Strabismus and amblyopia in children (squint and lazy eye)

Strabismus means the eyes are not looking in the same direction as each other. While one eye looks forwards to focus on an object, the other eye turns either inwards, outwards, upwards, or downwards. This means that the eyes do not always work together as a pair. Strabismus may also be called a squint and sometimes referred to as a ‘turn’ in the eye.

Strabismus develops mostly in young children. Strabismus can also develop in adults for different reasons than in children. This information will focus on childhood strabismus. You can contact us directly for information and support for all types of strabismus via our Helpline.

Sometimes when a child has strabismus, the sight in the eye which turns may be weaker. This is sometimes called a “lazy eye”. A lazy eye is an eye that doesn’t see well despite wearing the correct glasses. Different childhood conditions can cause lazy eye, including strabismus. The medical term for lazy eye is “amblyopia”.

Strabismus is common and affects around 3 in 100 children in the UK. This is similar to an average of one child in every class of 30 children.

Our eyes should work together as a pair. When we look at an object our eyes should point in the same direction and focus on the same point. This means the brain receives similar - but slightly different - pictures from each eye. It joins them together to provide binocular and three-dimensional (3D) vision. 3D vision gives us our depth perception, also known as stereopsis. This helps to judge how far away things are, such as judging the height of steps.

The movement of each eye is controlled by six muscles. These muscles move the eyeball in different directions. The muscles that move one eye coordinate with the muscles from the other eye so that they can work together.

When you are born, your eyes and brain learn to work together. As you grow, you use your eyes to collect visual information. This visual information is sent to the brain to process. This builds up a connection between the eyes and the brain, known as the visual pathway.

The visual pathway develops throughout your childhood and up to the age of about eight years old. During this time, it’s important that your eyes send clear and similar images to your brain. The eyes and brain use your visual experiences to allow your visual pathway to develop as fully as possible. This allows a good level of vision to develop in each eye separately. It also allows the two eyes to work together as a pair to allow you to see in 3D.

After the age of about eight years old, the visual pathways and the "seeing" parts of the brain are nearly fully developed and are difficult to change. That’s why it’s important to treat childhood vision problems before this age.

For some children, strabismus has no specific cause. Common causes can include:

Focusing problems (refractive errors)

Problems with the focusing power of the eye are very common, and this is known as having a refractive error. They are usually corrected with glasses. The refractive error most likely to cause strabismus is long-sightedness (hypermetropia). This is where your eye focuses better in the distance than when looking close-up. It causes the eye to work harder to see near things clearly.

Children's eyes have a lot of focusing power. This helps them see clearly in the distance and up close (for near vision). If your child is long-sighted their eyes will need to focus harder to make their vision clearer, particularly for near vision. This focusing is called ‘accommodation’. When we accommodate, our eyes naturally point inwards (converge), towards the nose. The more a child needs to accommodate, the more their eyes will also converge.

If a child is long-sighted, they will accommodate to see better. This can cause their eyes to develop an inward turn known as accommodative esotropia. Glasses can correct their long-sightedness and allow their focusing to relax and give clearer vision. The glasses may also straighten their eyes and remove the strabismus. This is because their over convergence will be relaxed too. In these cases, glasses may be the only treatment that is needed for the strabismus. It is important that the child wears their glasses and has a spare pair in case of breakage.

Eye conditions

Less commonly, strabismus or amblyopia may develop due to other eye conditions. Conditions such as congenital cataract, retinal or optic nerve conditions can cause poor vision. This can cause that eye to develop squint or amblyopia.

There are some risk factors that can increase the chances of a child developing strabismus:

Family history

Some types of strabismus can run in families. If a parent has had strabismus or needed glasses from an early age, there may be an increased chance that their child may also be affected. The way that strabismus may be inherited is not yet fully understood.

Prematurity or low birth weight

Children that are born early (before 32 weeks) may be at more risk of developing strabismus. Babies with low birth weights are also more at risk of developing strabismus.

Other conditions

Children with conditions such as cerebral palsy and Down syndrome may also be more at risk of developing strabismus.

Strabismus is when each eye is looking in a different direction. This means the eyes are sending different pictures to the brain. The brain finds it difficult to merge the two pictures into one clear image because the pictures are so different. This means the eyes are no longer able to work together. Ordinarily, in an adult, this would cause double vision. But, as a child's visual system is still developing, the brain adapts to this by ignoring the image coming from the eye with the strabismus. The brain will use only the vision from the better/straight eye. The brain ‘switching off’ the vision from the eye with strabismus is called ‘suppression’. This causes the vision in that eye to become poor because it is not being used. This will cause amblyopia (lazy eye).

Amblyopia (lazy eye)

Amblyopia is a condition that can develop during childhood when one eye is not able to send a clear image to the brain. This could be because of a strabismus or the inability of an eye to focus clearly. The brain finds it difficult to fuse together the images from the better eye and the weaker eye. So, it learns to ignore or “switch off” the image from the weaker eye. This means the visual pathway of the weaker eye won’t develop very well. The vision in that eye will be blurred even when your child is wearing the correct glasses. An eye which has amblyopia can be called an “amblyopic eye” or may be referred to as a “lazy eye”. Amblyopia generally affects one eye but rarely it can affect both. Although the vision is not clear, the eye may still be completely healthy.

Stereopsis (3D vision)

A strabismus can also mean that 3D vision can’t develop in a child. This is because the two eyes are not looking at the same image and are not being used together to provide a 3D image. This can affect depth perception and judging distances. It can make some skills more difficult, such as catching a ball. However, children can usually adapt to this and learn to judge distances using other clues.

It’s worth remembering, that if a squint is detected and treated early, these effects on vision can be reduced or treated.

Social and psychological impact

Having a squint can affect how your child feels about their appearance. It could reduce their confidence in social situations and impact their mental health. Generally young children are not conscious of this although they may become more aware as they get older.

Strabismus may be noticed by parents, relatives, friends or your health visitor or GP. There are a couple of routine checks to detect eye problems in babies and children. These are usually done at the new-born examination and at the six-to-eight-week review. There should also be routine eye screening when children start school between four and five years old. This check is to ensure that their vision is good and that their eyes work together.

This screening is usually managed by orthoptists. Orthoptists detect and help manage any treatment needed for strabismus. Unfortunately, this screening may not happen in some parts of the country. If you are in any doubt about whether your child's vision has been checked, you should ask at your child's school or nursery. If there is no screening programme in your area, it is important to book your child a routine eye test with your local optometrist. It’s a good idea to book this when they are four years old even if you do not have any concerns about their vision.

If you notice strabismus or eye problems in your child before this check, you should discuss this with an optometrist, GP or health visitor. They may be able to make a referral to an orthoptist. If you have a strong family history of strabismus, high refractive error or amblyopia, you should have your child’s eyes tested regularly by an optometrist. This is usually once a year for children, but your optometrist will let you know how often this needs to be for your child.

Orthoptists are usually based in the hospital eye clinic They are experts in how the two eyes work together (known as binocular vision). This includes strabismus, double vision and amblyopia. If your child has any of these conditions, they will be seen first by an orthoptist when they are referred to the eye hospital. Orthoptists are skilled in testing vision in young children, diagnosing strabismus, and prescribing treatments for strabismus and amblyopia. Children’s eye screening services at the age of 4-5 years old should also be managed and carried out by orthoptists.

Ophthalmologists are hospital-based eye doctors. Their job is to diagnose eye conditions and perform any treatment or surgery that may be needed. Your child may see an ophthalmologist for their strabismus. This is to check the health of their eyes and to make sure there is no underlying eye condition causing the strabismus.

Optometrists are trained to test your vision and prescribe glasses and contact lenses. They are also qualified to detect eye conditions, including strabismus and binocular vision problems. An optometrist may prescribe glasses to help treat strabismus. You may see an optometrist in the community or at the hospital.

Dispensing opticians are qualified in the dispensing and fitting of glasses. They can give professional advice about suitable frames and lenses for children. They usually work in community optical practices and in hospital eye clinics.

The aims of treatment for strabismus in childhood are:

• To achieve a good level of vision in both eyes
• To help the two eyes work together so that binocular and 3D vision can develop as well as possible
• To make the eyes look straight

For treatment to be successful, it needs to be given before the visual pathway finishes developing. Ideally this is before the age of about eight years old.

Most treatment for strabismus is on-going. It is usually treated by an orthoptist at the hospital eye clinic. Regular examinations at the hospital eye clinic are usually needed for some years. How often your child needs to be seen will depend on factors such as their age, the type of strabismus they have, and how well a treatment is working.

How your child's strabismus is treated will depend on the type of strabismus they have. Often more than one treatment or a combination of treatments may be needed.

Some of the most common ways that squint can be treated include:

Glasses

Usually, the first step in dealing with strabismus is a test to see if your child needs glasses. It’s important for your child to have correctly prescribed glasses to give them clear vision in both eyes. This can prevent the turning eye from becoming lazy. Most children with a strabismus will be prescribed a pair of glasses that they will need to wear all the time.

A strabismus may become less noticeable or disappear completely when a child wears their glasses. When the child takes their glasses off, their strabismus can be seen again. This type of strabismus is known as an accommodative strabismus. It is caused by long-sightedness. This means that when long-sightedness is corrected for with glasses, the strabismus is also corrected. Many children may only need to wear glasses to treat their strabismus.

It’s common for your child to say that they can see better without their glasses at first. This is because they have been used to focusing without glasses. They may find it difficult for their eyes to “relax” into the glasses and let the glasses do the focusing for them. It may help to gradually build up the wearing time. This usually settles once your child is wearing their glasses all the time. You can usually expect a follow up visit between one and four months after your child has been given their first pair of glasses.

Occlusion therapy (patching)

Occlusion therapy, or patching, is used to improve the level of vision in an amblyopic eye. Patching involves covering your child's good eye with a patch. Your child then uses their weaker eye to see, and this helps to build up the pathway between the weaker eye and the brain. This is to encourage the vision in their weaker eye to develop. In effect, the visual development of the weaker eye gets a chance to catch up. If patching is done early enough in childhood, the vision can improve, often up to a normal level.

If your child wears glasses, patching should always take place when glasses are worn. The patch should be worn underneath their glasses, so that they can’t ‘peep’ around the patch.

How long your child needs to wear their patch can vary. Your child’s orthoptist or optometrist will let you know how often and for how long your child needs to wear their patch. The patch may be worn for a few hours a day or for most of the day. When your child is wearing their patch, you may be asked to encourage your child to use their amblyopic eye. For example, by getting them to read, colour, watch television or play computer games. If your child is told they need to wear their patch during school hours, explain to your child's teacher how and when the patch should be worn. For some children, the vision will be quite poor when the patch is worn, so the child might need to sit near the front in class.

Most children take well to wearing their patch and some may see it as a fun game. But some children may find patching difficult. This is because if the vision in their weaker eye is poor, they may struggle to see well when they are wearing the patch. Lots of encouragement with reward charts and stickers can help. Patches of different designs or colours can also encourage children to wear their patch.

It can take several weeks or months for eye patching to be successful. Treatment is usually continued until there is no further improvement in vision or when the vision is normal.

Sometimes when patching is successful and has been stopped there is a chance that your child's sight may worsen slightly again. Because of this risk they may still need to be carefully monitored by their orthoptist or optometrist even when they don’t need to wear their patch anymore.

Sometimes eye drops are used as an alternative to a patch. Atropine drops can be used to blur the vision in your child's good eye so that they will use their weaker eye to see. This encourages the vision in the weaker eye to develop, just like when wearing a patch. The blurred vision can last up to seven days or more after each drop. The drops are prescribed by an ophthalmologist. They will give you instructions on how to instil the drops into your child’s eye and how many times per week. Children receiving this type of treatment will be followed up frequently by the eye clinic. Your child’s orthoptist or ophthalmologist will be able to discuss whether treatment with atropine drops is suitable for your child.

Eye exercises

In some types of strabismus, exercises can be useful to strengthen the ability of the eyes to work together. This type of treatment is usually helpful in older children with intermittent strabismus. It is normally used together with glasses and/or surgery.

Surgery

Some children may need an operation on the eye muscles to straighten the strabismus. This is usually needed if the strabismus is very large or is not improved by the proper correction with glasses.

Some children who have had strabismus from a very early age may need early surgery. This is to align the eyes so they work together, which may provide some 3D vision. This is normally planned for before the child is a year old. In older children, surgery may be used to make the eyes look straighter, although it may not always bring back 3D vision. Surgery can’t improve the level of vision in an amblyopic eye, so glasses or patching may still be needed following the surgery.

The operation usually weakens or strengthens the muscles of the eye, so that the eyes are better aligned. Generally, the risks of strabismus surgery are very low. The most common complication can be an over or under correction of the strabismus. So, it’s not uncommon for more than one operation to be necessary. This does not mean that something has gone wrong, but that fine-tuning may be needed to get the best results.

Strabismus surgery is performed under general anaesthetic. This means your child will be asleep (unconscious) and unable to feel any pain. Normally, the operation is a day case procedure so your child will not have to stay in hospital overnight.

For more detailed information on the treatments for strabismus, please download the full factsheet in the link above.

The treatments for squint and amblyopia are generally very effective if the squint is detected and treated early. In these cases, most children will have good vision in each eye in the long-term.

Wearing the correct glasses and patching the better eye, encourages your child’s visual pathway to develop in both eyes. This will help to improve their vision. Encouraging a good level of vision in both eyes also means they won’t only have their better eye to rely on in the future.

If a strabismus or amblyopia is not picked up before the age of about eight years old, it is less likely that treatment will be as effective. The level of vision in this eye will vary between individuals. Some may retain a reasonable level of sight. Most people who have had strabismus or amblyopia since childhood that hasn’t been successfully treated are totally adapted to having poorer vision in one eye and it doesn’t cause them any problems day to day.

Poor vision in one eye can reduce depth perception which can cause difficulties with judging distances as well as activities such as catching a ball or navigating steps. However, children with a lazy eye can easily adapt to this. Their brain finds other ways of judging distances, so these difficulties are generally not a problem. If your child has strabismus or amblyopia, they won’t be able to fully see the 3D effects in 3D films.

In the future, even if they have reduced vision in one eye, your child will still be able to drive a car. This is as long as the vision in their other eye is unaffected by other eye conditions and meets the driving standard. Some professions, such as being a pilot, police officer, some professional drivers, or some roles in the forces require a certain level of vision to be reached in both eyes and for both eyes to be working together. Keeping this in mind can help you and your child plan their career choice for the future. You can ask your child’s orthoptist or optometrist for more information about certain jobs and whether your child may be affected by this.

It’s completely natural to be worried when your child is diagnosed with strabismus or amblyopia, particularly if you haven’t noticed any problems with their eyes. It can be reassuring to know that prompt diagnosis and assessment of these conditions usually means that they can be dealt with and often treated successfully.

Children whose treatment isn’t as successful may have poor sight in one eye. This may not cause them any problems throughout their life as many people adjust very well to poor vision in one eye only. However, it’s important that someone with good vision in only one eye should have regular eye examinations with an optometrist to make sure that the eye they rely on is healthy. An optometrist will be able to give you advice on how often your child should have their eyes tested.