- How does vision develop?
- Good vision develops early in
life as a result of normal use of the eyes. Although infants
can see at birth, vision gradually improves as use of the eyes
increases. During the early childhood years, the visual system
is in a changeable state and continues to develop with proper
use of the eyes. However, if the eyes are not used to capacity,
visual ability decreases. After the first 10 years, development
of the visual system remains unchanged, whether it is used or
not.
- What causes amblyopia?
- Amblyopia is caused by an abnormality
which interferes with the normal use of the eyes and visual development.
Commonly, amblyopia is caused by strabismus, a condition in which
the eyes are misaligned. With strabismus, often referred to as
"cross eyes", the eyes do not work together and one
or both eyes turn in, out, up or down.
Amblyopia can also be caused
by vision problems such as nearsightedness, farsightedness, and
astigmatism. When there is a large difference in visual acuity
between the eyes, both eyes do not have equal focusing ability.
One eye is out of focus because of a stronger degree of nearsightedness,
farsightedness or astigmatism. Therefore, this weaker eye does
not develop properly. The eye with the better visual ability
does most or all of the visual work, allowing the other eye to
become lazy or amblyopic.
More rarely, amblyopia is caused
by an eye disease, such as cataracts, which interferes with proper
visual development. In addition, amblyopia is inherited in many
cases. Whatever the underlying cause, amblyopia is the result
of long standing suppression of one eye. The child favors the
eye which sees best and the other eye does not develop fully.
- How does amblyopia affect
vision?
- In normal vision, both eyes
look at an object at the same time and each sends a picture to
the brain. These two pictures are blended into one three-dimensional
image (fusion). When one eye is weaker than the other, both eyes
do not focus on one object simultaneously. As a result, two different
images are sent to the brain. The image sent by the stronger
eye is clear, while the message sent by the weaker eye is blurry.
Since the brain is unable to
blend the two images into one picture, a child quickly and unconsciously
learns to ignore the image seen by the weaker eye (suppression).
The normal eye takes over, while the weaker eye becomes lazy
from lack of use. If the condition is left uncorrected, the weak
or lazy eye will eventually develop amblyopia, or a loss of vision.
Because it usually causes no
symptoms, amblyopia often goes undetected. Unless the child has
a misaligned eye or other obvious abnormality, there is nothing
to suggest the condition to even the most perceptive parents.
The child accepts having one good eye and one poor eye and considers
amblyopia to be the normal situation. In most cases, amblyopia
must be detected by checking vision.
- How is amblyopia diagnosed?
- Amblyopia is often detected
when a substantial difference in vision between each eye is found.
Vision may be tested with the E test, in which the child is asked
to point in the same direction as the "fingers" of
a capital E on the eye chart. A series of progressively smaller
E's is used to determine how well the child can see. In very
young children, visual acuity can be estimated by how well the
child follows a small object with one eye covered. A normal eye
will look directly at an object while an amblyopic eye may look
to the side.
- How is amblyopia treated?
- Unfortunately, the treatment
of the cause of amblyopia does not cure amblyopia itself. After
the causal problem is corrected, amblyopia must be treated separately.
To correct amblyopia, the weak eye must be forced to work by
patching the good eye or using drops to blur vision in the good
eye. By impairing vision in the good eye, the weak eye is forced
to work until vision in both eyes becomes equal.
Amblyopia must be treated as
soon as possible if vision is to be restored. The results of
treatment depend on the duration and severity of amblyopia and
the age treatment is begun. Close parental supervision of the
child's treatment is necessary to ensure the return of good vision.
- Prevention is the best medicine
- Early eye examinations are extremely
important in the detection of amblyopia. Prompt treatment and
strict adherence to the treatment program are required to restore
good vision. If left undetected and untreated beyond early childhood,
amblyopia cannot be corrected. However, with early detection
and treatment, poor vision can usually be improved.
If your child has not had his
eyes checked, he should have a complete eye examination.
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