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What
are contact lenses?
 Contact
lenses are
small curved pieces of plastic which are used to
correct the specific vision defect of the user. The lenses are placed
directly on the cornea of the eye and float on a thin layer of tear fluid.
There are three types of contact lenses available-
Hard lenses
were the first type of contacts available on the market. Made of solid
plastic, these lenses are easy to keep clean because they do not absorb
proteins from the eye. They can, however, inhibit the flow of oxygen to
the cornea and must be removed at the end of each day.
Soft
lenses are the most popular form of contacts. Their softness and increased
comfort is the result of a high water content of 30 to 80
percent. These lenses allow more oxygen to reach the cornea, but are less
durable and present an increased risk of contamination because the water
provides a place where bacteria, dirt and chemicals can collect. Extended-wear
lenses are a form of soft contacts which can be worn continuously for
a number of days. Disposable extended-wear soft lenses are now available.
These one-time use lenses do not require cleaning.
Rigid gas permeable
lenses combine the features of the hard and soft contacts. They have
greater oxygen permeability than hard lenses and greater durability than
soft lenses. These lenses are designed for daytime use, but can be worn
continuously for a number of days. Contact lenses may also be made bifocal
as well as tinted to enhance eye color. The drawback to colored lenses
is that they may reduce visibility in low light situations.
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