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Glossary
of Eye terms
Cataract
What is a cataract?
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.
What
Causes a Cataract?
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 eye care practitioners recommend
wearing sunglasses and a wide-brimmed hat to lessen your exposure.
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.
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.*
Can a cataract
spread from one eye to the other?
No.
However, many people do develop cataracts in both eyes.
Will I know
immediately that I have a cataract?
When
a cataract is small, you may not notice any changes in your
vision. Cataracts tend to grow slowly, so vision gets worse
gradually. Some people with a cataract find that their close-up
vision suddenly improves, but this is temporary. Vision is likely
to get worse again as the cataract grows.
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.
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.
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.
-
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.
-
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.
How is a cataract detected?
A
thorough eye examination by your eye doctor can detect the presence
and extent of a cataract, as well as any other conditions that
may be causing blurred vision or discomfort. A comprehensive exam usually includes:
-
Tonometry:
This is a standard test to measure
fluid pressure inside the eye. Increased pressure may be
a sign of glaucoma.
The
doctor may also do other tests to learn more about the structure
and health of your eye. There may be other reasons for visual
loss in addition to the cataract, particularly problems
involving the retina or optic nerve.
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 (see illustration).
How do I prevent cataracts
from developing?
Although
we don't know how to completely protect against cataracts, protecting
the eyes from ultraviolet (UV) light from the sun will help.
Watch
the Video
Learn more on the next
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