Overview

A "lazy eye" is a childhood condition where the vision does not develop properly. It's known medically as amblyopia.

It happens because one or both eyes are unable to build a strong link to the brain. It usually only affects one eye, and means that the child can see less clearly out of the affected eye and relies more on the "good" eye.

It's estimated that 1 in 50 children develop a lazy eye.

How to tell if your child has a lazy eye

A lazy eye does not usually cause symptoms. Younger children are often unaware that there's anything wrong with their vision and, if they are, they're usually unable to explain what's wrong.

Older children may complain that they cannot see as well through one eye and have problems with reading, writing and drawing.

In some cases, you may notice that one eye looks different from the other. However, this is usually a sign of another condition that could lead to a lazy eye, such as:

• a squint – where the weaker eye looks inwards, outwards, upwards or downwards, while the other eye looks forwards
• short-sightedness (myopia), long-sightedness (hyperopia) and astigmatism
• childhood cataracts – cloudy patches that develop in the lens, which sits behind the iris (the coloured part of the eye) and pupil

If your child is too young to tell you how good their vision is, you can check their eyes by covering each eye with your hand, one at a time. They might object to covering the good eye, but they might not mind if you cover the lazy eye.

If they try to push your hand away from one eye but not the other, it may be a sign they can see better out of one eye.

When to get medical advice

Lazy eye is often diagnosed during routine eye tests before parents realise there's a problem.

If you want to be reassured about your child's vision, they can have their eyes tested when they're old enough to attend a sight test at a high-street opticians, which is usually after they're 3 years old.

All newborn babies in the UK have an eye test in the first days of life, and then again at 2 to 3 months old, to look for eyesight problems such as cataracts. Problems like squint and short or long sight may not develop until the child is a few years old.

It's difficult to treat lazy eye after the age of 6, so it's recommended that all children have their vision tested after their fourth birthday. This is the responsibility of your local council, which should organise vision testing for all children between 4 and 5 years of age. This is normally carried out at school. If you are worried that your child has missed this screening, you can visit your local optometrist/optician for a free sight test on the NHS to assess their vision.

You can also visit your GP if you have any concerns about your child's eyesight, or if there is a family history of a lazy eye. If necessary, they can refer your child to an eye specialist.

Causes of a lazy eye

The eyes work like a camera. Light passes through the lens of each eye and reaches a light-sensitive layer of tissue at the back of the eye called the retina.

The retina translates the image into nerve signals that are sent to the brain. The brain combines the signals from each eye into a three-dimensional image.

A lazy eye happens when the brain connections responsible for vision are not made properly. To build these connections, during the first 8 years of a child's life, the eye has to "show" the brain a clear image. This allows the brain to build strong pathways for information about vision.

A lazy eye can be caused by:

• a reduced amount of light entering the eye
• a lack of focus in the eye
• confusion between the eyes – where the 2 images aren't the same (such as a squint)

Left untreated, this can lead to the eye's central vision never reaching normal levels.

Treatment for lazy eye

In most cases it is possible to treat a lazy eye, usually in 2 stages.

If there's a problem with the amount of light entering the eye, such as a cataract blocking the pathway of light, treatment will be needed to remove the blockage.

If there's an eyesight problem such as short or long sight or astigmatism, it will first be corrected using glasses to correct the focus of the eye. This often helps correct a squint as well.

The child is then encouraged to use the affected eye again. This can be done using an eye patch to cover the stronger eye, or eyedrops to temporarily blur the vision in the stronger eye.

Treatment is a gradual process that takes many months to work. If treatment is stopped too soon, any improvement may be lost.

Treatment for lazy eye is most effective for younger children. It's uncertain how helpful it is for children over 8 years of age.

Read more about treating a lazy eye.

Who can get it

A lazy eye (amblyopia) is caused when something disrupts the normal development of vision.  It can affect any child but it tends to run in families, or those children born prematurely.

How vision develops

It's often assumed that younger children have the same vision as adults, but this is not the case.

Children have to learn how to see – more specifically, their brains have to learn how to interpret the nerve signals sent from the eyes to the brain.

It usually takes around 3 to 5 years before children can see as clearly as adults, and up to 7 years before the vision pathways in the brain become fully developed.

If something affects one of the images the eye shows the brain as the brain develops, the signals become disrupted.

The brain starts to ignore the poor-quality images, resulting in a "lazy eye". For most children this happens because of a problem with the image in one eye. As a result, the brain becomes increasingly reliant on the stronger eye, which makes the weaker eye even lazier.

Underlying eyesight problems

Common eyesight problems that disrupt the development of vision and can cause lazy eye include:

• squint
• long sight, short sight and astigmatism

Squint/strabismus

A squint is a common eye condition that affects around 1 in 20 children. If a child has a squint, one eye looks straight ahead but the other eye looks off to the left, right, up or down.

This causes the brain to receive two very different images that it cannot combine. In adults, this would result in double vision.

In children who are still developing, it can cause the brain to ignore images from the squinting eye, leading to a lazy eye.

Some babies are born with squints. Older children can develop a squint as a result of eyesight problems such as long sight, short sight or astigmatism

Long sight, short sight and astigmatism

Long sight, short sight and astigmatism are eyesight problems that are caused when the light rays entering the eye are not properly focused. This is because of problems with the structure of the eye.

• long-sightedness – is where distant objects appear normal but nearby objects are blurred
• short-sightedness – is where nearby objects appear normal but distant objects are blurred
• astigmatism – is where an irregular-shaped cornea or lens leads to blurred or distorted vision due to problems focusing

Many children with these eyesight problems develop normal vision in both eyes. However, in some children, they can cause the brain to ignore the signals from one or both eyes.

Less common eye problems

Less common eye problems that can cause a lazy eye include:

• a scar on the transparent layer at the front of the eye (cornea)
• childhood cataracts – clouding of the naturally clear lens of the eye
• a droopy eyelid

Diagnosis

A lazy eye ideally needs to be diagnosed and treated as early as possible, preferably before a child is 6 years of age.

However, it can often be difficult to know whether a child has a lazy eye as they might not realise anything is wrong with their vision.

This means a lazy eye may not be diagnosed until a child has their first eye test.

If an eye specialist suspects a lazy eye, they'll also test for other conditions, such as a squint.

Visit your GP or tell your health visitor if you have any concerns about your child's eyesight at any stage.

You can also take your child to a high-street optician for a free NHS sight test.. If a lazy eye is suspected it is likely that your child will have an extended eye test that includes drops in their eyes which may make their vision fuzzy but will help the optician see of your child needs glasses to help their sight develop and or a referral to a specialist department at your local hospital.

Routine eye tests

Your baby's eyes will be examined within 72 hours of birth. This simple examination is used to check for obvious physical problems, such as a cataract.

Your baby will have a second eye examination when they're between 6 and 8 weeks old.

A child's vision should develop in the following way over the first year of life:

• by 6-8 weeks old – follows a bright or interesting object, such as a face, with their eyes
• by 2-3 months old – shows interest in nearby objects 
• by 6 months old – focuses on objects that are both near and far away and is interested in pictures
• by 12 months old – able to see small objects, such as tiny bits of food and bits of fluff, is also able to recognise familiar people 

Shortly before or after having a baby, all new parents are given a Personal Child Health Record (red book), which highlights developmental milestones for vision.

When your child is around 1 or 2 years old, you may be asked whether you have any concerns about their eyesight during a review of their health and development.

If necessary, specific eye tests that check for vision problems can be arranged.

Your child's vision may also be tested when they start school, at around 4 or 5 years of age. 

Read more about routine eye tests for children.

Treatment

The younger the child is when a lazy eye is diagnosed, the more successful treatment is likely to be. Treatment is less successful if it's started after the age of 6, and it's unlikely to be successful if it's started after the age of 8.

The 2 main treatment options for a lazy eye are:

• treating or correcting any underlying eye problems
• encouraging the use of the affected eye so vision can develop properly

Treating underlying eye problems

Glasses

Short- or long-sightedness, can be corrected using glasses. These usually need to be worn constantly and checked regularly.

Glasses may also help to straighten a squint, and in some cases can fix the lazy eye without the need for further treatment.

Your child may say they can see better without their glasses. This is because their eyes have become used to working hard to focus and they now find it difficult to let the glasses focus for them.

They'll need plenty of encouragement to wear their glasses continuously.

Contact lenses are an alternative to glasses, but they may only be suitable for older children.

Surgery

In children, most cataracts are removed to allow better development of vision in the affected eye.

Cataract surgery for children is carried out under general anaesthetic. The procedure usually takes 1 to 2 hours.

Your child may be kept in hospital overnight to check their recovery, and will have to use eyedrops afterwards.

In some cases, surgery is used to improve the appearance of a squint. The operation will either strengthen or weaken the eye muscles of the lazy eye to change its position.

This means the lazy eye will appear to be better aligned with the good eye. The child's vision won't improve, but their eyes will appear straighter and it will help the eyes work better together.

A droopy eyelid can also be corrected using surgery.

Encouraging use of a lazy eye

A number of different treatment options can be used to encourage your child to use the affected eye.

Using a patch

This involves placing a patch with a sticky rim over the "good" eye so the lazy eye is forced to work. It can be very effective in improving the sight in the lazy eye. Patches often need to be worn with glasses.

The length of time the child will need to wear the patch will depend on how old they are, how serious the problem is, and how much they co-operate with wearing the patch.

Patches are most effective before a child reaches 6 years of age. Most children will need to wear the patch for a few hours a day for several months.

Using a patch to treat a lazy eye can be time-consuming and can often be an unpleasant experience for the child until they get used to it. This is understandable – from their point of view, you're making their vision worse by taking their good eye away from them.

This is why the most important thing for you to do is explain the reasons for using a patch, and the importance of sticking with the treatment, to your child so that they're motivated to do it.

If your child is too young to understand, try to think of incentives to encourage them to use the patch. While the patch is on, they should do close-up activities, such as playing with an electronic tablet, colouring, reading or schoolwork. Reward them with their favourite television programme.

Eyedrops

Atropine eyedrops can be used to blur the vision in the good eye. They expand (dilate) the pupil of the good eye and blur vision, which encourages the child to use the lazy eye.

Side effects that can occur after using eyedrops include:

• eye irritation
• reddening (flushing) of the skin
• headaches 

However, these side effects are usually rare and rarely outweigh the benefits of using eyedrops.

Eyedrops can be as effective as using a patch. Often the choice of eyedrops or patches is a matter of preference. Children who do not like having drops in their eyes can wear a patch, and those who do not like wearing a patch can use eyedrops.

If treatment does not work

In some cases, a lazy eye does not improve despite having proper treatment.

Sometimes poor results are due to the child or family finding it difficult to stick to using the patch or the eyedrops.

If you're having trouble with one kind of treatment, discuss the alternatives with your eye specialist.

If surgery is recommended, more than one operation may be required to improve the appearance of a squint, and glasses may still need to be worn after surgery.

If the treatment is stopped too soon, any improvements in the lazy eye can be lost. A patch may also need to be worn or eyedrops used, if the lazy eye returns.

Most children will be discharged with a lazy eye at the age of 7-8. At this point you will be encouraged to take them for a free regular eye examination at a local opticians.