Types of Contact lenses?
Classified by material, there are three types of contact lenses: Hard lenses These are made from PMMA — also known as Plexiglas or Lucite. These lenses are virtually obsolete and rarely used. Soft lenses These are by far the most commonly used lenses. They are usually made of a hydrogel polymer and fit snugly onto the cornea making them very comfortable to wear. Some soft lenses have silicone compounds added to allow oxygen permeability, thus permitting significantly increased wearing times, i.e. “Extended wear”. Rigid Gas Permeable lenses (RGP) These are smaller and are made from rigid, waterless plastics and initially less comfortable to wear but are especially good for presbyopia and high astigmatism. For some people they allow the sharpest vision, and their oxygen permeability allows them to worn all day. This type of lens should typically last at least a year before replacement is needed. A well known problem with RGP lenses is their tendency to temporarily change the shape of the
