Limited outdoor activity and extended periods of near-work are considered go-to contributors for myopia, but a new study in the British Journal of Ophthalmology suggests other environmental factors may increase the risk of children developing the condition, including dim light exposure, increased study demands, the use of LED lamps for homework, low sleeping hours, reading distances less than 25cm and living in an urban environment.

A team of researchers from Japan, Singapore and Poland reviewed 80 recent studies from 2013 to 2019 on the epidemiology and risk factors for myopia worldwide in school children between the ages of six and 19.

The review found myopia prevalence was higher in Asia (60%) compared with Europe (40%) based on cycloplegic refraction exams. On the other hand, studies that used non-cycloplegic measurements showed exceptionally high myopia prevalence rates in school children in East Asia (73%) and high rates in North America (42%). African and South American children were found to have a lower myopia prevalence of under 10%.

In several countries, the prevalence of myopia has increased in the last few years, the researchers noted. In a study from the Haidian District in Beijing, China, the prevalence of myopia in a cohort of 15-year-old schoolchildren increased from 55.95% in 2005 to 65.48% in 2015. In Fenghua City in eastern China, the prevalence of myopia in high school students increased from 79.5% in 2001 to 87.7% in 2015, and high myopia (greater than -6.0D) was a major contributor to this shift. Additionally, the Waterloo Eye Study showed a long-term increase of myopia in the United States. The prevalence rate reached 42.4% in 10- to 15-year-old children, and 53.9% in 15- to 20-year-olds.

In some migrant groups, and especially in those of East Asian origin, children were significantly more myopic than those of European origin, presumably because of more intensive education, the study reported. Additionally, children of East Asian ethnicity spent less time outdoors and more time in near work activities compared with European Caucasian children of all school ages, the researchers noted.

As the myopia prevalence rates in non-cycloplegic studies appeared to be overestimated, the investigators recommended considering only cycloplegic measurements when predicting worldwide myopia rates. 

Grzybowski A, Kanclerz P, Tsubota K, et al. A review on the epidemiology of myopia in school children worldwide. BMC Ophthalmol. January 14, 2020. [Epub ahead of print].