Vance Thompson, MD
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
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.
Researchers are gaining additional insights about what causes these
specific types of proteins (crystallins) to cluster in abnormal ways
to cause lens cloudiness and cataracts. One
suggests that fragmented versions of these proteins bind with normal
proteins, thus disrupting normal function.
Hazy or blurred vision may indicate a cataract.
Cataracts are classified as one of three types:
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 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 subcapsular cataract begins at the back of the lens.
People with diabetes, high
or those taking high doses of steroids may develop a subcapsular
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
If you think you have a cataract, see an
eye doctor for an exam to find out for
What Causes Cataracts?
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
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.
Left: A cataract is a clouding of the eye's natural lens.
Right: Cataracts affect vision by scattering incoming light.
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
Some eyecare practitioners believe that a diet high in
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
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.*
An intraocular lens (IOL) is implanted in the eye in place of the
patient's clouded natural lens. Shown is Alcon's new AcrySof Natural
IOL; the lens material is yellow because it filters out blue light,
which may be harmful to eyes.
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.
is very successful in restoring vision. In fact, it is the most
frequently performed surgery in the United States, with more than 3
million Americans undergoing cataract surgery 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.
potentially help you see at all distances, not just one. Another new
type of IOL blocks both ultraviolet and blue light rays, which
research indicates may damage the retina (see illustration).
Read more about what to expect if you have
and how to deal with rare
cataract surgery complications.
Also, men should be aware that certain prostate drugs can cause
intraoperative floppy iris syndrome
(IFIS) during a cataract procedure