Gas Permeable Contact Lenses
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Gas permeable contact lenses (also known as GP lenses, RGP lenses, oxygen permeable lenses, and rigid gas permeable lenses) are rigid lenses made up of durable plastic that transmits oxygen.
Unlike the hard lenses from a long time ago, which are no longer available, gas permeable contact lenses are rigid. The older lenses were made of polymethyl methacrylate (PMMA), a hard plastic material. The soft contact lenses we use today were introduced in 1971. Until then, contacts were of acrylic glass, which is another name for PMMA. Other names commonly used in the industry were Lucite, Plexiglas, and Perspex, to name a few.
Aside from having good optical properties, PMMA was a good alternative to glass for many other applications because it was lightweight and shatter resistant. However, the cornea requires oxygen to remain healthy and PMMA is impermeable to gases like oxygen.
Because oxygen could not get through a PMMA lens, wearers had to blink to wash tears under the lenses in order for oxygen to reach the cornea. PMMA lenses had to be made pretty small to make sure the tears could reach the cornea and there was a considerable gap between the lens and the cornea.
Because of the design of PMMA lenses, the lenses were not very comfortable and could not be worn for very long periods of time. Some people, especially athletes, even had trouble with the lenses falling off their eyes.
How are gas permeable lenses different?
Gas permeable lenses, developed in the 1970s, are newer technology than soft lenses. Gas permeable lenses are more flexible than PMMA because they contain silicone.
Oxygen passes directly through gas permeable lenses because silicone is oxygen permeable, which helps keep your eyes healthy without having to worry about pumping tears to allow oxygen to pass over the cornea.
Today’s rigid gas permeable lenses actually provide more oxygen to the cornea than many of the soft lenses available. There are, however, some soft lenses that transmit oxygen just as well—silicone hydrogel lenses.
Gas permeable lenses are larger than PMMA lenses and can be fitted closer to the eye’s surface because they allow sufficient oxygen to pass through to the cornea, unlike the smaller PMMA lenses that had to be smaller. Today’s rigid gas permeable lenses are much more comfortable and easier to wear than the PMMA lenses because of these design changes. Furthermore, sports and activities are not a problem because the gas permeable lenses stay in place, even with activity.
Compared to soft contact lenses, gas permeable lenses offer better vision improvement, durability, and deposit resistance. They are also more cost efficient in the long term because they last longer.
Getting used to gas permeable lenses
Gas permeable lenses take some time for wearers to get used to while soft lenses are pretty comfortable from the start. Eventually gas permeable lenses feel just as comfortable to wear as soft lenses, however, some people do not want to take the time to allow their eyes to adjust to the gas permeable lenses.
Gas permeable lens benefits
While gas permeable lenses do take some time to get used to, they do have some amazing benefits when compared to soft lenses. For instance, they retain their shape when you blink because they are made from a firmer plastic material. They also give you sharper vision than a pliable soft lens.
You can break gas permeable lenses, however, they are very durable—it would take something like stepping on them to break. Soft lenses also tear much easier than gas permeable lenses.
Soft lenses are made of materials that contain water while gas permeable lenses do not. Therefore, the protein and lipids from your tears stick to soft lenses much easier than gas permeable lenses.
As long as your prescription does not change and you take good care of them, you may not have to replace your gas permeable lenses for many years.
Who should wear gas permeable lens?
Although they are not as popular as soft lenses, the following people benefit from wearing gas permeable lenses:
- Those who see the benefit in going through the adjustment phase of gas permeable lenses—achieving sharper vision
- Those who have astigmatism and did not get the visual acuity they wanted
- gas permeable lenses are available in both bifocal and multifocal designs, so people with presbyopia
The numerous bifocal designs that are available are great for different people. Gas permeable bifocals offer the best combination of near and distance acuity.
- Those who have a cone-shaped cornea, called keratoconus, which causes severe visual distortion
- Those who have had refractive surgery and require contact lenses
Some people also use special gas permeable lenses at night, a method that reshapes the cornea to improve your vision.
Gas permeable lens disadvantages
Although you don’t have to wear them every day, you do have to wear gas permeable lenses on a regular basis, unlike soft lenses. Your eyes will have to readjust to the lenses if you don’t wear them for a while, whereas soft lenses do not require an adjustment period.
Because they are smaller than soft lenses, there is a greater risk of gas permeable lenses falling out of your eyes during activities like sports.
Gas permeable lenses will move when you blink, so there is a risk of debris getting under the lens, which could potentially scratch the cornea, which may cause damage or discomfort.
Because they have such a long shelf life (over one year), gas permeable lenses must be taken well care of.
Can you have the best of both worlds?
If you want the clarity of gas permeable lenses and the comfort of soft lenses, hybrid contacts may be a good option for you. Hybrid lenses may be the answer to the comfort problem people have with gas permeable lenses.
There are two parts to a hybrid lens—the central optical zone is made of a gas permeable material and the outside (a peripheral fitting zone) is made of silicone hydrogel, like that of a soft lens.
The only FDA approved manufacturer of hybrid lenses is SynergEyes. Sold as SynergEyes, Duette, and UltraHealth, these lenses are available in progressive and multifocal lenses, which can help those with presbyopia, keratoconus, as well as other corneal vision problems.
Learn more about gas permeable lenses from the Contact Lens Manufacturers Association website.
To find out if gas permeable or hybrid contact lenses are the best option for you, consult your eye doctor.