Myopia is a kind of ametropia, which means that distant objects cannot converge in the retina, but form a focus in front of the retina, thus causing visual distortion and blurring distant objects. Most people's myopia is caused by long-term unhealthy eye use, some of which are related to genetic factors. When the eyes are used at close range for a long time, the ciliary muscles are often in a state of contraction, which leads to accommodation tension or accommodation spasm. Without the traction of ciliary muscles, the lens will become thicker and convex. When you look far away, the focus will fall in front of the retina and you can't see clearly. It will cause myopia after a long time.
There are many reasons for myopia. Generally speaking, the ciliary muscle is often in a state of contraction when the eyes are used for too long at close range, which leads to accommodation tension or accommodation spasm. Without the traction of ciliary muscles, the lens will become thicker and convex. When you look far away, the focus will fall in front of the retina and you can't see clearly.
Myopia is also related to heredity. Parents are nearsighted, and children may be more prone to myopia. But at present, most teenagers' myopia is caused by their inattention to protect their eyes the day after tomorrow.