Up until the late 1970s, contact lenses were made from two materials. Hard contact lenses were made of polymethymethacrylate (PMMA), while the soft contact lenses were made of a hydrated polymer, hydroxyethylmethacrylate (HEMA), which contained 37.8% water by weight. These lenses provided clear vision and comfort, but there was a problem. These lenses did not allow oxygen to reach the cornea. Because of this, the cornea could change, adversely, in some contact lens wearers.

PMMA is now obsolete, and is replaced with rigid plastics, mostly hydrophobic materials with high oxygen permeability. These lenses are called Rigid Gas Permeable (RGP) lenses. For the manufacture of soft lenses, HEMA is being replaced by polymers which contain as much as 80% water. These soft lenses, often called hydrogels because of the amount of water have high oxygen transfer while retaining shape despite high water content. These new materials used in the manufacture of contact lenses as well as thinner lenses and greater oxygen transfer has reduced corneal issues, but there are still other possible complications.