Rigid Gas Permeable Lenses

Gas permeable contact lenses are rigid lenses made of durable plastics that allow oxygen to pass through the lens. These lenses also are called GP lenses, rigid gas permeable lenses, RGP lenses and oxygen permeable lenses.

What makes gas permeable lenses different?

Most gas permeable lens materials include silicone, which makes GP lenses more flexible than PMMA hard contacts. And silicone allows oxygen to pass directly through GP lenses to keep the cornea healthy without having to rely solely on oxygen-containing tears to be pumped under the lens with each blink. In fact, modern rigid gas permeable contacts allow more oxygen to reach the cornea than most soft contact lenses (although some silicone hydrogel soft lenses are comparable to GP lenses in oxygen transmission).

Because gas permeable contact lenses allow oxygen to pass through them, GP lenses can be made larger than PMMA hard contact lenses, and the edges of GP lenses can be fitted closer to the surface of the eye. These design changes make modern rigid GP lenses more comfortable and easier to get used to than old-fashioned hard contacts. They also help GP contacts stay more securely on the eye when worn during sports and other activities.

RGP lenses also provide better vision, durability and deposit resistance than soft contact lenses. And because they last longer than soft lenses, they can be less expensive in the long term.

Adapting to RGP lenses:

So why doesn't everyone wear gas permeable lenses? Primarily because soft lenses are instantly comfortable, and GP lenses require an adaptation period before they are as comfortable as soft contacts.

Some other downsides of RGP lenses are discussed below.

The benefits of RGP lenses:

Gas permeable contact lenses offer some outstanding benefits over soft lenses. For one, because GP lenses are made from a firm plastic material, they retain their shape when you blink, which tends to provide sharper vision than pliable soft lenses.

GP lenses also are extremely durable. Although you can break them (for instance, if you step on them), you can't tear them easily, like soft lenses. And they're made of materials that don't contain water (as soft contact lenses do), so organic materials (protein and lipids) from your tears do not adhere to GP lenses as readily as they do to soft lenses.

With a little care, gas permeable contact lenses can last for years, as long as you don't require a lens prescription change.

Where GP contact lenses excel:

Though they are less popular than soft lenses, gas permeable contacts are the best choice for many individuals, including:

· People who are very discerning and are willing to go through a period of adaptation to contact lens wear to achieve the sharpest vision possible.

· Some people with astigmatism for whom soft contacts don't produce the desired visual acuity. [Read about contacts for astigmatism.]

· People with presbyopia, because GP lenses come in numerous bifocal and multifocal designs. Different bifocal designs work well for different people, so having many choices is a real plus. Also, many people find that the best combination of near and distance acuity is obtained with GP bifocals.

· People who have a condition called keratoconus, where the cornea is cone-shaped and causes extreme visual distortion.

· People who need contact lenses after refractive surgery.

Gas permeable contacts also are used for ortho-k, where specially designed GP lenses are worn during sleep to reshape the cornea and improve vision.

Limitations of gas permeable lenses

Unlike soft lenses, to achieve maximum comfort with gas permeable contacts, you need to wear them regularly (though not necessarily every day).

If you don't wear your soft lenses for a week, they'll still be comfortable when you put them on a week later. But if you don't wear your GP lenses for a week, you'll probably need some time to get comfortable again.

Also, GP lenses are smaller in size than soft lenses, which means there is a greater risk of gas permeable lenses dislodging from the eye during sports or other activities.

And because gas permeable lenses are designed to move on the eye when the wearer blinks, there is a higher risk of dust and debris getting under the lenses, causing discomfort or a possible abrasion to the cornea.
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Finally, GP lenses do require care, since they are reused for one year or more.
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This information is provided by allaboutvision.com.