Amblyopia refers to diminished vision in either one or both eyes, for
which no cause can be discovered upon examination of the eye. Amblyopia is
the medical term used when the vision in one of the eyes is reduced
because the eye and the brain are not working together properly. The eye
itself looks normal, but it is not being used normally because the brain
is favoring the other eye. This condition is also sometimes called lazy
Lazy eye is a common non-medical term used to describe amblyopia because
the eye with poorer vision does not seem to be doing its job of seeing.
Amblyopia is the most common cause of impaired vision in childhood. It
affects approximately two or three out of every 100 children. Vision is a
combination of the clarity of the images of the eyes (visual acuity) and
the processing of those images by the brain. If the images produced by the
two eyes are substantially different, the brain may not be able to fuse
the images. Instead of seeing two different images or double vision
(diplopia), the brain suppresses the blurrier image. This suppression can
lead to amblyopia. During the first few years of life, preferring one eye
over the other may lead to poor visual development in the blurrier eye.
Unless it is treated successfully in early childhood, amblyopia usually
persists into adulthood and is the most frequent cause of monocular (one
eye) visual impairment among children.
The prevalence of amblyopia is difficult to assess, with estimates ranging
from 1.0 to 3.5 percent in healthy children to 4.0 to 5.3 percent in
children with other vision problems. It is seen in similar numbers in both
sexes and in all races.
Causes and symptoms
Amblyopia may be caused by any condition that adversely affects normal
visual development or use of the eyes. All babies are born with poor
eyesight. As babies grow, however, their eyesight usually progresses. Good
eyesight needs a clear, focused image that is the same in both eyes. If
the image is not clear in one eye, or if the image is not the same in both
eyes, the vision pathways will not develop as they should. In fact, the
pathways may actually worsen. Anything that blurs the vision or causes the
eyes to be crossed during childhood may cause amblyopia. Some of the major
causes of amblyopia are as follows:
Barring the presence of strabismus or ptosis, children may or may not show
signs of amblyopia. Children may position their heads at an angle while
trying to favor the eye with normal vision. They may have difficulty
seeing or reaching for things when approached from the side of the
amblyopic eye. Parents should see if one side of approach is preferred by
the child or infant. If an infant's good eye is covered, the child
Parents should call the doctor if their child demonstrates any signs
associated with amblyopia, including the appearance of crossed eyes, lazy
eye, a drooping eyelid, difficulty seeing, or if the child seems to favor
one side of approach over the other. However, since children do not always
show symptoms of amblyopia, it is important to get their eyes examined at
or before the age of three and no later than age five, while the disorder
is more easily treated.
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. Because children with outwardly normal eyes may have
amblyopia, it is important to have regular vision screenings performed for
all children. While there is some disagreement regarding the age children
should have their first vision examination, their eyes can, in actuality,
be examined at any age, even on the first day of life.
Some people recommend that children have their vision checked by their
physician, ophthalmologist, or optometrist at or before six months of
age. Others recommend testing by at least the child's fourth
birthday. There may be a critical period in the development of vision, and
amblyopia may not be treatable after age eight or nine. The earlier
amblyopia is found, the better chance there is for a positive outcome.
Most physicians test vision as part of a child's medical
examination. If there is any sign of an eye problem, they may refer a
child to an eye specialist.
There are objective methods, such as retinoscopy, by which to measure the
refractive status of the eyes. This form of examination can help diagnose
anisometropia. In retinoscopy, a hand-held instrument is used to shine a
light in the child's (or infant's) eyes. While the doctor
uses hand-held lenses, he can obtain a rough prescription. Visual acuity
can be determined using a variety of methods. Many different eye charts
are available (e.g. tumbling E, pictures, or letters). In amblyopia,
single letters are easier to recognize than when a whole line is shown.
This is referred to as the "crowding effect" and helps in
diagnosing amblyopia. Neutral density filters may also be held over the
eye to aid in the diagnosis. Sometimes visual fields to determine defects
in the area of vision will be performed. Color vision testing may also be
done. Again, it must be emphasized that amblyopia is a diagnosis of
Boy wearing eye patch used to treat amblyopia. The patch is worn
over the stronger eye to build the weaker one's strength.
(© Mark Clarke/Photo Researchers, Inc.)
Various medical problems can also cause a decrease in vision. An
examination of the eyes and visual system is very important when there is
an unexplained decrease in vision.
Amblyopia treatment is most effective when done early in the
child's life, usually before age seven. It is important that any
anisometropia and refractive problems be treated initially, because
sometimes amblyopia can be resolved with glasses alone.
The next step is to make the child use the eye with the reduced vision
(weaker eye). As of 2004, there are two ways to do this:
The younger the child, the better the chance for improvement with
occlusion and vision therapy. Success in the treatment of amblyopia also
depends on the amblyopia's severity, its specific type, and the
child's compliance with treatment. It is important to diagnose and
treat amblyopia early because significant vision loss can occur if it is
left untreated. The best outcomes result from early diagnosis and
Early recognition and treatment of amblyopia in children can help to
prevent permanent visual deficits. All children should have a complete eye
examination at least once between age three and five to avoid the risk of
allowing unsuspected amblyopia to go beyond the age where it can be
There are some rarer forms of amblyopia caused by various nutritional
deficiencies. In these cases, the doctor recommends the proper diet and
perhaps supplementation in order to resolve the problem.
—An eye condition in which there is an inequality of vision
between the two eyes. There may be unequal amounts of nearsightedness,
farsightedness, or astigmatism, so that one eye will be in focus while
the other will not.
—A condition in which the lens of the eye turns cloudy and
interferes with vision.
—A type of treatment for amblyopia in which the good eye is
patched for a period of time, thus forcing the use of the weaker eye.
—Sharpness or clearness of vision.
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Amblyopia: A Multidisciplinary Approach.
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Pratt-Johnson, John A., et al.
Management of Strabismus and Amblyopia: A Practical Guide.
New York: Thieme Medical Publishers, 2000.
Dutton, Gordon N., and Marie Cleary. "Should We Be Screening for
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British Medical Journal
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Finn, Robert. "Less Patching Fine for Amblyopia in Young Children:
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American Association for Pediatric Ophthalmology and Strabismus.
PO Box 193832, San Francisco, CA 94119–3832. Web site:
National Eye Institute.
31 Center Drive MSC 2510, Bethesda, MD 20892–2510. Web site:
Prevent Blindness America.
500 E. Remington Road, Schaumburg, IL 60173. Web site:
National Eye Institute
, June 2004. Available online at
http://www.nei.nih.gov/health/amblyopia (October 16, 2004).