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Categories of Contact Lenses

There are three main categories of contact lenses: Soft Disposable lenses, Rigid Gas Permeable lenses (RGPs), and Hard Plastic (PMMA) Lenses.  Figure 1 illustrates the relationship between the categories; a brief description of each will follow.

Figure 1: Categories of Contact Lenses

 

Soft Contact Lenses 

The majority of contact lens wearers chose soft lenses. The soft lenses of choice are disposables, which are available in daily, weekly or monthly packages. Soft lenses are made from a gel-like plastic, and have a high water content. When they absorb liquid, they become softer and can mold to the shape of the eye. In addition, they allow a great deal of oxygen to pass through to the eye. They are known to be very comfortable to wear. Most soft contact lenses can correct Myopia (nearsightedness), Hyperopia (farsightedness), and certain types of Astigmatism (irregular shaping of the cornea causing skewed vision). Soft contact lenses differ from RGP's (Rigid Gas Permeable lenses). Soft contact lenses differ from RGP's because they are more comfortable, fall out less, are easier to insert, and require less break-in time. Break in time is the time required for a patient to get used to wearing contact lenses.

Soft contact lenses are not for everyone. Although there are benefits of wearing a soft contact lens over wearing a RGP lens, there are also some disadvantages. Soft contact lenses are more expensive than RGP lenses, and they require more replacements as they are less durable. Also, wearers of soft lenses are more likely to get eye infections than wearers of rigid lenses. Maintenance of soft contact lenses may also require several cleaning and storing sterilization chemicals.

Only an eye care professional, like your local optometrist can help you decide if soft contact lenses are the right fit for you. Your eye care professional must also fit your contact lenses as the eye curvature in each patient differs.

 

Rigid Gas Permeable Lenses (RGPs)

Rigid Gas Permeable contact lenses (RGPs) are worn by about 15 percent of contact lens wearers. Unlike hard plastic lenses, RGPs are gas permeable. That is, they allow oxygen to pass through to the cornea. They are less expensive and more durable than soft contact lenses, and provide wearers with clearer, sharper vision.

Unlike soft contact lenses, RGPs have a low water content and therefore, resist protein deposits and bacteria. Because they are rigid, they hold their shape when the wearer blinks, allowing for crisper vision. Other benefits include ease of handling and ease of care. Because they do not contain water, proteins from the eye do not build up on the lens, so the lens stays cleaner, and requires less maintenance.

RGP's are not for every patient. Because of their rigid form, they require more break in time for the patient to become comfortable with wearing the lenses. Also, if you discontinue wearing your RGP's for a few days, it may be difficult to become used to wearing them again. RGP's differ from soft contacts in that becoming comfortable with wearing a rigid lens requires the patient to wear their lenses all the time. Soft contact lens users may discontinue wearing their lenses for a few days, and immediately be comfortable with having them inserted again.

Rigid Gas permeable are also known as Oxygen Permeable contact lenses. The plastic of these lenses is breathable, and they must be custom fit to the shape of the cornea. Only your eye care professional can help you decide which contact lenses are right for you.

 

Hard Plastic Lenses (PMMA)

Hard Plastic (PMMA) lenses do not allow oxygen to pass through to the cornea. They require a long adjustment period, and cannot be worn for more than 12 hours. These high-maintenance lenses were the first contact lenses on the market, but are now considered obsolete and are rarely used.

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The information contained on this site is general in nature and is not meant to substitute for the advice provided by your contact lenses physician or other professional. None of the statements on this site are suggesting, or in preference to a particular contact lenses, nor must they be considered as medical advice. If you are doubt about a disease or health related condition of any kind, please contact your health care professional immediately.
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Last updated June. 09, 2006
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