Contact lenses, also known simply as contacts,
are small, thin curved discs made of glass or plastic
and fitted on the eye. Today almost 30 million
people in the U.S. wear contacts. They have become
the first choice for those needing vision correction.
Contacts are very convenient eye aids compared
to traditional glasses. They provide all kinds
of vision corrections and more. They do not fall
off, do not become steamed up - hampering your
vision - and are very convenient for those having
very poor natural vision, which requires continuous
wearing of glasses or lenses.
However since they cover the eye cornea, depriving
it of nourishing oxygen, some corneal complications
can arise. Corneal complications among wearers
are a major problem. Another problem is that contacts
obstruct the smooth flow of tears. This can produce
another set of complications because tears serve
the very useful function of cleaning the eyes.
Current research development of contact lenses
is focused on lessening these complications by
making the lenses more permeable to oxygen and
less of a hindrance to tear flow. However, the
problems have not been resolved as yet.
Contacts were first introduced in the late 19th
century, when they were made of glass. These lenses
covered the entire eye and hence were called scleral
lenses. In the 1930s, lenses were made from a plastic
material called polymethyl methaclyrate. While
these were better than glass contacts, due to their
low oxygen permeability, their use was not popular.
The development of contacts began in a major way
in the 1950s when corneal lenses were introduced,
which covered only the cornea. Corneal lenses are
easier to fit and allow better flow of oxygen and
tears. Most lenses today are corneal or semiscleral.
Scleral lenses are preferred for those with severe
keratoconus, irregular corneas and certain other
special eye surface disorders.
Modern lenses are mainly corneal and made from
two types of plastics, rigid gas permeable (RGP)
and silicon-gel plastic.
Contacts are used for both refractive disorders
like near or far sightedness and astigmatism, and
also for non-refractive vision disorders like glaucoma
and cataracts. They are also used for therapeutic
purposes to protect the eyes after certain eye
surgeries. They are furthermore used for cosmetic
purpose to change the appearance of the eye or
to mask any eye injury.
Types of contact lenses
Contacts, as mentioned earlier, are mostly made
from silicon gel material and RPG. These are called
soft contacts and hard or rigid gas permeable RGP
They are used by about 75% of the contact lens
wearers today. They have higher water content,
making them flexible, soft and therefore comfortable
to wear. Soft contacts are of the following types.
Daily wear contacts: Most people choose to wear
daily wear contacts, which have to be inserted
and removed every day. Wearing them during sleep
is not advised. If cleaned and maintained well,
they should last around a year.
Disposable contacts: Depending on their composition,
they are used for periods ranging from one day
to three months, after which they are thrown away.
Their main advantage is that they carry less risk
Extended wear contacts: They are made from super
permeable silicon hydrogel and so have a higher
oxygen permeability allowing you to sleep with
them still on your eyes. Depending on the type
of lens, they are worn continuously for a week
to 30 days. Silicon lenses exhibit far fewer eye
RGP lenses are used to correct all types of vision
problems including astigmatism. They are made from
harder material and therefore feel uncomfortable
initially. However, RGP lenses have higher oxygen
permeability and carry fewer chances of corneal
infections than soft contacts. They are easier
to maintain and are more durable, lasting for two
to three years.
Lenses for astigmatism
A class of lenses, called toric lenses, is used
exclusively to correct types of astigmatism. These
are also made from RGP and soft contact material
but are given a special surface treatment to correct
astigmatism and, with some types of lens, for correcting
Contact lens complications
The fact that lenses are a barrier to normal flow
of oxygen to the cornea exposes the wearer to various
complications. These complications are unavoidable.
At best, with improved material and design we can
expect these complications to become easier to
Cleaning non-disposable lenses regularly is vital
not only for the lenses but also for your eyes.
Many complications are preventable if you strictly
follow the cleaning regimen prescribed by the doctor.
Indeed, complications due to a faulty cleaning
regimen are a common problem.