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Contact Lenses Basics:
Contact lenses can correct
your nearsightedness,
farsightedness and
astigmatism
Contact lenses can also
provide a full field of
unobstructed vision, which
is great for sports.
If you're new to contact
lenses, your first step is
to see an eye doctor. They
must be prescribed and
properly fitted by an
ophthalmologist. Your doctor
will evaluate your visual
needs, your eye structure,
and your tears to help
determine the best type of
lens for you.
The many types of contact
lenses currently available
can be grouped in various
ways according to:
Contact Lens Materials
Classified by material,
there are three types of
contact lenses:
-
Hard lenses are
made from PMMA. These
lenses are virtually
obsolete and rarely
used.
-
Soft lenses are
made from gel-like,
water-containing
plastics, and are most
common. They're a bit
larger in size than your
iris (the colored part
of your eye).
-
GP lenses, also
known as RGP or "oxygen
permeable" lenses, are
made from rigid,
waterless plastics and
are especially good for
presbyopia and high
astigmatism. These
lenses are usually about
eight millimeters in
diameter, which is
smaller than your iris.
Recently, new silicone
hydrogel contact lenses have
been introduced. They have
become the contact lenses of
choice for many eye care
practitioners, because they
allow more oxygen to pass
through the lens to the eye,
and they are less prone to
dehydration.
Contact Lens Wearing Time
Now, two types of lenses are
classified by wearing time:
-
Daily wear - must
be removed nightly
-
Extended wear -
can be worn overnight,
usually for seven days
consecutively without
removal
"Continuous wear" is a type
of extended wear lens that
can be worn for 30
consecutive nights.
Disposal Intervals for
Contact Lenses
One problem with soft
contact lenses is that
proteins and lipids - which
are naturally found in tears
- adhere to the surface of
the lens, sometimes causing
discomfort and providing
hiding places for
infection-causing germs.
Lens-cleaning products help.
But over time buildup still
occurs, necessitating lens
replacement. Disposable
lenses, first introduced in
1987, address this problem
in different ways. Here are
the options:
-
Daily disposable
- replaced every day
-
Disposable (used
for daytime wear) -
replaced every two weeks
-
Disposable (used
for overnight wear) -
replaced every week
-
Continuous wear
(used for 30-day wear) -
replaced monthly
-
Planned replacement
- replaced monthly or
less frequently
Contact Lens Designs
Many lens designs are
available to correct various
types of vision problems:
-
Spherical contact
lenses are the typical,
rounded design of
contact lenses, which
can correct myopia
(nearsightedness) or
hyperopia
(farsightedness).
-
Bifocal contact
lenses contain different
zones for near and far
vision to correct
presbyopia, which is the
age-related, decreased
ability to obtain a full
range of vision
-
Orthokeratology
lenses are specially
designed to reshape the
cornea during sleep,
providing lens-free
daytime wear
-
Toric contact
lenses correct for
astigmatism, as well as
for myopia and hyperopia
All of these lenses can
be custom made for
hard-to-fit eyes. Many
other additional lens
designs are available.
Typically these are less
common and fabricated
for use in special
situations, such as
correcting for
keratoconus.
Colored Lenses. Many
of the types of lenses
described above also come in
colors that can enhance the
natural color of your eyes -
that is, make your green
eyes even greener, for
example. Or these lenses can
totally change the eye's
appearance, as in from brown
to blue.
Prosthetic Lenses.
Colored contact lenses can
also be used for more
medically oriented purposes.
People with disfigured eyes,
as a result of accidents or
disease, can use a custom,
opaque colored lens to mask
the disfigurement and match
the appearance of their
normal eye
Custom Lenses. If
conventional contact lenses
don't seem to work for you,
you might be a candidate for
a customized design.
UV-Inhibiting Lenses.
Today, many contacts
incorporate an ultraviolet
blocker in the lens
material, to cut down on UV
light that can eventually
cause cataracts and other
eye problems. You can't see
this blocker by looking at
the lens. And since contacts
don't cover your entire eye,
UV blockers cannot
substitute for traditional
sun protection like good
quality sunglasses.
Hybrid Lenses. One
brand of lenses features a
GP center with a soft outer
skirt, providing wearers
with both the crisp optics
of a rigid lens and the
comfort of a larger, soft
lens.
Contact Lens Wear and Care
Caring for your contact
lenses: cleaning,
disinfecting and storing
them is much easier than it
used to be.
Today, most people can use
"multipurpose" solutions -
meaning that one product
both cleans and disinfects,
and is used for storage.
Some people who are
sensitive to the
preservatives in
multipurpose solutions might
need preservative-free
systems, such as those
containing hydrogen
peroxide.Of course, you can
avoid lens care altogether
by using daily disposables.
Contact Lenses and UV Light
Researchers have linked
ultraviolet (UV) light to
the formation of cataracts.
Exposure to excessive UV
light also may result in a
condition called
photokeratitis.
That's why some lenses now
incorporate a UV-blocking
agent. You can't tell if a
contact lens has a UV
blocker just by looking at
it - the blocker is provided
in clear form, so as not to
disturb vision. The contact
lens packaging will specify
if the product has a UV
blocker, or you can ask your
eye doctor.
Very important: UV-blocking
contacts are not meant to
replace sunglasses. A
contact lens covers only
your cornea, not your entire
eye.
However, UV-blocking contact
lenses do help protect the
portion of the white of your
eye that is covered from
formation of growths such as
pingueculae and pterygia.
Sunglasses with UV
protection can cover more of
your eye and the parts of
your face that surround the
eye, depending on the size
of the sunglass lens. That's
why contacts with UV
blockers are designed to
complement sunglass use as
an added protection.
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