Cataract Surgery
A cataract is the lens
inside the eye that has lost its clarity. As the lens becomes cloudy, vision gets worse.
At some point, the loss of vision becomes great enough that an individual is willing to
have an operation to improve the vision. The surgery is a cataract extraction. In this
procedure, the cloudy lens is removed from the eye. In most situations, an artificial
lens, called a lens implant, is placed inside the eye to take the place of the natural
lens that has been removed.
In order to understand the different types of cataract operations, one needs to know
about the structure of the lens. The crystalline lens inside
the eye has several parts. The center of the lens is a hard core called the nucleus. The
lens nucleus is made up of rings of cells, pushed together over time, similar to the rings
in the trunk of a tree. The nucleus starts out very soft in childhood, but gets
progressively harder with age. Surrounding the nucleus is the lens cortex. The cortex is a
softer material. The entire lens is enclosed by the capsule that is similar to a clear
bag. The lens is held in place by small fibers call the zonule.
A cataract operation is usually done with a local anesthetic. This means that medicine
is used to numb the eye so that the patient feels no pain. The patient is usually awake
during the operation.
There are several different techniques for removing a cataract. They are divided into
two groups: intracapsular and extracapsular. One common misunderstanding about cataract
surgery is that it can be done with a laser. A laser is a tool that is used commonly in
eye surgery, but it cannot be used to remove cataracts.
In an intracapsular cataract operation, the entire lens is removed with its capsule. A
large opening is made in the eyeball. A special medicine is injected into the eye that
causes the zonular fibers to dissolve. Then, a special instrument is placed on the lens.
Liquid nitrogen is used to cause the instrument to freeze to the lens. When the lens is
frozen to the probe, the lens is gently pulled out of the eye. Many stitches are necessary
to close the eye until it heals.
Intracapsular cataract operations are now rare. They were the most common type of
cataract surgery until the early 1980s. Now, extracapsular cataract extraction is the
method of choice for removing a cataract, except in very unusual conditions.
The difference between the two operations is that in an extracapsular cataract
operation, part of the capsule is left inside the eye. A smaller opening is made into the
eye. Then, an opening is created in the front of the capsule, large enough for the nucleus
of the lens to be removed. The nucleus can either be removed as a whole, or it can be
dissolved into tiny pieces and vacuumed out of the eye in a technique called
phacoemulsification. Then, the cortex is also sucked out of the eye, leaving just the back
part of the capsule to remain. Depending upon the type of operation, stitches may or may
not be necessary to close the eyeball.
In either type of operation, after the natural lens is removed, the lens implant can
be inserted into the eye. Most of these lenses are made of a hard plastic material.
Recently, some newer types of material such as silicone, acrylic and hydrogels have been
used. In an intracapsular cataract operation, the lens implant is placed in front of the iris, the colored part of the eye. In an extracapsular
operation, the implant is placed behind the iris, the lens' natural position. This is only
one of many advantages to the extracapsular approach to surgery.
After cataract surgery, glasses are usually worn to fine-tune vision. With a lens
implant in the eye, the vision is close to normal, even without glasses. If a lens implant
is not used, much thicker glasses may be necessary.
Any operation has benefits and risks. The benefit of cataract surgery is improved
vision. The results of surgery, however, cannot be guaranteed. Any operation can have
complications that can affect the outcome. If a problem develops during or after cataract
surgery, vision might not improve. It is even possible to lose all vision if a severe
problem occurs. In general, cataract surgery is usually safe and successful. On average,
95% of people that have the operation in this country have a good result.
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