Hard contact lenses
The first hard contact lenses were made of glass. In 1936 there was the discovery of PMMA – polymethylmethacrylate, which replaced the glass. It is a material with sufficient hardness, resistance to scratching and breakage and is easily processed, biologically harmless to dilute acids and solvents. Nonpolar surface minimizes deposits, which leads to a lower incidence of eye disease. A big disadvantage of hard contact lenses is their impermeability to gases.