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What
Is Strabismus?
Strabismus is a
visual defect in which
the eyes are
misaligned and point in different
directions.
The misalignment may
always be noticeable,
or it may come
and go. One
eye may be directed straight
ahead, while the other eye is turned inward,
outward, upward or downward. The
turned eye may
straighten at times and the
straight eye may turn.
Strabismus is a
common condition
among
children, affecting about four percent,
but can also occur later in life. It
occurs equally
in males and females and
may run in
families. However, many
people with
strabismus have no relatives
with the problem.
Vision and the
Brain
With normal binocular (two-eyed) vision, both eyes
are aimed at the same target. The visual portion of the brain
fuses the two pictures into a single 3
dimensional image.
When one eye turns,
as in strabismus, two different pictures
are sent to the brain. In a young child, the brain learns to ignore
the image of the misaligned eye and
see only the image from the straight or best
seeing eye. This causes loss of depth perception and binocular vision.
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
Normal alignment of
both eyes during childhood allows good vision to
develop in ; each eye. Abnormal
alignment, as in strabismus, may cause
reduced vision or amblyopia.
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 preferred or better seeing eye to strengthen and improve vision in the weaker eye. If amblyopia is detected in the first few years of life, treatment is often successful. If adequate treatment is delayed until later, amblyopia or reduced vision generally becomes permanent. As a rule, the earlier amblyopia is treated, the better the visual result.
Causes and Symptoms of
Strabismus
The
exact cause of the eye misalignment that leads to 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 control tilting movements.
To line up and focus both eyes
on a single target, all eye muscles of
each eye must be balanced and working
together with the
corresponding muscles of the opposite eye.
The brain controls the eye muscles which explains why
children with disorders that affect
the brain, such as cerebral
palsy, Down's syndrome. hydrocephalus. and brain tumors often
have strabismus. A cataract or eye
injury that affects vision can
also cause strabismus.
The primary symptom of strabismus is
an eye that is not straight.
Sometimes a youngster will squint one
eye in bright sunlight or tilt
their head in a specific direction
to use their eyes together. Signs of
faulty depth perception may
also he
noticed.