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Amblyopia, commonly known as lazy eye,
is the leading cause of vision loss in children and affects about 2 - 4%
of the population. Every year, about 120,000 children in the United
States develop amblyopia. Amblyopia is defined as a loss of vision in
one, sometimes two, eye(s), that does not have an obvious reason. For
example, the eye will look perfectly normal to the eye doctor but the
child will have reduced vision in the lazy eye. Reduced vision includes
reduced visual acuity, reduced depth perception, abnormal eye movements,
poor vision for low contrast objects, and sometimes distortions in
vision. Recent research also showed that the normal eye is also not
normal in an amblyopic child - the stronger eye or "dominant" eye also
has somewhat reduced vision!
Causes of Amblyopia
There are three main reasons why a
child develops amblyopia:
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There is a difference in the
refractive state of the two eyes, such that one eye may be normal
and not require a corrective lens, while the other eye is too
nearsighted (myopic) or too farsighted (hyperopic). The condition
is called Anisometropia, or difference in refractive error between
the two eyes. As a consequence, the eye that needs a corrective
lens will have a blurred image projected to the back of the eye
(retina) and, in turn, the brain receives a blurred image from that
eye. The eye (actually the brain) then becomes amblyopic. This
condition is also called refractive amblyopia. Anisometropic
amblyopia is very insidious; the child looks perfectly normal but
one eye is really very amblyopic. Treatment is often delayed
because the parents think that the child is fine and that there is
no reason to see an eye doctor for a comprehensive eye exam.
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There is a difference in the
alignment of the eyes such that, for example, one eye points
straight ahead and the other eye turns in toward the nose. When the
eyes point in different directions, the child is "strabismic" and
when one or sometimes both eyes appear to turn in the condition is
called esotropia or crossed eyes. When the eyes are not aligned,
the brain will receive two very different images from the eyes and
to correct this problem of double vision (diplopia) the brain will
suppress one of the images to achieve single vision. It is believed
that this suppression or turning-off of one eye's input to the brain
leads to reduced vision in the eye that is suppressed and thus leads
to amblyopia in the affected eye. Typically, it is the eye that
turns in toward the nose that becomes the amblyopic eye.
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The third type of amblyopia is
often referred to as derivational amblyopia. Whenever the two eyes
receive very different information or images, there is a high
probability of amblyopia. For example, if a child is born with a
cataract or cloudy lens such that only one eye receives a clear
image and the eye with the cataract receives a blurred image, then
the eye with the cataract will become amblyopic. If the infant has
a problem with the cornea in one eye, or one eye has excessive
matting such that the child keeps the one eye closed for a period of
time or if the child has a big astigmatism in one eye - all of these
conditions can lead to amblyopia.
Treatment
In general, the earlier the child has
the condition for the development of amblyopia the worse it may become.
For example, if a child has a cataract in one eye at birth, that eye may
become very amblyopia in a very short period of time. On the other
hand, if a child develops a cataract at, say, 5 years of age, then the
amblyopia will only gradually develop over a longer period of time. If
a child develops a cataract at say 10 years of age he/she may never
develop amblyopia.
Similarly, the sooner treatment is
instituted the faster the amblyopia will be cured. It may only take a
month of occlusion therapy to cure a 6 month old child with amblyopia
but it could take a year or more of occlusion to cure a 6 year old
child. So, the sooner the better in terms of treating amblyopia. The
longer a parent delays treatment the worse the amblyopia becomes and the
harder it is to cure the amblyopia.
In general, the main treatment for
amblyopia is occlusion therapy, in which the child has to wear a patch
over the stronger eye and force him/her to use of the amblyopic eye.
Occlusion treatment is not an easy treatment for the child or family or
for school personnel. Often, PARENTS will fail with the occlusion
therapy - They'll say something to the effect that " he just won't leave
the patch on." If the parents fail with occlusion, the child is often
left with only one good eye. Typically, an adhesive patch is use for
treating amblyopia but sometimes a patch can be placed over the child's
glasses, if he/she wears glasses.
If the child (read PARENTS) does not
tolerate the occlusion therapy AND if the child's vision isn't too bad
(generally better than 20/100 visual acuity) then sometimes the eye
doctor will try eye drops in the stronger eye. The eye drops will
dilate the pupil and cause blurred vision in the stronger eye. The
amblyopic eye has a better chance of regaining vision because the
stronger eye is now blurred. Unfortunately, the dilating drops have to
be used for a long time, sometimes 6 months or more, and such
"penalization" therapy only works if the amblyopia is only mild.
Although highly controversial, some eye
doctors also promote "vision therapy" or eye exercises to treat
amblyopia as well as other conditions. There is no set type of vision
therapy, and it can include almost anything. For most patients (about
80%), particularly if the parents are compliant with therapy, the
amblyopia can be cured with occlusion or penalization therapy.
The last and most recent advance in
therapy for amblyopia involves an oral medication, L-dopa, combined with
part time occlusion of the dominant eye. L-dopa (levodopa/carbidopa) is
a drug commonly used to treat Parkinson's disease and a number of
scientists have also found that L-dopa also helps in the treatment of
amblyopia. In general, L-dopa plus occlusion therapy improves vision by
about 2 lines on the visual acuity chart; or about 33%. L-dopa therapy
should only be used once the patient has gone through regular occlusion
therapy and if the amblyopia is not cured by conventional means. See
"Recent Breakthroughs" for additional information on L-dopa use in
amblyopia.
Another important aspect of therapy for
amblyopia is the correction of the initial cause of the amblyopia. For
example, if the child is anisometropic - has a difference in refraction
between the two eyes, then the child must be placed in corrective
glasses. Sometimes the glasses alone will cure the amblyopia. If the
child has a cataract, the cataract must be removed by surgery and a
corrective lens or contact given. If the child is crossed-eyed
(esotropic), then once the amblyopia is cured the child may need eye
muscle surgery or glasses to correct the eye misalignment.
Other Comments
Some authors say that amblyopia runs in
families (i.e., has a genetic component). Actually, it is not the
amblyopia that runs in families but, rather, the condition that leads to
amblyopia - such as crossed eyes. If the condition is detected early
and treatment instituted early then the child may never become
amblyopic.
Amblyopia is one of the key reasons a
child needs a comprehensive eye exam. A child should have an eye exam
by a eye doctor by 6 months of age, and then again at 3 years and
again before entering school. So, if your child has not had an eye exam
by an eye doctor, please schedule one today - you're child's vision may
depend upon it. It is important to note that a comprehensive eye exam
by an eye doctor IS NOT THE SAME as a vision screening; for
example, an eye test that a school nurse performs. Statistics show that
most children with amblyopia are missed by school screening programs.
Add to this the fact that about 80% of parents fail to take their child
to an eye doctor explains why most people with amblyopia are not
detected until it is too late for treatment. If the amblyopia is not
detected and treated during the first 9 years or so of life it is too
late - the child will remain amblyopic for the rest of his/her life.
An adult with amblyopia has no options
for treatment. He/she will have an increased chance of losing the
remaining good eye thus leading to blindness. An amblyopic adult cannot
qualify for certain jobs including driving an interstate commercial
truck, airline pilot, and any job that requires two good eyes.
An amblyopic older child or adult is
advised to wear protective glasses to protect the remaining good eye
from injury. Unfortunately, few eye doctors advise such patients about
protective glasses and fewer amblyopic patients comply with wearing
protective glasses. This is why some amblyopic children and adults end
up in the emergency room with injury to their remaining good eye. If
this happens, as it does on a regular basis, the person is left with a
life of visual impairment or legal blindness. |
