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Overview
A cataract is the clouding or opacity that
develops in the eye’s lens. The
crystalline lens is comprised primarily of protein
and water. Normally, the protein is bonded in a
way that allows light to pass through it. A
cataract forms when bonding changes and protein
molecules clump together. Eventually, these clumps
cloud the lens and block light. If left untreated,
cataracts may eventually cause blindness.
Incidence and Prevalence
In the United States, about 50% of those between
the ages 65 and 74, and 70% of those over age 75
have a cataract. Women are affected more
frequently than men. African Americans lose their
vision from both cataracts and
glaucoma at
twice the rate of Caucasian Americans, primarily
due to lack of treatment.
One in every 10,000 babies is born with congenital
cataracts. In some cases, it is related to the
mother having an infectious disease or engaging in
alcohol or drug abuse during pregnancy.
Types
The lens consists of three parts: the nucleus
(center of the lens), the lens cortex (periphery),
and the capsule (membrane that envelops the lens).
Cataracts can form in any of these parts.
Nuclear cataracts
develop in the nucleus and are the type most
commonly found in older patients. They can take
years to develop and often give the nucleus a
yellow tint.
Cortical cataracts
form in the lens cortex (peripheral area). They
eventually extend like spokes on a wheel into the
nucleus of the lens.
Subcapsular cataracts
develop in the envelope of the lens, and often in
the center. The onset of this type is rapid and
symptoms can develop over months, rather than
years.
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Causes and Risk Factors
Aging is the primary risk factor for cataracts.
Other factors determine overall risk for and
severity of the condition. When cataracts occur in
younger patients, they are usually caused by a
chronic medical condition, eye trauma, or
prescription drug.
Medical conditions
such as diabetes, myotonic dystrophy, or Wilson’s
disease increase the risk for cataracts,
regardless of age. Slowly progressing cortical
cataracts are common in diabetics. Diabetic
patients or those who take high doses of steroids
are more at risk for subcapsular cataracts.
Certain drugs
can stimulate cataract development. These include
the following:
-
Amiodarone (Cordarone®), heart medication
-
Chlorpromazine (Largactil®), sedative
-
Corticosteroids (e.g., prednisone), used to
treat inflammation in many acute and chronic
illnesses
-
Lovastatin (Mevacor®), cholesterol-lowering drug
-
Phenytoin (Dilantin®), antiseizure drug used to
treat epilepsy
Fetal exposure
to infection, radiation, steroids, alcohol, and
other substances of abuse during pregnancy are
risk factors for congenital cataracts.
Smoking and alcohol abuse
increase the risk for cataracts. Individuals who
smoke 20 or more cigarettes a day have twice the
risk of nonsmokers for developing cataracts.
Long-term alcohol abuse leads to vitamin
deficiencies that may lead to development of the
condition.
Deficiencies
in vitamins C and E, selenium, beta carotene, and
lycopene may be linked to cataract development.
These antioxidants protect the body from free
radicals that cause damage to cell walls and other
cell structures, as well as the genetic material
within cells.
African Americans
may be at higher risk for cataracts, possibly
because of this group’s higher risk for chronic
conditions (e.g., diabetes) that increase the risk
for cataracts.
Prolonged exposure to sunlight,
specifically ultraviolet B (UVB), is a risk factor
for cataracts. The longer the exposure, the
greater the risk. However, even a low level of
exposure increases risk.
An eye injury may increase the risk for a
cataract.
Eye disease
(e.g., uveitis) or infection can lead to
cataracts. A tumor can also cause changes that may
lead to the development of cataracts.
Signs and Symptoms
Symptoms depend on the cataract’s location in the
lens and the amount of clouding. Cataracts are
painless and often progress slowly, so many years
may pass before a patient experiences symptoms. If
only one eye develops a cataract, the patient may
never experience symptoms, as long as sight in the
other eye remains stable.
Common symptoms of cataracts include:
-
Blurry vision
-
Colors appear faded
-
Frequent changes in prescription eyeglasses or
contacts
-
Poor night vision
-
Seeing a halo around lights
-
Sensitivity to bright sunlight or headlight
glare at night
Diagnosis
To detect a cataract, an eye care professional
examines the lens using a slit lamp microscope.
This microscope has a light attached, which allows
the doctor to examine the cornea, iris, and lens
under high magnification. Pupil dilation (the
pupil is widened after administering eye drops)
allows the doctor to see the lens and retina
better.
Visual acuity at various distances is determined
using the standard eye chart. The examination
helps detect vision loss due to a cataract. |
