Gas Permeable (GP) Contact Lenses
Gas permeable (GP) contact lenses, also known as rigid gas permeable (RGP) lenses, are rigid contacts made of silicone-containing compounds that allow oxygen to pass through the lens material to the eye. Though not as popular as soft contact lenses, GP lenses offer a number of advantages.
Advantages of Gas Permeable Lenses
GP lenses allow your eyes to "breathe." Getting oxygen to the eye reduces the risk of problems caused by hypoxia (reduced oxygen supply). Because GP lenses are made with oxygen-permeable silicone, they allow more oxygen to reach the front surface of the eye than traditional hydrogel soft contact lenses. (However, many of the new silicone hydrogel soft contact lenses are comparable to GPs for oxygen delivery.)
GP lenses provide sharper vision. Because they maintain their shape on the eye, GP lenses provide sharper vision than soft lenses, which can fluctuate in shape. And gas permeable lenses don't contain water, so they are not prone to drying out. Many soft lenses contain a large percentage of water and will compromise vision if they start to dry out.
GP lenses last longer. GP lenses are rigid, so there's no worry about ripping or tearing them. They are also easier to keep clean and don't need to be replaced frequently like soft lenses. With proper care, a single pair of GP lenses can last a year or longer. Since they're long-lasting, GP lenses can be less expensive than soft lenses in the long run.
GP lenses can slow the progression of nearsightedness. GPs used for overnight orthokeratology - also called corneal reshaping, or ortho-k - have been shown to reduce the progression of myopia (nearsightedness) in some children. Overnight ortho-k also enables clear daytime vision without the use of glasses or contacts.
GPs are great for multifocal designs and problem corneas. Many wearers feel that GP multifocals offer superior vision to soft bifocals. GPs are also the most common choice for eyes that have been compromised by corneal diseases, or for people who still need vision correction after refractive surgery such as LASIK.
The Downside of GP Contact Lenses
So why doesn't everyone wear GP lenses? Potential disadvantages of GP lenses (compared with soft lenses) include:
Need for adaptation. Unlike wearing soft lenses, which are immediately comfortable, you may need a few weeks before you can wear GP lenses comfortably all day. Initially, you may be able to wear the lenses only a few hours daily until your corneas adapt to them. But if you can tough it out for those first few days, you may be pleasantly surprised at how comfortable GP lenses become.
Inability to wear part-time. To fully adapt to GP lenses and to stay comfortable wearing them, you have to wear them every day. If you stop wearing them for several days, you will be more aware of the lenses on your eyes and you'll have to re-adapt to the lenses.
Increased possibility of dislodging. Because they are smaller than soft lenses, gas permeable lenses can dislodge from your eyes during contact sports or if you rub your eyes aggressively.
Vulnerability to sand and dust. GP lenses don't conform to the shape of your eye like soft lenses do, so it's possible for sand or dust to get under your lenses at the beach or on a windy day. (You can minimize this risk by wearing wrap-style sunglasses outdoors.)
Higher initial and replacement costs. Unlike soft lenses, which come in off-the-shelf sizes, GP lenses are always custom-made to the shape of your eye. This makes GP lenses more expensive to purchase, and to replace if you lose them. Also, it can take up to a week to get a GP lens replaced. So it's a good idea to purchase a spare pair to avoid the inconvenience of being without your GP lenses if you lose or break one.
Hybrid Contact Lenses
Since comfort is the primary barrier to GP use, an interesting innovation is the hybrid contact lens. These lenses have a GP center, surrounded by a soft lens "skirt." The goal of hybrid lenses is to provide the clarity of a gas permeable lens and wearing comfort of a soft lens.
Call for More Information and a Trial Fitting
To see if gas permeable lenses are right for you, call our office for more information and to schedule a trail fitting.
Orthokeratology, or "ortho-k," is the process of reshaping the eye with specially designed rigid gas permeable (GP) contact lenses. The goal of ortho-k is to flatten the front surface of the eye and thereby correct mild to moderate amounts of nearsightedness and astigmatism. This process is also known as corneal reshaping, and by brand names such as CRT (Corneal Refractive Therapy) and Bausch & Lomb's Vision Shaping Treatment (VST).
How Ortho-k Works
The GP lenses for ortho-k are applied at bedtime and worn overnight. While you sleep, the lenses gently reshape the front surface of your eye (the cornea) to correct your vision, so you can see clearly without glasses or contact lenses when you're awake. The effect is temporary - generally enough to get you through a day or two - so you must wear the reshaping lenses each night to maintain good vision during the day.
Who Is a Candidate for Ortho-k?
Orthokeratology is frequently a good option for nearsighted individuals who are too young for LASIK surgery or for some other reason are not good candidates for vision correction surgery. Because it can be discontinued at any time without permanent change to the eye, people of any age can try the procedure, as long as their eyes are healthy.
Ortho-k is particularly appealing for people who participate in sports, or who work in dusty, dirty environments that can make contact lens wear difficult.
What Results Can You Expect from Ortho-k?
The goal for ortho-k is to correct your vision to 20/20 without eyeglasses or contact lenses during the day. In FDA trials of both CRT and VST lenses, more than 65% of patients were able to achieve 20/20 visual acuity after wearing the reshaping lenses overnight. More than 90% were able to see 20/40 or better (the legal vision requirement for driving without glasses in most states).
Success rates for ortho-k tend to be higher for mild prescriptions. Call our office to find out if your prescription is within the range that can be successfully treated with ortho-k.
Ortho-k Can Slow the Progression of Nearsightedness
Several clinical studies have indicated that corneal reshaping lenses can reduce the rate of myopia progression in nearsighted children. When worn only at night, these lenses can slow down eye growth - the source of progressing myopia - by more than 50% compared with glasses and soft contacts, according to multiple studies. In another study, published in 2014, participants used a daytime-wear GP in one eye and an ortho-k lens in the other, and no eye growth was found over a one-year period in the ortho-k eye.
How Long Does Ortho-k Take?
Though you may see some improvement in your vision after a day or two of overnight ortho-k, it can take several weeks for the full effect to be apparent. During this time, your vision will not be as clear as it was with glasses or contacts, and you are likely to notice some glare and halos around lights. It's possible you may need a temporary pair of eyeglasses for certain tasks, like driving at night, until your vision is fully corrected by the ortho-k lenses.
Is Ortho-k Comfortable?
Some people have comfort issues when attempting to wear gas permeable contact lenses during the day. But since ortho-k GP lenses are worn during sleep, comfort and lens awareness are generally not a problem.
Cost of Orthokeratology
Ortho-k is a significantly longer process than a regular contact lens fitting. It requires a series of office visits and potentially multiple pairs of lenses. Also, GP lenses used for ortho-k are more costly than most regular contact lenses. Therefore, fees for orthokeratology are higher than fees for regular contact lens fittings.
Can I Have LASIK After Ortho-k?
Yes, it's possible to have LASIK surgery after orthokeratology. But because ortho-k lenses reshape your corneas, you must stop wearing the lenses for a period of time (usually several months) so your eyes can return to their original shape and stabilize. Be sure to tell your LASIK surgeon that you've worn ortho-k lenses, so they can advise you how long you should wait before having the surgery.
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