(1) Hard lenses: PMMA (polymethylmethacrylate) was invented in 1934; in 1947, the first all-plastic contact lens was made from PMMA. Advantages: better corrected vision, longer lens life; Disadvantages: brittle, poor air permeability, and strong foreign body sensation.
(2) Soft lenses: PHEMA hydroxyethyl methacrylate was discovered in 1960; the first pair of soft contact lenses was produced (the father of soft lenses: Otto Wichterle); obtained FDA permission in 1971. Advantages: soft, oxygen permeable, comfortable, no foreign body feeling; Disadvantages: easy to absorb and settle, short life.
(3) Rigid gas permeable lenses (RGP): Born in 1970, Polycon was patented in 1972. The material is mainly made of PMMA and silicone polymerized. Advantages: good oxygen permeability, lower hardness than PMMA; disadvantages: lack of comfort.