Researching the Link Between Vision Impairment and Cognitive Decline

We all hate aging — well, most of us do — and many of us take extra steps to prevent our personal think-tank from losing members (and memories) along the way. Whether we take seven different supplements backed by research (and maybe some that aren’t), or do our daily sudoku, there are lots of different ways to keep the brain healthy as we age.

A major tip is having an active and varied lifestyle to keep our brains energized into our golden years. Trying new things that force our brains to construct new neural pathways is one of the best ways. We can switch from that sudoku to Wordle, try an elliptical instead of a treadmill, change around our COVID-19-imposed home desk setup, get into racquetball, or pick up a new hobby building ships-in-bottles.

Seeing the Future

But in order to build a ship-in-a-bottle or do a Wordle, we have to be able to see it. And there’s nothing more frustrating and depressing than gradually losing the ability to fit a hook in a bottleneck (for said ship). Therefore, it seems obvious that proper optical care is essential to mental health care. But what about the research? How exactly is visual impairment tied to cognitive impairment and what disorders are the most connected?

Dr. Varshini Varadaraj, MD, MPHA, and her team at Wilmer Eye Institute at Johns Hopkins Medicine in Baltimore, Maryland (USA) set out to answer that question after they read studies correlating the two types of disorders and found a gap connecting specific visual impairments to specific cognitive impairments.

Visual Decline = Cognitive Decline?

Researching the Link Between Vision Impairment and Cognitive Decline

In their paper Association of Vision Impairment with Cognitive Decline Across Multiple Domains

in Older Adults,* the team decided to look at the oddly-specific number of 1234 community-dwelling Baltimore residents, aged 60 and up. They found that 32 volunteers were unable to pass tests screening those with prior onset of dementia or cognitive impairment and removed them from the study, leaving 1202 patients with a mean age of 71.1 years young. 

The specific domains tested were visual acuity, contrast sensitivity and visual fields for visual impairment; and language, memory, attention, executive function and visuospatial ability for cognitive function. 

While they found definite differences for each of these visual variables in association with cognitive decline, contrast sensitivity was the most correlated across each domain. This is notable because it is generally tested much less frequently than visual acuity. While there was little research in that domain, The Epidemiology of Hearing Loss Study showed the same correlation over a period of 10 years of follow-up. If there is one take-away from this, it’s that contrast sensitivity needs more research about its connection to cognition. 

Blazing New Pathways

What prior research exists has relied on general cognitive performance tests such as the Mini-Mental State Examination (MMSE). So as mentioned, there is very little research testing if vision impairment is associated with general decline or specific domains. However, this study found particular connections with language and memory. This was bolstered by a small amount of prior research and well-documented evidence associating age-related macular degeneration with drops in testing scores on memory and verbal fluency. 

There have been several proposals to explain these associations, such as a shared neuropathological cause like microvascular disease. This study was careful to rule out other causes of vascular disease such as diabetes, hypertension and smoking.

Another connection are vision limiting activities that actively stimulate the brain, such as reading and physical activity. As you age, you need to exercise both your brain and body — and this is much more difficult when you can’t read your Wordle or see a racket ball. 

A significant issue with prior research was ruled out for this study. Most cognitive tests are vision dependent. Therefore, more work needs to be done utilizing vision independent testing, such as verbal fluency, category fluency and Rey Auditory Verbal Learning tests.

Limited Vision

The paper notes several interesting limitations to its own methodology. A Digit Symbol Substitution Test (DSST) was ruled out because it was not used prior to 2005, two years after the study began. Similarly, testing of acuity and contrast sensitivity changed in 2015, which forced the researchers to harmonize data under various protocols. While compensating for the 2015 change in testing, analysis concluded that pre-2015 testing yielded data with larger declines in mental capability, but the results stayed consistent.

Survivor bias was another unfortunate issue, since many patients with only the baseline visit were more likely to be older and less healthy. Reverse causation was also a factor, because patients with cognitive problems are also less likely to do well on visual tests. This study was also made up of a group of older, white, and well-educated patients and future research should incorporate more diverse groups. 

Don’t forget to … what was I saying?

This study found that older, visually declining adults without dementia are more likely to have cognitive decline. Its central point, however, is that cognitive decline differs based on the type of vision that is measured. In particular, a link was found between contrast sensitivity and broad cognitive decline across categories. 

More research is suggested about this connection. In the meantime, remember to take your supplements and try new things. Maybe get into yoga or pick up a guitar and start your own punk-rock band. As long as you’re healthy, challenging your brain, and keeping active, you’re doing the best you can. But remember that in order to have a new perspective you need to be able to have perspective in the first place.

*Varadaraj V, Munoz B, Deal JA. Association of Vision Impairment With Cognitive Decline Across Multiple Domains in Older Adults. JAMA Netw Open. 2021; 4(7): e2117416.

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