Types of contact lenses

Several different types of contact lenses are available to treat vision problems. Consult an eye care professional who is willing to work with you to select the best type of lens for your needs and lifestyle.

Hard contact lenses

Most hard (rigid) lenses are made of gas-permeable materials that allow oxygen to reach the cornea. This reduces problems that may occur when the cornea does not get enough oxygen. They correct refractive errors, including astigmatism, with no distortion.

Conventional hard lenses (PMMA)

Conventional hard contact lenses are made of a fairly stiff plastic (polymethyl methacrylate, or PMMA), which does not mold to the shape of the eye. They correct refractive errors (including astigmatism) with no distortion. They are inexpensive and durable, but they are the least comfortable type of contact lens. Because they reduce the amount of oxygen that reaches the cornea, people who wear them are at risk of overwearing syndrome and other problems.

Rigid gas-permeable (RGP) lenses

Gas-permeable lenses cost more than conventional hard lenses and are somewhat less durable, but they are more comfortable than conventional hard lenses. Some gas-permeable lenses are designed for extended wear (overnight, up to 7 days), although many eye specialists advise against wearing them for the extended period.

Soft contact lenses

Soft (hydrophilic or hydrogel) lenses are made of soft, very flexible plastics that absorb water (up to 90% of the lens weight). Many people find them more comfortable to wear than hard lenses, but hard lenses usually provide sharper vision. Soft lenses are also more fragile than hard lenses and require more intensive cleaning. Soft lenses can correct astigmatism (they are called toric lenses).

Daily-wear lenses

Daily-wear soft lenses are removed and cleaned at night and reinserted in the morning. They provide sharp vision but do not correct astigmatism as well as hard lenses do. They take less time to get used to than hard lenses, but they are less durable.

Extended-wear lenses

Extended-wear lenses can be worn for up to a week at a time, day and night. They are then removed, cleaned, and reinserted. But some people cannot tolerate the extended wear. Their eyes become irritated if the contacts are not regularly removed and cleaned. Extended use may be uncomfortable and increases the risk of damaging the eye.

The recommended wearing time for extended-wear lenses has been shortened from 30 days to 7 days because of the increased risk of eye infections. Ideally, you should never sleep in contact lenses.

Disposable lenses

Disposable soft lenses were designed to be worn for up to several weeks and then discarded. Many new contact lens wearers now choose disposable lenses.

Disposable lenses were introduced because it was thought that replacing lenses more often would reduce the risks of infection of the cornea (infectious or bacterial keratitis), a dangerous complication of soft lenses. But later studies have shown that people who wear disposable lenses, especially extended-wear lenses, may have a much higher risk of keratitis.

There are two types of disposable lenses:

• Daily-wear disposable lenses are removed and cleaned daily, just like conventional lenses. They are worn for 2 to 4 weeks and then discarded.
• Most extended-wear disposable lenses are designed to be worn day and night for 1 week and then discarded. Some lenses have recently been approved by the U.S. Food and Drug Administration (FDA) for 30-day extended wear. But some people cannot tolerate the extended wear; their eyes become irritated if the contacts are not regularly removed and cleaned. The recommended wearing time for extended-wear lenses has been cut from 30 days to 7 days. Although approved by the FDA, extended-wear contact lenses increase your risk of infection.