Rigid/Gas Permeable Contacts
Gas permeable contacts, also called GP or RGP lenses, are rigid (hard) contact lenses. Like hydrogels used for soft lenses, materials used to create GP contact lenses also are "gas permeable," allowing oxygen to pass through the lenses to the cornea.
Unlike soft contact lenses, however, rigid gas permeable lenses do not contain significant amounts of water. Instead, GP lenses rely on their microscopically porous nature to transmit oxygen to the cornea.
Because of their hardness and because they do not fluctuate significantly in their water content, gas permeable contacts generally have superior optical characteristics and provide sharper vision than soft lenses. However, despite advances in GP lens technology, some people cannot adapt to wearing rigid GP lenses and choose soft lenses for comfort reasons.