Strabismus, also known as crossed eyes, is a condition in which the eyes don't look towards an object together. One of the eyes may look in or out, or turn up or down. The eye turning can occur all of the time or only sometimes, such as during stressful situations or illness.

Some people are born with eyes that do not align in the usual way. This is called congenital strabismus. In many children, there is no clear cause of strabismus. In some cases, it is a result of a problem with the nervous system, especially the part that controls the muscles of the eyes. If it is not corrected, strabismus can continue into the adult years. Most adults who have strabismus were born with it.

If strabismus does not appear until later in life, it will cause double vision. If the eyes become misaligned in an adult who did not have strabismus as a child, it could be a sign of a serious condition such as a stroke. A sudden, misalignment of the eyes or double vision are important reasons to see a doctor immediately.

Someone who is born with strabismus will see without having double vision. There might be other effects on vision, however. Because the two eyes are not working well together, depth perception and peripheral vision (vision off to the side) will not be very good. Eyestrain and headaches can occur frequently. It might also be necessary to turn the head in unusual ways in order to see in certain directions.

A doctor may recommend that patients go through physical therapy to help strengthen their eye muscles. Vision therapy is also used to help a person correct their vision when suffering with strabismus. This therapy helps train a patient's brain to be able to align their eyes and focus and visually process images. Vision therapy uses computerized optical devises, including lenses and filters, to develop the eye muscles.

Yes. Surgery to correct strabismus is performed to strengthen or weaken the effect of one or more of the muscles that move the eye. When this procedure is performed on adults, it is usually done under local anesthesia. (The eye is numb, but the patient is awake.)

The surgeon will first make an opening into the outer layer of the eyeball. This allows the surgeon to reach the muscle that will be strengthened or weakened.

Strengthening the muscle means removing a small section from one end and then stitching it back together. This makes the muscle shorter, which tends to turn the eye toward the side of that muscle.

"Weakening" the muscle means making a cut across one end, but not removing any of the muscle to shorten it. Instead, a gap is left where the muscle was cut, and the ends of the muscle are tied back together with a suture (thread). This has the effect of making the muscle longer, which lets the eye turn further away from the side of that muscle.

At the end of the procedure, the surgeon will close the opening in the eye with stitches. The patient will often have double vision for a few weeks after surgery. This goes away as the brain adjusts to the new way of seeing.

Reviewed by the doctors at The Cleveland Clinic Cole Eye Institute.