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Spending more time studying may increase levels of myopia, future visual disability

02 Jul 2018

More years spent in education contributes to the rising prevalence of myopia, a recent study has found.

“Increasing the length of time spent in education may inadvertently increase the prevalence of myopia and potential future visual disability,” researchers said.

Every additional year of education correlated with a more myopic refractive error of –0.18 dioptres/year (95 percent CI, –0.19 to –0.17; p<2e-16), as suggested by conventional regression analyses of the observational data. The true causal effect was even more robust in Mendelian randomization analyses (–0.27 dioptres/year; –0.37 to –0.17; p=4e-8). [BMJ 2018;361:k2022]

Little evidence suggested, however, that myopia affected education (years in education per dioptre of refractive error, –0.008 dioptre/year; –0.041 to 0.025; p=0.6).

“Thus, the cumulative effect of more years in education on refractive error means that a university graduate from the United Kingdom with 17 years of education would, on average, be at least −1 dioptre more myopic than someone who left school at age 16 (with 12 years of education),” researchers said. “Myopia of this magnitude would be sufficient to necessitate the use of glasses for driving.”

In secondary analyses, there was minimal evidence for genetic confounding which could have biased the causal effect estimates.

Myopic individuals possess better near vision vs distance vision and require less accommodative effort for near work and study. Consequently, myopia is perceived to be an educational advantage. [Am J Optom Arch Am Acad Optom 1959;36:12-21]

Although people with myopia are generally seen as more studious than those without myopia, little evidence supports that being myopic leads to people remaining in education for longer, according to researchers.

In developed East and Southeast Asian countries, the current epidemic of myopia over the past decades appears to be associated with widening exposure to primary and secondary education. Conversely, educational outcomes such as scientific, reading and mathematical literacy are less clearly related to myopia, since many Western countries achieve top international rankings in student assessments without the same high prevalence rates of myopia. [Ophthalmic Physiol Opt 2013;33:329-338]

“Moreover, there are countries with poorly developed education systems in which the prevalence of myopia is low, and hence any causal relation between intelligence and myopia is unlikely,” researchers said. [Ophthalmic Epidemiol 2012;19:16-22; Acta Ophthalmol (Copenh) 1985;63:323-326; Optom Vis Sci 1999;76:282-285; Ophthalmology 2012;119:2021-2027]

Other well-established associations exist between myopia and urbanization, reduced light exposure, socioeconomic position, near work and prenatal factors, according to researchers, adding that many of these either confound the relation between education and myopia or may work together to worsen the effect (eg, in countries with high prevalence of myopia). [JAMA Ophthalmol 2016;135:47-53; Ophthalmic Physiol Opt 2015;35:252-262; Ophthalmology 2011;118:797-804; Prog Retin Eye Res 2018;62:134-149]

“Despite the robust associations between exposure to education and myopia reported by many of these previous studies, they have not shown causality,” they added.

The present study obtained available genetic data from two consortiums applied to a large, independent population cohort. Genetic variants used as proxies for myopia and education years were derived from two large genome-wide association studies (23andME and Social Science Genetic Association Consortium [SSGAC], respectively).

In total, 67,798 participants in the UK with available information for years of completed education and refractive error were analysed. Researchers performed Mendelian randomization analyses in two directions: the first exposure was the genetic predisposition to myopia, measured with 44 genetic variants strongly associated with myopia in 23andMe; and the second was the genetic predisposition to higher levels of education, measured with 69 genetic variants from SSGAC.

“This study provides strong evidence that more time spent in education is a causal risk factor for myopia,” researchers said. “Policy makers should be aware that the educational practices used to educate children and to promote personal and economic health may have the unintended consequence of causing increasing levels of myopia and later visual disability.”

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