As people age, problems with vision and mental functioning often occur together, and medical researchers have become increasingly interested in understanding the link between the two. Might one cause the other, and if so, might correcting one improve the other?
The vision-memory connection
In a 2016 article published in Current Opinion in Ophthalmology, researchers from the Shiley Eye Institute at the University of California, San Diego, reviewed current clinical studies about using cataract surgery to improve mental functioning in patients with cognitive impairment. They cited several recent studies that found a strong relationship between vision problems and mental functioning issues.
In one of those studies, the researchers found that near-vision problems predicted cognitive decline over a seven-year period.
In another, vision problems left untreated resulted in a nine times greater risk for the development of Alzheimer’s. And even without dementia, untreated vision problems were associated with a five times greater risk of some form of cognitive impairment.
However, when the review authors took it a step further and examined studies focusing on the potential cognitive benefits of cataract surgery, they found the outcomes were mixed: Some studies reported that the surgery significantly improved cognitive test scores, while others found no difference before and after surgery.
The review authors noted that the number of studies supporting the cognitive benefits of cataract surgery was growing. But they concluded that there still was not enough evidence to support the idea that cataract surgery could benefit people with impaired cognitive abilities.
Evidence is mixed
The findings parallel those of an earlier review published in the British Journal of Ophthalmology in 2011. In that article, researchers from the University of Newcastle reported that in six different studies between 2003 and 2008, results were mixed.
Two of the studies supported the idea that cataract surgery improves cognitive performance, and two showed no effect as a result of cataract surgery.
Another study found that patients who underwent surgery showed improvement in their cognitive function, but the control group in the same study showed the same improvement without surgery.
One possible explanation for the improvement in cognitive scores is a learning effect; the same cognitive test was used several times during the follow-up. Results from the sixth study were unreliable due to problems with the study’s design.
The quest continues
Ongoing research is attempting to determine whether cataract surgery has any real effect on improving cognitive status. A clinical study currently under way at Case Western Reserve University in Cleveland is examining what effect cataract surgery might have on the quality of life, vision, and cognition in patients with Alzheimer’s disease.
According to the researchers, preliminary findings suggest that cataract surgery can slow the progression of dementia as well as significantly improve the quality of life for both Alzheimer’s patients and caretakers.
Still, the consensus seems to be that it’s not yet known whether cataract surgery, while beneficial in terms of improving vision for people with cognitive impairment, will actually make a difference in the treatment of cognitive decline.
Researchers do seem to agree on the nature of the questions that still need to be answered before the relationship between visual impairment and cognitive decline can be fully understood:
• Do deficits in vision reduce physical and mental activities and thus contribute to the further decline in cognitive abilities?
• Are there common elements underlying both the visual and cognitive decline that need to be identified and addressed?
• Is there no connection between impaired vision and impaired mental abilities beyond common risk factors such as age?
For an aging population, the issues raised are significant. Surgery is currently the only way to restore vision loss caused by cataracts.
But as one study noted, caution must be exercised when considering a cognitively impaired patient for surgery, especially with regard to patient consent.
Read more about cataract risk factors and what to expect when undergoing cataract surgery.