Myopia and astigmatism are both types of refractive error, with myopia often being expressed in terms of spherical lenses and astigmatism in terms of cylindrical lenses. If you are calculating the total number of diopters, such as when fitting contact lenses or keratoconus, you may sometimes need to refer to the equivalent spherical lens, which is the number of diopters of myopia plus half the number of diopters of astigmatism to calculate the number of diopters of astigmatism. With contact lenses, you need to calculate the equivalent spherical lens, because often contact lenses do not come with a degree of astigmatism. But corneal reshaping lenses tend to be based on myopia and astigmatism is added separately depending on the configuration. In the case of myopia surgery, it is the amount of myopia and astigmatism that is calculated together in order to calculate the thickness of the cornea that needs to be cut. Based on the thickness of the cut cornea in order to know the remaining thickness after the surgery, in order to ensure the safety of the cornea thickness value, in order to carry out a certain surgery. So if it’s glasses, there is a conversion between myopia and astigmatism. In case of surgery, myopia and astigmatism are usually calculated together.