There are three types of refractive errors in the eyes: myopia, hyperopia, and astigmatism. Most astigmatism patients are only aware of this when they have their glasses examined, and when they have astigmatism, they have reduced vision, often squint when looking at distant or near objects, and have visual fatigue. Astigmatism is commonly known as “light scattered”, light entering an eye without astigmatism will be precisely focused on the retina, eyes with astigmatism, often can not form a single focus, will form two or more focus. So eyes with astigmatism will see things with double vision and blur. Since most of the refractive power of the eye comes from the cornea, whether or not we have astigmatism in the eye depends largely on the traits of the cornea. The most common cause of regular astigmatism is an inconsistency in the radius of curvature of the corneal diameters. The two main radii of curvature, horizontal and vertical, are the most different. Simply put, when we are young our cornea resembles a rugby ball, as we age the anterior and posterior diameters, the left and right diameters gradually change, and in old age it becomes a longitudinal “rugby ball”, gradually forming astigmatism. This is the main reason. Of course, the lens can also produce astigmatism, but it is rare. Irregular astigmatism is commonly caused by cone corneas, corneal scarring due to corneal disease, or refractive surface and height irregularities of the lens due to lens disease. Only 10% of the population has no astigmatism at all, and most people have varying degrees of astigmatism. Astigmatism cannot be cured, but there are many ways to correct it, and it is recommended to seek medical attention for astigmatism and corrective treatment according to the situation.