STRABISMUS (Crossed Eyes)
An excerpt from the book Taking
Care of Your Eyes.
Strabismus (struh-BIZ-muss) is a broad medical term that refers
to various misalignments (deviations) of the eye, such as
the two eyes to be properly aligned, they need to have similar
vision and focusing ability, and the muscles that move them
need to work together. Only then can a person have binocular
vision and depth perception, meaning that the images from
each eye are fused (blended) by the brain into a single image
that appears three-dimensional. If one eye does not look in
the same direction as the other, binocular vision cannot exist.
In a young
child, the deviating eye may eventually lose its ability to
see clearly. This is called amblyopia, or "lazy eye."
"Comitant" strabismus, the type usually seen in
children, means that no matter in what direction the eyes
look, the amount of misalignment (deviation) is the same.
This is in contrast to "incomitant" strabismus,
in which the amount of deviation is constantly changing, depending
on which direction you look. Strabismus affects about two
to four percent of all children (boys and girls equally) and
tends to run in families.
there is no identifiable cause -- the child is simply born
with a misalignment or develops it early in childhood. But
there are also many known causes, for example: one eye that
is blind or has defective vision from birth (as from a congenital
cataract); one eye that is extremely nearsighted, farsighted
or astigmatic, or the amount of eyeglass correction required
by the two eyes is vastly different; one or more absent, injured
or defective nerves to the eye muscles, causing the muscles
controlled by the nerve to function improperly; damage to
an area of the brain dealing with eye movement or eye muscle
control; injury from trauma that damages any eye muscles or
nerves; blindness from disease or injury.
crossing the eyes is never a cause of strabismus; the eyes
cannot get "stuck" in a crossed position.
common type, in which one eye turns inward (crossed eyes),
is esotropia. It is also called "convergent strabismus"
because the eyes converge or turn toward each other. With
exotropia (wall eyes), one eye turns out; it is also called
"divergent strabismus." Less common are hypertropia
(one eye turns upward) and hypotropia (one eye turns downward).
people it is always the same eye that deviates. In others
the deviation shifts from one eye to the other; this is called
alternating. Alternating strabismus can be confusing to parents.
You notice that one eye seems to turn, and just when you have
concluded which one it is, the other eye seems to be the culprit.
strabismus" is any misalignment that comes on after normal
binocular vision has developed (usually by the age of 8).
Unlike childhood strabismus, the adult type usually creates
symptoms, such as double vision (diplopia), which may be accompanied
Is a Phoria?
is another word for strabismus (as in esoTROPIA). "Phoria"
is a related condition in which the misalignment is not apparent.
It is only a tendency, and it is usually kept under control
so that the eyes appear normal and work together normally.
(The misalignment can be unmasked by covering either one of
the eyes.) Phorias are named in the same way as tropias: esoPHORIA
(tendency for one eye to turn in), exophoria (out), hyperphoria
(up), and hypophoria (down).
phorias cause no symptoms at all. But if the phoria is large,
great effort may be needed to keep the eyes aligned and working
together - to avoid seeing double - and this may cause eyestrain
when the strabismus is intermittent, the eyes stay aligned
and appear straight some of the time, but lapse into strabismus
at other times. The tropia
is more likely to occur late in the day, in the bright outdoors,
or when you are ill. As the years go on, intermittent strabismus
tends to become more constant and less intermittent.
should be examined as soon as you even suspect that they might
be crossing or wandering, no matter how small the misalignment
might be. No child is too young to be seen and early care
can prevent later heartache. The sooner treatment is begun,
the better your child's chance for achieving normal vision
in each eye and good binocular depth perception. Correction
after the age of 6 or 7 is more difficult and the result less
your doctor will try to achieve normal appearance, good vision
in each eye (with or without glasses), binocular vision, and
depth perception. In adults, the goals are binocular vision
(which eliminates double vision) and relief of any discomfort.
If an adult has a childhood strabismus that was never treated,
it is too late to improve any amblyopia or depth perception,
so the goal may be simply cosmetic -- to make the eyes appear
to be properly aligned -- though sometimes treatment does
enlarge the extent of side vision.
may consist of eyeglasses, patching, eye coordination exercises
(called orthoptics) and/or surgery on the eye muscles.
with or without patching, are often tried first and can usually
reduce the amount of deviation. This is especially true for
accommodative esotropia, a type of strabismus in which farsightedness
is a major part of the problem. (Eyeglasses can be worn by
infants as young as a few months.) The glasses must usually
be worn constantly, often for life. If surgery is thought
necessary, it is designed to correct only the deviation that
remains with the glasses on.
of slight or intermittent misalignment, orthoptics exercises
are occasionally useful, but only in very specific circumstances.
Used inappropriately, orthoptics can be wasteful and can lead
to delay in starting proper treatment.
is the main treatment for infants and young children who have
poor vision (amblyopia) associated with strabismus. A patch
is placed over the normal (preferred eye), to force the use
of the deviant (amblyopic) eye until vision improves and equalizes.
Generally, surgery is postponed until that happens.
a patch over one eye is one method of eliminating any double
vision. Prisms incorporated into the eyeglasses is another.
Surgery consists of tightening some eye muscles and loosening
others, to change their pull on the eyeball and bring the
eyes into alignment. (Occasionally, a loosening effect can
be accomplished without surgery by injecting a paralyzing
medication directly into the muscle.)
is sometimes performed on infants as young as a few months
of age when there is a good chance of obtaining binocular
vision. Children require a general anesthetic. Adults often
prefer to have a local. During the first month or two following
surgery, exercises may be designed to redevelop the ability
to use both eyes together normally.
surgery is quite safe, though it does involve some risks as
does any surgery and anesthesia. If an operation is necessary
in your case, your doctor will explain the risks along with
the potential benefits. Many times, more than one operation
is necessary to obtain good eye alignment. Glasses may also
be required after surgery to obtain the best possible visual
of treatment is dependent on many factors, such as the type
of strabismus, age of onset, and visual acuity of each eye.
It often involves years of commitment and care. Most patients
can obtain comfort and a highly acceptable appearance with
good eye alignment; some also gain fully normal function,
with coordinated use of both eyes (binocular fusion and depth
perception). Each patient's potential for a good result is
different. This fact must be well understood to avoid disappointment.