Gas-permeable contact lenses, also called rigid gas perms (RGP), are a high-quality contact lens made of silicone. This type of contact is individually fit for each eye by taking specific corneal measurements and having a complete vision exam by an eye doctor. RGP lenses have very specific wearing schedules.
Gas-permeable contacts were first introduced in the 1970s by Bausch and Lomb. They were designed to improve on hard contact lenses, which are made of plastic. Making the new rigid lenses out of silicone, instead of PMMA plastic, gave patients more comfort and better oxygen permeation, which is important for eye health. Rigid lenses historically give better vision, last longer and are easier to care for. Gas-permeable lenses continue to evolve as technology improves. One of the newest type of RGPs is an overnight lens.
Gas-permeable contact lenses are individually designed by your eye doctor by measuring your cornea and determining lens power, size, diameter and curvatures. RGP lenses stay in place better than soft lenses and give crisp, clear vision. They have less buildup then soft lenses and require less maintenance.
Gas-permeable lenses have the ability to correct for the irregular curvature of the cornea, called astigmatism. RGP lenses are also a good choice for bifocal contacts because the lenses stay in place better than soft lenses. New extended-wear gas-permeable contacts are available, buy they must be fit by an experienced practitioner and the wearing schedule and followup is monitored very closely.
Initially, wearing time is one of the most challenging features of gas-permeable contacts. Patients usually start out wearing lenses four hours a day, and increase an hour each day until reaching the maximum wearing potential. Once you are wearing RGP lenses all day, if you stop wearing the lenses for any significant amount of time, you will have to start your wearing schedule over and build up gradually.
The same is true for special overnight RGP lenses. Because the technology is newer and the possibility for infection and swelling is greater with this type of lens, your eye doctor will want to monitor your individual overnight wearing very closely. Most doctors also recommend not wearing the lenses every night, but rather leaving them out several nights a week.
The length and amount of wearing time will depend on your specific situation, prescription, lens material and eye health.
Overnight lenses are a wonderful option for people who have strong prescriptions. Being able to see upon waking without searching for glasses is not just a convenience, but also helpful in emergencies.
People who wear contacts and work in occupations that include night duty, such as medical and emergency personnel, also appreciate the advantages of having contacts that can be slept in.
Patients who have difficulty inserting and removing lenses, such as the elderly or very young, and require rigid lenses, would also be helped by wearing overnight RGPs.
Never wear gas-permeable lenses not designed or prescribed for overnight wear. Corneal damage, temporary or permanent, can result. The severity of complications can range from pain and irritation to complete loss of vision.