At present, there are two kinds of lens materials on the market, one is glass material, the other is resin material. Resin materials are divided into CR-39 and polycarbonate (PC material).
Bifocal lenses or bifocal lenses are lenses that contain two correction areas at the same time and are mainly used to correct presbyopia. The far area corrected by the bifocal lens is called the far area, and the near area is called the near area and the reading area. Usually, the distal region is large, so it is also called the main film, and the proximal region is small, so it is called the sub-film.