What is amblyopia?
Amblyopia (pronounced “am-blee-O-pee-uh”) is reduced
vision in an eye that did not develop normally in early childhood.
To understand the problem, imagine you are looking at a tree a short
distance away. When vision is normal, both eyes are pointed in the
same direction and the image of the tree is in clear focus in each
eye. Your brain receives an image of the tree from each eye and
these two images are combined into a single three-dimensional (3-D)
image. This allows you to see depth and understand approximately
how far away you are from the tree. The images your brain receives
from each eye are slightly different because the eyes are a few
inches apart on your head and each see the tree from a slightly
different angle. When the images are combined, they allow you to
see in 3-D.
How does this relate to amblyopia? In the previous example each
eye is able to see the tree in clear focus. With amblyopia however,
the brain receives an image from one eye that is very different
from the other. When this occurs the brain is not able to properly
combine the two images into a single 3-D image. Since “seeing
double” is confusing and uncomfortable, the brain “turns
off” the image from the blurry eye that doesn’t see
as well and just pays attention to the image from the better eye.
As vision is developing in early childhood it is critical that both
eyes get used. When the blurry eye doesn’t receive attention
and isn’t used, it gets weak and if it isn’t treated
early may eventually become functionally blind.
What causes amblyopia?
With amblyopia, one eye sees worse than the other and the brain
only pays attention to the image from the good eye. The main causes
1. Misaligned or “crossed” eyes (strabismus).
This problem causes one eye to point in a different direction than
the other and is the most common cause of amblyopia. When one eye
crosses in, wanders out, or is misaligned in some other way, the
brain will ignore the image from the crossed eye to avoid double
vision. When ignored by the brain and not used, the eye will develop
2. Unequal focus of the eyes (anisometropia).
In this case the brain receives images from the eyes that are very
different because one eye does not focus as well as the other. In
other words, one eye is more nearsighted, farsighted, or astigmatic
than the other and may develop amblyopia if it is ignored by the
brain. Children are often able to compensate and hide this problem
so it may be the most difficult type of amblyopia to detect.
3. Cloudiness of the eye (cataract, among other problems).
A cataract is a clouding of the lens of the eye. When one eye is
cloudy and sees an out-of-focus image, the brain will ignore this
image and just pay attention to the eye that sees clearly. When
it isn’t used, the eye with the cataract may develop amblyopia.
What are some of the signs or symptoms of amblyopia?
It is not always easy to recognize amblyopia unless your child
has a highly noticeable problem such as a misaligned eye or she
becomes upset when you try to cover her good eye with your hand
or a patch. Because amblyopia is difficult to recognize, early vision
screening is essential.
It is also important to remember that you can’t depend on
your child to tell you he is having an eye problem. Most children
believe that everyone sees the same way they do, even if they don’t
see clearly in one or both eyes.
In addition to amblyopia, you may be interested in learning about
of possible eye trouble in children from the Prevent Blindness
How many people have amblyopia?
Amblyopia is a common condition that affects approximately 2 or
3 out of every 100 people. Looking at children’s eye health
more broadly, it has also been reported that in the age range of
3 to 5 years, 1 child in 20 has some kind of eye problem (National
Society to Prevent Blindness brochure, "Amblyopia").
What is strabismus?
Strabismus is a problem where the eyes are misaligned and point
in different directions. With normal vision the eyes focus on the
same object and send similar images to the brain. These two images
are then combined to form a single three-dimensional (3-D) image,
allowing depth perception. When a child has strabismus and one of
the eyes points in a different direction, the brain stops paying
attention to the image from that eye— a cause of amblyopia.
Approximately 4% of children in the US have strabismus, but only
about half of these children will develop amblyopia.
Is amblyopia genetic (does it run in families)?
Some causes of amblyopia run in families, however, most children
with amblyopia come from families where no one else is affected.
Children that have a family history of amblyopia should be checked
by an ophthalmologist earlier and more frequently than other children.
See “When and how often should a child
be screened for amblyopia?” for normal guidelines and
check with your doctor for guidance.
How is amblyopia detected?
One method for detecting amblyopia is through measuring a child’s
visual acuity (how well she sees) in each eye when she reaches an
age when she can recognize letters or symbols. When there is a significant
difference between how well the two eyes see, amblyopia may be suspected
and vision should be checked by an ophthalmologist.
How is amblyopia treated?
The first step in treating amblyopia is to find the underlying
cause. The following is a list of common underlying causes and what
first steps may be taken for treatment.
1. Misaligned or “crossed” eyes (strabismus). In some
cases glasses may be prescribed to help stimulate the crossed eye.
In other cases, surgery on the eye muscles may be necessary to straighten
2. Unequal focus of the eyes (anisometropia). When a child is nearsighted,
farsighted, or astigmatic, glasses are usually prescribed to correct
the focus of the eye.
3. Cloudiness of the eye (cataract). Surgery may be necessary to
restore vision in the eye with the cataract.
After the underlying cause of amblyopia has been corrected, the
child will need to strengthen the weaker eye. This is accomplished
by “forcing” the weaker eye to work harder. The two
most common methods are to put a patch over the better eye or to
put eye drops in the better eye that blur vision. When the better
eye can’t see, either by patching it or causing it to be blurry
with eye drops, it will force the weaker eye to work harder. Patching
or eye drops will stimulate the brain to use the weaker eye and
vision in that eye will generally improve. These treatments may
be necessary for a time period of months up to years, until vision
is normal or stops getting better.
When should treatment begin?
The earlier the child is treated, the better the chances are for
restoring normal vision. Cases that are detected at age 3 and earlier
have the best chances for full recovery.
Why is early treatment important?
Early childhood is the most critical period of development for
the vision system. When a child reaches the age of about 8 or 10,
the vision system has finished developing and it is not usually
possible to make improvements to counteract the effects of amblyopia.
If a child with amblyopia hasn’t been treated by this age,
the chances for restoring vision are low. Early diagnosis and treatment
is critical to improving or restoring vision to normal.
What happens if amblyopia is left untreated?
When left untreated, amblyopia may lead to a permanent reduction
of sight in the affected eye and a loss of depth perception (seeing
in 3-D). This permanent reduction in sight may be severe enough
that the eye becomes functionally blind. In fact, amblyopia is a
leading cause of blindness in one eye. Another concern is that if
a person has untreated amblyopia in one eye and the better eye becomes
injured or diseased later in life, there is no longer a “backup”
eye so the person may become legally blind.
When and how often should a child be screened
Academy of Ophthalmology and the American Association for Pediatric
Ophthalmology and Strabismus have recommended that every child
be screened for vision problems at the following intervals:
1. At birth (routinely done at the hospital)
2. At the age of 6 months to 1 year (during a regular appointment
3. At the age of 3 to 3 ½ years
4. Routinely during the school years
Any child who fails one of these screenings should have a complete
ophthalmological exam. In addition, if there is family history of
amblyopia or other eye problems, vision should be checked more frequently
as indicated by an ophthalmologist. The American Academy of Ophthalmology
has more information on these guidelines.