Children are born with "hyperopia", and their "hyperopia reserve" should be cherished in this way

Long before children develop myopia, their "hyperopia reserve" is quietly consumed. How does the hyperopia reserve protect children's eyesight? How to prevent the hyperopia reserve from being overdrawn in advance?

Written by reporters Lai Tianying and Li Yunfeng

Editor/Ding Lin New Media Editor/Chen Xuanzhi

Interview experts:

Feng Jing (Deputy Chief Physician, Department of Ophthalmology, Beijing Chaoyang Hospital, Capital Medical University)

Song Hongxin (Executive Deputy Director of the Ophthalmology and Optometry Center, Beijing Tongren Hospital)

Zou Liuhe (Chief Physician of Ophthalmology, Beijing Tongren Hospital)

Xu Li (member of the expert group of China Campus Action Eye Protection Bright Eyes Project)

In recent years, myopia among Chinese youth has become more common, younger, and more severe. According to data from the National Health Commission, the overall myopia rate among Chinese children and adolescents was 53.6% in 2018. Myopia is also the most common eye disease among adolescents worldwide. According to the World Vision Report released by the World Health Organization, there are 2.6 billion people with myopia worldwide, of which 312 million are children under the age of 19. The incidence of myopia is higher in East Asia.

When many parents take their children for eye examinations, the doctor tells them that "the child's hyperopia reserve is relatively low and will become myopic if not paid attention to." What is hyperopia reserve? Does a high hyperopia reserve mean that there will be no myopia?

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What is "hyperopia reserve"?

Most of human perception and cognition of the world is acquired through the eyes. Vision is formed in the following way: light is refracted by the eye's refractive system (cornea, lens, etc.) and reaches the retina, and then converted into electrical signals by the retinal photoreceptor cells. These signals are then transmitted through nerves to the visual center of the brain for imaging.

"The human eye is like a zoom camera," explained Feng Jing, deputy chief physician of the Department of Ophthalmology at Beijing Chaoyang Hospital affiliated to Capital Medical University. From birth to the age of 3, the front-to-back axis of the eyeball is relatively short, so the focus of the image will fall behind the camera film (retina), similar to the situation of farsightedness. However, the refractive power of the child's lens is very strong, and the image can be adjusted by the muscles of the eye to fall on the retina.

As children grow older, their eye axis lengthens and they gradually develop into emmetropia. These hyperopia "reserve" is also gradually consumed. The eyeball grows fastest in the first year after birth, and the growth rate slows down when they reach 3 years old. At 10 years old, the eyeball size is basically fixed, and physiological hyperopia basically disappears. This process is called "emmetropization". Generally speaking, the growth rate of children's eyes is different at different times, and the growth rate of the back of the eyeball is faster than that of the front.

"Generally, children aged 3-4 years old have physiological hyperopia of about 200-300 degrees, which can be used as a 'reserve' for consumption, protecting them from developing myopia so quickly." Feng Jing said. In other words, it is a normal physiological phenomenon for children to have a mild "hyperopia reserve".

△Hyperopia and emmetropia (picture from the Internet)

Xu Li, a member of the expert group of the China Campus Action Eye Protection and Bright Eyes Project, said that under normal eye use, there is a rough standard for hyperopia reserve in each age group: generally 200 degrees at the age of 6, 150 degrees at the age of 7, 50 degrees at the age of 9, and basically disappear at the age of 10.

However, it should be noted that not all children have the same hyperopia reserve value. The value of hyperopia reserve is related to the length of the eye axis and the corneal curvature. If both parents are highly myopic, the child's hyperopia reserve will be relatively low.

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Hyperopia reserve is the "predictor" of myopia

There are many reasons for myopia in adolescents, which can be divided into two aspects: congenital heredity and acquired environment. Among them, genetic factors play an extremely important role in the formation of high myopia (referring to a refractive error of 6.0D or more, accompanied by a high degree of axial elongation). Song Hongxin, executive deputy director of the Ophthalmology and Optometry Center of Beijing Tongren Hospital, said: "If both parents are highly myopic, the possibility of inheriting the disease to their offspring will be 90%; if one parent is highly myopic, the possibility of inheriting the disease to their offspring is 50%, but there are also incomplete manifestations."

For children, a high reserve of hyperopia is actually a natural advantage, just like a child with a tall father or mother will have an advantage in height. If a child's natural reserve of hyperopia is higher than that of his peers, he will develop myopia more slowly than his peers. On the contrary, children with low reserve of hyperopia are more likely to develop myopia.

A large number of studies have found that once the hyperopic reserve is consumed, it is irreversible. If children do not pay attention to their eye habits, the lengthening of the eye axis and the consumption of hyperopic reserve will exceed the normal "emmetropization" process and may cause myopia. It can be said that hyperopic reserve is the "prophet" of myopia. The decline of hyperopic reserve is an early warning sign of myopia.

So will myopia definitely occur if the hyperopia reserve disappears? Not necessarily. Zou Liuhe, chief ophthalmologist at Beijing Tongren Hospital, said: If the hyperopia reserve disappears before the age of 10, it only means that the probability of myopia will increase in the future. Whether or not a child will develop myopia in the future has a lot to do with the child's eye habits. Moreover, the hyperopia reserve is not the only decisive factor in causing myopia. It can only be said that the hyperopia reserve is a signal to remind doctors and parents whether their children are at risk of myopia.

(Map: Qin Tong)

In addition, there is no limit to a child's hyperopia reserve: "the higher the better." If the hyperopia before the age of 3 exceeds 350 degrees, the child's eye adjustment ability is not enough to allow the image to fall on the retina, which can easily cause amblyopia and strabismus problems. "Therefore, excessive hyperopia also requires glasses (hyperopia glasses) to treat it," said Feng Jing.

Therefore, the disappearance of hyperopia reserve does not necessarily mean that you will develop myopia, and the normal hyperopia reserve value does not mean that you can sit back and relax. If you do not pay attention to your eye habits, the hyperopia reserve will decay very quickly, so you still need to pay attention to it.

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Can wearing hyperopia glasses prevent myopia?

Since the probability of myopia increases after the hyperopia reserve is exhausted, can we slow down the attenuation of hyperopia reserve by wearing hyperopia glasses? Zou Liuhe said that in medicine, there is a kind of glasses called "reading glasses", which is essentially a 200-degree hyperopia glasses. Its function is to make up for the child's adjustment lag. If a child wearing reading glasses reads too close to the book, he will not be able to see clearly, so he will naturally stand farther away.

The picture comes from the Internet

However, reading glasses themselves cannot prevent myopia. They only control the distance between the child's eyes and the book and help the child correct his sitting posture. Generally speaking, if the child reads and writes very close and cannot control it, wearing reading glasses will be better, but not all children are suitable. Whether to wear reading glasses should be determined under the guidance of a doctor. If children are blindly wearing them, it will also have a bad effect on their visual function.

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Increase outdoor activities and reduce the use of electronic products

Feng Jing believes that children with low congenital hyperopia reserves cannot change their current situation, so it is more meaningful to focus on changing the acquired environment. For example, if parents have severe myopia, try to postpone the age at which children are exposed to electronic products; ensure at least 2 to 3 hours of outdoor exercise every day, and try to choose more outdoor activities in extracurricular classes, and reduce the time spent on close-up eye activities such as piano, calligraphy, reading, and online classes; go to the ophthalmology department regularly to monitor changes in children's vision and eye axis.

In fact, compared with monitoring hyperopia reserve, axial length change is a more sensitive indicator of pathological high myopia (for every 1mm increase in axial length, myopia increases by about 300 degrees), so a more effective solution is to monitor axial length changes. Various myopia control measures, whether it is low-concentration atropine, orthokeratology lenses, correct sitting posture and eye habits, and increasing outdoor exercise time, are ultimately aimed at slowing down the growth of the axial length.

"Once it is confirmed that the child has true myopia, please accept the fact that the child needs to wear glasses for treatment. In the clinic, there are often parents who cannot accept the fact that their children are myopic, thinking that the longer they wear glasses, the worse it will get. However, the length of the eye axis is the same as height and cannot be shortened. Therefore, if true myopia patients do not wear glasses, the image will not be able to fall on the retina, which will accelerate the progression of myopia."

"After the epidemic was brought under control, we clearly felt that the proportion of children with myopia who came to the clinic increased. Therefore, the reduction in outdoor sports and the extensive use of electronic products have a great impact on the occurrence and degree of myopia in children," said Feng Jing. For children who already have myopia, increasing the time spent outdoors can significantly slow down the increase in myopia and the length of the eye axis; for children who do not yet have myopia, increasing the time spent outdoors can also significantly reduce the risk of myopia.

Produced by: Science Central Kitchen

Produced by: Beijing Science and Technology News | Science Plus Client

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