Studying too much can make you short-sighted

More time spent in education, according to a study, is a risk factor for myopia.

Photograph: Ahmad Masood/Reuters

According to a study conducted at University of Bristol and Cardiff University, spending more years in full-time education is associated with a greater risk of developing short-sightedness (myopia).

The researchers said their study provides 'strong evidence' that more time spent in education is a risk factor for myopia, and that the findings 'have important implications for educational practices.'

Myopia, or short-sightedness, is a leading cause of visual impairment worldwide. Currently, 30 to 50 per cent of adults in the United States and Europe are myopic, with levels of 80 to 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.

So researchers based at the University of Bristol and Cardiff University set out to determine whether education is a direct (causal) risk factor for myopia, or myopia is a causal risk factor for more years in education.

Using a technique called Mendelian randomisation, 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.

Analysing genetic information in this way avoids some of the problems that afflict traditional observational studies, making the results less prone to unmeasured (confounding) factors, and therefore more likely to be reliable.

An association that is observed using Mendelian randomisation therefore strengthens the inference of a causal relationship.

After taking account of potentially influential factors, Mendelian randomisation analyses suggested that every additional year of education was associated with more myopia (a refractive error of 0.27 dioptres a year).

To put this into context, a university graduate from the UK with 17 years of education would, on average, be at least 1 dioptre more myopic than someone who left school at 16 (with 12 years of education). This level of myopia would mean needing glasses for driving.

By contrast, there was little evidence to suggest that myopia led people to remain in education for longer.

The study appears in the journal The BMJ.