The more educated a person is, the more myopic they are likely to become, according to researchers at the University of Bristol, UK.
Studies have linked education with myopia for more than a century, but until now, researchers have not been able to shed light on whether one causes the other or if a third factor is responsible.
Prospective trials have shown that time spent outdoors reduces the risk of myopia. Weaker evidence has associated close work with myopia. But researchers have not previously been able to elucidate how education fits into this equation.
For example, they have not been able to rule out the hypotheses that being myopic stimulates people to spend more time studying, or that a factor such as intelligence or higher socioeconomic status could both cause myopia and lead people to spend more time studying.
The best way to establish cause and effect is a randomised, controlled trial. But it would be unethical to assign one group of children to receive more education than another. So the Bristol researchers turned to Mendelian randomisation. In this approach, they used random aspects of the subjects’ genomes as proxies for the kind of randomisation that would have been done in a controlled trial.
They drew their data from a large population cohort, known as the UK Biobank, examining cross sectional data from the UK Biobank collected between 2006 and 2010. UK Biobank recruited 502,664 participants aged 40 to 69 years through 22 assessment centres across the UK.
To determine the genotype of participants, one of two platforms was used: the BiLEVE Axiom array (Affymetrix) or the Biobank Axiom array (Affymetrix). The participants completed sociodemographic questionnaires, including questions on past educational and professional qualifications. About 23% of participants also completed an ophthalmic assessment.
For every additional year spent in education, the researchers found an increase in myopic refractive error of 0.27 D. This suggests that a UK university graduate with 17 years in education would, on average, be one dioptre more myopic than an individual who left school at 16 with 12 years of education. This difference in myopia severity is enough to blur vision for driving below legal standards.
“Our study provides strong evidence that length of time spent in education is a causal risk factor for myopia,” said Dr Atan. “Axial eye growth happens mainly during school years and since levels of myopia tend to even out in adulthood, any interventions to stop or prevent myopia need to be given in childhood.”
He added: “Policymakers should be aware that the educational practices used to teach children, and to promote personal and economic health, may have the unintended consequence of causing increasing levels of myopia and later visual disability as a result.”
The study could not determine exactly how education impacts eyesight, but previous studies provide some hypotheses. Children from developed East and Southeast Asian countries regularly say that they spend less time outdoors than children from Australia or the United States, where the prevalence of myopia is lower.
Other research has associated higher light exposure with lower myopia risk, and it is possible that individuals who spend more time in education have less exposure to natural light. The progression of myopia is faster in winter months, which supports this theory. It has led some schools in Southeast Asia to invest in “Bright Light” classrooms, but it is too early to know whether this intervention is effective.
Time spent outdoors appears to be independent of near work activities, since measures of the two do not usually correlate. Children with myopia are less likely to engage in physical activity, such as sports, but physical activity does not seem to protect against myopia.
The researchers concluded that the best recommendation for preventing myopia is to spend more time outdoors.
“With the rapid rise in the global prevalence of myopia and its vision-threatening complications, together with the economic burden of visual loss, the findings of this study have important implications for educational practices,” said Dr Denize Atan, consultant senior lecturer in ophthalmology at Bristol Medical School, in a press release.
Myopia is one of the leading causes of visual disability in the world. The global prevalence is rising rapidly and has reached epidemic levels in the developed countries of East and Southeast Asia.