Gas permeable contact lenses

Gas permeable hard lenses are produced from pure silicon or cellulose acetate butyrate. It is similar to hard lenses in terms of high image quality, durability and cleaning ease, also oxygen and carbon dioxide permeable. Gas transfer is an important issue for the lenses. As transparent layer has no vessels, the oxygen requirements for this tissue is provided by air. Moreover, gas permeable hard lenses are more flexible than hard lenses and easier to transmit heat. These features are important for long term use. Gas permeable hard lenses are between hard lenses and soft lenses as ranking of comfortability.