What is strabismus?
Strabismus is a common eye condition among children. It is when the eyes are not lined up properly and they point in different directions (misaligned). One eye may look straight ahead while the other eye turns in, out, up, or down. The misalignment can shift from one eye to the other.
Six eye muscles control eye movement
One muscle moves the eye to the right, and one muscle moves the eye to the left. The other four muscles move the eye up, down, and at an angle. In order to focus on a single image, all six eye muscles must work together.
Strabismus affects vision, since both eyes must aim at the same spot together to see properly. If someone’s eyes are lined up properly during childhood, vision should develop well. But if the eyes are not aligned, a condition called amblyopia can develop. This is when the misaligned eye has weaker vision.
What causes strabismus?
To line up and focus both eyes on a single target, all muscles in both eyes must work together. The brain controls these muscles. Children who have strabismus may have disorders affecting their brain. Some of those problems may include:
- cerebral palsy
- Down syndrome
- hydrocephalus (extra fluid in the brain)
- brain tumor
- premature birth
Having a cataract (cloudiness of the eye’s naturally clear lens) or eye injury can also cause strabismus. Most children with strabismus, however, have none of these problems.
Having family members with strabismus can increase a child’s chance of having it themselves.
How does strabismus affect vision?
With normal vision, both eyes aim at the same spot. Our brain combines the two images from our eyes into a single, three-dimensional (3-D) image. This is how we can tell how near or far something is from us (called depth perception).
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. Instead, it sees only the image from the straight or better-seeing eye. As a result, depth perception may be affected.
Adults who develop strabismus after childhood often have double vision. This is because their brains have already learned to receive images from both eyes. Their brains cannot ignore the image from the turned eye, so they see two images.
Signs of strabismus
You may notice that your child’s eyes look in different directions at the same time. You may also notice that your child closes one eye or tilts their head when looking at an object. This may be your child’s way of getting both eyes to work together—a sign of strabismus. Also, your child may squint with one eye when in bright sunlight.
Your child’s pediatrician, school nurse, or teacher may notice these signs, too. If you think your child might have strabismus, visit a pediatric ophthalmologist for a complete eye exam.
When children are less than a year old, their eyes may look crossed when they really are not. This is called “pseudostrabismus.” It usually happens if the child has a wide, flat nose or a fold of skin at the inner eyelid.
A child can outgrow pseudostrabismus, but not strabismus.
Pseudostrabismus. Although the eyes appear misaligned, the light reflection is in the same place in both eyes.
A photograph showing an off-center reflection of light in left eye—a sign of strabismus.