dioptrics
Di*op"trics, n. Etym: [Gr. dioptrique.] (Optics) Defn: The science of the refraction of light; that part of geometrical optics which treats of the laws of the refraction of light in passing from one medium into another, or through different mediums, as air, water, or glass, and esp. through different lenses; -- distinguished from catoptrics, which refers to reflected light.