What is strabismus?
Strabismus is a visual defect in which the eyes are
misaligned and point in different directions. One eye
may look straight ahead, while the other eye turns inward,
outward, upward, or downward.
You may always notice the misalignment, or it may come
and go. The turned eye may straighten at times, and
the straight eye may turn.
Strabismus is a common condition among children. About
4% of all children in the United States have strabismus.
It can also occur later in life.
It occurs equally in males and females. Strabismus
may run in families. However, many people with strabismus
have no relatives with the problem.
How do the eyes work together?
With normal vision, both eyes aim at the same spot.
The brain then fuses the two pictures into a single,
three-dimensional image. This three-dimensional image
gives us depth perception.
When one eye turns, two different pictures are sent
to the brain. In a young child, the brain learns to
ignore the image of the misaligned eye and sees only
the image from the straight or better-seeing eye. The
child then loses depth perception.
Adults who develop strabismus often have double vision
because the brain is already trained to receive images
from both eyes and cannot ignore the image from the
turned eye.
Amblyopia
Good vision develops during childhood when both eyes
have normal alignment. Strabismus may cause reduced
vision, or amblyopia, in the weaker eye.
The brain will recognize the image of the better-seeing
eye and ignore the image of the weaker or amblyopic
eye. This occurs in approximately half the children
who have strabismus.
Amblyopia can be treated by patching the "good"
eye to strengthen and improve vision in the weaker eye.
If amblyopia is detected in the first few years of life,
treatment is usually successful.
If treatment is delayed until later, amblyopia usually
becomes permanent. As a rule, the earlier amblyopia
is treated, the better the visual result.
What causes strabismus?
The exact cause of strabismus is not fully understood.
Six eye muscles, controlling eye movement, are attached
to the outside of each eye. In each eye, two muscles
move the eye right or left. The other four muscles move
it up or down and at an angle.
To line up and focus both eyes on a single target,
all of the muscles in each eye must be balanced and
working together. In order for the eyes to move together,
the muscles in both eyes must be coordinated. The brain
controls the eye muscles. Strabismus is especially common
among children with disorders that affect the brain,
such as:
-
cerebral palsy
-
Down's syndrome
-
hydrocephalus
-
brain tumors.
A cataract or eye injury that affects vision can also
cause strabismus.
What are the symptoms of strabismus?
The main symptom of strabismus is an eye that is not
straight. Sometimes children will squint on eye in the
bright sunlight or tilt their head to use their eyes
together.
How is strabismus diagnosed?
Strabismus can be diagnosed during an eye exam. It
is recommended that all children have an eye exam by
an ophthalmologist at or before their fourth birthday.
If there is a family history of strabismus or amblyopia,
an ophthalmologist can check vision even earlier than
age three.
What is pseudostrabismus?
The eyes of infants often appear to be crossed, though
they actually are not. This condition is called pseudostrabismus.
Young children often have a wide, flat nose and a fold
of skin at the inner eyelid that can make the eyes appear
crossed.
This appearance of strabismus may improve as the child
grows. A child will not outgrow true strabismus.
An ophthalmologist can usually tell the difference
between strabismus and pseudostrabismus.
How is strabismus treated?
Treatment for strabismus works to:
After a complete eye examination, an ophthalmologist
can recommend appropriate treatment.
In some cases, eyeglasses can be prescribed for your
child. Other treatments may involve surgery to correct
the unbalanced eye muscles or to remove a cataract.
Covering or patching the strong eye to improve amblyopia
is often necessary.
Most common types of strabismus
ESOTROPIA
Esotropia, where the eye turns inward, is the most
common type of strabismus in infants.
Young children with esotropia do not use their eyes
together. In most cases, early surgery can align the
eyes.
During surgery for esotropia, the tension of the eye
muscles in one or both eyes is adjusted. The tight inner
muscles may be removed from the wall of the eye and
placed further back on the eye.
This adjustment weakens their pull and allows the eyes
to move outward. Sometimes the outer muscles are tightened
by shortening the muscle length to allow the eyes to
move outward.
ACCOMODATIVE ESOTROPIA
Accommodative esotropia is a common form of esotropia
that occurs in farsighted children usually two years
or older.
When the child is young, he or she can focus the eyes
to adjust for the farsightedness, but the focusing effort
(accommodation) to see clearly causes the eyes to cross.
Glasses reduce the focusing effort and can straighten
the eyes. Sometimes bifocals are needed for close work.
Eyedrops, ointment, or special lenses called prisms
can also be used to straighten the eyes.
EXOTROPIA
Exotropia, or an outward turning eye, is another common
type of strabismus. This occurs most often when a child
is focusing on distant objects.
The exotropia may occur only from time to time, particularly
when a child is daydreaming, ill, or tired. Parents
often notice that the child squints one eye in bright
sunlight.
Although glasses, exercises, or prisms may reduce or
help control the outward turning eye in some children,
surgery is needed.
How is strabismus surgery done?
The eyeball is never removed from the socket during
any kind of eye surgery. The ophthalmologist makes a
small incision in the tissue covering the eye to reach
the eye muscles.
Certain muscles are repositioned during the surgery,
depending on which direction the eye is turning. It
may be necessary to perform surgery on one or both eyes.
When strabismus surgery is performed on children, a
general anesthetic is required. Local anesthesia is
an option for adults.
Recovery time is rapid. People are usually able to
resume their normal activities within a few days.
After surgery, glasses or prisms may be useful. In
many cases, further surgery may be needed at a later
stage to keep the eyes straight.
For children with constant strabismus, early surgery
offers the best chance for the eyes to work well together.
In general, it is easier for children to undergo such
surgery before school age.
As with any surgery, eye muscle surgery has certain
risks. These include infection, bleeding, excessive
scarring, and other rare complications that can lead
to loss of vision.
Strabismus surgery is usually an effective treatment
for eye misalignment. It is not, however, a substitute
for glasses or amblyopia therapy.
|
