Astigmatism is a state of refractive error of the eye, caused by the inconsistent curvature of the cornea or lens surface, such as an olive sphere, resulting in two mutually perpendicular meridians with different refractive forces unable to focus on a point, forming an unclear or overlapping image, and seeing far and near is not clear. Clinically, there are two types of astigmatism: regular astigmatism and irregular astigmatism. 1, regular astigmatism maximum refractive power and minimum refractive power of the main meridian perpendicular to each other for the rule of astigmatism. Regular astigmatism is also divided into cis-ruled astigmatism, retro-ruled astigmatism and oblique astigmatism. According to the refractive state of each meridian, regular astigmatism is divided into simple myopic astigmatism, simple hyperopic astigmatism, compound myopic astigmatism, compound hyperopic astigmatism and mixed astigmatism. 2, irregular astigmatism eye refractive state not only the refractive power of each radial line is not the same, in the same radial line the refractive power of each part is also different, there is no rule to follow, can not form the front and back two focal lines, also can not be corrected with column lens, common in the cone cornea, corneal clouding or lens disease caused by corneal or lens refractive surface irregularities.