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Fact sheet: Amblyopia in children – when one eye sees better than the other

Last Update: September 26, 2011.

Photo of teddybear with an eyepatch
Normally, the brain processes the information coming in from both eyes equally. This is needed for the best possible vision. In some children, however, one eye is favored by the brain because it provides a better image. If this happens, the other eye is neglected from childhood on, and it does not get the chance to develop well. This is known as amblyopia or “lazy eye”.

Amblyopia cannot be fixed instantly by putting on prescription glasses that correct the problem. But there are different ways to help the affected eye catch up with its partner, or at least help make sure that the problem does not get worse over time. Treatment might only be needed for a few weeks, but sometimes it needs to continue for quite a long time to get the best results.

Until recently it was thought that treatment could only make a difference when children are very young. A trial has now shown, though, that amblyopia can probably still be treated in teenagers too. This fact sheet explains what amblyopia is and describes the treatment options.

What is amblyopia and why has the brain chosen a favorite eye?

Amblyopia, the medical term for lazy eye, is taken from ancient Greek and literally means “dull vision”. Amblyopia is a common eye problem in childhood. In European countries like Germany, it is estimated that about 4 to 6% of children are affected (4 to 6 out of every 100). It usually does not develop after the age of 7 or 8.

Squinting often leads to amblyopia

One main reason why amblyopia develops is a squint (strabismus or “crossed eyes”). If a child has a squint, one of his or her eyes will look straight ahead while the other looks up, down or to the side. It is normal for babies to squint in the first few months of life. It is not completely clear why some children have squints and others do not.

If the eyes send two different images to the brain, the brain cannot combine these images to form one picture, and we see double. In order to see more clearly, the brain might then ignore the images that are coming from the weaker eye.

Most children who have a squint have amblyopia: somewhere around 60 to 70 out of 100 children with a squint are affected by it (60 to 70%). Amblyopia is much less common in children who do not have squints: only about 2 out of 100 children who do not have a squint have amblyopia (2%).

Other causes of amblyopia

Another common cause of amblyopia is refractive errors (focusing problems). These problems are the most common cause for having to wear glasses. There are 3 different kinds of refractive error:

  • Near-sightedness (or short-sightedness), where the eye can only focus clearly on objects that are close
  • Far-sightedness, where the eye can only focus clearly on objects that are far away
  • Astigmatism, where everything that the affected eye sees looks blurred. This is usually because the lens or cornea is not shaped exactly as it needs to be to send sharp images to the brain. You can read more about the different parts of the eye and how the eye works here.

The chances of a child developing amblyopia are higher if he or she has a refractive error in one eye and not in the other, or if one eye is far sighted and the other is near sighted

In rare cases amblyopia could be caused by a certain eye disease – for example, when a cataract develops and makes the eye cloudy, or because the child has developed a droopy eyelid (called ptosis) or does not have a lens in an eye (aphakia).

How can I find out whether my child has amblyopia?

If your child has a squint or you think he or she may have an eye problem, it is important to have it checked out by an ophthalmologist (specialist eye doctor). Difficulties recognizing objects could be a sign of amblyopia too. For example, if your child has to hold toys and other things very close to their eyes or turn their head to one side to see them.

There are several tests that can be done to find out whether your child has amblyopia:

  • The doctor can use eye charts to see how good your child’s vision is. The exact kind of test will depend on several factors, including your child’s age. There are special tests for babies and toddlers.
  • A physical check-up can be done to see whether the poor eyesight is caused by something else, like a cataract. A test can also be done to see whether your child’s eyes are aligned properly. A slight squint is not always visible to the naked eye.
  • The exact refractive power of your child’s eyes can be determined using a special instrument called a retinoscope. This involves shining light into the eye and seeing how the light reflects off the retina at the back of the eye. By holding different corrective lenses in front of the light, it is possible to determine exactly how well the eye can focus.
  • Once the refractive power has been determined, a further eye test can be done using an eye chart. This time the child wears glasses that correct any focusing problems he or she may have.

These tests are generally safe. People are usually given eye drops to dilate (open) their pupils before having a retinoscopy examination. The eye drops can sometimes make their eyes burn or irritate their skin.

In Germany, each child is routinely offered eye-screening tests as part of some of the health screening programs (“U-Untersuchungen”). Signs of amblyopia or risk factors are some of the main things that the doctors will be looking for. Researchers at the German Institute for Quality and Efficiency in Health Care (IQWiG) – the publisher of this website – assessed the research on routine screening for vision problems in small children. They found that there are still many unanswered questions about this screening program. For example: which tests are best for detecting vision problems? And what is the best age at which to have these tests? We have summarized the results of their research here, including more information about research on treatment in older children.

What are the treatment options?

There are different treatments for amblyopia, depending on the type and severity of the problem, as well as other factors. The standard treatment options are:

  • Glasses to correct refractive errors.
  • Occlusive therapy (eye patch): The word occlusion comes from Latin and means “closure”. In occlusive therapy the better eye is covered for several hours a day using a patch over the eye, or over one side of the glasses if the child wears glasses. The idea is to encourage the weaker eye to work harder so that vision improves in that eye.
  • Medication: Eye drops that have a drug such as atropine in them are used to temporarily blur vision in the “good” eye. They relax the muscles in the eye, which means that the lens of the eye cannot focus for a few hours.

The child usually wears glasses for several weeks and then starts wearing an eye patch too. This treatment typically takes a few months, during which regular eye tests are done. If the child has poor vision due to a refractive error, he or she will have to continue wearing glasses after treatment has finished in order to see well.

If amblyopia is caused by another problem, such as a cataract, that problem is treated first. Children who have a severe squint sometimes have surgery. This kind of surgery involves tightening or relaxing the eye muscles to correct the misalignment of the eyes so that they move parallel to each other again, as far as possible. The aim is to improve spatial vision and make the squint less obvious. This surgery generally does not have anything to do with treatment for amblyopia. Sometimes amblyopia gets better on its own, but it is not clear how common this is.

For a long time, it was widely believed that treatment is only successful if it is started early. However, a comparison of two small trials involving children and teenagers aged 7 to 17 showed that later treatment can probably improve eyesight too. Vision problems can get worse and become permanent if amblyopia is not treated.

Which treatments can improve vision?

Researchers from the Cochrane Collaboration – an international network of researchers – analyzed the trials testing different treatments for amblyopia. They found that there is hardly any research on treatments for amblyopia caused by a squint. Still, there is some evidence that wearing glasses and an eye patch could improve children’s vision more than wearing glasses alone.

Wearing an eye patch as well as glasses has been shown to improve the vision of children who have one amblyopic (“lazy”) eye and whose eyes have different refractive powers. Generally speaking, they only have to wear the eye patch for 2 to 6 hours a day, depending on how poor their eyesight is. Sometimes wearing glasses is enough and no eye patch is needed.

Some people worry that patching could make the healthy eye weaker, because it is used less during the treatment. But this has not been shown to be a problem in the trials that have tested eye patching treatment for amblyopia. Eye patches can irritate some children’s skin, however.

Two trials compared eye patches with drug therapy, where eye drops are used once a day to numb the muscles of the healthy eye. The lens is then no longer able to focus for some time. These trials showed that the results of both treatments did not vary much.

Eye drops can have adverse effects like sensitivity to light or burning eyes. Sometimes treatment with eye drops leads to the child not being able to see quite as well with the healthy eye for some time after the treatment. In the trials this effect was only temporary. Drug treatment can be an option especially for children who find it difficult to wear an eye patch.

Sometimes children are encouraged to train the affected eye by doing activities like drawing or making things while wearing the eye patch. In a recent trial, this was not shown to lead to a greater improvement in vision in most children. However, it cannot be ruled out that children who have a very “lazy” eye could benefit from such activities.

Whether or not the treatment will work depends on many factors, and cannot be predicted for individual people. For example, the child’s age, the time of treatment and the type and severity of the amblyopia could influence how successful treatment is. It can take quite a long time until treatment shows some benefit, and that can be very frustrating for the child and their parents.

What can I do to help my child?

Most children do not have any problems wearing their eye patch in everyday life. But some find it hard to wear it as much as they are meant to. There are several reasons for this. For instance, they can only see with their weaker eye if their “good” eye is covered up, so they cannot see as well as usual during treatment, which may cause problems when they are playing or doing school work. They may also be teased about their eye patch in kindergarten or at school, or by their friends and siblings.

Children who have to wear their eye patch for longer may feel more self-conscious than children who only have to wear it for a few hours a day, so you can talk to the doctor to find out what is the least amount of time to improve your child’s vision. Parents use different strategies to try to help their child cope with a patch. Some find it helpful to make sure their child understands why the patch is important, or carefully explain the results of eye tests to show that the eye is really getting stronger.

Children like to know that they are “normal”. Some parents have reported that doing things like putting eye patches on toys – or even wearing patches themselves – helps make eye patches “normal”.

Some parents find it helpful to also use praise or small gifts to encourage their child to wear the patch, while other parents find it better to not make a big deal out of it.

The patches can be unattractive or boring. Some children like it better if they can cover up their glasses with something more interesting that they choose themselves. And as with so many things, having a regular daily routine with wearing the patch can be important to children. And the good news is that in a few months’ time this ritual will most likely be a thing of the past.

Author: German Institute for Quality and Efficiency in Health Care (IQWiG)

Next planned update: March, 2014. You can find out more about how our health information is updated here.


  • IQWiG health information is based on research in the international literature. We identify the most scientifically reliable knowledge currently available, particularly so-called “systematic reviews”. These summarize and analyze the results of scientific research on the benefits and harms of treatments and other health care interventions. This helps medical professionals and people who are affected by the medical condition to weigh up the pros and cons. You can read more about systematic reviews and why these can provide the most trustworthy evidence about the state of knowledge here. The authors of the major systematic reviews on which our information is based are always approached to help us ensure the medical and scientific accuracy of our products.
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  • German Institute for Quality and Efficiency in Health Care (IQWiG): Screening for visual impairment in children younger than 6 years. Final report S05-02. Version 1.0. Cologne: IQWiG. April 2008. [Executive summary]  [Full text in German] [PubMed: 23101092]
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© IQWiG (Institute for Quality and Efficiency in Health Care)

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