With normal vision, the eyes work together to form 1 image. When your child looks from an object that’s far away to one that’s close, the lens inside the eye changes its shape. The hole that lets light into the eye (pupil) becomes smaller. And the eyes move slightly inward (converge). The eye and brain work together to make all of these changes. The result is a single, focused image. When reading, the eyes and brain also have to do quick, complex eye movements to look across and down a page.

Researchers are not yet sure what causes CI. There may be problems in the complex actions that the brain and eyes do. This may be because of genes. CI tends to run in families. In some cases a health condition can contribute to CI, such as:

• Head injury and concussion

• Graves disease

• Myasthenia gravis

Your child is mostly likely to have symptoms of CI when doing work close up, such as reading or writing. Symptoms are more likely if he or she is reading or writing for a long period of time. Fatigue also can bring on symptoms. Symptoms can include:

• Headache

• Double vision

• Eye fatigue

• Blurred vision

• Sleepiness when reading

• Needing to reread things several times

• Trouble concentrating on what he or she is reading

• Losing his or her place in the text when reading

• Squinting while reading

You may also notice that one of your child’s eyes sometimes turns outward as he or she reads. This may cause blurred vision. Or you may notice your child squinting or closing one of his or her eyes while reading. This can make it easier to see a single, focused image. Symptoms tend to get worse during the teens and 20s. They are often steady after that.

The eye doctor will ask about your child’s past health. He or she will give your child an eye exam. This will include testing for visual sharpness. He or she will also test how your child’s eyes converge. This is done while your child looks closely at something. Your child may do this test with each eye separately, and then together.

CI is most often treated with special exercises. Your child will be shown how to do these exercises. He or she and may need to do them regularly at home. Some of these exercises are done while looking through prisms. Your child’s symptoms may go away in a fairly short period of time if your child does the exercises regularly. Computer programs can help treat CI. These can make the eyes better able to converge. They can also measure how the eyes are getting better over time.

Covering one eye may ease symptoms for a short time, but it does not help correct CI. It also does not give your child practice working with both eyes together, which is important in order to correct CI. Your child may need to cover one eye for a short time if he or she has a lot of reading to do. But keep in mind that it’s not a long-term solution.

In some cases, the symptoms of CI do not go away with treatment. Your child’s eye doctor may prescribe special prism glasses for reading. These can help your child read more comfortably. In very rare cases, an eye care doctor may advise surgery.

Exercises to treat CI work well for most children. But to work well they need to be done regularly. You can help your child by making sure he or she does the exercises as often as directed by the eye doctor.