Gas Permeable (GP) or Rigid Gas Permeable (RGP) contact lenses are an alternative to soft contact lenses that are made from a hard, oxygen permeable material. GP lenses are currently less popular than soft lenses but offer a number of advantages and are continuing to improve as research and technology advance.
GP contacts are made of a firm plastic material which allows the passage of oxygen through the lens to your cornea and the front surface of your eye – essentially allowing your eye to “breathe”. This increases comfort, health and safety during contact lens wear.
Benefits of GP or RGP Contact Lenses
Because of the strong material and the ability to diffuse oxygen, GP lenses offer a number of advantages over soft contact lenses.
Health and Hygiene Benefits:
Unlike soft lenses, GPs don’t contain water which makes them less likely to attract and breed bacteria that can cause eye infections. Further protein deposits won’t build up on the lens, keeping them cleaner and healthier.
Because they are made with a strong durable material, GP lenses won’t tear and are easy to clean and disinfect. RGPs maintain their firm shape and will not dehydrate. Further GPs last longer than soft lenses – when cared for properly, a pair can last a year or more. Frequently, we have had patients in our practice that have been wearing the same pair of RGP's for 7+ years, when fitted properly, a RGP contact lens is a great alternative for patients on tight financial budgets.
GP contact lenses are custom made for each patient based on the eye’s individual curvature, size, corneal shape. Their ability to transmit oxygen reduces eye problems such as dry eyes caused by reduced oxygen that are common in many brands of soft lenses or hard (non-GP) lenses.
GP lenses have a smaller diameter than soft contacts, meaning that they cover less of the surface of your eye. While this may take some time getting used to initially, ultimately many find that they are just as if not more comfortable than soft contacts.
Better Vision Than What Soft Contact Lenses Can Provide
Due to the rigid material, GPs have a smooth surface and maintain their shape, moving along with the eye to hold their place. This provides sharp and stable vision. Further they do not dehydrate, which is often a cause for reduced vision with other lenses.
Because they last so long, GPs are much more cost effective than soft lenses, especially disposable lenses that require a constant supply. Because they are made to order, there is an initial cost investment and they will take up to a week to manufacture if you do need a replacement pair.
RGPs for Astigmatism
GP lenses are ideal for individuals with astigmatism that may have been told that they cannot wear soft contacts. Because of the rigid nature of the lens, they hold their shape on the eye allowing for more clear and stable vision correction. By vaulting the astigmatic cornea, a RGP forms a "tear lens" behind the RGP and in front of the cornea. The "tear lens" aids in the providing a second refractive medium to correct astigmatic refractive error, thus, clearer, more natural overall vision.
Adapting to (GP) Contact Lenses
One of the downsides of GP contact lenses is that they require an adaptation period, particularly if you are used to soft lenses with a larger diameter. One of the major differences is an experience of “lens awareness” in which you feel the edge of the lens when you blink. It could take up to a few weeks to get used to the lenses but many people report that after this initial period they find that GP lenses are just as if not more comfortable than soft lens varieties.
GP Lenses for Myopia Control and Ortho-K
Orthokeratology, commonly called ortho-k, is a method used to correct myopia (nearsightedness) by wearing rigid gas permeable contact lenses overnight, so that no vision correction is needed during daytime hours. Research shows that gas permeable lenses "might" be effective in slowing the progression or worsening of myopia or nearsightedness, particularly in children. As of this writing, the results of a 25 year long study by the National Eye Institute (www.nei.nih.gov) are still to be published on the long term effects on children and progression of myopia. They are also used in Orthokeratology (ortho-k), a vision correcting procedure in which you wear the lenses at night to reshape your cornea for improved vision during the day.
Gas permeable (GP) lenses specialized for ortho-k are inserted at bedtime and worn as you sleep. Throughout the night, the lenses reshape your cornea gently so that your vision becomes clear on the following morning. The correction is temporary, and ideally no eyeglasses or contact lenses will be needed on the next day or two. In order to maintain sharp visual acuity on a daily basis, you need to wear the ortho-k reshaping lenses every night.
At present, two brands of ortho-k contact lenses are approved for use by the FDA. Paragon Vision Sciences produces “Corneal Refractive Therapy” (CRT), and Bausch and Lomb manufactures “Vision Shaping Treatment” (VST).
Candidates for Ortho-k:
Ortho-k is very suitable for nearsighted people who are not appropriate candidates for vision correction surgery, such as children. Individuals of all ages with healthy eyes can try ortho-k, namely because it can be discontinued at any point without permanent effects to the eyes.
People who require vision correction and engage regularly in sports or work in extremely dusty, dirty environments will also appreciate the convenience of ortho-k.
Vision Results from Ortho-k:
Success rates for ortho-k are generally higher for more mild vision prescriptions. The ideal goal is to provide 20/20 vision without any need for eyeglasses or contacts during the day.
According to FDA trials conducted on both CRT and VST lenses, more than 65% of ortho-k patients were provided with 20/20 visual acuity. A whopping number of more than 90% of ortho-k patients achieved 20/40 vision or better (this is the legal requirement for driving without vision correction in Missouri). Consult with your Dr. Gunnerson to find out if your vision prescription is within range for successful ortho-k treatment.
Note that although improvement in vision is generally reported within a day or two of wearing ortho-k overnight, the full effects may not be experienced until the lenses are worn for a few weeks. During this transition period, your vision will probably not be as crisp as it was with regular contacts or eyeglasses, and glare or halos around lights may be visible. Until ortho-k works fully, a temporary pair of eyeglasses may be required for specific actions, such as driving at night.
How Does Ortho-k Feel?
Although some people have trouble wearing regular gas permeable contact lenses during the day, ortho-k GP lenses are worn while sleeping – so discomfort and awareness of the lenses in your eyes is generally not an issue.
Is Ortho-k expensive?
Professional fitting for ortho-k requires a series of visits to your eye doctor. A number of pairs of contact lenses are also generally needed. GP lenses that are special for ortho-k are more costly than standard contacts. In sum, the fees for ortho-k add up to a higher total than regular contact lenses. We often caution our Ortho-K clients that the correction is only temporary, you will only have sharp daytime vision as long as you continue to wear, at night, the Ortho-K lenses.
LASIK after Ortho-k
Refractive surgeries, such as LASIK, are possible after treatment with ortho-k lenses. Yet because ortho-k works to reshape your cornea, you are required to stop wearing the lenses for approximately several months before undergoing LASIK. This allows your eyes to return to their original shape. It’s important to inform your LASIK surgeon if you’ve been wearing ortho-k lenses, and you will be advised as to how long of a wait is necessary before having the laser procedure.
Is Ortho-K safe and effective for kids?
Yes! Ortho-K is a acceptable treatment for kids. Besides the "proposed" health benefits of slowing myopic vision progression in children, the wearing of Ortho-K lenses adds the benefit of not worrying about lost or broken glasses. Because Ortho-K lenses are worn at night, your child does not have to deal with the hassle of daytime contact lenses or cumbersome glasses worn during sports or other daytime activities.