Convex lenses are light concentrating, focusing light at a focal point can be used to correct farsightedness and presbyopia, farsightedness glasses and presbyopic lenses are made from convex lenses. Farsightedness is a condition in which the refraction of light through the refractive system of the eye forms a diffuse ring after the retina, which cannot form a clear image. By placing a convex lens in front of the eye, the focus formed by the convergence of parallel rays is shifted forward and can be focused exactly on the central macula, thus forming a clear image. On the contrary, the concave lens has a diverging effect on the light, so that the focus is shifted back, and can be used to correct myopia, myopia glasses are made of concave lens.