There are three main categories of contact lenses, based on the materials they are made of: soft contacts, rigid gas permeable (GP) contacts, and hybrid contact lenses.
Soft contacts are made of pliable hydrophilic ("water-loving" plastics called hydrogels. Hydrogels absorb significant amounts of water to keep the lenses soft and supple.
Because of this water-loving characteristic, the water content of various hydrogel contact lenses can range from approximately 38 to 75 percent (by weight).
The water content of soft lenses allows oxygen to pass through the lenses and keep the cornea healthy during contact lens wear.
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 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.
Hybrid contact lenses have a rigid GP central optical zone, surrounded by a peripheral fitting zone made of a soft contact lens material.
plastics called hydrogels. Hydrogels absorb significant amounts of water to keep the lenses soft and supple.
