Have foresight, not myopia

Author: Wang Xue China Rehabilitation Research Center

Reviewer: Jiao Yonghong, Chief Physician, Beijing Tongren Hospital

According to the data of the White Paper on Myopia Management (2022), the myopia rate among Chinese teenagers is as high as 52.7%. In the future, there will be at least 960 million myopic people in China. Myopia has become a major disease affecting the visual health of teenagers. As parents, how can we take good care of our children's eyes and protect their bright vision?

1. Understanding myopia will lead to attention

1. Let’s first talk about what myopia is?

When the human eye is in a relaxed state, parallel light rays are focused in front of the retina after passing through the eye's refractive system, which is called myopia . Myopia can be divided into three categories according to the degree of myopia.

Low myopia : -0.50～-3.00D (50～300 degrees).

Moderate myopia : -3.25～-5.75D (325～575 degrees).

High myopia : less than or equal to -6.00D (more than 600 degrees).

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2.Why should we control myopia?

Myopia of more than 600 degrees is considered high myopia. The axial length of the eyeball of high myopia is significantly longer than that of a normal eyeball. The elongated eyeball will cause the retina to thin and atrophy, thus increasing the risk of retinal tears, retinal detachment, glaucoma and macular hemorrhage. These lesions will seriously affect visual function and even cause low vision and blindness, thus seriously affecting the quality of life.

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3.What are the causes of myopia?

At present, there is no theoretical system that can explain all the causes and control mechanisms of myopia. The widely recognized mechanism is that environmental factors are the main factor, supplemented by genetic factors. Among the environmental factors, the most core factor is long-term close-up use of the eyes .

When the eyes look at something close, the ciliary muscle contracts. Looking at something close for a long time will cause the ciliary muscle to be in a state of continuous over-tension and contraction. The contraction of the ciliary muscle will exert a certain amount of pressure on the wall of the eyeball, causing the eyeball to lengthen axially. From a biological point of view, continuous close-range use of the eyes will cause the eyeball to try to focus close images directly on the retina without adjustment, which will cause the eye axis to lengthen and cause myopia.

In the latest research, the "accommodative lag-hyperopic defocus" theory is considered to be an important cause of myopia. The "Myopia Management White Paper (2022)" explains the main theories related to myopia mechanisms (Table 1).

Table 1 Main theories related to the mechanism of myopia

Here, we need to explain what is " regulatory lag "?

The human eyeball is like a very high-performance zoom camera. The lens is equivalent to the lens of the camera, which can focus accurately in real time, ensuring that we can see distant or near objects instantly. However, we cannot feel the process of eyeball focusing, because the human eye's lens adjustment ability is very sensitive and accurate. When people look at close objects, the lens becomes convex to ensure that the image of the object is formed on the retina. However, the human eye is sometimes "lazy", and the actual adjustment response when looking at close objects is often less than the actual adjustment stimulus, that is, the adjustment lags , which will cause the image to fall behind the retina . Over time, the retina will grow backwards to find the image, eventually leading to the elongation of the eye axis. Therefore, parents must regularly check the adjustment function of the lens of their children to avoid myopia caused by adjustment lag!

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2. The most effective way to prevent myopia

Ensure more than 2 hours of outdoor activities every day ! The most effective, no doubt!

Children need to spend more than 2 hours a day under 10,000 lux of light to effectively prevent myopia. Note that 2 hours is just enough to reduce the risk of myopia.

So what does 10,000 lux mean? At noon in the summer, under a cloudy sky, it is about 100,000 lux; wearing sunglasses or standing in the shade of a tree is about 10,000 lux; under a sky covered with heavy clouds, it is about 5,000 lux; in a well-lit indoor office or classroom, it usually does not exceed 500 lux; in an ordinary living room, artificial light is about 100 lux. This is why we should let children do outdoor sports. Even on a cloudy day, the outdoor light will be much stronger than indoors!

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Why can outdoor activities prevent myopia?

According to the above data, the light intensity outdoors is much higher than that indoors. Sunlight stimulates the retina to release dopamine, and dopamine prevents the eye axis from growing. When indoors, the retina releases low levels of dopamine, and the eye axis grows faster. Regardless of whether you are nearsighted or not, the eye axis growth is significantly correlated with light exposure. Studies have found that children's myopia grows faster in winter than in summer, which may be related to the short daylight hours and low sunlight illumination in winter.

So, how can we ensure that we can pass the outdoor test?

If you are going out for a short distance, try not to drive if you can walk or ride a bike; after school, do some appropriate outdoor exercise before doing your homework during daylight; try to choose outdoor physical exercise.

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Spending 2 to 3 hours outdoors every day may sound difficult, but if you plan your time, it is actually not difficult at all! A lot of outdoor activities can not only significantly slow down the progression of myopia, but may even reverse it.

III. Two indicators for myopia prevention and monitoring

1. Hyperopia reserve

Generally speaking, the eyes of newborns are in a state of hyperopia, which is physiological hyperopia, called "hyperopia reserve". As the eyeball develops, the eye axis continues to grow, and the degree of hyperopia gradually decreases and tends to emmetropia. This process is called "emmetropization" of the eyeball. Long-term bad eye use behavior will cause the eyeball to develop too fast and quickly consume the "hyperopia reserve". Therefore, it is very important to detect the "signs of myopia" in time when the "reserves are insufficient" or "just used up the reserves".

2. Axial length

Axial length refers to the length from the center of the cornea to the optic nerve and the fovea of ​​the retina. It is an important indicator for judging the progression of myopia. Measuring the axial length is like measuring the height of the eyeball. If the height of the eyeball grows too fast and is longer than that of children of the same age, it means that myopia is developing rapidly. The axial length development of children and adolescents can be divided into two stages. From newborns to 3 years old, the axial length grows fastest, and the total length growth in 3 years is about 5mm. From 3 to 15 years old, the axial length growth rate gradually slows down.

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The Expert Consensus on Hyperopia Reserve, Axial Length, Corneal Curvature Reference Range and Related Genetic Factors of Chinese School-Age Children (2022) shows that the increase in the axial length of children is most obvious between the ages of 6 and 11, especially between the ages of 7 and 8 (Table 2). If the axial length can be monitored well at this stage, abnormal changes in axial length can be detected in time, and myopia intervention and management can be intervened in advance , the myopia management effect will be better and the benefits will be greater.

Table 2 Mean and increase of axial length of children aged 6 to 15 years

4. Develop good eye habits

1. Reasonably control the length of time you use your eyes at close range

Everyone knows that electronic devices such as mobile phones and tablets are bad for the eyes, but there is a misunderstanding here! As long as you use your eyes at close range , including reading, drawing, writing, and playing Lego, you must control the time and take regular breaks. Make sure you use your eyes at close range for 30 minutes and take a 10-minute break to look into the distance.

2. Avoid bad eye habits

Ensure adequate lighting when reading and writing, 800-1200 lux, with even lighting. Turn on both the ceiling light and the desk lamp when reading and writing at night. Do not read or write while walking, eating, lying in bed, in a car, in dim light, or under direct sunlight. Maintain the correct reading and writing posture, that is, " one fist, one foot, one inch " - the chest is one fist away from the table; the eyes are one foot away from the book; the fingers holding the pen are one inch away from the tip of the pen.

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3. Check your eyesight regularly

Don't wait until your child can't see the blackboard before you go to the hospital! Go to the hospital for a checkup every 3 months or at least every 6 months . Because the refractive state of the eye is determined by the corneal curvature, eye axis, and lens refractive power. Among them, the eye axis is the main factor determining the refractive state. Therefore, in addition to routine vision, the examination should also include refractive examination, measurement of eye axis length and corneal curvature, and other fundus examinations.

4. Ensure sleep and nutrition

Primary school students should ensure 10 hours of sleep per day, junior high school students should ensure 9 hours of sleep per day, and high school students should ensure 8 hours of sleep per day. A healthy work and rest schedule can ensure the normal secretion of neurotransmitters such as dopamine and acetylcholine related to myopia, and slow down the progression of myopia. Eat more whole grains, fish, fruits, dark green and yellow vegetables and other foods that are beneficial to vision health.

5. The use of electronic devices is indeed unavoidable. Here are a few key points to note:

(1) The smaller the screen of an electronic device, the greater the damage to the eyes.

(2) 20-20-20 eye protection rule: After using your eyes for 20 minutes, look away and look at something at least 20 feet (about 6 meters) away for at least 20 seconds.

5. What should I do if I am nearsighted?

If you find that your vision is declining and you suspect that you are nearsighted, you should go to the ophthalmology department of a regular hospital for treatment.

Ciliary muscle paralysis eye examination , check for eye diseases, and clarify whether it is true myopia or false myopia. If the child really develops myopia, in addition to improving eye habits and increasing outdoor activities, you can choose appropriate myopia control methods according to the child's specific situation, such as orthokeratology lenses, defocus frame glasses, defocus soft lenses, and low-concentration atropine eye drops. If myopia control is not ideal after 6 months of the above optical strategies or drug treatments, and the axial length grows ≥0.4 mm/year or the myopia increases ≥0.75D/year, you can choose a combined myopia control plan to maximize the effectiveness of myopia control.

In short, prevention of myopia is better than cure! Let us be far-sighted parents and prevent or delay myopia in our children. We hope that through the efforts of families and the whole society, we can jointly protect children's eyes, safeguard their bright vision, and let them have a bright future!