What are contact lenses?
Contacts are thin, clear disks of plastic that float on the tear film that coats the
cornea, the curved front surface of the eye. The health of the corneal surface and
tear film are very important to your comfort and the clarity of your vision when you
are wearing contacts.
Contact lenses are used to correct the same conditions that eyeglasses correct:
• Myopia (nearsightedness)
• Hyperopia (farsightedness)
Millions of people around the world wear contact lenses — more than 24 million in
the United States alone. Depending on your lifestyle, your motivation and the health
of your eyes, contact lenses may provide a safe and effective alternative to
eyeglasses when used with proper care and maintenance.
What are the different types of contact lenses?
Many different plastics are used in the manufacture of contact lenses, but basically
there are two general types of lenses: hard and soft.
Hard lenses include the PMMA contacts that were first developed in the 1960s but
are rarely used today; and rigid gaspermeable, or RGP, contacts. RGP contacts
combine plastics with other materials such as silicone or fluoropolymers to produce a
lens that holds its shape, yet allows the free flow of oxygen through the lens to the
cornea. These lenses are more "wettable," easier to adjust to and more comfortable
to wear than the old PMMA hard lenses.
RGP lenses may be the best choice when the cornea has enough astigmatism (is
shaped like an egg instead of an orange) that a soft lens will not provide sharp
vision. They may also be preferable when a person has allergies or tends to form
protein deposits on his or her contacts.
Soft lenses are the choice of most contact lens wearers for their comfort as well as
for the great number of options available in soft contacts. These options include:
• Daily wear. These lenses are the least expensive, are removed nightly and
are replaced on an individualized schedule.