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

Learning about amblyopia:	What is amblyopia? What causes amblyopia? What are the symptoms of amblyopia? What increases the risk of amblyopia? How does normal vision develop?
Being diagnosed:	How is amblyopia diagnosed? How can I tell if my child has amblyopia? When and how often should my child have an eye exam?
Getting treatment:	How is amblyopia treated? Will an eye patch help my child develop normal vision? Are there medicines that can treat amblyopia? Can amblyopia be treated at home?
Ongoing concerns:	Will amblyopia get worse? Is amblyopia inherited?
Living with amblyopia:	How can I get my child to wear an eye patch as directed by a doctor?

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Author:	Robin Parks, MS	Last Updated July 17, 2007
Medical Review:	Michael J. Sexton, MD - Pediatrics Christopher J. Rudnisky, MD, FRCSC - Ophthalmology
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