What is Strabismus?
Strabismus is a visual problem in which the eyes are not
aligned properly and point in different directions. One eye
may look straight ahead, while the other eye turns inward,
outward, upward or downward. The eye turn may be constant,
or it may come and go. Which eye is straight (and which is
misaligned) may switch or alternate.
Strabismus is a common condition
among children. About 4 percent of all children in
the United States have strabismus. It can also occur
later in life.
Strabismus occurs equally in males and females. It
may run in families; however, many people with
strabismus have no relatives with the problem.
The exact cause of strabismus is not fully
understood. In some cases, strabismus may be due to
problems with the muscles controlling eye movement.
Six eye muscles that control eye movement are
attached to the outside of each eye. In each eye,
one muscle moves in the eye to the right, and one
muscle moves the eye to the 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 these muscles.
With normal vision, both eyes aim at the same
spot. The brain then combines the two pictures into a single,
three-dimensional image. This three-dimensional image gives us
When one eye is out of alignment,
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
Adults who develop strabismus
often have double vision because their brains have
already learned to receive images from both eyes and
cannot ignore the image from the turned eye. A child
generally does not see double.
In some cases, strabismus may result from
problems in the brain. Sometimes, a child’s brain may not be
correctly combining the two images it receives from the eyes. In
rare cases, a tumor may affect how the brain processes visual
information. Often children experience strabismus as a result of
problems that can be easily treated with glasses.