According to an article submitted to allaboutvision.com, RGP contact lenses, or Rigid Gas Permeable lenses, transmit more oxygen to the wearer's eye. Unlike the "hard contacts" of the 1970s, RGPs are made of polymers that make the contacts permeable to oxygen. These lenses can be worn for a number of ailments, including astigmatism and presbyopia.

Features

Gas Permeable (GP) contact lenses are also known as oxygen permeable lenses and Rigid Gas Permeable lenses (RGPs). Compared to traditional soft contact lenses, gas permeable lenses are proven to transmit more oxygen to the wearer's eyes.

Benefits

Gas Permeable lenses are made of a stiff material, so when a wearer blinks, the lenses retain their shape, which provides better vision. GPs are not easily torn, as most soft contact lenses are. They can last for years unless a prescription change is needed.

Downsides

Full-time lens wear can prohibit "spectacle blur," or blurry vision, which can occur when the wearer takes his lenses out. Spectacle blur can be noticed even when the wearer takes his contacts out and puts his glasses on.

Potential

GPs can come in different bifocal and multifocal designs, so people who have presbyopia, or blurred near vision, may benefit from wearing these. Also, people with astigmatism, who have an irregularly shaped cornea or lens or keratoconus (people who have a cone-shaped cornea) can also wear GPs.

Fun Fact

Before 1971, all contact lenses were made of polymethyl methacrylate, or PMMA, which is not permeable. Soft contact lenses and GPs have since been introduced and these other "hard contact lenses" were made obsolete.

Source:

Allaboutvision.com: Gas Permeable Contact Lenses