What is amblyopia?

Amblyopia (pronounced “am-blee-O-pee-uh”) is reduced vision in an eye that did not develop normally in early childhood. To understand the problem, imagine you are looking at a tree a short distance away. When vision is normal, both eyes are pointed in the same direction and the image of the tree is in clear focus in each eye. Your brain receives an image of the tree from each eye and these two images are combined into a single three-dimensional (3-D) image. This allows you to see depth and understand approximately how far away you are from the tree. The images your brain receives from each eye are slightly different because the eyes are a few inches apart on your head and each see the tree from a slightly different angle. When the images are combined, they allow you to see in 3-D.

How does this relate to amblyopia? In the previous example each eye is able to see the tree in clear focus. With amblyopia however, the brain receives an image from one eye that is very different from the other. When this occurs the brain is not able to properly combine the two images into a single 3-D image. Since “seeing double” is confusing and uncomfortable, the brain “turns off” the image from the blurry eye that doesn’t see as well and just pays attention to the image from the better eye. As vision is developing in early childhood it is critical that both eyes get used. When the blurry eye doesn’t receive attention and isn’t used, it gets weak and if it isn’t treated early may eventually become functionally blind.

What causes amblyopia?

With amblyopia, one eye sees worse than the other and the brain only pays attention to the image from the good eye. The main causes are:

1. Misaligned or “crossed” eyes (strabismus). This problem causes one eye to point in a different direction than the other and is the most common cause of amblyopia. When one eye crosses in, wanders out, or is misaligned in some other way, the brain will ignore the image from the crossed eye to avoid double vision. When ignored by the brain and not used, the eye will develop amblyopia.

2. Unequal focus of the eyes (anisometropia). In this case the brain receives images from the eyes that are very different because one eye does not focus as well as the other. In other words, one eye is more nearsighted, farsighted, or astigmatic than the other and may develop amblyopia if it is ignored by the brain. Children are often able to compensate and hide this problem so it may be the most difficult type of amblyopia to detect.

3. Cloudiness of the eye (cataract, among other problems). A cataract is a clouding of the lens of the eye. When one eye is cloudy and sees an out-of-focus image, the brain will ignore this image and just pay attention to the eye that sees clearly. When it isn’t used, the eye with the cataract may develop amblyopia.

What are some of the signs or symptoms of amblyopia?

It is not always easy to recognize amblyopia unless your child has a highly noticeable problem such as a misaligned eye or she becomes upset when you try to cover her good eye with your hand or a patch. Because amblyopia is difficult to recognize, early vision screening is essential.

It is also important to remember that you can’t depend on your child to tell you he is having an eye problem. Most children believe that everyone sees the same way they do, even if they don’t see clearly in one or both eyes.

In addition to amblyopia, you may be interested in learning about other signs of possible eye trouble in children from the Prevent Blindness America organization.

How many people have amblyopia?

Amblyopia is a common condition that affects approximately 2 or 3 out of every 100 people. Looking at children’s eye health more broadly, it has also been reported that in the age range of 3 to 5 years, 1 child in 20 has some kind of eye problem (National Society to Prevent Blindness brochure, "Amblyopia").

What is strabismus?

Strabismus is a problem where the eyes are misaligned and point in different directions. With normal vision the eyes focus on the same object and send similar images to the brain. These two images are then combined to form a single three-dimensional (3-D) image, allowing depth perception. When a child has strabismus and one of the eyes points in a different direction, the brain stops paying attention to the image from that eye— a cause of amblyopia. Approximately 4% of children in the US have strabismus, but only about half of these children will develop amblyopia.

Is amblyopia genetic (does it run in families)?

Some causes of amblyopia run in families, however, most children with amblyopia come from families where no one else is affected. Children that have a family history of amblyopia should be checked by an ophthalmologist earlier and more frequently than other children. See “When and how often should a child be screened for amblyopia?” for normal guidelines and check with your doctor for guidance.

How is amblyopia detected?

One method for detecting amblyopia is through measuring a child’s visual acuity (how well she sees) in each eye when she reaches an age when she can recognize letters or symbols. When there is a significant difference between how well the two eyes see, amblyopia may be suspected and vision should be checked by an ophthalmologist.

How is amblyopia treated?

The first step in treating amblyopia is to find the underlying cause. The following is a list of common underlying causes and what first steps may be taken for treatment.

1. Misaligned or “crossed” eyes (strabismus). In some cases glasses may be prescribed to help stimulate the crossed eye. In other cases, surgery on the eye muscles may be necessary to straighten the eyes.

2. Unequal focus of the eyes (anisometropia). When a child is nearsighted, farsighted, or astigmatic, glasses are usually prescribed to correct the focus of the eye.

3. Cloudiness of the eye (cataract). Surgery may be necessary to restore vision in the eye with the cataract.

After the underlying cause of amblyopia has been corrected, the child will need to strengthen the weaker eye. This is accomplished by “forcing” the weaker eye to work harder. The two most common methods are to put a patch over the better eye or to put eye drops in the better eye that blur vision. When the better eye can’t see, either by patching it or causing it to be blurry with eye drops, it will force the weaker eye to work harder. Patching or eye drops will stimulate the brain to use the weaker eye and vision in that eye will generally improve. These treatments may be necessary for a time period of months up to years, until vision is normal or stops getting better.

When should treatment begin?

The earlier the child is treated, the better the chances are for restoring normal vision. Cases that are detected at age 3 and earlier have the best chances for full recovery.

Why is early treatment important?

Early childhood is the most critical period of development for the vision system. When a child reaches the age of about 8 or 10, the vision system has finished developing and it is not usually possible to make improvements to counteract the effects of amblyopia. If a child with amblyopia hasn’t been treated by this age, the chances for restoring vision are low. Early diagnosis and treatment is critical to improving or restoring vision to normal.

What happens if amblyopia is left untreated?

When left untreated, amblyopia may lead to a permanent reduction of sight in the affected eye and a loss of depth perception (seeing in 3-D). This permanent reduction in sight may be severe enough that the eye becomes functionally blind. In fact, amblyopia is a leading cause of blindness in one eye. Another concern is that if a person has untreated amblyopia in one eye and the better eye becomes injured or diseased later in life, there is no longer a “backup” eye so the person may become legally blind.

When and how often should a child be screened for amblyopia?

The American Academy of Ophthalmology and the American Association for Pediatric Ophthalmology and Strabismus have recommended that every child be screened for vision problems at the following intervals:

1. At birth (routinely done at the hospital)
2. At the age of 6 months to 1 year (during a regular appointment with pediatrician)
3. At the age of 3 to 3 ½ years
4. Routinely during the school years

Any child who fails one of these screenings should have a complete ophthalmological exam. In addition, if there is family history of amblyopia or other eye problems, vision should be checked more frequently as indicated by an ophthalmologist. The American Academy of Ophthalmology has more information on these guidelines.

What is the difference between an ophthalmologist, optometrist, and an optician?

1. Ophthalmologists (M.D.) are licensed physicians who specialize in the diagnosis and treatment of eye diseases and disorders. They have completed 12 years of education beyond high school including 4 years of college, 4 years of medical school, at least 1 year of general clinical training, and at least 3 more years of residency training in medicine and eye surgery. In addition, some ophthalmologists spend at least another year in a subspecialty fellowship in an area such as retinal disease, pediatric ophthalmology and strabismus, or glaucoma. An ophthalmologist is licensed to practice medicine and qualified to diagnose and treat all eye diseases, perform surgery, and prescribe glasses and contact lenses.

2. Optometrists (O.D.) are licensed to practice optometry and have at least 6 years of education beyond high school, but they do not receive medical degrees. They are qualified to prescribe glasses and contacts and screen for some eye conditions.

3. Opticians are technicians trained to fit eyeglass lenses, frames, and contact lenses as prescribed by an ophthalmologist or optometrist. They either complete a 2-year opticianry degree and/or receive on-the-job training. They are not qualified to diagnose or treat eye diseases.