Contact lenses are thin, curved plastic disks designed
to cover the cornea, the clear front covering of
the eye. Contacts cling to the film of tears over
the cornea because of surface tension, the same force
that causes a drop of water to cling to the side
of a glass.
Contact lenses are used to correct the same conditions
that eyeglasses correct:
(trouble reading with age)
contacts can be used to change the color of the eyes
to various degrees. Contact lenses
are sometimes used therapeutically in eye diseases
where an uneven cornea blurs vision, such as keratoconus
or scarring. They are also sometimes used for corneal
abrasions to assist in healing.
Rigid contacts were the first lenses; they were developed
in the 1960's. They are made of a type of plastic called
PMMA, which is very durable, but does not allow oxygen
in the air to directly reach the cornea. When the eye
blinks, the lens moves, which allows the oxygen dissolved
in the tears to reach the cornea. While rigid lenses
are probably the least comfortable type of contacts
to wear, some users prefer them for their durability
and lower cost.
Newer rigid lenses made of plastic combined with
other materials, such as silicone and fluoropolymers,
allow oxygen in the air to pass directly through
the lens. They are called gas permeable. Gas-permeable
lenses are less durable than conventional rigid
lenses but are more comfortable. Some gas-permeable
lenses are extended wear and may be worn overnight
for up to seven days.
Soft contact lenses
These lenses are made of plastic materials that incorporate
water. The water makes them soft and flexible,
as well as allowing oxygen to reach the cornea.
More than 75% of contact lens wearers in the United
States use soft contact lenses. Some soft contact
lenses are extended-wear lenses, which means they
are designed to be left in the eye overnight. It
is recommended that extended-wear lenses be removed
weekly, at a minimum, for thorough cleaning and
disinfection. The FDA has newly approved a contact
lens for wear up to 30 days. Soft daily wear lenses
should never be used as extended-wear lenses. Extended-wear
lenses can be used as daily-wear lenses. Studies
have shown increased risk of corneal infections
associated with extended wear contact lens use.
soft contact lenses
Disposable lenses for daily or extended wear are available and very popular. The lenses are discarded
and replaced each week. These lenses are convenient
and may reduce the chance of allergic reaction
and deposit formation.
Toric contact lenses
Toric lenses correct moderate astigmatism. They are
available in both rigid and soft materials.
These lenses correct both reading and distance vision.
They can eliminate the need for reading glasses.
When comparing the price of contact lenses, it's
important to consider what services are included.
Does the fitting include a thorough eye examination
and follow-up? Can you exchange lenses during the
initial fitting, and is insurance for lost lenses
available? If you need treatment for an eye condition
not directly related to the contact lenses, such
as inflamed eyelids or dry eyes, there may be additional
What are the risks of wearing contact lenses?
Rigid lenses that are not gas permeable are more
likely to scratch the cornea if the lens does
not fit properly of if the lens is worn while
sleeping. They are also more likely to slide
off the cornea and become hidden under the
Rigid lenses traditionally had a reputation
for "popping out" of the eye. New
lens designs have minimized the chance of losing
contact even during vigorous exercise. Rigid
gas-permeable lenses may allow more protein
build-up than rigid non-gas-permeable lenses.
build-up results in discomfort, blurring and
intolerance to the lenses. You will need special
cleaning solutions to dissolve the protein.
lenses should never be worn as extended-wear
lenses. Misuse can lead to temporary and even
permanent damage to the cornea. People who wear
any type of lens overnight have a greater chance
of developing infections of the cornea. These
infections are often due to poor cleaning and
Contact lenses must be properly cleaned and disinfected
when you remove them to kill germs and prevent
infection. At the time you insert your contact
lenses, you should thoroughly rinse the case
with warm water and allow it to dry. All contact
lens cases need frequent cleaning, including
disposable lens cases.
Soft extended-wear contacts
are the most likely to have protein build-up
and cause lens-related
allergies. Soft daily-wear lenses are less
likely to create problems. Rigid gas-permeable
or disposable lenses may be good choices for
someone with allergies.
Homemade saline solutions
have been linked to serious eye infections
and should never
Any eye drops, even nonprescription ones, can
interact with all types of contact lenses.
Check with you ophthalmologist before you use
any eye drops.
Most people who need vision correction can wear
contact lenses, but there are some exceptions.
Some of the conditions that might keep you from
contact lenses are:
eyes (improper tear film)
work environment that is very dusty or dirty
to handle and care for the lenses properly
The health of you eyes should be you
main concern. An ophthalmologist is the
physician specialist who can help you decide
contact lenses are right for you.