Gas Permeable Contacts
Both the first glass contact lenses, created in 1887, and the first polymethyl methacrylate, or PMMA lenses, created in 1949, did not allow much oxygen to reach the cornea. This caused eye problems in some patients.
Contact lens science branched in the 1970s, with the development of two different types of gas permeable contacts: rigid and soft.
Rigid gas permeable contacts were developed with polymers that maintain the shape necessary to correct vision, while allowing the cornea to “breathe.” These lenses can provide good vision in people with astigmatism or distortion of the shape of the cornea. RGP technology is also used to make bifocal contact lenses, which have a small lens area at the bottom, much like bifocal eyeglasses, for close vision. RGP lenses are also very durable; with proper care, they may last for several years before they need to be replaced.
The other development was hydrophilic gels, which enabled the production of soft, or hydrogel, contact lenses. These were first approved in the United States in 1971. Soft lenses, from the beginning, offered superior comfort. As newer polymers were developed, the amount of oxygen able to reach the cornea increased.
An exciting development came in 1999, when the first silicone hydrogels were introduced. These gas permeable contacts offered even greater oxygen permeability, allowing contact lenses to be safely worn overnight. The original silicone hydrogels caused eye dryness in some patients, which led to the addition of other molecules to the lens to keep them moist. Some silicone hydrogel lenses are approved for up to 30 days of continuous wear.
Hybrid lenses are also available, which combine some of the advantages of both rigid and soft lenses. Eye care professionals are trained to help patients to choose the best corrective lenses, including the continually improving gas permeable contacts.