Regular glasses mainly consists of lenses, prisms, contact lenses, etc. to rectify vision, in order to eliminate vision fatigue, protect or treat the eyes. There are many types of glasses, and optical glasses and contact glasses are mainly used to correct refractive errors.
Correction of myopia:
A concave lens of appropriate power should be worn so that the light is properly diverged by the concave lens and then refracted by the eye to form a clear image on the retina.
A convex lens of appropriate power should be worn to allow the parallel rays in the distance to be properly concentrated by the convex lens, and then refracted by the eye to form a clear image on the retina.
Correction of astigmatism:
It varies depending on the type of astigmatism. For simple hyperopic astigmatism, a convex cylindrical lens with appropriate degree and a certain axial direction should be worn; for simple myopic astigmatism, a concave cylindrical lens with appropriate degree and a certain axial direction should be worn; for complex astigmatism, the degree and axial direction should be worn. Suitable convex (or concave) composite cylindrical lens; for mixed astigmatism, a cylindrical lens with appropriate degree and suitable axial convex and concave composite should be worn. However, regardless of the type of astigmatism, the glasses should be strictly measured in the axial direction of the cylindrical lens, so that the astigmatism can be effectively corrected on the meridian surface that needs to be corrected. For irregular astigmatism, since the refractive power is different on the same meridional surface, it cannot be corrected with a cylindrical lens, and the contact lens (contact lens) can be used for correction.