Lazy eye (amblyopia)
A lazy eye, also known as amblyopia, is a childhood condition that occurs when the vision in an eye does not develop properly.
This usually means that the child can see less clearly out of one eye and relies more on the "good" eye.
An estimated 1 in 50 children will develop a lazy eye and children are usually diagnosed with the condition around the age of four.
How do I know if my child has a lazy eye?
A lazy eye does not usually cause symptoms. 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.
In some cases you may notice that one eye looks different to the other. However, this is usually a sign of another condition that could lead to a lazy eye, such as a squint (when the eyes don't look in the same direction).
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 a vision test between the ages of four and five.
However, you should see your GP if you are concerned about your child's eyesight as they can refer your child for further testing by an eye specialist (opthalmologist).
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 onto 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 connections responsible for vision are not made properly. This can be because 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 are not the same (such as a squint)
Left untreated, this can lead to the central vision of the eye never reaching normal levels.
Treating a lazy eye
The majority of cases of lazy eye can be treated, usually in two stages.
The underlying problem is first corrected. This can be done 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 with eye patches to cover the stronger eye, or using eye drops to temporarily impair the vision in the strong eye.
Treatment is often effective, but it's a gradual process, taking many months to work.
Symptoms of lazy 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 – cloudy patches that develop at the front of the eye (the lens)
ptosis – 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 that they can see better out of one eye.
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 GP, who can refer your child for further testing by an eye specialist (ophthalmologist).
A paediatric consultant explains the causes of squints, a misalignment of the eye. He describes how to identify the symptoms and the treatment options.
Causes of lazy eye
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, the quality of the signals becomes disrupted and this affects the images seen by the brain.
The brain then begins to ignore the poor quality images and becomes increasingly reliant on the stronger eye.
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. 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.
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 a group 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 examples of refractive errors that could lead to a lazy eye include:
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 lead to the brain relying 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:
an eye disease such as a corneal ulcer (a sore on the transparent layer at the front of the eye) or a scar
childhood cataracts – clouding of the lens of the eye that is present from birth
a droopy eyelid (ptosis)
Diagnosing lazy eye
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. A lazy eye therefore may not be diagnosed until your child has their first eye test.
If an eye specialist (optometrist) suspects a lazy eye, they will also test for other conditions, such as:
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 first be examined within 72 hours of birth. This simple examination is used to check for obvious physical defects.
They will have a second eye examination when they are between six and eight weeks old, which will usually be carried out by your GP.
Shortly before or after having a baby, all new mums are given a Personal Child Health Record (PCHR), which highlights developmental milestones for vision.
A child's vision should develop in the following way over the first year of life:
6 weeks old – follows a colourful 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
Your child's vision may also be tested before they start school, but this varies depending on where you live.
There are a number of tests that may be carried out to check for vision problems in babies and children.
Treating lazy eye
A lazy eye (amblyopia) is often diagnosed and treated by an orthoptist under the supervision of an ophthalmologist.
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 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 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 these may only be suitable for older children.
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, and the procedure can sometimes take as little as 20 to 30 minutes.
Your child may be kept in hospital overnight to check their recovery process, and they may have to use eye drops 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 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.
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 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.
The orthoptist and opthalmologist will determine how often follow-up checks are needed.
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 and the importance of sticking with the treatment so that they are motivated to do it.
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:
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.
Lack of compliance
In some cases, a lazy eye does not improve despite proper treatment being received. However, some poor results of the treatment of a lazy eye are because of a lack of compliance from either the parent or carer, or the child. It is very important that a suitable treatment is found that can be stuck to.
If you are having trouble with one kind of treatment, you should discuss an alternative with your orthoptist (specialist in childhood eye problems).
If surgery is recommended, you should be aware that it can take more than one operation to improve the appearance of a squint. Also, after surgery, glasses may still need to be worn, and if the lazy eye returns, a patch may still be necessary.
If surgery is recommended to improve the position of the eyes (for example, to treat a squint), more than one operation may be required and glasses may still need to be worn.
Generally, surgery is offered after successful treatment for a lazy eye, but patches or drops (occlusion treatment) may still be required after surgery to treat a squint.