Hard contact lenses - traditional vision correction. 

Hard contact lenses, as their name implies, are made from a very tough and rigid material. Traditionally, these contacts were made from polymethylmethacrylate (PMMA), which is a type of clear plastic. Nowadays, PMMA is combined with other materials in order to increase the oxygen permeability of today’s contacts. This type of hybrid lens is known as the rigid gas permeable (RGP) lens. There are also non-gas permeable hard contact lenses. 

Non-gas permeable hard contact lenses are relatively inexpensive and can be worn for up to ten years. However, they do require a substantial adjustment time and cannot be worn during vigorous physical activity. 

Gas-permeable hard contact lenses are more comfortable then the non-gas permeable variety because they allow oxygen to pass from the lens to the cornea. These lenses have a life of about five years, and they should not be used during exercise. 

Hard contact lenses are ideal for people with very dry eyes. These contacts are unable to absorb water. Hence they will not dehydrate the eyes of a wearer that already has problems with lubrication. However, most modern wearers of contacts do not choose the hard contacts. Most prefer the rigid gas permeable varieties. 

Hard contact lenses - non-dehydrating contacts.