Cataract surgery may reduce the risk of Dementia, study finds

More than 55 million people worldwide are living with Dementia. While there is no known cure, new findings show there might be a way to reduce the risk. Researchers at the University of Washington found patients who had cataract surgery had a lower chance of developing Dementia. Cecilia Lee, Klorfine Family Associate Professor in Ophthalmology, and Eric Larson, Founding Principle Investigator for the Adult Changes in Thought Study, join us to share their results and the connection between eyes and brain.

The following transcript was created by a computer and edited by a volunteer.

Dave Miller:  Researchers at the University of Washington announced a major finding recently. Looking at Kaiser Permanente data from a decades long study, they found that older people who’d had cataract surgery were 30% less likely to get dementia over the next 10 years. Cecilia Lee is the lead author of the paper which was published in JAMA Internal Medicine. She is an Associate Professor in Ophthalmology at the University of Washington. She joins us now along with Eric Larson. He is the founding principal investigator for the ACT or Adult Changes in Thought study.  Can you just help us understand this finding? What exactly is the correlation you found between cataract surgery and the significantly lower incidence of dementia?

Cecelia Lee:  One of the things that we found previously is that certain retinal diseases such as age-related macular degeneration or diabetic retinopathy are associated with a much higher risk of developing Alzheimer’s disease or dementia. So then our question was whether there is an impact of intervening or stopping one of the eye diseases that [would] have necessarily any impact on future development of dementia.  And cataract is the most commonly found aging related. It’s actually not a disease. It’s a natural aging process of the lens. So we wanted to ask whether if we do cataract surgery whether cataract surgery was associated with a lower risk of developing dementia in the future.

Miller:  What does it tell you that cataract surgery was associated with the lower incidence of dementia, but glaucoma surgery wasn’t?

Lee:  One of the things that we found was as we had hypothesized - cataract surgery was associated with much lower risk of developing dementia in the future. And that actually really surprised us.  Even though that was what we had hypothesized, the actual magnitude of the reduction was quite surprising to us. So one of the common errors or challenges of looking at a data set like this [is that] this is an observational data. This is not a trial per se. And we wanted to look at the potential impact or association of an intervention like cataract surgery. One of the things that we worry about is whether there is this healthy-patient bias, meaning if patients are too sick or have too much going on with medical problems, then they’re less likely to go ahead and do this optional surgery, which is cataract surgery.

So we thought that people who are able to afford to have or undergo cataract surgery would probably have much better health and also be more health conscious per se. So we wanted to control as much as we could in terms of other indicators or other factors that would suggest either they have good health or not. In addition to that, one of the controls that we did or comparison we made is with glaucoma surgery, as you mentioned.  Glaucoma surgery is an outpatient eye surgery, which means that patients who are able to undergo glaucoma surgery should at least have some type of health that would allow them to undergo glaucoma surgery, similar to cataract surgery. One of the main differences between cataract and glaucoma surgeries is that glaucoma surgery does not lead to improved visual acuity or visual function, because glaucoma surgery is meant to stop the progression of glaucoma, which is another common aging disease.  And we found no associations between glaucoma surgery and a risk of dementia. This meant that the reduced risk of developing dementia that we found in cataract surgery patients is probably related to cataract surgery itself or more specific to cataract surgery and not the fact that a patient could have been healthier to have undergone any eye surgery such as glaucoma. It gave us more reassurance about our results.

Miller:  And to really put a fine point on that, the idea is that the improved eyesight that comes from the cataract surgery itself is playing a role here.

Lee:  Yes, that’s what we’re thinking.

Miller:  I want to hear more about the hypothesis behind that because that’s, in a lot of ways, the most fascinating part of this research. But I want to reintroduce Erik Larson here, the founding principal investigator for the ACT or Adult Changes and Thought Study because it is the thousands of people, the data that’s come from this for decades that you relied on. So Eric Larson, what is the ACT Study?

Eric Larson:  The ACT Study is what we call a longitudinal cohort study. And it’s unique because it’s set in a health care system. We started when we were Group Health up here in Seattle and would randomly select people over the age of 65 who were not demented and ask them if they were willing to be part of our study.

And over the decades - we started this particular study in 1994 - about 5,800 people have enrolled in the study and we follow them every two years.  If they show signs of cognitive decline, we do a comprehensive evaluation to determine if they have dementia or Alzheimer’s disease. And we create essentially massive amounts of data. And the whole purpose of the study, initially, was to look for markers of dementia.

But our current focus is like Dr. Lee described. We’re looking for ways that would give us clues to how to prevent the disease or delay the onset as late as possible in a person’s lifespan. And we’re extremely grateful for our subjects and their families who participate in the study. And we’ve been fortunate because the findings of this study, because they’re community-based, apply to the population-at-large as opposed to just people who filter their way into a very select population, say into a dementia clinic for example.

The other point that’s really important for allowing studies like Dr. Lee’s to happen is that we have tons of clinical records on our subjects. Some of them have been in the delivery system and have complete medical records going back to 1947 or 48 when Group Health was founded. And now all those records are on the electronic record. So the median number of years that people are in our study before they enroll, over the age of 65, is over 30. So, all this data is available for investigators to work on to find clues as to how we might delay the onset of the disease.

Miller:  A tantalizing trove of data for researchers. I imagine that there have been a lot of findings from the study over the years. Can you put this latest one in perspective, numerically, I mean, how significant is a 30% lower risk of developing dementia in the 10 years following the operation, compared to other correlations that other researchers have found?

Larson:  That’s a really good question. And I will tell you that everything I say is not as precise as it sounds.  30% sounds like we really know but it’s a range of about 30%. But to put it into context, one of the most important findings of our study was that any amount of regular exercise reduces the risk of dementia by about 35-38%. So the finding that Dr. Lee reports and our team reports in this article is on the order of magnitude as the protective effect of exercise. So at the individual level, you know, how do you perceive the 30% risk reduction? Hard to say. But at the public health level, if this finding is confirmed, this has enormous consequences for allowing people to function better cognitively later and later in life.

Miller:  So to me, the biggest question here, why, what’s your hypothesis for why it is that cataract surgery can reduce the chance of somebody getting dementia?

Lee:  I think one of the most common hypotheses has been really spearheaded by Dr. Larson I think over a decade ago. The idea is that sensory impairment plays a major role in dementia development. And so I think this paper, our teamwork, shows that the fact that cataract surgery is associated with reduced risk of dementia suggests that preventing visual loss or I guess improving visual acuity and also visual function leads into improved visual stimuli, better brain stimuli and then also more neurocoronal connections which are likely protective from dementia.

Miller:  Does it also lead to people living their lives in different ways, in more social ways. Does it lead to more reading, more watching television - just more experiences of life coming into your eyes and into your brain?

Lee:  Absolutely. So I think another hypothesis is that the secondary effect of a person experiencing better vision or better visual function is that the participants or the person can interact with the world better. Maybe they may be willing to go out more, become more social or go exercise more. And all those factors have been shown to be associated with being protective of dementia such as exercise. So I think that also is likely playing an important role here as well.

Miller:  What does this suggest for everybody? As we get older, whether or not we’re dealing with cataracts?

Larson:  Yeah, this is another really good question. To me it suggests what I would call optimism for how people can live out their life in better health and better brain health. We used to think that you really couldn’t prevent or change the course of brain aging.  And over the duration of the ACT Study, thirty or forty years, we now know that these, [what] we call modifiable risk factors, can lead to better quality of life and taking this period of when you get so old that you can’t function, [and] moving that closer to the time that you’re going to die. We call that the compression of morbidity or in my view, in this case, it’s a compression of cognitive morbidity - of moving that to as late as possible in life. And the thing that I’m thinking after years of doing this is that almost anything that improves your general health and well being likely has an effect on how your brain functions later and later in life.

Miller:  What’s next in terms of your research? What are the big questions you want to answer?

Lee:  Well, there are several projects that we’re working on. I think it would be great to continue trying to explore the potential mechanisms - why we are seeing such an important association between cataract surgery and also dementia risk reduction. And our research is really focused on looking at this connection between the aging eyes and aging brain and then how we could use the eye to understand better the health of the brain and then also future risk of developing Alzheimer’s or dementia.

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