Two types of contact lenses exist:

• hydrophilic soft lenses
• rigid, or hard type materials.

Soft lenses  contain 36%-74% water and are made of plastics. The diameter varies from 10.5mm to 15.5mm. Soft lenses are available in almost any optical correction, including myopia, hyperopia, astigmatism and bifocal. They can be colored with either transparent hues or opaque patterns to change apparent eye color or to mask cornea or iris malformations. They are available for daily, weekly and bi-weekly "disposable" use, one to three months "frequent replacement" use and annual replacement lenses.

Hard lenses used to be manufactured from a material called PMMA. They have generally been replaced by gas-permeable materials and are called RGP (rigid, gas permeable). As with soft lenses, they are available in almost all possible optical corrections. RGP lenses have diameters between 8.0mm-10mm and inside ³base curves² which match the curvature of the cornea. There are also a number of lenses which combine soft and RGP materials. The NovaLens is an RGP lens with a modified hydrophilic surface. SoftPerm has an RGP center and soft periphery. These are unique lenses with characteristics that help with certain f itting situations.