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Amblyopia (lazy eye)

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Introduction


Lazy eye, also known as amblyopia, is an early childhood condition where the child's vision does not develop properly. It usually occurs in one eye, but it can occur in both eyes. Lazy eye affects approximately 2% of children.

A baby is able to see as soon as it is born, and vision continues to develop up until around seven or eight years of age. After this, no further development occurs until sight deteriorates with age, or after eye injury or disease.

How the eye works

Light rays travel through the lens (transparent structure) at the front of the eye, and form images on the retina. The retina is a light sensitive surface at the back of the eye that sends messages to the brain so that it recognises the objects that you are seeing.

During early childhood, it is important that clear images are formed in the eye and are sent to the brain, so that the child's vision develops normally. If there is a problem with this development, it may result in impaired vision (amblyopia).

Retina


The retina is the nerve tissue lining the back of the eye, which senses light and colour, and sends it to the brain as electrical impulses.

Brain


The brain controls thought, memory and emotion. It sends messages to the body, controlling movement, speech and senses.

Symptoms of lazy eye


If your child has a lazy eye (amblyopia), they will not receive clear images through one of their eyes, and therefore a clear image will not be received by their brain.

If your child has a lazy eye, they will not be able to focus properly with one of their eyes. However, their other eye will often make up for the problems in the affected eye, resulting in the affected eye becoming 'lazy'.

Your child may not notice that they have a lazy eye

If your child has lazy eye, they may not notice that there is a problem. Therefore, a lazy eye is often not diagnosed until the child has their first eye test.

As the affected eye is not able to send clear, sharp images to the brain, the main symptom of a lazy eye is blurred, or double, vision. Some children may also have a noticeable squint (where the eye turns inwards, outwards, upwards, or downwards), a droopy eyelid, or a cataract (clouding of the lens of the eye).

Glossary

Brain
The brain controls thought, memory and emotion. It sends messages to the body controlling movement, speech and senses.
Double vision
Double vision is to see two images of a single object instead of one.

Causes of lazy eye


There are a number of different eye disorders that can cause a lazy eye (amblyopia). These are described below.

Strabismic amblyopia

Strabismic amblyopia is the most common cause of a lazy eye. The condition involves a squint (strabismus) in one eye, which is noticeable because the eyes look in different directions.

For example, one eye may look straight ahead and the other may look inwards, outwards, up, or down. To avoid double vision, the brain ignores the signals from the eye with a squint and only 'sees' images from the normal eye. As the affected eye is not being used, over time the squinting eye will become lazy.

Strabismus can be inherited, or it may be caused by long- or short-sightedness, an injury, or a viral illness.

Anisometropic amblyopia

Anisometropic amblyopia is where a refractive error (poor focussing of light) occurs due to short-sightedness (myopia), long-sightedness (hypermetropia), or astigmatism (where the surface of the lens is uneven, causing blurred vision).

A refractive error means that there is a difference of refraction in each eye. Refraction is where light rays change direction when they pass between two mediums of different densities, such from the air into the eye. Both eyes are usually affected to the same degree.

However, in anisometropic amblyopia, a child who is long-sighted, for example, will be more long-sighted in one eye compared with the other. As a result, their brain will ignore the signals from the eye that has the biggest refractive error (is most long-sighted). As a result, this eye may become lazy.

Ametropic amblyopia

Ametropic amblyopia is a reduction in the vision of both eyes. It usually occurs when a child has large, uncorrected refractive errors. The image that is produced on the retina, at the back of the eye, is constantly blurred as a result of undetected long- sightedness, or astigmatism.

Stimulus deprivation amblyopia

Stimulus deprivation amblyopia is the rarest form of amblyopia, but it is often the most severe. It is caused when one eye or both eyes are prevented from seeing and become lazy. This may be due to:

  • 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 eye lid (ptosis, or blepharoptosis), or
  • glaucoma (a group of eye conditions that affect vision).

Stimulus deprivation amblyopia can also be caused by an eye injury, or surgery to the eye.

Glossary

Double vision
Double vision is to see two images of a single object instead of one.
Brain
The brain controls thought, memory and emotion. It sends messages to the body controlling movement, speech and senses.
Congenital
Congenital means a condition that is present at birth- the condition could be hereditary or develop during pregnancy.
Ulcer
An ulcer is a sore break in the skin, or on the inside lining of the body.
Retina
The retina is the nerve tissue lining the back of the eye, which senses light and colour and sends it to the brain as electrical impulses.

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 sometimes 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 examination

In the UK, children are usually given a routine eye examination 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.

Following the results of your child's eye test, if the eye specialist (ophthalmologist) suspects a lazy eye, a full eye examination will be carried out in order to make a firm diagnosis. Each eye will be tested separately to determine whether there is any serious, long- or short-sightedness. Both eyes will also be tested together to see if there is a squint.

During their eye test, the structure of your child's eyes may also be examined to determine whether there are any abnormalities, such as astigmatism (where the surface of the lens is uneven, causing blurred vision).


Treating lazy eye


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, and
  • making the affected eye work so that vision can develop properly.

Treating underlying eye problems

You may not realise that your child has a vision problem unless their sight is tested. For example, if your child has anisometropia (unequal vision), the sight in one of their eyes will be good and will become the main source of vision. However, the eye that is not being used may become lazy.

Glasses

Vision problems, such as long- or short-sightedness, can be corrected using glasses. These will usually need to be worn constantly so that the orthoptist can check the effect that they are having on the lazy eye. 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 in order to correct the lazy eye.

Surgery

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.

A droopy eye lid (ptosis, or blepharoptosis) can also be corrected using surgery.

Making the affected eye work

A number of different treatments options can be used in order to make the affected eye work. These are outlined below.

Using a patch

Using a patch is also known as occulation. It involves placing a patch with a sticky rim is over the 'good' eye so that the lazy eye is forced to work. A patch will not straighten your child's eyes if they have a squint, but it can be very effective at 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 after three months, though this could be more frequent if your child is very young or has a high dose of occulation

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 both the parent, or carer, and the child. Therefore, it is important that the parent, or carer, and the child (if they are old enough) are made aware of the reasons for using a patch and that they are motivated to carry it out.

Eye drops

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, and
  • headaches.

However, these side effects are usually infrequent and they rarely outweigh the benefits of using eye drops.

Eye drops should be used once a day. They can be as effective as using a patch and are less obtrusive for the child. Eye drops may be more suitable if the child cannot tolerate using a patch.

Eye surgery

If the lazy eye is caused by another problem, such as a squint, or a cataract, surgery may be needed. Patch treatment may also be used after the operation

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 in order 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.

Surgery can also be used to help the eyes work better together. The lazy eye can be realigned to improve binocular vision (the ability to focus on an object with both eyes to create a single visual image). If surgery is needed, it is better for it to be carried out sooner rather than later in order to increase the chance of both eyes being able to work together.

Vision therapy

Vision therapy is sometimes used to help your child's vision develop. It involves using exercises and games that require your child to use their affected eye. It can sometimes be a useful treatment for older children, and can be used alongside other treatments, such as glasses, or surgery .


Complications of lazy eye


Squint

Sometimes, a lazy eye (amblyopia) can result in a noticeable squint (strabismus). It can also result in permanent loss of sight in the eye if left untreated.

Central vision

If the lazy eye is not treated at an early age, your child's central vision (equal sight in both eyes) may not develop properly. This will affect daily activities, such as reading and writing, and it may prevent your child using a computer and driving (when they are older).

Lack of compliance

Most poor results of the treatment of a lazy eye are due to a lack of compliance from either the parent, or carer, or the child. It is very important that a suitable treatment is found which can be stuck to.

If you are having trouble with one kind of treatment, you should discuss an alternative with your orthoptist (a 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, following surgery, glasses may still need to be worn and, if the lazy eye returns, a patch may still be necessary.


References


Powell C, Hatt SR. Vision screening for amblyopia in childhood. Cochrane Database of Systematic Reviews 2009, Issue 3. Art. No.: CD005020. DOI: 10.1002/14651858.CD005020.pub3.


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Map of Medicine: squint in children


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