There is one in three people. Why are there more and more Chinese people with myopia?

Abstract: myopia is certainly not as terrible as cancer or heart disease, but the large-scale prevalence of myopia brings more than the inconvenience of wearing glasses. In particular, high myopia may not be a big deal when young, but it is easy to induce cataract and glaucoma after middle age.

China is already a big country that can’t see clearly, and the number of myopia is the first in the world. Genetics alone cannot explain such a wide range of myopia, and books and television may only be scapegoats for myopia.

when you see this article, you might as well look around you and observe your colleagues, your classmates and strangers around you. You will find that most people wear glasses, and you don’t have to ask. Most of them are myopic.

myopia, as an epidemic, has only appeared on a large scale in China in recent decades. In 2014, the economist reported that in the 1970s, less than one-third of Chinese teenagers aged 16-18 were myopia. But today, nearly four fifths of teenagers suffer from myopia.

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the national visual health report released by Peking University in 2016 also shows that China’s myopic population over the age of 5 has reached 450 million and will exceed 700 million in 2020. China has become a truly invisible country.

▌ parents decide your eyesight?

we have to answer a question first, what is myopia. In short, your eyes contract or relax the muscles that control the lens in order to see a nearby or distant object, so that the shape of the object can be projected onto the retina. Myopia is due to the lengthening of the eyeball. After the light comes in, it does not focus on the retina, but on a little bit in front.

myopia is certainly not as terrible as cancer or heart disease, but the large-scale prevalence of myopia brings more than the inconvenience of wearing glasses. In particular, high myopia may not be a big deal when young, but it is easy to induce cataract and glaucoma after middle age.

if the parents are myopic, the child is indeed more likely to be myopic. In 2012, a joint study by Sun Yat sen University and Australian National University showed that among 15-year-old teenagers in Guangzhou, China, if a pair of parents are myopic, the child’s myopia rate will be as high as 83.3%; If one of the parents has myopia, the myopia rate of the child is a little worse, 88.9%; If parents have good eyesight, the child’s myopia rate will drop to 68.2%.

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Heredity do play a role, but it is impossible to set off this wave of myopia by genetic alone. Contemporary myopia is not only a genetic problem, but also a social problem.

▌ we may have wrongly blamed books and television

in order to catch the culprit of large-scale damage to vision, scientists tried to blame myopia on “nearwork”. After all, compared with European and American students, Chinese students have to spend more time on books.

according to a 2014 OECD report, 15-year-old students in Shanghai spend 14 hours a week doing their homework, while American students spend only 6 hours a week, and British students spend less, only 5 hours.

the myopia rate of Chinese students is rising, accompanied by the infinite extension of their learning time. In addition to learning to read endlessly, watching TV, playing with mobile phones and playing with computers have also become the object of parents’ blame. However, no matter how hard scientists try to associate “close work” with myopia, the causal relationship between them is not so strong.

in 2006, the National University of Singapore conducted a three-year study on a group of 7-9-year-old Singaporean students. It was found that reading a few books a week could not be used to predict whether children would become myopia in the next few years.

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then the researchers analyzed the length of time spent reading and playing computer every day, and found that myopic students may just prefer reading, rather than reading leads to myopia.

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constantly have new evidence challenging the traditional cognition of “myopia caused by seeing too close”. In 2015, Ohio State University also released a study that overturned the tradition. The 20-year study of 4512 American children shows that reading, watching TV or playing computer for a long time and sitting too close are not the direct causes of myopia.

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although the research is aimed at American children, the research spans white, black, Aboriginal, Latino and Asian children in the United States. The reasons are similar.

▌ Chinese children are too short of outdoor sunshine.

close reading, watching TV or playing games should not be the pot for myopia. Who will carry the pot? Scientists have not yet fully understood the real cause of myopia, but they are reaching a consensus that the less outdoor exercise, the more likely they are to get myopia.

children who often participate in outdoor activities receive more light intensity. Light can stimulate the release of dopamine in the retina. This neurotransmitter can protect the eyeball from becoming too long, so as to prevent myopia. On sunny days, the outdoor light intensity may range from 20000 to 100000 lux (lighting units), while the indoor light intensity may be less than 500 lux. China’s Ministry of education requires that the average illumination on the desk of primary and secondary school classrooms should not be less than 300 lux.

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some scientists have experimented with chickens, sloths and monkeys, and the results have supported the above hypothesis. However, some scientists have criticized The “light dopamine” mechanism is too simple and rough. Outdoor exercise can reduce myopia for a variety of complex reasons. Andy Fischer of Ohio State University pointed out that the outdoor vision is better, and the eyes can be in a relatively relaxed state, which may block the poor growth of the eyes.

anyway, even if the underlying mechanism is not clear for the time being, it has gradually become a consensus that outdoor sports can help protect eyesight. In 2012, a study conducted in southern Taiwan showed that all school students aged 7-11 were driven outdoors in only 80 minutes after class. A year later, the myopia rate of this group of students was higher than that of the students next door