Myopia is a common form of visual impairment. In the United States, more than 40 percent of people aged 12–54 have the condition.
Uncorrected myopia is "the leading cause of distance vision impairment" worldwide.
Studies have estimated that by 2050, 5 billion people will have myopia and a further 1 billion will have developed high myopia, which is a condition that increases the risk of retinal detachment, cataract, and glaucoma.
Previous studies have documented a link between education levels and short-sightedness, but the causality between the two has remained unclear.
So, scientists at the University of Bristol and Cardiff University, both in the United Kingdom, set out to explore whether education directly raises the risk of myopia, or whether having myopia leads to more years spent in school.
Edward Mountjoy, of the Bristol Medical School at the University of Bristol, is the lead author of the new paper, which was published in The BMJ.
Each additional year of education raises risk
Mountjoy and team examined the genetic data from a total of 67,798 men and women between 40 and 69 years old who were registered in the UK Biobank database.
More specifically, the researchers looked at 44 gene variations that have been previously linked with short-sightedness, as well as 69 genetic variations linked to the number of years spent in education.
The scientists used Mendelian randomization to analyze this information in an effort to escape the common errors that often prey upon observational studies, such as confounding factors.
Applying Mendelian randomization makes a causal link more plausible, explain the researchers.
The study revealed that each year of education was linked with more short-sightedness. More specifically, each year of education contributed to a yearly refractive error of -0.27 dioptres.
"Thus," explain the authors, using the U.K. educational system as a reference, "the cumulative effect of more years in education on refractive error means that someone attending university would be likely to have at least -1 dioptre more myopia than someone who left school at age 16."
"A difference of this magnitude would [...] affect the ability to drive without glasses," they go on.
On the other hand, Mountjoy and team did not find enough evidence to support the opposite relationship — that is, that short-sightedness makes people pursue education for longer. The authors conclude:
"This study shows that exposure to more years in education contributes to the rising prevalence of myopia, and highlights a need for further research and discussion about how educational practices might be improved to achieve better outcomes without adversely affecting vision."
In an accompanying editorial, Prof. Ian Morgan — at the Australian National University in Canberra — and his colleagues weigh in on the findings. They write that "environmental and social factors [may] have major effects on myopia."
"Early onset allows more time for myopia to progress to high and potentially pathological myopia," the authors continue, "and this is probably the major concern with the myopia epidemic."
Educational systems "must change to help protect the visual health of future generations," warn Prof. Morgan and colleagues, who also cite studies showing that more time spent outdoors prevents or slows down the progression of myopia.