Spending more years in full time education increases the risk of developing short-sightedness or myopia - a leading cause of visual impairment worldwide, a study has found.
The findings, published in The BMJ journal, have important implications for educational practices, researchers said.
Myopia, or short-sightedness, is a leading cause of visual impairment worldwide. Currently, 30-50 per cent of adults in the US and Europe are myopic, with levels of 80-90 per cent reported in school leavers in some East Asian countries.
Based on existing trends, the number of people affected by myopia worldwide is expected to increase from 1.4 billion to 5 billion by 2050, affecting about half of the world's population. Almost 10 per cent of these people - around 9 million - will have high myopia, which carries a greater risk of blindness.
Many studies have reported strong links between education and myopia, but it is not clear whether increasing exposure to education causes myopia, myopic children are more studious, or socioeconomic position leads to myopia and higher levels of education.
Researchers based at the University of Bristol and Cardiff University in the UK set out to determine whether education is a direct risk factor for myopia, or myopia is a causal risk factor for more years in education.
They analysed 44 genetic variants associated with myopia and 69 genetic variants associated with years of schooling for 67,798 men and women aged 40 to 69 years from the UK Biobank database.
Analyses suggested that every additional year of education was associated with more myopia.
To put this into context, a university graduate from the UK with 17 years of education would, on average, be more myopic than someone who left school at 16 (with 12 years of education).
By contrast, there was little evidence to suggest that myopia led people to remain in education for longer.
"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," researchers said.