A spherical lens in its simplest form is the magnifying glass. This lens is convex on both sides, and those faces are shaped like sections of spheres. The strength of the lens is described in diopters A spherical lens that is convex on both sides is a "plus" lens, and is used to treat hyperopia. The next type of spherical lens to know is the simple minus lens, which is concave on both faces, and is used to treat myopia. Most opticians produce minus lenses that are actually concave on one side and convex on the other, but have a net minus power.