Astigmatism is caused by corneal misalignment. It is mostly congenital, but individual chalazia can also cause astigmatism when the eyelid is pressed against the eye for a long time. A normal corneal surface should be round like a basketball, with the same radius of refraction horizontally, vertically or obliquely, so that light will focus on the same point when it passes. However, in astigmatism, the corneal surface is not round or rugby-ball shaped, because the horizontal and vertical radii of refractive index are different, so it cannot be focused on the same point, and the image it sees may appear clearer in the horizontal or vertical lines, but blurred in the relative 90 degree direction. This is called “regular astigmatism” due to defects in the optical system of the eye, and “irregular astigmatism” due to inflammation or trauma to the corneal surface. Astigmatism can be myopic or hyperopic or mixed astigmatism where one path is farsighted and the other is myopic. High astigmatism without correction is more likely to cause headaches and eye soreness, as well as poor posture such as head tilting; therefore, severe astigmatism must be corrected. Astigmatism is usually corrected with ordinary glasses or contact lenses. Astigmatism is usually congenital, but there are also individual causes of astigmatism, such as trauma and untreated chalazia, which can cause long-term pressure on the eye and cause astigmatism. In some cases, astigmatism can also be combined with pseudomyopia, so the pseudomyopia part should be removed and the astigmatism should be corrected with glasses.