Gas Permeable Contact Lenses

What are gas permeable contact lenses?

Gas permeable contact lenses are small, curved pieces of durable, slightly flexible plastic shaped to fit your eyes. They float on the tear film in front of the cornea (the clear outer layer on the front of the eyeball). Contact lenses work the same way that glasses do to improve your vision.

The plastic used for gas permeable lenses allows oxygen to reach the cornea. The original hard contact lenses, which were made of a plastic that did not allow oxygen to reach the cornea, are rarely prescribed today. Although gas permeable lenses are not the same as the hard lenses of the past, people sometimes still refer to gas permeable lenses as "hard" or "rigid" lenses. This is because they are harder and more durable than soft contact lenses.

Because of improvements in materials used to make them, gas permeable lenses have several advantages over soft lenses and are being prescribed more often.

When are they used?

Gas permeable contact lenses correct most of the vision problems for which glasses are prescribed. Gas permeable lenses have the following advantages over soft lenses:

• They often correct vision better than soft lenses do, especially for people with severe astigmatism or scarred or irregular corneas.
• Allergic and toxic reactions to lens care solutions are less frequent. Unlike soft lenses, gas permeable lenses do not absorb liquids.
• Gas permeable contact lenses are easier to clean than soft contacts.
• Gas permeable lenses are less expensive than soft lenses because:
  • They last longer because they are more durable.
  • They can be polished and reground when scratched or outgrown.
  • The materials used to make them are less expensive.
  • Gas permeable lenses require fewer cleaning solutions than soft lenses do.

The main reason gas permeable contacts are not more widely used is that they are harder to get used to.

What are the types of gas permeable contact lenses?

Gas permeable lenses are available for daily wear and extended wear. However, many eye care providers recommend that you not wear contacts, even so-called extended-wear types, when you sleep. Ask your eye care provider how long you can safely leave in your lenses.

Two types of bifocal gas permeable lenses are available. In one type, the reading prescription is a ring around the outside of the lens. The other type has the reading prescription and a weight at the bottom of the lens so the reading position stays at the bottom when the lens is in your eye. Fitting these lenses can be difficult, and some people never adjust to them.

Tinted gas permeable lenses are available for cosmetic reasons such as to change your eye color, or to use as sunglasses.

How can I get gas permeable contact lenses?

You need to have a thorough eye exam with an ophthalmologist (a medical doctor who specializes in eyes) or an optometrist, who will:

• determine whether your eyes are suitable for contact lenses
• recommend either gas permeable or soft lenses
• check your eyes regularly after you begin wearing your lenses full time

Slight discomfort when you first start wearing contact lenses is normal. If you have any pain in your eyes, see your eye care provider. Checkups of new lenses are recommended after 1 week, 2 weeks, 1 month, 6 months, and 1 year.

What precautions should I take with contact lenses?

• When you first start wearing contacts, carefully follow the break-in schedule prescribed by your eye care provider.
• Wash your hands with soap and water before you put in or take out your lenses.
• Do not wear your lenses while swimming because they may float out of your eyes and increase your risk of infection.
• Use aerosol sprays, such as deodorant and hair spray, before you put in your lenses.
• Always insert your contact lenses before applying makeup. Use water-soluble makeup, and avoid lash-building mascara, which may drop particles into your eyes.
• Do not put contact lenses into your mouth to moisten or clean them because this may cause an eye infection.
• If there is a possibility that you may lose consciousness from seizures or other medical problems, include the fact that you wear contact lenses on your Medic Alert bracelet or card.
• If you have burning, redness, pain, unusual light sensitivity, or blurry vision, remove your contacts and see your eye care provider right away.

What are some problems with contact lenses?

You may find it difficult to wear contact lenses if you have:

• severely irritated eyes from allergies or exposure to dust or chemicals at your job
• an overactive thyroid, uncontrolled diabetes, severe arthritis, or a tremor in your hands
• dry eyes because of pregnancy, birth control pills, diuretics, antihistamines, or decongestants

Other possible problems include:

• allergic reactions to lens care solutions and contaminants on or in the lenses
• inflammation (redness) of the eye
• scratching of the cornea
• infection of the surface of the eye

Reviewed for medical accuracy by faculty at the Wilmer Eye Institute at Johns Hopkins. Web site: http://www.hopkinsmedicine.org/wilmer/

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