Several different types of contact lenses are available to
treat vision problems. Consult an eye doctor who is
willing to work with you to select the best type of lens for your needs and
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 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), although many eye
specialists advise against wearing them for an extended period of time or while sleeping. RGP lenses usually need to be replaced after 2 to 3 years of use.
Soft contact lenses
Soft (silicone 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 more fragile than
hard lenses and require more intensive cleaning. Soft lenses that can correct
astigmatism 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 day and night. After several days, you take
them out, clean them, and wear them again. But some people's eyes
become irritated if the contacts are not routinely removed and cleaned.
Extended use may be uncomfortable and increases the risk of damaging the eye.
Even though the U.S. Food and Drug Administration (FDA) has approved some
of these lenses for 30-day use, many eye doctors recommended that people remove them every day.
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 the extended-wear
kind, may have a 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. The
FDA has approved some lenses for 30-day use.
But some people cannot tolerate the extended wear. Their eyes become irritated
if the contacts are not routinely removed and cleaned. Also, the risk of infection is greater when a person wears the lenses all day and night. Many eye
doctors recommend that people remove them every day.
How this information was developed to help you make better health decisions.