At present, myopia is quite common among children, and many primary and secondary school students wear myopic glasses. Children suffering from myopia show reduced distance vision when looking at distant objects, but for close targets, the refractive system of the eyeball still makes a clear image on the retina, so the near vision is normal. Due to the lack of clarity of distant objects, myopic children often like to squint their eyes to see objects, which can make the light in the eye focused, and also can change the state of the eyeballs, so that the image of the macular area of the retina becomes a little clearer. Generally speaking, the higher the degree of myopia, the worse the distance vision. But sometimes encounter this situation, one eye myopia 200 degrees, naked eye visual acuity of 0.2, while the other eye myopia 1000 degrees, naked eye visual acuity is also 0.2, this phenomenon may be related to the examination of vision whether to maintain the natural state, such as squinting the eyes, highly myopic eyesight with the same as not squinting low myopia eyesight. This indicates that sometimes the good or bad distance vision of the naked eye is not consistent with the degree of myopia, and children with myopia like to squint when looking at distant objects. Why does myopia occur in children? This is related to the following factors: ① premature birth: premature birth is an important cause of myopia. The incidence of myopia in preterm babies is higher than that of full-term babies because of the low living capacity of preterm babies, many preterm babies have to be given oxygen, and the prolonged use of high concentration of oxygen can cause retinal edema, vitreous liquefaction, so that the eye axis is overstretched and myopia is caused. ② nutritional deficiencies: the normal development of children’s eyes is closely related to the nutritional status, nutritional deficiencies, especially protein, vitamin and calcium deficiencies, myopia and myopia have an important impact on the development of myopia. In addition, it has been found that chromium deficiency has a certain relationship with the occurrence of myopia, chromium deficiency can promote lens convexity, increase the eye cancer luminosity, and the body’s chromium content with the development of children gradually decline. Therefore, the lack of chromium in the diet can increase the occurrence of myopia in children. Preterm babies are born with rapid growth and development and require more nutrients, making them more susceptible to nutritional deficiencies. Nutritional deficiencies make the sclera underdeveloped and thin, unable to withstand the impact of normal intraocular pressure, so that the anterior and posterior diameters of the eyeballs are elongated, and myopia in infancy and early childhood is often related to this. ③Not paying attention to eye hygiene: this is the most important environmental factor causing myopia. Some children use their eyes for a long time at close range, such as watching TV, playing video games, playing the piano, etc., so that the eyes are in a state of tension adjustment for a long time; sometimes children read and write, like to twist their bodies and tilt their heads, or their eyes are very close to the book; or lying down, lying on the ground to read a book, or reading books in direct sunlight and dim light, all of these make the regulation of the eyes very laborious, very easy to cause visual fatigue, prompting the occurrence of myopia. Promote the occurrence of myopia. Survey shows that children do not pay attention to eye hygiene, the incidence of myopia is higher than pay attention to eye hygiene; in addition, now the heavy course load of elementary school students, extracurricular homework, often need to spend 1-2 hours, or even longer to complete; some children’s books, extracurricular homework questions of poor printing quality, the handwriting is not clear or too small; coupled with the child literacy opportunities to read books, some children even walking, toilets, and so on. Some children even read when walking, going to the toilet or riding in the car, all these are the reasons for the increase of myopia in elementary school children. Genetic factors: the occurrence of myopia has a certain relationship with heredity, but the proportion of myopia caused entirely by heredity is very small. It can be seen that the vast majority of myopia among children is caused by the influence of adverse acquired factors during the development of the eyeballs. Measures should be taken mainly to prevent myopia by improving the environment, paying attention to eye hygiene, reducing the burden of study on students and paying attention to the nutritional balance of children.