What is a cataract?
A cataract is a cloudy or opaque area in the lens of the eye. The lens
is located behind the pupil and iris. It helps focus light onto the
retina, the light-sensitive tissue that lines the inside of the back of
the eye. Usually, the lens is transparent. But if it becomes clouded,
the passage of light is obstructed and vision may be impaired (Figure 1).
What causes a cataract?
When a cataract forms, there is a change in the chemical composition
of the lens, but scientists do not know exactly what causes these
chemical changes. The most common form of cataract is related to aging,
although this type can occur at age 50 or even earlier. Cataracts also
may be associated with diabetes, other systemic diseases, drugs, and eye
injuries. Sometimes babies are born with congenital cataracts or develop
them during the early years of life.
What are the symptoms of a cataract?
Here are some signs of cataract:
- Cloudy, fuzzy, foggy, or filmy vision.
- Changes in the way you see colors.
- Problems driving at night because headlights seem too bright.
- Problems with glare from lamps or the sun.
- Frequent changes in your eyeglass prescription.
- Double vision.
- Better near vision for awhile only in farsighted people.
These symptoms also can be signs of other eye problems.
See your eye doctor to find out what you have and how it can be
treated.
How Is a Cataract Diagnosed?
A regular eye exam is all that is needed to find a cataract. Your eye
doctor will ask you to read a letter chart to see how sharp your sight
is. You probably will get eye drops to enlarge your pupils (the round
black centers of your eyes). This helps the doctor to see the inside of
your eyes. The doctor will use a bright light to see whether your lenses
are clear and to check for other problems in the back of your eyes.
Other eye tests may also be used occasionally to show how poorly you
see with cataract or how well you might see after surgery:
- Glare test.
- Contrast sensitivity test.
- Potential vision test.
- Specular photographic microscopy.
Only a few people need these tests.
When should a cataract be removed?
A cataract should be removed surgically when it has progressed to the
point where resulting vision problems interfere with one's daily
activities. A second reason for cataract surgery, more urgent but less
common than the first, is that the cataract has become completely opaque
(mature, Figure 2). It is possible for a mature cataract to swell and even
disintegrate inside the eye. Such changes can permanently endanger
vision.
With congenital cataracts, it used to be standard practice to postpone surgery until the child was at least 6 months old. Recently, however, cataracts have been removed from the eyes of newborn infants with good results. Early removal of severe congenital cataract(s) is an important advance because it reduces the risk of visual loss resulting from the disuse of one or both eyes during childhood.
How are cataracts treated?
Treating cataracts really involves two steps. The first is removal of
the clouded lens by an ophthalmologist. Surgery is the only method
proven effective for removing cataracts. The second is finding an
appropriate substitute for the natural lens. The decision about which
substitute lens to use is usually made before surgery.
There are two general methods of removing a cataract: intracapsular
and extracapsular extraction of the lens. Intracapsular extraction is
sometimes used to remove senile cataracts. In this method, the entire
lens, including its capsule, is removed.
Extracapsular extraction involves removal of most lens tissue but the
back part of the lens capsule is left in place. In infants and young
children, whose lenses are relatively soft, the lens tissue may be
withdrawn through a hollow needle, a procedure called aspiration. A
variety of extracapsular techniques are also used to remove the lens in
adults.
One technique is called phacoemulsification. High-frequency sound
vibrations (ultrasound) are used to soften and liquefy the lens so it
can be aspirated through the needle.
Phacoemulsification should not be confused with another form of eye
surgery, photocoagulation, in which laser light--not ultrasound--is used
to treat some eye disorders other than cataract. A laser cannot remove a
cloudy lens or make it clear again. However, some doctors may use a
laser to open the front part of the lens capsule before removing the
lens or to help patients who develop "after-cataract."
How safe is cataract surgery?
Cataract surgery is one of the most successful operations done
today--more than 90 percent of the people who have this surgery find
that they can see better. Complications may occur, but most are
treatable. Serious complications that threaten vision are rare.
Certain people may not benefit much from cataract surgery. They
include people whose cataracts are not advanced enough to impair vision
seriously and those whose vision is impaired by another eye disease as
well.
In summary, each cataract patient should discuss the possibility of
surgery with the doctor who examines his or her eyes to determine
whether the potential benefits of cataract surgery outweigh the risks.
It is also very important to decide in advance, with the help of the
doctor, what form of substitute lens would be most suitable. Patients
may want to get a second opinion on the advisability of surgery and on
the most appropriate substitute lens to use after surgery.
What are the choices for a substitute lens?
There are three options for replacing the natural lens removed in
cataract surgery: eyeglasses, contact lenses, or an intraocular lens
implant. Each has advantages and drawbacks.
Eyeglasses. This is a safe and time-proven solution to the problem of
seeing without a natural lens. But cataract eyeglasses can have some
unpleasant effects. Patients may be bothered by the fact that these
glasses magnify objects 20-35 percent, affect depth perception until the
person relearns how to judge distances, and limit side vision.
If only one eye requires cataract surgery, eyeglasses may well cause
problems because the person is unable to fuse the different-sized images
formed by the operated and unoperated eyes. Such patients are often
advised before surgery that it would be best to use a contact lens, or
have a lens implant.
Contact lenses. These usually provide better vision than eyeglasses
and also are quite safe if handled and maintained properly. A contact
lens may be especially helpful after cataract extraction in one eye.
With a contact lens in the operated eye, the difference in the size of
the images seen by the two eyes is much smaller. Soft contact lenses are
commonly used for cataract patients.
Another option is the extended-wear contact lens. These lenses can be
left in the eye for a longer period of time without being removed, even
for sleep. They may be especially useful for people who have trouble
inserting and removing a contact lens, because an eye care specialist
can remove and clean them periodically. However, extended-wear lenses
have some disadvantages: They are very fragile; some serious infections
have been reported; their long-term safety is still being assessed; and
they do require periodic removal, cleaning, and reinserting.
Intraocular lenses. These devices, sometimes called IOLs, are clear
plastic lenses that are implanted in the eye during the cataract
operation. Lens implants have certain advantages: They usually eliminate
or minimize the problems with image size, side vision, and depth
perception noted by people who wear cataract eyeglasses. Also, because
lens implants remain in the eye and do not have to be removed, cleaned,
and reinserted, they are more convenient than contact lenses. This is
particularly true for people who have physical problems that would make
it difficult for them to carry out the procedures involved in using
contact lenses.
Because of these advantages, lens implants have been used with
increasing frequency in recent years. About three-fourths of all people
now undergoing cataract surgery have an IOL inserted at the same time,
and the vast majority are very pleased with the results. Of course
ophthalmologists will continue to study IOLs for many years in an effort
to assess the long-term effects of implantation on the eye as well as
the short-term complications.
What happens after surgery?
Most people who undergo cataract surgery are treated as outpatients
and can go home the same day. For others, a stay in the hospital of 1-3
days may be required. In either case, during the early stages of
recovery, patients need to take special care to avoid strenuous physical
activity.
Can a Cataract Return?
A cataract cannot return because all or part of the lens has been
removed. However, in about half of all people who have extracapsular
surgery or phacoemulsification, the lens capsule becomes cloudy. This
cloudiness of the lens capsule, if it occurs, usually develops a year or
more after surgery. It causes the same vision problems as a cataract
does.
The treatment for this condition is a procedure called YAG
capsulotomy. The doctor uses a laser (light) beam to make a tiny hole in
the capsule to let light pass. This surgery is painless and does not
require a hospital stay (Figure 3).
Most people see better after YAG capsulotomy, but, as with cataract
surgery, complications can occur. Your doctor will discuss the risks
with you. YAG capsulotomy should not be performed as a preventive
measure.
Is Cataract Surgery Right for Me?
Most people who have a cataract recover from surgery with no problems
and improved vision. In fact, serious complications are not common with
modern cataract surgery. This type of surgery has a success rate of 95
percent in patients with otherwise healthy eyes. But no surgery is risk
free. Although serious complications are not common, when they occur
they could result in loss of vision.
If you have a cataract in both eyes, experts say it is best to wait
until your first eye heals before having surgery on the second eye. If
the eye that has a cataract is your only working eye, you and your
doctor should weigh very carefully the benefits and risks of cataract
surgery.
You will be able to make the right decision for yourself if you know
the facts. Ask your doctor to explain anything you do not understand.
There is no such thing as a "dumb" question when it comes to your
health.
Here are some questions you might ask:
- Do I need surgery right away?
- If not, how long can I wait?
- What are my personal risks?
- What benefits can I expect?
- If I choose surgery, which type is best for me?
- Which lens replacement is best for me?
- What are the chances of developing cloudiness in the lens capsule
after cataract surgery?