Many people know about myopia and farsightedness, but know little about astigmatism, so what is astigmatism? Astigmatism is the inability of the optical system of the eye to form a dotted image of the external point of view, and is also a state of refractive error of the eye, related to the curvature of the cornea and the position of the crystal, refractive index, etc. The human eye is not a perfect optical system. If the cornea has a steeper curvature in one path and a flatter curvature in other paths, the light will not be accurately focused on the retina and astigmatism will be formed. For example, in a purely myopic, hyperopic or orthoptotic eye, the curvature of each pathway is the same as that of a soccer, while in an astigmatic eye, the curvature is different in the horizontal and vertical directions, like a rugby ball. In addition, astigmatism can also be caused by the deviation of the lens and the different refractive indices of the various parts of the lens. Although there are many reasons for astigmatism, and most of them are congenital, it is also related to the growth and development of people, and is often aggravated by bad eye habits. For example, lying down to read a book, lying down to read a book, squinting or squinting to read a book, etc. can cause improper pressure on the eyelids, which affects its normal development and causes an increase in astigmatism. Mild astigmatism, if there is no visual fatigue and vision loss, does not need correction; if any of the above symptoms occur, even if the astigmatism is very low, it should be corrected. For higher astigmatism and oblique axis astigmatism, if the patient has difficulty adapting to it, it can be corrected at a low degree first, and then gradually increased, both to improve visual acuity and to reduce visual disturbance symptoms. For regular astigmatism, columnar lenses or rigid gas permeable corneal contact lenses (RGP) can be used for correction; for ultra-high astigmatism, cone corneas and irregular astigmatism, only RGP can be used for correction.