from Triad's Eye Care Notes
© 1989-2005 by Triad Publishing
Strabismus (struh-BIZ-muss) is a term that describes eyes
that are not properly aligned or do not move together as they
should. One eye may look straight ahead, while the other eye
turns inward, outward, upward, or downward.
the two eyes to remain 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.
a young child, the deviating eye may eventually lose its ability
to see clearly. This is called amblyopia, or "lazy eye." Strabismus
affects about four percent of all children, boys and girls
equally, and tends to run in families.
often, 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 a part 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. Intentionally
crossing the eyes never causes strabismus; the eyes cannot
get "stuck" in a crossed position.
most common type, in which one eye turns inward (crossed eyes),
is esotropia. With exotropia (wall eyes), one eye turns out.
Less common are hypertropia (one eye turns upward) and hypotropia
(one eye turns downward). In some people it is always the
same eye that deviates. In others the deviation shifts from
one eye to the other; this is called "alternating."
other distinctions are important. A misalignment may be constant
or intermittent. And it may be comitant or incomitant. Comitant
strabismus, the type usually seen in children, means that
no matter which way the eyes look, the amount of misalignment
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" is any misalignment that comes on after normal
binocular vision has developed, usually by age 8. Unlike childhood
strabismus, the adult type usually creates symptoms, such
as double vision, which may be accompanied by nausea.
Is a Phoria?
is another word for strabismus (as in esoTROPIA). "Phoria"
is a related and much more common condition in which the misalignment
is only a tendency. The eyes appear aligned and work together
normally because the phoria is kept under control, but it
can be unmasked by covering either eye.
are named in the same way as tropias: esoPHORIA (tendency
for one eye to turn in), exophoria (out), hyperphoria (up),
and hypophoria (down). If a phoria is large, much (unconscious)
effort may be needed to keep the eyes aligned and working
together to avoid seeing double, and this effort may cause
eyestrain and headache. But usually a phoria causes no symptoms
is another descriptive term related to strabismus. When strabismus
is intermittent, the eyes are aligned and appear straight
some of the time, but lapse into strabismus at other times.
These lapses are more common with exo (outward) deviations
than with other types. At the times when the eyes are straight,
only an exophoria (a tendency toward exotropia) is present;
if one eye suddenly turns out, the exophoria has become an
exotropia. The tropia is more likely to appear 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.
eyes 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
complete eye examination and refraction (measurement of vision
and a check for glasses) involves the use of eyedrops to dilate
the pupils and temporarily paralyze the focusing mechanism.
Eye movements, quality and degree of stereopsis (3-D vision),
and the ability to recognize double vision will all be checked,
depending on the age and cooperation of the patient. Determination
of the cause may involve referral to other types of specialists.
children, we would like 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 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.
Eyeglasses, 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.
Patching is the main treatment for infants and young children
who have amblyopia (lazy eye). A patch is placed over the
normal (preferred) eye, to force the use of the amblyopic
eye until vision improves and equalizes. Generally, surgery
is postponed until that happens. In adults, a patch over one
eye is one method of eliminating any double vision. Prisms
incorporated into the eyeglasses is another.
Orthoptic exercises may be useful when the deviation is slight
or intermittent, and then only in very specific circumstances.
Used inappropriately, orthoptics can be wasteful and can lead
to delay in starting proper treatment.
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, called Botox, directly into the muscle. The effect
of this treatment does not last and may need to be repeated
every few months.) Surgery is sometimes performed on infants
as young as a few months of age when there is a good chance
of obtaining binocular vision. During the first month or two
following surgery, orthoptic exercises may be designed to
develop the ability to use both eyes together normally. Many
times, more than one operation is necessary to obtain good
eye alignment. Glasses may also be required after surgery
for the best possible visual result.
outcome 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.
from Triad's Eye Care Notes
© 1989-2005 by Triad
Patients: for more information about your eyes, see: Taking
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