lancet Commission’s meta-analysis included 14 prospective cohort studies and over 6.2 million older adults who were cognitively intact at baseline.
Findings could help reshape care
“With these very large database studies, you don't really have cutoffs to say: Moderate or severe age-related macular degeneration increases your risk for dementia, but mild doesn't. Or glaucoma at this certain stage does not increase your risk, but glaucoma at this stage does," Pelak said.
Finding the critical points in progression and adjusting standards accordingly could lead to more effective care, she said.
“Maybe we need to be taking out cataracts earlier than we currently have as the standard to decrease the risk even further,” Pelak said, noting that the current surgical standard is about 20/40, the same as the driver's license standard.
“But maybe it's 20/30 vision plus a family history of dementia where you need to be taking your cataracts out. That's the kind of fine-tuning that's going to be really important,” she said.
“So now, it's really up to us as researchers and investigators to try to figure out: Is there a certain profile when you have vision loss that makes you more susceptible? Is it a certain degree of macular degeneration, or is it macular degeneration plus a vascular risk factor?”
While there is no clear understanding of how vision loss directly affects brain structure and function, theories exist. One is that by decreasing visual input, you're decreasing activity of the neurons and the connections they make.
“Maybe we need to be taking out cataracts earlier than we currently have as the standard to decrease the risk (of dementia) even further.” – Victoria Pelak, MD
Untangling the vision-brain link
“The less information you're getting in through your eyes to those primary cells that are processing visual information, the less those cells stay healthy. The less those cells stay healthy, the less they're communicating to other areas of the brain, so you just get this domino effect where the brain connections, the brain activity, is lowered.”
Then there’s the sociological side. Maybe people become less engaged in life when they begin losing vision.
“We see how their world gets smaller,” Pelak said. “It's not a giant leap to think this could potentially increase your risk for things like dementia, knowing that social, intellectual and physical activity are really critical for preventing dementia. We already know that through many other studies.”
Drawing from database studies largely focused on aging, the Lancet review mainly included subjects 50 and older. But that doesn’t mean correcting vision earlier in life is not protective of brain health, Pelak said.
“There are a lot of data showing how important childhood correction of treatable eye conditions is for maintaining other things,” she said, citing social life, education, economic viability and overall health.
“We see how their world gets smaller. It's not a giant leap to think this could potentially increase your risk for things like dementia, knowing that social, intellectual, and physical activity are really critical for preventing dementia. We already know that through many other studies.” – Victoria Pelak, MD
Addressing the issue from all sides
Economic status matters, because someone with fewer resources whose sight begins to fade might not be able to seek and receive eye care. They also might be less likely to get the proper treatment that they need for other issues that are precursors of dementia, such as diabetes and cardiovascular disease, Pelak said.
Lower income status could also reduce needed social and intellectual engagement. “We have some data that show that that is likely true. They are not plugged into the resources they need to stay intellectually engaged, because you certainly can stay intellectually engaged without having your vision be perfect 20/20. It’s about access.”
And, as the Lancet report noted, vision care is underprioritized and underutilized, particularly in other countries, Pelak said.
“The message for policymakers is that, in low- and middle-income countries with very few resources, we can intervene with things that don’t have high price tags, such as eyeglasses or cataract surgery programs, and potentially have a big impact.”
For now, reseachers, providers and policymakers need to continue working to find more answers and next steps. "For instance, is it really condition-dependent?" Pelak said. "Maybe this really is just about vision loss.” Either way, the best advice is clear, she said: “Make sure that you're correcting vision loss and treating eye disease as early as possible.”
