Myopia, or short-sight, 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. Now a new study, led by the University of Bristol, has shed some light on why the length of time spent in education is a causal risk factor for myopia.
For more than a century, observational studies have reported links between education and myopia, but whether time spent in education causes myopia, children with myopia are more studious, or socioeconomic position and a higher level of education leads to myopia has not been known with any certainty.
To find out whether more time spent in education is a causal risk factor for myopia, the research team from the Bristol Medical School used Mendelian randomisation (MR) applied to a large, population cohort, known as the UK Biobank. The research showed that for every additional year spent in education, there was an increase in myopic refractive error of ‑0.27 dioptres/year. 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.
Dr Denize Atan, Consultant Senior Lecturer in Ophthalmology at the Bristol Medical School: Translational Health Sciences and Honorary Consultant in Neuro-ophthalmology at the Bristol Eye Hospital, who co-led the research with Professor Jez Guggenheim from Cardiff University School of Optometry & Vision Sciences, said: “Our study provides strong evidence that length of time spent in education is a causal risk factor for myopia. 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.
“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. 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.”
Exactly how increasing levels of education cause myopia cannot be known from MR analyses, although there are possible clues from recognised environmental risk factors. Children from developed East and Southeast Asian countries regularly say that they spend less time outdoors than children from Australia or the US and randomised controlled trials have shown that more time spent outdoors during childhood protects against the development of myopia.
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. Near work activities, such as reading, have been associated with myopia, although not as consistently as lack of time spent outdoors. Children with myopia are also less likely to do physical activity, such as sports, but it is not thought that physical activity protects against myopia. The progression of myopia is faster in winter months, which supports the theory that exposure to natural light is important. This theory has been one of the main drivers for recent investment in “Bright Light” classrooms to protect against myopia in Southeast Asia.
The research team suggest that less time spent outdoors is a possible link between education and myopia, and they recommend children spend more time outside. It is not known whether “Bright Light” classrooms provide protection against myopia and replicate the effects of increasing time spent outdoors and the research team suggest that future studies could look at whether this intervention works against myopia.
‘Education and myopia: assessing the direction of causality by mendelian randomisation’ by Ed Mountjoy et al in BMJ
For a primer on Mendelian randomisation, see: https://www.youtube.com/watch?v=LoTgfGotaQ4