Astigmatism mainly comes from corneal astigmatism and lens astigmatism. And the astigmatism of the eye depends mainly on the corneal astigmatism. Most patients still consider it to be caused by congenital development. Because the cornea of the human eye, in fact, is not the ideal spherical shape, but is flat and spherical, the mirror astigmatism that exists on the surface of the cornea is corneal astigmatism. According to the regularity of corneal astigmatism, it is divided into regular astigmatism, and irregular astigmatism. Regular astigmatism, in general, is determined by the level of development of the human eye, which clinically begins in infancy. Therefore, most of the astigmatism of the eyes in childhood and adolescence is regular astigmatism, and the corneal astigmatism is relatively stable. After middle age and old age, most of them gradually turn into retro-regular astigmatism, which may be related to the decrease of the adjustment function of the crystal. Irregular astigmatism is considered to be caused by corneal disease, or after eye trauma or eye surgery. If you find that the astigmatism of the eye is changing, the degree of astigmatism is deepening, and the astigmatism is clearly irregular, you need to be alert to the possibility of cone cornea.