Researchers referenced in their paper that previous studies estimated that visual impairment is present in about 32.5% of dementia patients. Photo: Joseph Sowka, OD. Click image to enlarge.

Globally, cataracts are the leading cause of preventable blindness, especially among older individuals. Previous research has discovered that cataracts, or visual impairments in general, are associated with the cognitive decline in the elderly. Since cataracts can easily be managed with surgical treatment, researchers in Singapore conducted a study to find out if there were any potential cognitive benefits to cataract surgery.

In their systematic review and meta-analysis, researchers included 24 studies comprising 558,276 participants.¹ They included studies with populations of patients diagnosed with cataracts who had undergone some form of surgery as well as some comparing patients with uncorrected cataracts to control subjects without cataracts. Additionally, they included single-arm studies without a control group if the study featured results comparing cognitive outcomes before and after cataract surgery. The mean age for the participants in this study was 66.4 years old.

The researchers pooled their data and results into various groups and subgroups. From a group of 246,640 participants, they discovered there was a 25% lower risk of long-term cognitive impairment and dementia in patients who had undergone cataract surgery compared to those with uncorrected cataracts. Interestingly, in a pool of 308,795 participants, healthy controls without cataracts had a risk of long-term cognitive decline similar to the patients with surgical treatment. In a much smaller pool of 662 patients, researchers noted a statistically significant 4% improvement in short-term cognitive test scores, which assessed general cognitive function among participants with normal cognition.

“Two further observations may be inferred from our findings,” mentioned the researchers in their study, published recently in Ophthalmology. “Firstly, participants who underwent cataract surgery had comparable hazards for cognitive impairment and dementia as healthy controls without cataracts, possibly suggesting that cataract surgery may negate the excess risk of cognitive impairment and dementia imposed by cataracts. Secondly, for patients with pre-existing cognitive impairment, cataract surgery was not associated with subsequent improvement in short-term cognitive test scores.”

There were two studies the researchers reviewed that disagreed with their meta-analysis findings. One concluded that cataract surgery did not strongly correlate with better cognitive test scores in health adults.² Another observed patients in a nursing home who had undergone cataract surgery, but these patients showed no improvement in cognitive function.³

Although there are limitations to their study, the researchers bolstered the possibility of vision impairment from cataracts as being a modifiable risk factor for cognitive decline. “Physicians should be aware of the cognitive sequelae of cataract-associated vision impairment, and the short-term and long-term cognitive benefits of cataract surgery,” they concluded in their study.