Nearsightedness is a refractive state in which parallel light rays are refracted through the eye’s refractive system and fall in front of the retina when the eye is not using accommodation. Therefore, myopic eyes cannot see distant targets clearly. If the target is gradually moved closer to the eye and the light emitted is spread out to a certain extent to the eye, the focal point is shifted backward, when the target is moved closer to a point in front of the eye. The closer this point is to the eye, the deeper the degree of myopia. Myopia occurs mostly because the anterior and posterior axes of the eye are too long (called axial myopia), followed by a strong refractive power of the eye (called refractive myopia). Myopia occurs mostly in adolescence, and genetic factors have some influence, but its occurrence and development are closely related to inadequate lighting, improper reading posture, and working at close range for a longer period of time. Most myopia occurs in adolescents, and it deepens year by year during the development and growth stages, but does not develop or develops slowly after maturity. The myopia rarely exceeds 6D, no degenerative changes occur in the fundus, and the vision can be corrected with glasses, which is called simple myopia. The other type of myopia occurs earlier (between the ages of 5 and 10) and progresses rapidly, continuing to develop after the age of 25, with myopia reaching more than 15D, often accompanied by changes in the fundus, and vision not easily corrected, called degenerative myopia. In addition, it is customary to refer to myopia below 3D as mild myopia, 3 to 6D as moderate myopia, and above 6D as high myopia. Etiology: The cause of myopia is still not well understood, and the accepted view is that myopia is caused by a variety of factors. Recent evidence suggests that a combination of environmental and genetic factors are involved in the development of myopia. I add: exogenous factors – prolonged close viewing of things, so that the ciliary muscle in the eye for a long time to press the lens and cause the lens can not recover (thicker than natural), so myopia occurs. Genetic factors: Studies have concluded that families with two parents with high myopia have a higher incidence of myopia in the next generation, and it is well established that myopia has a certain genetic predisposition, especially for high myopia. However, the genetic predisposition for general myopia is not so obvious. Environmental factors: The occurrence and development of myopia is closely related to the use of eyes at close range. The eyeballs of adolescents are in the growth and development stage, the adjustment ability is very strong, the stretching of the eyeball wall is also relatively large, reading, writing and other close-up work, not only need to play the role of eye regulation, both eyeballs also need to converge, so that the extraocular muscles exert a certain pressure on the eyeballs, over time, the front and back axis of the eye may become longer. The majority of this myopia is simple myopia, which is generally low, below 6 diopters, and progresses more slowly around the onset of puberty. The formation of myopia (1) the eye distance is too close. According to the data, myopia in adolescents is most often caused by prolonged use of the eyes at too close a distance. The distance between the book and the eye is 7-10 cm, but if you often read and write at this distance, you will have abnormal strain on your eyes, which can lead to refractive (regulatory) myopia, the so-called pseudomyopia. If over-regulation for a long time, the ciliary muscle can not stretch flexibly, due to over-regulation and convergence caused by strengthening, so that the extraocular muscle pressure on the eye, intraocular pressure increased, intraocular tissue congestion, coupled with the youth eye tissue is delicate, the eye wall pressure gradually extended, the front and back axis of the eye becomes longer than normal, the formation of axial myopia, the so-called true myopia. The normal reading distance should be 30-35 cm. (2) Too much time spent with the eyes. Some teenagers read and write to do homework, watch TV and so on for 3-4 hours without rest, or even to sleep and rest late at night, which not only affects physical health, but also overloads the eyes, the muscles inside and outside the eyes for a long time in a state of tension and do not get rest, over time, when looking at the distance, the eye muscles can not relax and spasm state, so look at the distance to feel blurred and the formation of myopia. Some students’ eyesight declines significantly after a summer vacation for this reason. It is generally advocated that continuous reading and writing or watching TV for 40-50 minutes should be rested for a moment or look into the distance for a while. (3) Lighting is too strong or too weak. If the light is too strong, such as sunlight shining written, will cause strong reflection, stimulate the eyes, eye discomfort, it is difficult to see the font, on the contrary, the light is too weak, written illumination is not enough, the eyes can not clearly see the font, the head will be forward, close to the book, the above two cases can eye fatigue easily, eye regulation or spasm and the formation of myopia. (4) in the car or walking when reading books. Some adolescents make full use of the time to read books while walking or reading in the walking carriage, which is very bad for the eyes. Because the carriage is vibrating, the body is shaking, the eyes and the book distance can not be fixed, coupled with poor lighting conditions, increasing the burden on the eyes, often so it may cause myopia. (5) lying down to read a book. Many teenagers like to lie in bed to read, which is a bad habit. Because the human eye should maintain the horizontal state of reading, so that the regulation and collection (convergence) to achieve consistent, reduce eye fatigue. If lying down to read, both eyes are not in the horizontal state, eye and book distance is not consistent, both eyes are not consistent with the line of sight up and down, uneven illumination on the book, will make the eye regulation tension and easy to move the book close to the eye, which can increase the burden on the eye 2-3 times, the formation of myopia over time. (6) Sleep deprivation. When sleep deprivation, the next day, the spirit is not invigorated, dizzy, the brain is not fully rested, fatigue is not eliminated, increasing the burden on the eyes, prompting myopia to occur. Sleep deprivation is a very important cause of myopia. (7) Desks do not meet the requirements, writing posture is not correct. If the desk and chair are too low, so that the head tilted forward, the spine bent, the chest is pressed, the eyes are relatively tense adjustment. Or desks and chairs too high, feet hanging, the lower limbs are easy to swing, can not maintain the correct posture, can make eye fatigue, over time, it is easy to myopia. (8) the impact of the current space rays. Often watch TV, especially the signal is insufficient, reception rate is not high in rural areas, no shared antenna, the screen is not clear, the snow point is also more, it is easy to make eye muscle fatigue, often play video games students are more likely to damage vision, the mall sold Ze Wang learning machine, can directly cause students myopia, today’s computer calculator is an indispensable course, too long operation caused by eye dryness and fatigue prone to myopia. All need to properly control the use of time. (9) Corneal curvature or lens curvature behind the front becomes larger, this condition is mostly congenital changes, less common clinically.