The easiest way to distinguish between a concave lens and a convex lens is to hold your glasses and look at your hand or the words on the book through the glasses. If the hand or the word gets bigger, it is a convex lens, on the contrary, if the word or the hand gets smaller, it is a concave lens. Myopic eyes need to wear concave lenses, which have the effect of gathering light. When myopic patients wear concave lenses, they can make the light from far away focus on the retina through the concave lens and the refractive system of the eye, which plays the role of correcting myopia. In contrast, a convex lens has the effect of dispersing light. When worn by farsighted patients and presbyopes, it allows light from a distance to pass through the convex lens and the refractive system of the eye and be focused on the retina, which is used to correct farsightedness and presbyopia.