Environmental factors drive myopia epidemic in study of Chinese twins and parents

A new epidemiology study published in The British Journal of Ophthalmology reported that the prevalence rates and severity of myopia have seen major increases between generations because of increased axial elongation in the children. The investigators, led by first author Xin Chen, MD, noted that these increases are associated with increased educational pressures and decreased time spent outdoors.¹

Chen is from the State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangdong Provincial Key Laboratory of Ophthalmology and Visual Science, Guangdong Provincial Clinical Research Center for Ocular Diseases, Guangzhou, Guangdong, People's Republic of China.

“Myopia was once believed to be tightly genetically determined, based on the high heritability observed in twin studies.^2,3 However, the speed with which the prevalence of myopia has increased, over only one to two generations, is not consistent with a dominant role for genetic determination, since population gene pools rarely change that fast.^4,5 This picture has been established on the basis of a number of different population-based studies, but as yet there has been no study on a sample of parents and their children, where the adult refractions of the children have been determined to more precisely define intergenerational effects,” the investigators commented.

Twin and parental study

Considering this rapid increase in myopia, Chen and colleagues conducted a longitudinal cohort study of twins and their parents with the goal of exploring the intergenerational changes in the myopia epidemic in China.

The study included 686 children who at baseline were aged 7 to 15 years. The participants were followed annually from 2006 to 2018 with cycloplegic refractions and ocular biometry; the parents were followed with noncycloplegic refractions and ocular biometry.

What myopic findings did the investigators uncover?

The major findings were as follows:

“The myopia prevalence in the young adult children was 78.0%, while it was 42.1% in the parents. The prevalence of high myopia (9.6% vs 5.2%) and moderate myopia (38.8% vs 9.9%) was higher in the children, while the percentage of mild hyperopia (9.5% vs 16.3%) and emmetropia (10.6% vs 40.0%) was lower,” Chen and colleagues reported.

The investigators did not see significant differences in extremely high myopia (2.2% vs 1.9%) and severe hyperopia (1.9% vs 1.6%), respectively, in the children and parents.

They also found that the distribution of refraction in the children had a marked plateau at −6.0 diopters (D) to −0.5 D, rather than the tighter peak that they observed around −1.0 D in the parents.

Increased knowledge about myopia

The authors pointed out that within the span of 1 generation in Guangzhou, the prevalence rate of myopia approximately doubled due to increased axial lengths. The children sustained significant increases in the prevalence rates of moderate and high myopia. However, the prevalence rates of severe hyperopic refractions, defined as +2.0 D or greater, and extreme myopic (≤−9.0 D) refractions, defined as –9.0 D or less, did not change. “Children did not appear to significantly inherit their position in the distribution from their parents,” they said.

Chen and associates believe that the changes in social environments and not the genetic background seem to have spurred the myopia epidemic in China. This recognition may cast a positive light, in that the factors that drove the epidemic are reversible.

The authors concluded: “Taken together, the present findings demonstrate a very different distribution of refraction and axial in the parental and offspring generations. Similar changes were detected for refraction and AL, showing that the development of the myopia epidemic is based on axial elongation, rather than changes in other biometric parameters. There is only a modest correlation between percentile position of parental refractions and that of the children, ruling out the possibility that environmental factors shift the population mean but do not affect the distribution. Overall, these results suggest that environmental influences have overwhelmed any genetic influences on refractive development, except for extreme refractions such as very high myopia or high hyperopia, where environmental effects seem to be less significant.”

References:

1. Chen X, Hu Y, Morgan I, He M, Ding X. Intergenerational change in China’s epidemic of myopia: the impact of the social environment. Br J Ophthalmol. 2025;109(10):1093-1098. doi:10.1136/bjo-2025-327401

2. Sorsby A, Fraser GR. Statistical note on the components of ocular refraction in twins. J Med Genet. 1964;1(1):47-49. doi:10.1136/jmg.1.1.47

3. Chen Y, Wang W, Han X, Yan W, He M. What twin studies have taught us about myopia. Asia Pac J Ophthalmol (Phila). 2016;5(6):411-414. doi:10.1097/APO.0000000000000238

4. Morgan IG, French AN, Ashby RS, et al. The epidemics of myopia: aetiology and prevention. Prog Retin Eye Res. 2018;62:134-149. doi:10.1016/j.preteyeres.2017.09.004

5. Morgan I, Rose K. How genetic is school myopia? Prog Retin Eye Res. 2005;24(1):1-38. doi:10.1016/j.preteyeres.2004.06.004