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A
lazy eye, technically referred to as amblyopia, means that one eye has not
developed normally and always has blurred vision, even with the best glasses
or contacts the eye doctor can prescribe.
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| Clear vision out of an
eye with normal sight |
Blurry
vision out of a lazy eye, even with glasses
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Amblyopia
is caused when the brain favors one eye and refuses to use the other.
Simply stated, amblyopia is a dysfunction of the brain which blocks vision
from one eye because it can't use the two eyes together. Because the eye
is "turned off, " clear vision does not develop in the lazy eye.
Amblyopia affects 2 to 3 percent of the population.
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How
a Lazy Eye Develops
Children
with normal vision learned to use both eyes together in the first few months
of life. Their brains developed the ability to take the pictures coming
in from both their left and right eyes and "fuse" the two pictures
into a single image. This is called "binocularity," or normal
two-eyed vision.
The
brains of children who have a lazy eye, however, did not learn to use their
two eyes together. At an early age, these children only used one eye, and
their brain "turned off" or blocked the in-coming picture from the
other eye. Turning off an eye is called suppression. Because the brain
suppressed the lazy eye very early in life, normal sharpness of vision, called
acuity, did not have a chance to develop. This "use it or lose
it" syndrome means that the child has lost the ability to see clearly out
of the lazy eye, even with the best pair of glasses or contacts the eye doctor
can prescribe. How poor the vision is in the weak eye depends in part upon how
early in the child’s visual development the brain turned the eye off.
Common
Causes of a Lazy Eye
Amblyopia
is caused by various conditions which prevent the brain from using both eyes
together. In some cases, the tendency for a lazy eye may be inherited.
Refractive
Amblyopia: One type of lazy eye, called
refractive amblyopia, is caused when one eye is more nearsighted or farsighted
than the other, making it difficult for the eyes to focus together.
Refractive amblyopia starts early in life. An infant has no way of
telling his parents one of his eyes isn't seeing as clearly as the other, so
his visual system has to try to handle the problem on its own. Because
it's difficult to fuse a clear image with a blurry one, the brain learns
vision is better if it suppresses the blurry eye that's interfering and just
uses the clear one. The long-term suppression of the blurry eye causes vision
to stop developing. Once this type of lazy eye is discovered, treatment
involves prescribing glasses or contacts to help equalize the vision in both
eye. Eye patching can help improve the sharpness of vision in the lazy
eye, and vision therapy is often needed to establish binocularity and assist
development of the compromised visual skills that didn't have a chance to
develop on their own because of suppression. (Please see information
below on how vision therapy can help a lazy eye.) Refractive amblyopia
is the easiest type of lazy eye to correct.
Strabismic
Amblyopia: Another common cause of lazy eye
is strabismus. Strabismus, often referred to as a crossed or wandering
eye, is a condition in which the brain is unable to properly align the eyes.
As a result, one eye may point in or out, up or down. When the eyes are
not pointing at the same place, two different pictures are being sent to the
brain. Because the brain can't combine two obviously different pictures into a
single image, the result is double vision. The brain is then forced to turn
off the picture coming in from the misaligned eye to avoid seeing double.
The child only uses his straight eye to see, and vision in the turned eye does
not have a chance to develop. (See our web page on "Crossed
Eyes" for more complete information on strabismus.)
Treatment
for a Lazy Eye
To
correct amblyopia, the blurry eye must first be forced to work in order to
allow the opportunity for clear vision to develop. This is usually done by
patching the clear eye for specific periods of time, forcing the blurry
eye to "turn on" so that visual cells are stimulated, allowing
clearer vision to develop. Secondly, glasses are prescribed to provide the
blurry eye with the best support possible. Finally, if the
underlying cause of the lazy eye is strabismus, then the eye turn must also be
addressed.
In
addition to glasses, there are three different approaches to the treatment of
a lazy eye: 1) patching alone, 2) patching combined with surgery,
and 3) patching combined with vision therapy.
It is imperative that parents of a child with a lazy eye fully
understand their treatment options so they can make the best choice for their
child.
Patching
Only
When
the treatment procedure involves patching only, the child's clear eye is
covered for 2 to 8 hours a day over a long period of time, from 3 months to a
year. (Sometimes blurring drops are used instead of a patch.) By forcing the
blurry eye to work, its vision improves. However, there are serious
drawbacks to this option. First, because the good eye is covered, the
child cannot see well and is often frustrated and uncooperative. It
becomes difficult for the parents to keep the patch on the child, especially
if the doctor has recommended extended patching time. Often the patch
has to be taped over the child's eye to prevent him from removing it.
Over a period of time, the skin around the eye can become irritated and raw.
Also, there is danger of loss of vision in the clear eye when it is covered
most of the time for weeks on end. In the face of these hardships,
patching often fails because the child and parents give up.
Note:
Recent research indicates that not nearly as much daily patching time is
necessary as was previously thought. A study by the National Eye
Institute showed that 2 hours a day was as beneficial as patching six hours or
more. Hopefully, most eye doctors are adapting their recommendations in
light of the new research. If your eye doctor is recommending more than
two hours of daily patching for your child, please referring him to this link
for more information: www.childrensvision.com/patching.htm.
Unfortunately,
the gains from patching can be limited in the degree of visual improvement
that can be achieved, and these gains are not always permanent. While
patching usually improves vision, it is not always possible to restore the
child to normal 20/20 vision with the patch alone, especially if the child had
really poor acuity in the eye to begin with. Even if the family successfully
makes it through the original patching ordeal and vision improves, it is not
uncommon for the child to lose some of these gains over time. This is
because strabismus, the underlying cause of the lazy eye, was never addressed.
If you don't take care of the root of the problem, you still have a problem.
For a permanent solution, the brain must be taught to stop suppressing the
blurry eye and trained how to align and use the two eyes together--something a
patch by itself cannot do. If this is not done, a child's visual system
will still suppress the lazy eye once the patch is removed. As a result,
some of the improvement from patching will be lost over time. Once
patching is stopped, the vision in the lazy eye often degenerates if nothing
has been done to teach the child's brain to use both eyes together.
Patching
with Surgery
In
addition to a patching regimen, eye surgeons sometime recommend surgery for
the crossed/wandering eye. Unfortunately, eye surgery does nothing to restore
normal two-eyed vision, a learned process of the brain. Surgery simply
makes the eyes appear straight by cutting and stretching muscles to reposition
the eye, a cosmetic "fix" but not a visual cure. Surgery cannot
correct the improper habits the brain learned which caused the misalignment
problem to begin with, nor can surgery train the brain how to use both eyes
together.
Most children who have undergone surgery for a crossed eye still suppress one
eye full time. In order for the problem to be truly corrected, the brain must
learn not to suppress and be trained to use both eyes together. (For a more
complete discussion on the limits of surgery to correct strabismus, see our
web page "Crossed and Wandering Eyes.")
On
average, less than 20% of children who undergo eye surgery eventually achieve
normal two-eyed vision. The few who do are nearly always very young children
under the age of six whose visual systems were still developing and fluid
enough to fall into binocularity on their own.
Misconceptions
about the "Critical Stage" for Treatment
It
is for this reason that some parents are told that a lazy eye can only be
corrected when the child is very young, usually age six or under, the time
when a child's visual system is still naturally "moldable." Some
doctors feel that if treatment is not undertaken during this "critical
stage" of development, the amblyopia becomes fixed and untreatable.
Parents of older children with lazy eyes are often told that it is too late to
treat the problem.
While
these doctors are well intentioned, they are wrong. Eye doctors who
believe that a lazy eye cannot be treated after age six simply lack the
background and necessary training to correct a lazy eye in older children.
Because they are not schooled in the functional remediation of binocular
vision problems, they do not have the training to treat older children.
A lazy eye can be treated at any age when glasses and
patching are combined with vision therapy.
(Click
here for the story of a 66-year old grandmother whose lazy eye was fully
corrected after three months of vision therapy!)
Vision
Therapy
Vision
therapy is highly successful in remediating a lazy eye. Much akin to
other physical therapies, vision therapy stimulates and guides visual
development, training the brain to perform visual functions that did not
develop on their own. Vision therapy is prescribed by developmental
optometrists (sometimes called behavioral optometrists) who
specialize in children's vision and who have received board certification in
this area of care. The title of a pediatric optometrist who specializes
in vision therapy is Fellow in the College of Optometrists in Vision
Development, noted with the credentials of F.C.O.V.D. included in his or her
professional title.
Vision
therapy is highly successful in improving the function and performance of a
lazy eye. Therapy corrects not only the poor vision in the lazy
eye, but it also corrects the underlying problem of the brain's inability to
align and use both eyes together, so the gains are permanent. During
therapy, the patient's brain is trained to stop suppressing the lazy eye, the
visual pathways from brain to eyes are improved so the patient can keep both
eyes aligned, and finally the brain is taught to fuse the images coming in
from both eyes for normal binocular ("two-eyed") vision.
Research shows that vision therapy restores the visual system to normal in
over 90% of cases. Even in the remaining 10% of cases, those most severe
instances of lazy eye complicated by additional circumstances, therapy can
improve the child's vision to more functional levels. And this can
be done at any age. (It should be noted, however, these statistics are
for children who have never undergone surgery. Scare tissue and nerve
damage drops the success rate for a child who has already had one surgery to
fifty percent, and the therapy prognosis for children who have had more than
one surgery is poorer still.)
Like
other interventions, vision therapy usually involves patching the clear eye to
force the blurry eye to work, but for much shorter periods of time.
Rather than full time patching for up to twelve hours a day, a patient in
vision therapy will usually be asked to patch for two hours. Much less
patching time is necessary when the child's visual system is also being
trained how to use the weak eye properly. By the end of therapy, the child's
patching time has been eliminated altogether.
The
gains achieved in vision therapy are permanent. This is because once the
child's brain learns binocularity, or how to fuse the images from both
eyes, the child's visual system is restored to normal. Binocular fusion
is the glue which permanently holds the vision system in place, simply because
it's easier to see correctly than to have each eye fighting each other to see
separately. Binocular fusion keeps the eyes from drifting out of
alignment, and because there is no longer a need for the lazy eye to suppress,
its improved acuity, or sharpness of vision, is not lost over time.
Final
Word
A
lazy eye is not always easily recognized. A child may not even be aware that
one of his eyes is not working with the other. If the eye turn is so slight
that the child does not have an obvious misalignment, parents will rarely be
able to tell something is wrong just by looking.
It
is extremely important for children to develop equal vision in both eyes in
order for them to function normally. Good sharpness of sight and
two-eyed binocular vision are vital for children to succeed in school, sports,
or any other activity that requires clear vision, good hand-eye coordination,
and strong depth perception. When children with untreated amblyopia grow to be
adults, their choice of career may be limited and, if they are unlucky enough
to lose vision in their one good eye, they could be visually impaired or
legally blind for life.
For
these reasons, it is extremely important for parents to have their child’s
eyes examined by an optometrist as early as possible so vision problems can be
found and treated. Vision can be tested in infants and very young children,
and it is recommended that a child be examined at least by the age of three.
In Kansas, the "See to Learn" program sponsored by the Kansas
Optometric Association allows every three-year-old to be checked for free.
 However,
if you are a parent of a child with a lazy eye who was diagnosed after age
six, please do not be misled. There is help. If you need
assistance locating a developmental optometrist who
provides vision therapy in your area, call the national certifying board of
the College of Optometrists in Vision Development at 1-888-268-3770 or visit
their web site at http://www.covd.org.
Also, your family optometrist can be a good resource. Ask if he or she
provides vision therapy or if they can make a referral to a colleague who
does.
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