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Cataract
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(click image for
larger view)
The dilated pupil in this eye appears
white due to an advanced cataract.
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A cataract is a loss of clarity, or clouding,
of the normally clear lens inside the eye. As one ages,
chemical changes occur in the lens that make it less transparent.
The loss of transparency may be so mild that vision is hardly
affected or it may be so advanced thatvision is very compromised
and reading is blurred. When the lens gets cloudy enough
to obstruct vision to any significant degree, it is called
a cataract. Sometimes a new prescription for glasses can
improve the blurred vision a cataract causes. If the cataract
continues to progress, glasses will no longer correct the
situation.
Cataracts most commonly form as an aging
process. Other causes include trauma, medications such as
steroids, systemic diseases such as diabetes and prolonged
exposure to ultraviolet light. Occasionally, babies are
born with a cataract.
In understanding a cataract, it is helpful
to compare the eye to a camera. Light rays focus through
your lens on the retina, a layer of light sensitive cells
lining the back of the eye. Similar to film in a camara,
the retina allows the image to be "seen" by the
brain. When a cataract forms, the lens is cloudy and prevents
light rays from passing clearly through it and on to the
retina.
The typical symptom of cataract formation
is a slow, progressive, and painless decrease in vision.
Other vision changes include glare, particularly at night,
frequent eyeglass prescription changes, a decrease in color
perception, and in rare cases, double vision.
Ironically as the lens gets harder, farsighted
or hyperopic people experience improved reading vision and
are less dependent on glasses. This is called second sight.
However, nearsighted or myopic people become more nearsighted
or myopic, causing distance vision to be worse. Some types
of cataracts affect distance vision more than reading vision,
while others affect reading vision more than distance vision.
There has been some evidence that reducing
the amount of ultraviolet light exposure by wearing a wide-brim
hat and ultraviolet light-blocking sunglasses may reduce
risk for developing cataract. However, once a cataract has
developed, there is no way to reverse it. Only surgical
removal will improve vision lost from cataract formation.
Outpatient surgery can remove the cataract through either
a small incision (phacoemulsification) or a large incision
(extracapsular extraction). The time to have surgery is
your decision, and should be considered when your vision
is so poor that it interferes with your lifestyle. It is
a myth to think you must wait until a cataract is "ripe"
for removal. Rather, the benefit of surgery and chance for
improved vision is weighed against the small risk that accompanies
the procedure. This is an informed decision you should make
with your surgeon.
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