A lazy eye is a childhood condition that occurs when the vision in one eye does not develop properly.
This means that the child can see less clearly out of one eye and relies more on the ‘good’ eye.
The medical term for lazy eye is amblyopia.
A lazy eye is an uncommon but certainly not rare condition. It is estimated that 1 in 50 children will get one. Children are usually diagnosed with a lazy eye around the age of four.
How do I know if my child has a lazy eye?
Children with a lazy eye usually have problems accurately judging the distance between themselves and objects, which can make tasks such as catching a ball more difficult. In some cases you may notice that one eye looks different to the other (this could be due to a squint).
Younger children are often unaware that there is anything wrong with their vision and if they are, they are usually unable to explain what is wrong. Older children may complain that they can’t see as well through one eye.
Read more about the symptoms of a lazy eye.
When to seek medical advice
Many cases of lazy eye are diagnosed during routine eye tests before parents realise that there is a problem. Children should have an eye test before they start school and then further tests at least every two years.
However, you should see your doctor if you are concerned about your child’s eyesight as they can refer your child for further testing by an eye specialist (ophthalmologist).
Read more about diagnosing a lazy eye and [vision tests in children].
What causes a lazy eye?
The eyes work like a camera. An image made up of light comes through the lens of each eye and is beamed on to a light-sensitive layer of tissue called the retina.
The retina translates the image into nerve signals that are sent to the brain. The brain then combines the signals from each eye into a three-dimensional image.
A lazy eye occurs when the brain ignores one of the eyes and relies more heavily on the other. This can be due to a number of eye problems, including a squint (when the eyes don't look in the same direction) or a difference in the quality of vision between the eyes - for example, if one eye is short-sighted.
Left untreated this can lead to a permanent loss of vision in the affected eye.
Read more about the causes of a lazy eye.
Treating a lazy eye
The majority of cases of lazy eye can be treated, usually in two stages.
Firstly, the underlying problem is corrected, for example using glasses to correct a squint.
The child is then encouraged to use the affected eye again. This can be done with eye patches to cover the stronger eye or using eyedrops to temporarily impair the vision in the strong eye.
Treatment is effective, but it's a gradual process, taking many months to work.
Read more about treating a lazy eye.
Providing the condition is properly diagnosed and treated at an early age (ideally around two), then the outlook for children with a lazy eye is usually good.
The weaker eye will not normally return to perfect vision, but there is usually enough vision to avoid problems later in life.
It's more difficult to treat if the eyesight has finished developing (usually around the age of seven), although it is still possible to significantly improve the vision in the weaker eye.
Younger children are often unaware that they have a problem with their vision, so the only noticeable symptoms of a lazy eye may be related to an underlying condition, such as:
- a squint – where the weaker eye looks inwards, outwards, upwards or downwards, while the other eye looks forwards
- childhood cataracts – which are cloudy patches that develop at the front of the eye (the lens)
- ptosis – which is where the upper eyelid drops over the eye, impairing vision
One way to check your child’s eyes is to cover each eye, one at a time, with your hand. If they try to push your hand away from one eye, but not the other, it may be a sign they they can see better out of one eye.
Another sign is your child having problems with their depth perception. Due to the mismatch between each eye, children with lazy eyes have difficulty judging how far away objects are.
Signs to look out for include:
- being unusually clumsy for their age, such as running into furniture or falling over a lot
- problems catching a ball
- poor performance in sports
Older children may complain that their vision is better in one eye and that they have problems with reading, writing and drawing.
When to seek medical advice
Many cases of lazy eye are diagnosed during routine eye tests before parents realise that there is something wrong with their child’s vision.
If you are concerned, visit your doctor, who can refer your child for further testing by an eye specialist (ophthalmologist).
A lazy eye (amblyopia) is caused when something disrupts the normal development of vision.
How vision develops
It is often assumed that younger children have the same vision as adults, but this is not the case. Children have to learn how to see, or more specifically, their brains have to learn to how to interpret the nerve signals that are sent from the eyes to the brain.
It normally 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 (see below), the quality of the signals becomes disrupted and this in turn affects the images seen by the brain.
The brain then begins ignoring these images and becomes increasingly reliant on the stronger eye. This can then trigger a vicious circle – the less the brain uses the eye, the worse the vision in that eye becomes; the worse the vision in that eye becomes, the less likely it is that the brain will use it, and so on.
Common conditions that disrupt the development of vision and cause lazy eye are discussed below.
A squint is a common eye condition affecting around 1 in 20 children. In cases of 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, resulting in blurred and double vision.
Left untreated, the brain begins to ignore images from the squinty eye leading to the development of a lazy eye.
Some babies are born with squints. Older children can develop a squint as a result of groups of eye conditions called refractive errors.
Refractive errors are caused when the light rays coming into the eye are not properly focused. This is caused by problems with the structure of the eye.
Some common refractive errors are:
- short-sightedness (myopia) – where close objects appear normal, but objects that are further away are blurred
- long-sightedness – where distant objects appear normal but nearby objects are blurred
Refractive errors can lead to a lazy eye if they cause a squint or a condition called anisometropia – where one eye is short-sighted and the other is long-sighted.
The brain tends to then just rely on the signals from one eye (usually the short-sighted eye) and the other eye then becomes lazy.
Less common conditions
Less common conditions that can cause a lazy eye include:
- an eye disease, such as a corneal ulcer (a sore on the transparent layer at the front of the eye), or scar
- a congenital cataract – clouding of the lens of the eye that is present from birth
- a droopy eyelid (ptosis)
- glaucoma – a group of eye conditions that affect vision
A lazy eye (amblyopia) ideally needs to be diagnosed and treated as early as possible, preferably before a child is six years of age.
However, it can be difficult to know whether a child has a lazy eye because they often do not realise that there is anything wrong with their vision. Therefore, a lazy eye may not be diagnosed until your child has their first eye test.
Routine eye test
Children are often given a routine eye test before they start school. This means that if a child has a lazy eye, it is possible to diagnose and treat the condition before it is too late to correct.
During their eye test, the structure of your child’s eyes is examined to see if there are any abnormalities, such as astigmatism (where the surface of the lens is uneven, causing blurred vision).
Other tests include:
- in younger children who are unable to talk – covering each eye in turn to see if this makes them upset due to loss of their normal vision
- in children who can talk – a chart containing symbols of different sizes of objects such as a ball, a boat or a flower is shown to the child – they are then asked to name each object in turn until the object becomes too small for them to see; a significant difference between each eye would suggest a diagnosis of lazy eye
- in children who know their alphabet – a similar test, that uses letters rather than symbols, can be used
If the eye specialist (ophthalmologist) suspects a lazy eye, a full eye examination will be carried out which will include each eye being tested separately for problems, such as long- or short-sightedness. Both eyes will also be tested together to see if there is a squint.
Once diagnosed, a lazy eye (amblyopia) is treated by an eye specialist (ophthalmologist) and an orthoptist (a specialist in childhood eye problems).
The younger the child is when a lazy eye is diagnosed, the more successful treatment is likely to be. If treatment is started after the age of eight, it is unlikely to be as successful.
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 that 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 are regularly checked.
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 that 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 hard to let the glasses focus for them. They will need plenty of encouragement to wear their glasses continuously.
An alternative to glasses are contact lenses although this may only be suitable for older children.
Cataracts can be removed to treat blurred and distorted vision.
Cataract surgery can be carried out either under local, or general, anaesthetic, and the procedure can sometimes take as little as 20 minutes.
Your child may be kept in hospital overnight to check their recovery process, and they may have to use an eye patch, or eye drops, afterwards.
Read more about the treatment of 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 that the lazy eye will appear to be better aligned with the good eye. The child’s vision will not 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 treatments 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 is over the ‘good’ eye so that 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. They should have a follow up check after three months, although this could be more frequent.
Patches are most effective before a child reaches seven or eight 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 it can sometimes be an unpleasant experience for the child. It is important to explain to your child the reasons for using a patch, the importance of sticking with the treatment so that they are motivated to carry it out.
Atropine eye drops can be used to blur the vision in the good eye. They dilate (expand) 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
- flushing (reddening) of the skin
However, these side effects are usually infrequent and they 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. So children who don’t like having drops in their eyes can wear a patch and vice versa.