Could climate affect our eyes? Canadian study finds higher temperatures linked with vision impairment

As climate change continues to warm the planet, there may be yet another consequence heading our way: according to a new study, higher temperatures are associated with a higher likelihood of vision impairment.

Canadian researchers found that American adults 65 years and older were far more likely to have serious vision impairment if they lives in warmer regions compared to their peers who lived in cooler ones.

It’s the first large-scale study to look at the association between higher temperatures and issues with vision, authors say.

They looked at the average temperatures in U.S. counties, and found that the chance of having severe vision issues was 44 per cent higher for those living in counties where the average temperature was higher than 15.5 C, compared to those living in the coolest counties.

“This link between vision impairment and average county temperature is very worrying if future research determines that the association is causal,” Esme Fuller-Thomson, director of University of Toronto’s Institute of Life Course and Aging and first author of the study, said in a press release. “With climate change, we are expecting a rise in global temperatures. It will be important to monitor if the prevalence of vision impairment among older adults increases in the future.”

The study, which was published last month in the peer-reviewed journal Ophthalmic Epidemiology, drew from a data pool of more than 1.7 million Americans.

The association between temperature and vision impairment persisted even when researchers factored in age, sex, income and the education of participants.

“It was powerful to see that the link between vision impairment and temperature was consistent across so many demographic factors including income,” Elysia Fuller-Thomson, a graduate student at the University of Toronto and one of the study’s co-authors, said in the release.

In order to track vision impairment and cross-reference it with temperature, researchers looked at the American Community Survey, looking at data collected between 2012 and 2017 through mail, telephone and in-person interviews. The survey, which focused on adults aged 65 and older who were living in the same state they were born in, included a question pertaining to serious vision impairment, allowing participants to indicate if they were blind or struggled to see even with glasses.

Researchers then took temperature data from the National Oceanic and Atmospheric Administration to create averages for the counties included, and compared this data to the vision data.

Counties with an average temperature of less than 10 C were the coolest counties in the dataset. Researchers found that compared to those in the coolest regions, the risk of severe vision impairment was 14 per cent higher for those living in countries where the average temperature was between 10 and 12.7 C, and 24 per cent higher for those in counties between 12.7 and 15.4 C.

Although the link existed across all demographics, there were populations for whom the association was even stronger. Higher temperatures seemed to correlate more with the chance of severe vision loss among men, individuals aged 65-79 compared to those who were 80 years or older, and white Americans compared to Black Americans.

Co-author ZhiDi Deng, a recent pharmacy graduate from the University of Toronto, pointed out that vision loss and impairment can have huge impacts on the lives of those who have to struggle with it.

“We know that vision problems are a major cause of disabilities and functional limitations,” Deng said in the release. “Serious vision impairment, for example, can increase the risk of falls, fractures, and negatively impact older adults’ quality of life. Taking care of vision impairments and their consequences also cost the U.S. economy tens of billions each year. So, this link between temperature and vision impairment was quite concerning.”

Although the research appears to show a strong association, just how the temperature actually works to affect our vision is still unknown.

Researchers theorize that the cause could be due to increased ultraviolet light exposure, air pollution, or folic cid degradation that comes with higher temperatures.

However, as this study was designed only to look at whether there was an association at all, more research needs to be done to unravel the mechanisms through which skyrocketing heat affects our eyeballs — especially considering average temperatures across the planet continue to rise.

Authors noted in their conclusion that “the predicted rise in global temperatures could impact older Americans affected by severe vision impairment and the associated health and economic burden.”

Fuller-Thomson said they were “very surprised” by the strong association they found.

“But this novel finding introduces more questions than it answers, including what the connection between average county temperature and vision impairment is.”

She added that the next step for this specific team is going to be investigating whether heat is associated with any “other disabilities among older adults such as hearing problems and limitations in daily activities.”