Patient education: Crossed eyes and lazy eye (The Basics)

What are crossed eyes and lazy eye? — Crossed eyes is a condition in which the eyes don't line up with each other, and don't look in the same direction. The term doctors use for this is "strabismus." In some places, people use the word "squint" to describe crossed eyes.

Lazy eye is a condition in which 1 eye doesn't see as well as the other eye. The term doctors use for this is "amblyopia."

Strabismus and amblyopia are usually found in childhood. In many cases, a child has both conditions. This is because if the eyes are often crossed, it can cause 1 eye to become lazy. But some children with crossed eyes don't get lazy eye.

If your child has crossed eyes or lazy eye, get treatment as early as possible. If these conditions aren't treated early, there can be lifelong vision and eye problems.

What causes these conditions? — Different things can cause these conditions:

●Crossed eyes is caused by a problem with the muscles that make the eyes move. Different conditions can cause problems with the eye muscles. Crossed eyes can run in families.

●Lazy eye is most commonly caused by crossed eyes. That's because when someone has crossed eyes, each eye sees and sends a different image to the brain. This is confusing for the brain, so the brain ignores the images from 1 eye. Over time, the ignored eye becomes weaker and doesn't see as well.

The other main cause of lazy eye is when 1 eye focuses better than the other. Usually, the problem is that 1 eye is farsighted, meaning it has trouble focusing on things that are close, and the other is not. This causes the same type of confusion for the brain as when a person has crossed eyes. The brain ignores the images from the eye that doesn't focus as well, and over time, the ignored eye becomes weaker.

Other eye problems like cataracts can also cause lazy eye. But these are uncommon in children.

What are the symptoms of crossed eyes and lazy eye? — When people have crossed eyes, their eyes don't line up or move together (figure 1). This can happen all the time or only sometimes, such as when the person is tired.

In newborn babies, the eyes sometimes look crossed. This is normal, as it takes at least few weeks for a baby to learn how to focus their eyes. But if a newborn's eyes are crossed all or most of the time, or if they continue to have eye crossing after they are 4 months old, it could be a sign of strabismus.

With lazy eye, the vision in 1 eye is weaker than in the other eye. This can cause double vision and trouble with "depth perception." (Depth perception is how the eyes see objects as "3D" instead of flat.)

These symptoms can be hard to see, so parents or caregivers might not notice them. Many times, the problem is found though routine vision screening during a doctor's check-up or at school.

Will my child need tests? — Your child's doctor or nurse should be able to tell if your child has crossed eyes or lazy eye (or both) by talking with you and doing an exam. During the exam, they will check how your child's eyes see and move.

Sometimes, the doctor or nurse will use a special machine to look at your child's eyes more closely. The machine is called a "photoscreener" or "autorefractor." It can tell if there is a problem with how well the eyes can focus. It can also tell if the child has mild eye crossing that might not be noticeable by just looking at them. These machines can be used even for very young children.

If the doctor or nurse thinks that your child has crossed eyes or lazy eye, they will have your child see an eye specialist. The specialist, or "ophthalmologist," will do a more detailed eye exam. They will probably use special eye drops to "dilate," or enlarge, the pupils. This allows them to get a good look inside the eyes. Afterwards, your child might have blurry vision for a few hours. Bright light might also bother their eyes. For these reasons, it's best to schedule the appointment at a time when your child will be able to rest after. Bring a pair of sunglasses for them to wear after the exam.

How are these conditions treated? — Helping your child see clearly is the first step in treating both of these conditions. This usually involves having your child wear glasses.

Further treatment depends on your child's condition and its cause.

Treatment for lazy eye involves making the weaker eye work harder so that it can get stronger. To make the weaker eye work harder, the doctor can:

●Put a patch over your child's stronger eye so that eye can't see

●Prescribe eye drops for you to put in your child's stronger eye to make the vision in that eye blurry

Treatment for crossed eyes involves ways to make the eyes line up and work together. The doctor can do this by using special glasses, eye drops, or eye patches.

If these treatments don't work, or if your child has severe crossed eyes, they might need surgery to fix the eye muscles.

See the eye doctor regularly, even after treatment is finished. That's because these conditions sometimes come back.