A lazy eye (amblyopia) is a childhood condition where the vision in one eye doesn't develop properly.
This usually means that the child can see less clearly out of the affected eye and relies more on the "good" eye.
An estimated 1 in 30 to 1 in 50 children will develop a lazy eye. The condition is usually diagnosed around the age of four.
Lazy eye can sometimes affect both eyes, although this is rare.
How do I know if my child has a lazy eye?
A lazy eye doesn't 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 can't 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
- refractive errors - where a person is either short-sighted (myopia) or long-sighted (hyperopia)
- childhood cataracts - cloudy patches that develop in the lens, which is located behind the clear layer of tissue at the front of the eye (cornea)
One way to check your child's eyes is to cover 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 seek medical advice
Lazy eye is often diagnosed during routine eye tests before parents realise there's a problem.
Children should have their eyes tested once they're old enough to attend a sight test, which is usually after they are 3.5 years old.
It's difficult to treat lazy eye after the age of 4.5, so it's a good idea for children to have an eye test between the ages of 3.5 and 4.5.
However, visit your GP if you have any concerns about your child's eyesight. If necessary, they can refer your child to an eye specialist (ophthalmologist) for further testing.
Read more about diagnosing a lazy eye.
What causes 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 occurs when the brain connections responsible for vision aren't made properly.
This can be the result of:
- a reduction in the amount of light entering the eye
- a lack of focus in the eye
- confusion between the eyes - where the two images aren't the same (such as a squint)
Left untreated, this can lead to the eye's central vision never reaching normal levels.
Read more about the causes of a lazy eye.
Treating a lazy eye
In most cases it is possible to treat a lazy eye, usually in two stages.
The underlying problem is first corrected using glasses to correct the focus of the eye, which often helps to 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 eye drops to temporarily impair the vision in the stronger eye.
Treatment is often effective, but it's a gradual process that takes many months to work.
Read more about treating a lazy eye.
A lazy eye (amblyopia) is caused when something disrupts the normal development of vision.
How vision develops
It's often assumed that younger children have the same vision as adults, but this isn't 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 three to five years before children can see as clearly as adults, and up to seven years before the eyes become fully developed.
If something affects one of the eyes as it develops, the signals become disrupted, which affects the quality of the images interpreted by the brain.
The brain starts to ignore the poor-quality images and becomes increasingly reliant on the stronger eye.
Common conditions that disrupt the development of vision and can cause lazy eye are discussed below.
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 can't combine. In adults, this would result in double vision.
In children who are still developing, it causes 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 a group of eye conditions called refractive errors.
Refractive errors are caused when the light rays entering the eye aren't properly focused. This is caused by problems with the structure of the eye.
Two examples of refractive errors that could lead to a lazy eye are:
- long-sightedness - where distant objects appear normal but nearby objects are blurred
- astigmatism - where an irregular-shaped cornea or lens leads to blurred or distorted vision
Refractive errors can cause the brain to rely on the signals from one eye, meaning the other eye fails to develop properly.
Less common conditions
Less common conditions that can cause a lazy eye include:
A lazy eye (amblyopia) ideally needs to be diagnosed and treated as early as possible, preferably before a child is five 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.
Visit your GP or tell your health visitor if you have any concerns about your child's eyesight at any stage.
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 defects.
Your baby will have a second eye examination when they're between six and eight weeks old.
A child's vision should develop in the following way over the first year of life:
- 6 weeks old - follows a bright or interesting object, such as a face, with their eyes
- 2-3 months old - starts to reach for things they see
- 3-5 months old - starts to mimic facial expressions and look at objects more closely
- 6-12 months old - focuses on objects that are both near and far away, sees simple shapes, scribbles with a crayon, and is interested in pictures
Shortly before or after having a baby, all new parents are given a Personal Child Health Record (PCHR), which highlights developmental milestones for vision.
When your child is around one or two 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 before they start school when they're around four or five years old, but this varies depending on where you live.
Read more about routine eye tests for children.
A lazy eye (amblyopia) is often diagnosed and treated by an orthoptist under the supervision of an ophthalmologist.
An orthoptist specialises in problems relating to vision development and eye movements.
An ophthalmologist is a doctor who specialises in the treatment of eye conditions.
The younger the child is when a lazy eye is diagnosed, the more successful treatment is likely to be. Treatment is unlikely to be successful if started after the age of eight.
The two 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
Vision problems such as 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.
In children, most cataracts are removed to allow better development of vision in the affected eye.
Your child may be kept in hospital overnight to check their recovery process, and may have to use eye drops afterwards.
Read more about treating cataracts in children.
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.
Read more about treating squints.
A droopy eyelid (ptosis) can also be corrected using surgery.
Encouraging the use of the eye
A number of different treatment options can be used to encourage your child to use the affected eye. These are outlined below.
Using a patch
Using a patch is known as occlusion. It 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.
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.
The orthoptist and ophthalmologist will determine how often follow-up checks are needed.
Patches are most effective before a child reaches five years of age. Most children will need to wear the patch for a few hours a day for several weeks.
While the patch is on, the child should do close-up activities, such as colouring, reading or schoolwork. Patches can be worn with glasses.
Using a patch to treat a lazy eye can be a time-consuming process, and can sometimes be an unpleasant experience for the child.
It's important to 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.
Atropine eye drops can be used to blur the vision in the good eye. They expand (dilate) the pupil of the good eye and blur near vision, which encourages the use of the lazy eye.
Side effects that can occur after using eye drops include:
- eye irritation
- reddening (flushing) of the skin
However, these side effects are usually infrequent and rarely outweigh the benefits of using eye drops.
Eye drops can be as effective as using a patch, and often the choice of treatment is a matter of preference. Children who don't like having drops in their eyes can wear a patch, and vice versa.
Lack of compliance
In some cases, a lazy eye doesn't improve despite proper treatment being received.
However, sometimes poor results are down to a lack of compliance from either the parent or carer, or the child.
It's very important that a suitable treatment is found that can be stuck to. If you're having trouble with one kind of treatment, you should discuss an alternative with your orthoptist.
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.
A patch may also need to be worn, or eye drops used, if the lazy eye returns.