Gas permeable (GP) contact lenses are also known as rigid gas permeables (RGP’s). Although today’s gas permeable lenses are made of a rigid material that is not flexible, they differ greatly from the original hard lenses of yesteryear. Hard contact lenses made of polymethylmethacrylate (PMMA), were introduced in the 1930’s. Considered innovative and technologically advanced for the time, these hard lenses were nearly rendered obsolete by soft lenses that debuted in the early 70’s.
A decade later, rigid gas permeable lenses appeared on the scene. For clarification, vision specialists refer to these contacts by several names: gas permeable (GP) or Rigid Gas Permeables (RGP’s). RGP’s are constructed of flourosilicone acrylate. There are several reasons why RGP’s may be the right choice for some patients, including:
- Eye health
- Ability to diffuse oxygen (unlike hard lenses)
- Less likely to transmit infection
- Easily cleaned
- Unlike soft lenses RGP’s retain shape and do not dehydrate
- Long lasting
- Clearer vision
- Custom made for each patient
It is easy for people with healthy eyes to take vision for granted, but the human eye is a remarkable organ. The makeup of the human eye and the series of natural occurrences within it, that allow a human being to see clearly, is at the very least, astounding. For instance, the cornea’s surface is clear and contains absolutely no blood vessels. It is unlike any other tissue in the human body that utilizes blood vessels for nourishment and protection. Gas permeable contact lenses, allow oxygen to flow to the eye and assist the cornea in defending the eye from infection and disease; protecting overall eye health.
Gas permeable contact lenses promote eye health
The overall health of the cornea is extremely important. The cornea or the window of the eye, in a combined effort with the sclera (white part of the eye), lashes and tears protect the internal eye from debris and germs. The five layers of the cornea must remain clear without any opacity. Oxygen is essential in the process and is necessary to keep the cornea healthy so that it may in turn, protect the rest of the eye.
The surface of a gas permeable lens is more resistant to deposits than soft lenses. In contrast, rigid gas permeable lenses are less sponge-like and will not soak up substances that can house bacteria. GP lenses are more durable than soft lenses and because they are obviously harder, they retain better shape.Gas permeable contact lenses play an important role, allowing the proper interaction of the eye with oxygen from the air. The cornea draws oxygen from the air as tears act as a dissolving agent. The tears dissolve the oxygen from the air and transport it through the cornea, mimicking the job of blood vessels in other parts of the body. A second gas, carbon dioxide, is a byproduct of the process and is eliminated by the cornea. Interruption of this complex process makes the eye vulnerable to maladies such as corneal scarring, loss of transparency, blood vessels, and corneal warping.
Initially, gas permeable lenses take a little more getting used to than soft lenses. Within a short amount of time, however, the eyes become accustomed to wearing rigid lenses. Whereas the adaptability to soft lenses is almost immediate, it could take up to a week or two before patients find gas permeables as comfortable.
Using gas permeable lenses to correct myopia (orthokeratology)
If you can see objects that are in close proximity more clearly than those that are viewed from a distance, an eye health professional will most likely diagnose your condition as nearsightedness-otherwise defined as myopia. Myopic eyes are unable to correctly focus the light that enters it. Eyes that are unaffected by myopia are able to refract or bend the light correctly, throwing it back to the retina.
A myopia diagnosis does not indicate that eyes are unhealthy. Healthy eyes are often nearsighted. This occurs when an eye’s physical length is greater than its optical length, resulting in a blurring of distant objects. There is no way to prevent nearsightedness because we cannot change the physical size and shape of the eye. Male and females are equally affected and in the case of children, myopia usually gets worse with age. Once the child completes the growing process, myopia stops progressing. Though there is no way to prevent nearsightedness from occurring, special gas permeable contact lenses that gently reshape the cornea can be used to help correct myopia. This process is called Orthokeratology. Orthokeratology may be more effective in correcting myopia than wearing eyeglasses and is a non-invasive alternative to permanent, non-reversible, corrective surgery.
How orthokeratology works
Orthokeratology is the process of using special gas permeable lenses to temporarily correct/reduce myopia by reshaping the cornea. An eye health professional may refer to this process as corneal reshaping (CR) as corneal refractive therapy or vision shaping. The first step a doctor will take is to measure the refractive error of the eye. This determines the patient’s degree of nearsightedness. A tool, the corneal topographer, is used to map out the shape of the front surface of the eye. The resulting digital map will assist the doctor in defining the parameters and exact shape and size of the RGP lens that will effectively and gently change the surface of the cornea, and improve the patient’s vision.
Patients wear the corrective gas permeable lenses for at least eight hours, generally at night while they sleep. Orthokeratology can reduce or eliminate the regular use of eyeglasses or contact lenses during the day. Nearsightedness will be eliminated for longer periods of time with continued night use of the rigid gas permeable corrective lenses, much in the same way that a retainer helps to keep teeth straight. The patient may be instructed by their eye health professional to keep a specific schedule that will improve vision over time so that optimum vision is achieved. The most common scenario that patient’s may expect is nighttime wear; but a doctor will make the choice concerning length and times of wear, which is dependent upon the patient’s eyes and subsequent diagnosis.
Orthokeratology is a possible alternative for those individuals who have been identified as nearsighted with -4.00 diopters (refractive power) or less. Your eye care provider can advise you if you are a good candidate for orthokeratology.
Who is a good candidate for orthokeratology?
Orthokeratology can be an option for almost anyone who wants to improve vision clarity.
Children between eight and twelve years of age are excellent candidates for wearing the lenses. It is at this age that many parents discover their children’s sight challenges. Often a child is unable to see the white board at the front of his classroom, or to adequately focus on the ball when playing sports. Because nearsightedness progresses with age, and the fact that kids have a lot of growing to do, gas permeable lenses can be of great benefit. Athletes for instance, have difficulty wearing cumbersome glasses. Choosing to wear RGP’s at night will correct vision, sometimes for days at a time, allowing children to avoid wearing glasses during sports practices and sporting events.
Gas permeable contact lenses may also be suitable for adults who are dissatisfied with the clarity of their vision. Adults, who are averse to invasive laser surgery, to remove tissue from the eyes in an attempt to correct vision, may choose orthokeratology.
Who is a good candidate for rigid gas permeable lens wear?
Former hard or soft contact wearers who were dissatisfied with past results, should give rigid gas permeable contact lenses a try. Technological advances have made gas permeable lens wear an option for many people for whom it may not have been an option for in the past.
Bifocal or multifocal lens wearers
Presbyopia, according to the American Optometric Association, is a “vision condition in which the crystalline lens of [the] eye loses its flexibility, making it difficult to focus on close objects”. Presbyopia, like myopia, is not an eye disease and is a natural occurrence associated with age. The average age in which persons begin to notice changes that signal presbyopia is between 35 and 45 years old. People with presbyopia may find gas permeable contact lenses to be another option rather than wearing bifocals or multi-lens glasses. There are many very good bifocal and multifocal rigid gas permeable lenses available. Your eye care provider can help determine if these lenses are appropriate for you.
Patients who have astigmatism
Astigmatism is defined by the National Eye Institute as ”a common type of refractive error… a condition in which the eye does not focus light evenly onto the retina, the light-sensitive tissue at the back of the eye”. Persons with astigmatism may experience blurred vision at near and far distances. One of the symptoms associated with the eye condition is difficulty driving at night. At the same time, it is not unusual for slight astigmatism to go unnoticed and therefore undiagnosed. Once your health professional does detect astigmatism through an eye examination, gas permeable contact lenses can be offered to help correct astigmatism.
Persons who are dissatisfied with the results of refractive surgery
For former refractive surgery patients who did not receive visual clarity, gas permeable contacts may be an option.
Scleral contact lenses
Scleral lenses are a type of gas permeable lens that are made from the same durable material and have the same benefits associated with regular gas permeable lenses. However, scleral lenses are larger and can be fit to a larger portion of the eye. Scleral lenses cover the entire cornea and rest on the scleral (the white part of the eye). The design of scleral lenses provides a more comfortable fit for those who have experienced irritation associated with sensitive eyes, an irregular shaped cornea or dry eyes. An eye health professional can explain the differences between the four types of scleral lenses, listed below and will prescribe the one that is best suitable for your eye prescription.
- Full scleral lenses
- Mini-scleral lenses
- Cornea-scleral lenses
- Semi-scleral lenses
Handling and caring for your gas permeable contact lenses
To avoid eye infection it is tremendously important to always wash and dry hands thoroughly before applying contacts to eyes. To avoid dispersing debris onto the contact lens-dry your hands with a towel that is lint free before inserting the contact into your eyes. Only the eye solution that is specific to your contact lens and suggested by the contact lens professional should be used. Never top off solution and add only fresh lens solution to the lens case. Avoid contamination of the bottle and case by rinsing the case and allowing it to air-dry completely each day. Never change lens solutions without discussing it first with an eye care or contact lens professional. Finally, never wear contacts beyond the recommended amount of time.
Advantages over eyeglasses
Gas permeable lenses are less cumbersome and are not susceptible to climate change. Temperature change will not fog contact lenses, which can be worn during sports activities. Vision may be clearer for gas permeable contact wearers, since the contact sits directly on the cornea. The proximity of eyeglasses to the eyes is not ideal for perfect vision, especially peripherally. With correct handling and care, gas permeable contact lenses can last for several years. Glasses are susceptible to breakage. Additionally, contact wearers can more easily wear sunglasses.
The bottom line is that rigid gas permeable lenses can be worn by just about anyone. An eye exam by a certified eye health professional, an optometrist or ophthalmologist, is the first step necessary to confirm whether or not you are a good candidate to wear RGP’s.