Amblyopia

Topic Overview

What is amblyopia?

Normal vision develops with regular, equal use of the eyes. Amblyopia, commonly called "lazy eye," usually occurs when one eye is not used enough for the visual system in the brain to develop properly. The brain ignores the images from the weak eye and uses only those from the stronger eye, which leads to poor vision. Amblyopia usually affects only one eye, but it may occur in both eyes. Children can develop amblyopia between birth and about age 7.

A child with amblyopia may not even know that he or she is using only one eye. Ignoring the image from the weak eye is an unconscious response over which the child has no control.

What causes amblyopia?

Any condition that prevents a child's eyes from forming a clear, focused image or prevents the normal use of one or both eyes can result in amblyopia.

Many cases of amblyopia result from eyes that look at two different points in space at the same time, sending two different images to the brain. This condition is called strabismus. In a young child with strabismus, the brain learns to avoid the confusion of two images by ignoring (suppressing) the image from one eye. For more information, see the topic Strabismus.

Amblyopia may also develop if a child is much more nearsighted or farsighted in one eye than in the other. If one eye sees much more clearly than the other, the brain learns to ignore the blurry image from the weaker eye. Amblyopia can develop in both eyes if they are very nearsighted or very farsighted.

Conditions that prevent light from entering the eye for a long period of time can also cause amblyopia. A defect in the lens, such as a cataract, or in the clear "window" at the front of the eye (the cornea) may cause amblyopia in this way. Amblyopia from these causes is rare but serious. Without early treatment, the child may never develop normal vision in the affected eye.

What are the symptoms?

Some children with amblyopia may appear to have an eye that wanders or does not move with the other eye. But in most cases, amblyopia does not cause symptoms. Therefore, early detection is important.

Other symptoms of amblyopia include eyes that do not move in the same direction or fix on the same point, crying or complaining when one eye is covered, squinting or tilting the head to look at something, or an upper eyelid that droops.

What increases the risk of amblyopia?

Factors that put a child at higher risk of developing amblyopia include:

• Misaligned eyes (strabismus).
• Unequal vision in the eyes, such as one eye being much more nearsighted or farsighted than the other.
• Extreme nearsightedness or farsightedness in both eyes.
• Anything that prevents light from passing through the eye, such as a defect in the cornea or the lens (cataract) or, in rare cases, a droopy eyelid.
• A family history of amblyopia or strabismus.
• Low birth weight.
• Premature birth.

How is amblyopia diagnosed?

Amblyopia is diagnosed with an eye exam. If the exam shows that a child has poor vision in one eye, the doctor may diagnose amblyopia after ruling out other causes. The doctor will ask about symptoms, any family history of vision problems, other possible risk factors such as low birth weight, and whether the child has trouble reading or seeing the board or television.

You should have an ophthalmologist examine your child's eyes anytime you have reason to worry about his or her vision. No child is too young for an eye exam. Early diagnosis and treatment of amblyopia is vital to the development of normal vision.

How is it treated?

Treatment for amblyopia involves making the weak eye work to catch up with the strong eye. This can be done by blocking the strong eye with an eye patch (also called occlusion) or by blurring the strong eye with eyedrops or glasses (also called penalization). This causes the brain to use the weak eye. Over time, this usually corrects the vision in the weak eye.

Treatment during early childhood (preferably before age 6), before a child's eyes are fully developed, can usually reverse amblyopia. Treatment later than that will most likely be less helpful but may still improve vision in some cases. A child with amblyopia who does not get treatment may have poor vision for life.

Frequently Asked Questions

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	Amblyopia: Wearing an eye patch

Symptoms

Some children with amblyopia have an eye that wanders or does not move with the other eye. This is sometimes called "lazy eye." But in many children amblyopia is hard to detect. Signs that could point to amblyopia or a condition that raises the risk for amblyopia include:

• Eyes that do not move together in the same direction.
• Eyes that do not fix on the same point.
• Crying or complaining when one eye is covered.
• Squinting or tilting the head up, down, or sideways to look at something.
• Cloudiness in the black center of the eye (cataract).
• An upper eyelid that droops and covers most of the eye (ptosis).

Parents may not be able to tell whether a child has a vision problem. There may be no warning signs, and young children may not complain about poor vision. Most doctors recommend eye exams for children before they start school.

Exams and Tests

A doctor may diagnose amblyopia after detecting poor vision in one eye during an eye exam and ruling out other causes for this poor vision. Tests that find misaligned eyes (strabismus), unequal vision in the eyes, or any other condition that leads to amblyopia can help in the diagnosis.

Before the doctor tests your child's eyes, you will need to answer questions about:

• The child's symptoms.
• Any family history of vision problems.
• Other possible risk factors, such as low birth weight or premature birth.
• Whether teachers have noticed the child having trouble seeing the board or reading.

The doctor first checks the child's eyes to see if they both look in the same direction at the same time. A child with amblyopia may have an eye that wanders or lags behind the movement of the other eye.

For children age 2 and older, the doctor asks the child to identify or point to pictures or letters on the wall or on a handheld chart. These tests measure how well the child sees shapes and details both up close and far away. They may reveal that the child's eyes have unequal vision (anisometropia).

Other tests, including dilating the child's eyes, may be done to determine the need for corrective lenses and to check the structure and function of the eyes. The doctor may also perform tests to detect cataracts and strabismus, both of which raise the risk of amblyopia.

Vision screening can be done by a family doctor, pediatrician, physician assistant, or nurse practitioner. If a problem is detected, the child will be referred to an ophthalmologist or optometrist for a full vision exam.

Doctors may have difficulty performing vision screenings on some small children. In these cases, a technique called photoscreening may be used. In photoscreening, a special camera or video system is used to obtain images of the eye and its reflexes, requiring minimal cooperation from the child. While photoscreening is not a substitute for a normal vision test, it can provide information about sight-threatening conditions.

Other vision tests may be done to check the child's eyes and vision.

Early detection

The U.S. Preventive Screening Task Force recommends screening to detect amblyopia, strabismus, and defects in visual acuity in children younger than 5 years.¹ Vision screening is recommended for infants who were either born at or before 30 weeks, whose birth weight was below 1500 g (3.3 lb), or who have serious medical conditions. The first screening is recommended between 4 and 7 weeks after birth.²

Do not wait if you detect possible signs of amblyopia in your child at an earlier age. No infant is too young for an eye exam by an ophthalmologist, and an exam should be done whenever you have questions about the health of your child's eyes.

The American Academy of Ophthalmology recommends that all infants be screened by 6 months of age by a pediatrician, a family doctor, or an ophthalmologist. Newborns and infants should be screened for eye problems-such as cataracts-that can prevent light from entering the eye and cause amblyopia. Amblyopia from these causes is rare but serious. Without early treatment, the child may not develop normal vision in the affected eye.

Eye exams for children and infants

Treatment Overview

Treatment for amblyopia begins as soon after diagnosis as possible. Early treatment usually can reverse the condition. Treatment should begin before a child's vision has fully developed (around age 9 or 10). The younger the child is when treatment begins, the better his or her chances are for developing good vision.

Amblyopia can be hard to correct after age 9. But studies suggest that treatment beyond this age can still correct amblyopia.³

Amblyopia is usually treated by an ophthalmologist.

To be successful, treatment must address both the amblyopia and the underlying cause. Glasses or contact lenses improve some conditions, such as unequal vision. Other conditions, such as cataracts and some forms of strabismus, may require surgery.

A child born with a cataract or any defect that keeps light out of the eye needs immediate treatment because amblyopia may become permanent within a few months. Amblyopia that results from misaligned eyes (strabismus) or unequal vision in the eyes (anisometropia) usually develops more slowly.

Treatment corrects amblyopia by training the brain to use visual signals from the eye with weaker vision, building a stronger connection between the brain and the weak eye, and allowing vision to develop normally in that eye.

There are several ways to force the weak eye to get stronger. Methods include wearing an eye patch (also called occlusion) and using eyedrops or glasses (also called penalization).

Wearing an eye patch (occlusion)

By covering the stronger eye, the brain is forced to use and develop better vision in the weaker eye.

Covering the stronger eye with an adhesive patch or a dark patch on an elastic band is the most common method of treatment. If a child wears glasses, the doctor may patch part of one lens. The child may have to wear the patch all the time or for just part of each day over the course of a few weeks or months. Severe cases may take longer. One study showed that, along with an hour of activities that exercise near vision, wearing an eye patch daily for 2 hours produces improvements similar to wearing an eye patch daily for 6 hours.⁴

Using eyedrops or glasses (penalization)

These treatments blur or obscure vision in the child's dominant eye, rather than blocking it completely. This causes the brain to rely on the eye with weak vision. Eyedrops or glasses are used less commonly than eye patches. Eyedrops or glasses work best for mild cases of amblyopia: with severe amblyopia, it is difficult to blur or obscure the vision in the stronger eye enough that the brain will prefer to use the weaker eye. These treatments are also called penalization.

• Eyedrops. The most common type of penalization treatment uses eyedrops (usually atropine) to blur the vision in the stronger eye and force the brain to use the weaker eye.
• Glasses. Eyeglasses with a blurry lens over the stronger eye force the brain to use the weaker eye.

Your doctor will probably schedule some breaks during treatment to allow your child to use his or her strong eye, to prevent it from becoming damaged or weakened.

Amblyopia can return even after successful treatment, so children should have regular follow-up exams until age 9 or 10.

Home Treatment

Treatment for your child's amblyopia takes place day in and day out at home or in school. Do everything you can to make the treatment a success. If eyedrops are used, make sure your child uses them as directed by your doctor. Explain the situation to your child's teachers so that they can help support the child during treatment.

To be effective, an eye patch must be worn as directed. It is important for you to help your child comply with this treatment so that he or she can develop the best vision possible. The major cause of failure in the treatment for amblyopia is that the child does not wear the patch as directed by the doctor.

Amblyopia: Wearing an eye patch

If your child has received treatment for amblyopia, follow the doctor's advice about getting regular follow-up eye exams. Amblyopia can return even after successful treatment.

The younger the child is, the better the results of treatment for amblyopia will be. If you think that your child has amblyopia or another vision problem, schedule an eye exam. Begin treatment for amblyopia as soon as the condition is discovered.

Amblyopia is difficult to correct after about age 9. But treatment for some forms of amblyopia may improve vision even in older children and adults.³

Other Places To Get Help

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Related Information

• Cataracts
• Eye Problems, Noninjury
• Nearsightedness (Myopia)
• Strabismus

References

Citations

1. U.S. Preventive Services Task Force (2004). Screening for visual impairment in children younger than age 5 years: Recommendation statement. Rockville, MD: Agency for Healthcare Research and Quality. Available online: http://www.ahrq.gov/clinic/uspstf/uspsvsch.htm.

2. American Academy of Pediatrics Section on Ophthalmology, et al. (2006). Screening examination of premature infants for retinopathy of prematurity. Pediatrics, 117(2): 572-576. Also available online: http://aappolicy.aappublications.org/cgi/reprint/pediatrics;117/2/572.pdf. [Erratum in Pediatrics, 118(3): 1324. Also available online: http://aappolicy.aappublications.org/cgi/reprint/pediatrics;118/3/1324-a.pdf.]

3. Pediatric Eye Disease Investigator Group (2005). Randomized trial of treatment of amblyopia in children aged 7 to 17 years. Archives of Ophthalmology, 123(4): 437-447.

4. Pediatric Eye Disease Investigator Group (2003). A randomized trial of patching regimens for treatment of moderate amblyopia in children. Archives of Ophthalmology, 121(5): 603-611.

Other Works Consulted

• Diamond GR (2004). Amblyopia. In M Yanoff, JS Duker, eds., Ophthalmology, 2nd ed., pp. 615-621. St. Louis: Mosby.

• Wright KW (2003). Amblyopia and strabismus. In Pediatric Ophthalmology for Primary Care, 2nd ed., pp. 21-32. Denver: American Academy of Pediatrics.

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