Myopia can be divided into two types depending on the refractive component: the first is refractive myopia, which is a condition in which the refractive power of the eye is beyond the normal range mainly because the curvature of the cornea or lens is too large, however, the length of the eye axis is still normal, called refractive myopia. The second type of myopia is axial myopia, in which myopia occurs because the length of the eye axis is outside of the normal range, but the curvature of the cornea and lens are still within the normal range. The purpose of this distinction is to determine the degree of progression of myopia, because axial myopia increases gradually with age and has a very high probability of becoming high myopia. Once it enters high myopia, it brings about pathological changes such as retinal pigment disorders or optic disc atrophy arc.