Beijing, China - One in three children around the world is short-sighted and the number is growing rapidly, according to new research that suggests the increase is associated with youngsters spending more time indoors gazing at screens.

Short-sightedness, or myopia, is a "pervasive global public health concern, particularly among the younger population," says the research team.

Some 40% of children worldwide aged five and up will be short-sighted by 2050, says the researchers based in China.

Myopia usually begins in childhood, with distant objects appearing blurry.

Although it may have a genetic factor, medics now say behavioral changes such as spending time indoors and a lot of screen time are mainly responsible for the sharp increase seen in recent years.

Myopia has already become significantly more prevalent between 1990 and 2023. While the number of affected children and adolescents was largely stagnant between 1990 and 2010 at 24% to 25%, the increase has since accelerated.

Most affected are people in East Asia or in urban areas, girls, adolescents and high school students, says the study based on data from more than 5.4 million children and adolescents aged between 5 and 19, of whom more than 1.9 million were short-sighted.

Girls are affected slightly more often than boys, which is partly because girls tend to spend less time outdoors and more time doing activities that focus on close-range objects, researchers say.

Longer periods of schooling and living in a city also increase the likelihood of myopia, say the researchers.

Myopia could become a global health burden in the future, as it is likely to increase more in low- and middle-income countries than in high-income countries, the study says.

Right now, the phenomenon is most widespread in Japan and South Korea, affecting almost 86% and 74%, respectively, from 1990 to 2023, followed by Russia, Singapore, and China.

Myopathy is less common in African countries such as Uganda and Burkina Faso, affecting just 1.3% in each. It also affects fewer than 1% of children and young people in Paraguay, the study notes.

But by 2050, the number of myopic youngsters may pass 740 million, says the Chinese research team based on their review of studies from 50 countries worldwide.

By then, the condition will be most prevalent in Asia, at 69% – which may be partly because children there start school earlier, researchers say.

The team, led by Yajun Chen of Yat-sen University in Guangzhou, China, evaluated studies and reports from 50 countries worldwide and published their findings in the British Journal of Ophthalmology.