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What is Strabismus?
Strabismus (deviation of the eyes) affects approximately two percent
of the nation's children, half of whom are born with the condition.
It is critical that this handicap be diagnosed and corrected at an
early age since children with uncorrected strabismus may go on to
develop amblyopia ("lazy eye"), a dimming of vision in an eye that has
not been used.
The term strabismus is used to describe eyes that are not straight
or properly aligned. This misalignment results from the failure of the
eye muscles to work together. One eye, or sometimes both, may turn in
(crossed eyes), turn out (wall eyes), turn up or turn down. Sometimes,
more than one of the "turns" are present. The deviation may be
constant or it may come and go. It may be present at birth, become
apparent at a large age, or result after an illness or accident.
The patterns of deviation can vary among individuals. In
alternating strabismus, the eyes "take turns" wandering. Strabismus
can be more marked in some people when they use their eyes for near
activities and in others when they are focusing for distance or simply
day-dreaming. In the young child, strabismus may vary not only from
day-to-day, but during the course of a day. Usually the condition is
worse when a child is tired, ill or emotionally upset.
At birth, an infant's eyes cannot always focus directly on objects.
They may appear to move quite independently at first, sometimes
crossing, and sometimes wandering outward. But by the age of 3 to 4
months, an infant's eyes should have the ability to focus on small
objects and the eyes should be straight or parallel. A 6-month-old
infant should be able to focus on both distant and near objects.
If parents notice crossed or wall eyes persisting in a child 4
months of age, they should immediately take the child to an eye care
professional for an examination. Early medical attention is
recommended for another important reason -- to rule out the presence
of a serious disease, such as a tumor. It is recommended that all
children have an eye exam by the age of 6 months.
How Does Vision Work?
In order to understand strabismus, it is helpful to know how vision
works. The process of vision is complex. The eye receives light
waves which are focused on the retina (the rear lining of the eye) and
transmitted from there to the brain. The brain, in turn, creates a
single image from the separate ones it has received from the two eyes;
this is known as fusion.
To develop normal, binocular (two-eyed) vision, a child needs two
healthy, well-coordinated eyes with relatively equal vision in each so
that the images that form on the retina will have comparable clarity.
If the muscles that move each eyeball have developed correctly, the
eyes will work together as a team.
If the eye muscles are not coordinated and one eye is looking
directly at an object while the other turns in or out, the message from
the eye that is on target will usually be stronger that the message
from the other eye. As a consequence, the brain may simply ignore the
weaker message. This solves the child's double vision problem, but
creates another; the eye whose message is ignored develops weaker
vision -- amblyopia.
Appearances Can Be Misleading
Certain children may appear to have strabismus when, in fact, they
do not. An extra fold of skin that hides some of the white in the
inner corner of the eyes may cause the eyes to look crossed. A broad,
flat nose, or eyes that are unusually close together may also produce
such an effect. Occasionally, if the child's eyes are set somewhat
apart, it may appear as if one eye is turning outward. All of these
are examples of false strabismus. This false strabismus should
disappear as the child's face grows. Treatment in such cases is
unnecessary. After a professional examination, a parent's concern can
be quickly dispelled if false strabismus is present.
What are the Causes?
Strabismus may occur from several causes, such as birth injuries,
heredity, faulty muscle attachments, need for glasses, excessive
farsightedness, or body illnesses.
The major goals in treating strabismus are the development of normal
vision in each eye, including fusion and depth perception.
Accomplishing these goals often involve straightening the eyes and
preventing amblyopia from developing.
What Are the Signs and Symptoms?
The preschool years are critical ones in the development of a
child's eyes. Parents should continue to watch for any misalignment,
slight or marked, and for wandering of one or both eyes.
A professional eye examination for every child, including those who
do not display any signs of eye trouble, is recommended shortly after
birth, at 6 months of age, before entering school (age 4 or 5) and
periodically throughout the school years.
By the time a child is 5 or 6, vision is usually 20/20, or at the
normal adult level, which means that lettering of a certain size can be
seen from 20 feet. An eye deviation that persists until a child is 7,
may result in permanent visual impairment.
Besides hindering the development of useful vision, strabismus may
affect the child's personality. A child may suffer embarrassment from
a cosmetic defect that makes him look different.
What Treatment is Available?
Strabismus cannot be outgrown, nor will it improve by itself.
Treatment to straighten the eyes is needed. The types of treatment
listed below may be used alone or in combination. The choice and
order vary with the type of strabismus and its cause.
- GLASSES are commonly prescribed to improve focusing and redirect
the line of sight, enabling the eyes to straighten.
- MEDICATION in the form of eye drops or ointment that blur vision
in one eye, can be a substitute for patching. Use of blurring drops
is not appropriate in every case and is generally a less successful
approach. In other cases, different drops may be used to replace
glasses, or to add to the strength of glasses when more help is needed
to control increased visual problems at near viewing. Injected
medication may be used to selectively weaken an eye muscle that is
overly active.
- SURGERY may be performed on the eye muscles to straighten the eyes
if non-surgical means are unsuccessful.
- EYE EXERCISES (orthoptics), a limited form of treatment, may be
recommended either before or after surgery to teach proper eye
coordination.
There are many types of strabismus and no single treatment is best
or all-inclusive, nor is it always successful. Successful treatment
of strabismus far outnumbers failures, however, especially if the
parents seek help when the child is still young.