The length of the eye is also known as the length of the eye axis. Normally, the length of the eye axis in adults is about 23-24mm. In the case of children, the eye axis is shorter than normal because the eyes have not yet developed to a mature state. The eye axis of a three-year-old child is usually around 20mm, and can reach 21-22mm at the age of six, and can develop into an adult state by the age of eight. If the usual eye habits are not normal, it may cause the growth of the eye axis, which may lead to myopia. Once the growth of the eye axis occurs, there is no way to reverse the process, which means that once axial myopia occurs, it is impossible to restore it to normal by conservative methods, but only through the use of glasses to improve vision. Therefore, in order to avoid this situation, it is important to maintain reasonable eye habits in general.