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A cataract is a clouding of the eye's natural lens, which lies behind the
iris
and the
pupil
. The lens works much like a camera lens, focusing light onto
the retina
at the back of the eye. The lens also adjusts the eye's focus,
letting us see things clearly both up close and far away.
The lens is mostly made of water and protein. The protein is arranged in a
precise way that keeps the lens clear and lets light pass through it. But as we
age, some of the protein may clump together and start to cloud a small area of
the lens. This is a cataract, and over time, it may grow larger and cloud more
of the lens, making it harder to see.
Cataracts are classified as one of three types:
 | A nuclear cataract is most commonly seen as it forms. This cataract
forms in the nucleus, the center of the lens, and is due to natural aging
changes.
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| A cortical cataract, which forms in the lens cortex, gradually extends
its spokes from the outside of the lens to the center. Many diabetics develop
cortical cataracts.
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| A subcapsular cataract begins at the back of the lens. People with
diabetes, high farsightedness
, retinitis pigmentosa
or those taking high doses
of steroids may develop a subcapsular cataract. |
Cataract Symptoms and Signs
A cataract starts out small, and at first has little effect on your
vision. You may notice that your vision is blurred a little, like looking
through a cloudy piece of glass or viewing an impressionist painting. A cataract
may make light from the sun or a lamp seem too bright or glaring. Or you may
notice when you drive at night that the oncoming headlights cause more glare
than before. Colors may not appear as bright as they once did.
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The type
of cataract you have will affect exactly which symptoms you experience and
how soon they will occur. When a nuclear cataract first develops it can
bring about a temporary improvement in your near vision, called "second
sight." Unfortunately, the improved vision is short-lived and will
disappear as the cataract worsens. Meanwhile, a subcapsular cataract may
not produce any symptoms until it's well-developed.
If you think
you have a cataract, see an eye doctor for an exam to find out for sure.
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Hazy or blurred vision may indicate a cataract.
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What Causes a Cataract?
No one knows for sure
No one knows for sure why the eye's lens changes as we age, forming
cataracts. Researchers are gradually identifying factors that may cause
cataracts — and information that may help to prevent them.
Many studies suggest that exposure to ultraviolet light is associated with
cataract development, so eyecare practitioners recommend wearing sunglasses and
a wide-brimmed hat to lessen your exposure. Other types of radiation may also be
causes. For example, a 2005 study conducted in Iceland suggests that airline
pilots have a higher risk of developing nuclear cataract than non-pilots, and
that the cause may be exposure to cosmic radiation. A similar theory suggests
that astronauts, too, are at risk from cosmic radiation
Other studies suggest people with diabetes are at risk for developing a
cataract. The same goes for users of steroids, diuretics
and major
tranquilizers, but more studies are needed to distinguish the effect of the
disease from the consequences of the drugs themselves.
Some eyecare practitioners believe that a diet high in antioxidants, such as
beta-carotene (vitamin A), selenium and vitamins C and E, may forestall cataract
development. Meanwhile, eating a lot of salt may increase your risk.
Other risk factors include cigarette smoke, air
pollution and heavy alcohol consumption. A small study published in 2002 found
lead exposure to be a risk factor; another study in December 2004, of 795 men
age 60 and older, came to a similar conclusion. But larger studies are needed to
confirm whether lead can definitely put you at risk, and if so, whether the risk
is from a one-time dose at a particular time in life or from chronic exposure
over years.
Cataract Treatment
When symptoms begin to appear, you may be able to improve your vision for a
while using new glasses, strong bifocals, magnification, appropriate lighting or
other visual aids.
Think about surgery when your cataracts have progressed enough to seriously
impair your vision and affect your daily life. Many people consider poor vision
an inevitable fact of aging, but cataract surgery is a simple, relatively
painless procedure to regain vision.
Cataract surgery is very successful in restoring vision. In fact, it is the
most frequently performed surgery in the United States, with over 1.5 million
cataract surgeries done each year. Nine out of 10 people who have cataract
surgery regain very good vision, somewhere between 20/20 and 20/40.
During surgery, the surgeon will remove your clouded lens, and in most cases
replace it with a clear, plastic intraocular lens
(IOL). New IOLs are being
developed all the time to make the surgery less complicated for surgeons and the
lenses more helpful to patients. One example is a new IOL that lets patients see
at all distances, not just one. Another new IOL blocks both ultraviolet and blue
light rays, which research indicates may damage the retina
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