Nerds wear glasses — or that's what society taught us to believe growing up. In TV shows and movies, the clever characters almost always have bad eyesight. You can probably think of a few kids in your school classes who followed the trend, too.
There are a few theories for where the association came from, some of which are discussed in a thread on Quora. One is that if you have bad eyesight, you're more likely to sit at the front and easily ignore the people behind you, leading to better learning.
Another is that having an accessory on your face immediately makes you look different and thus an outsider — and kids aren't always nice to those. So perhaps in lieu of popularity, kids with glasses turn to books and academia. Additionally, as pointed out by an article in Inverse, people who can't see well aren't likely to be as involved in sports, which can be isolating at school.
According to a new study, published in the journal Nature Communications, the association may run deeper at the genetic level. The research found an association with myopia — the scientific word for shortsightedness — and greater cognitive function.
Bad eyesight being linked to intelligence is a good headline, so it has been picked up on in the news, but the study actually looked at many genetic characteristics that were related to having better cognitive function.
The researchers, led by Gail Davies from the University of Edinburgh, analysed data from over 300,000 people aged between 16 and 102 who had taken part in previous studies in Europe, North America and Australia.
"This study, the largest genetic study of cognitive function, has identified many genetic differences that contribute to the heritability of thinking skills," she said. "The discovery of shared genetic effects on health outcomes and brain structure provides a foundation for exploring the mechanisms by which these differences influence thinking skills throughout a lifetime."
Overall, there were 148 regions of DNA that were associated with having better cognitive function, 58 of which have never been reported before. And one of the specifics was how subjects with high cognitive ability were about 30% more likely to have genes associated with bad eyesight than others, according to the results.
As well as supposedly higher intelligence, the genetic factors associated with higher cognitive function also seemed to be linked to better cardiovascular heath, decreased risk of lung cancer, better mental health, and living longer.
The study didn't investigate the causation for the findings. According to another lead researcher, Ian Deary, more research is needed to see the bigger picture, but the findings could help with understanding brain diseases like Alzheimer's.
"We also need to study our results closely to see what they can tell us about the possibility of understanding the declines in cognitive function that happen with illness and in older age," he said.
This study wasn't the first to find the association between poor eyesight and cognitive function, as myopia has been consistently associated with intelligence. For example one paper, published in the Lancet in 1988, found that out of 5,943 poor sighted and 9,891 regular sighted 18-year-old men, those with myopia had significantly higher test scores and educational levels.
The exact reasons are not known, and it's worth mentioning that intelligence is highly subjective and almost impossible to measure. Also, there are so many factors, both genetic and environmental, that contribute to how someone's brain turns out.
What is clear, though, is that the association doesn't seem to be going away any time soon. There is evidence that wearing glasses whether you need to or not makes people think you're more intelligent anyway, which is why defence lawyers recommend clients wear them during a trial.
In other words, whether it's based on genetic truth or not, glasses are an easy prop to convey intelligence. And if used in real life, or on screen, the majority of your audience will understand what you're getting at.