Convex lenses are light concentrators, focusing light rays in a focal point can be used to correct farsightedness and presbyopia, farsightedness glasses and presbyopia glasses are made of convex lenses. Hyperopia refers to the relaxed state of eye regulation, light refracted by the refractive system of the eye after the formation of the focal point in the retina, the formation of a dispersion ring, can not form a clear image, through the front of the eye to place a convex lens, parallel light rays are concentrated after the formation of the focal point of the front, can be focused on the macular center of the concave, so as to form a clear image. Concave lenses, on the other hand, have a dispersing effect on the light rays, shifting the focus backward, which can be used to correct myopia, and myopia glasses are made of concave lenses.