Rigid Gas Permeable (GP, RGP) Contact Lenses
Gas permeable contact lenses are sometimes referred to as GP or rigid gas permeable contact lenses (RGP’s). Gas permeable contacts began being prescribed in the late 1970’s, which means that they are actually a newer technology than the soft contact lens.
It is important not to confuse GP lenses with their predecessor, the traditional "hard" contact lens. Older hard contact lenses were made of PMMA (polymethylmethacrylate), which provided the wearer with exceptionally clear optics, but were not able to transmit oxygen to the eye. This caused many problems, and as a result, traditional hard lenses became a thing of the past.
Gas permeable, as the name suggests, allow a sufficient amount of oxygen to reach the cornea, maintaining the health of the eye. Gas permeable lenses can rival or surpass in many instances the amount of oxygen that a non-silicone hydrogel lens transmits to the eye.
GP Contact Lenses Are Not Instantly Comfortable
Because they are a rigid design, they provide clearer optics than a patient can get with soft contact lenses. However, while soft contact lenses are comfortable from the first insertion, it can take a while for a patient to achieve comfort from a gas permeable contact lens. One of the reasons for this is because the GP lens has a much smaller diameter than a soft contact lens. This means that the eyelids have to pass over the edges of the GP lens each time the wearer blinks, and can cause more lens awareness than with soft contact lenses. With frequent use, the wearer can quickly adapt to the feel of the GP lens.
The benefit of gas permeable contact lenses is that they not only have two optical systems to work with, but instead three. In addition to the lens of your own eye and the contact lens itself, a GP contact lens makes use of a third component, the tear fluid located between the two. This tear fluid is quite basically water but has a fraction index which makes up an actual lens in optic terms.
There are some downsides to GP lenses. If not worn frequently, the wearer will experience lens awareness each time a rigid gas permeable lens is inserted. This is not true with soft contact lenses. The reason for this is that GP lenses do more cornea reshaping than do soft lenses, allowing for sharper vision. Also, because of the small size of the contact lens, some GP contact lens wearers also have complaints of their lenses "popping out" during physical activity.
Points to Think About
There are some important factors in regards to gas permeable lenses that need to be considered before making any permanent decisions.
- GP lenses do not sit still on your eye. They follow the flow of the lid in upward and downward motions. This type of movement is necessary for the fluid exchange which is required to make this type of contact lens work properly.
- The main problem with GP contact lenses is that the first pair doesn't always fit. This can be an expensive type of trial and error. It can be difficult to find the right pair to fit your own eye shape.
- Studies have been recently stating that people with astigmatism can actually benefit in more ways than one from choosing GP contact lenses. They are less expensive than fully corrective lenses and the fluid may even have the ability to lessen the affects of astigmatism.
It can be difficult to adapt to this type of contact lens in the beginning, even if you have worn contacts in the past. Many opticians will recommend this type of lens for people suffering from specific eye conditions or for those rare patients who have trouble finding the right pair of lenses. Never exclude this type of lens from your decision list, there are many medical benefits which can be found within this unique form of vision correction.
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