What is amblyopia?
Amblyopia is poor vision in an eye that did not develop
normal sight during early childhood. It is sometimes
called "lazy eye." When one eye develops good
vision while the other does not, the eye with poorer
vision is called amblyopic. Usually, only one eye is
affected by amblyopia.
The condition is common, affecting approximately 2
or 3 out of every 100 people. The best time to correct
amblyopia is during infancy or early childhood.
How does normal vision develop?
Newborn infants are able to see, but as they use their
eyes during the first months of life, vision improves.
During early childhood years, the visual system changes
quickly and vision continues to develop.
If a child cannot use his or her eyes normally, vision
does not develop properly and may even decrease. After
the first nine years of life, the visual system is usually
fully developed and usually cannot be changed.
The development of equal vision in both eyes is necessary
for normal vision.
Many occupations are not open to people who have good
vision in one eye only. If the vision in one eye should
be lost later in life from an accident or illness, it
is essential that the other eye have normal vision.
Without normal vision in at least one eye, a person
is visually impaired.
For all of these reasons, amblyopia must be detected
and treated as early as possible.
When should vision be tested?
It is recommended that all children have their vision
checked by their pediatrician, family physician, or
ophthalmologist at or before their fourth birthday.
Most physicians test vision as part of a child's medical
examination. They may refer a child to an ophthalmologist
if there is any sign or an eye condition.
New techniques make it possible to test vision in infants
and young children. If there is a family history of
misaligned eyes, childhood cataracts, or a serious eye
disease, an ophthalmologist can check vision even earlier
than age three.
What causes amblyopia?
Amblyopia is caused by any condition that affects normal
use of the eyes and visual development. In many cases,
the conditions associated with amblyopia may be inherited.
Children in a family with a history of amblyopia or
misaligned eyes should be checked by an ophthalmologist
early in life.
Amblyopia has three major causes:
Strabismus (misaligned eyes)
Amblyopia occurs most commonly with misaligned or
crossed eyes. The crossed eye "turns off"
to avoid double vision and the child uses only the
better eye.
Unequal focus (refractive error)
Refractive errors are eye conditions that are corrected
by wearing glasses. Amblyopia occurs when one eye
is out of focus because it is more nearsighted, farsighted,
or astigmatic than the other.
The unfocused (blurred) eye "turns off"
and becomes amblyopic. The eyes can look normal but
one eye has poor vision. This is the most difficult
type of amblyopia to detect since it requires careful
measurement of vision.
Cloudiness in the normally clear eye tissues
An eye disease such as a cataract (a clouding of
the eye's natural lens) may lead to amblyopia. Any
factor that prevents a clear image from being focused
inside the eye can lead to the development of amblyopia
in a child. This is often the most severe form of
amblyopia.
How is amblyopia diagnosed?
It is not easy to recognize amblyopia. A child may not
be aware of having one strong eye and one weak eye.
Unless the child has a misaligned eye or other obvious
abnormality, there is often no way for parents to tell
that something is wrong.
Amblyopia is detected by finding a difference in vision
between the two eyes. Since it is difficult to measure
vision in young children, your ophthalmologist often
estimates visual acuity by watching how well a baby
follows objects with one eye when the other eye is covered.
Using a variety of tests, the ophthalmologist observes
the reactions of the baby when one eye is covered. If
one eye is amblyopic and the good eye is covered, the
baby may attempt to look around the patch, try to pull
it off or cry.
Poor vision in one eye does not always mean that a
child has amblyopia. Vision can often be improved by
prescribing glasses for a child.
Your ophthalmologist will also carefully examine the
interior of the eye to see if other eye diseases may
be causing decreased vision. These diseases include:
How is amblyopia treated?
To correct amblyopia, a child must be made to use the
weak eye. This is usually done by patching or covering
the strong eye, often for weeks or months.
Even after vision has been restored in the weak eye,
part-time patching may be required over a period of
years to maintain the improvement.
Glasses may be prescribed to correct errors in focusing.
If glasses alone do not improve vision, then patching
is necessary.
Occasionally, amblyopia is treated by blurring the
vision in the good eye with special eye drops or lenses
to force the child to use the amblyopic eye.
Amblyopia is usually treated before surgery to correct
misaligned eyes, and patching is often continued after
surgery as well.
If your ophthalmologist finds a cataract or other abnormality,
surgery may be required to correct the problem. An intraocular
lens may be implanted. After surgery, glasses or contact
lenses can be used to restore focusing, while patching
improves vision.
Amblyopia cannot usually be cured by treating the cause
alone. The weaker eye must be made stronger in order
to see normally. Prescribing glasses or performing surgery
can correct the cause of amblyopia, but your ophthalmologist
must also treat the amblyopia.
If amblyopia is not treated, several problems may occur:
-
the amblyopic eye may develop a serious and permanent
visual defect
-
depth perception (seeing in three dimensions) may
be lost
-
if the good eye becomes diseased or injured, a
lifetime of poor vision may be the result.
Your ophthalmologist can give you instructions on how
to treat amblyopia, but it is up to you and your child
to carry out this treatment.
Children do not like to have their eyes patched, especially
if they have been depending on the eye being patched
to see clearly. But as a parent, you must convince your
child to do what is best for him or her.
Successful treatment mostly depends on your interest
and involvement, as well as your ability to gain your
child's cooperation. In most cases, parents play an
important role in determining whether their child's
amblyopia is to be corrected.
Loss of vision is preventible
Success in the treatment of amblyopia also depends
upon:
If the problem is detected and treated early, vision
can improve for most children. Sometimes part-time treatment
may have to continue until the child is about nine years
of age. After this time, amblyopia usually does not
recur.
If amblyopia is first discovered after early childhood,
treatment may not be successful. Amblyopia caused by
strabismus or unequal refractive errors may be treated
successfully at a much older age than the amblyopia
caused by cloudiness in tissues in the eye.
If you have additional questions or would like any
further information, contact your ophthalmologist.
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