Squint, also called strabismus, is an eye condition where the eyes do not look in the same direction as each other.
This means that 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 work together as a pair all the time.
Most squints occur in young children. Sometimes when a child has a squint, the sight in the eye which turns may be weaker (this is called a "lazy eye"). Squints can also develop in adults but for different reasons to what causes them in young children. This information will take a look at childhood squints.
What is a childhood squint?
Squints are common affecting around 2-3 per cent of children in the UK.
A squint is where one of your eyes points in a different direction from the other eye. This may be more noticeable when a child focuses on a small object or is tired; although in some children the squint is noticeable when they are NOT focusing directly on something.
How do the eyes work together?
Most people have eyes that work together as a pair. When you look at an object your eyes will be pointing in the same direction and focusing at the same point. Your brain will receive similar but slightly different pictures from each eye so it can join them together to allow you to have binocular and three dimensional (3D) vision. This allows you to have depth perception (also known as stereopsis) and to judge how far away things are.
The movement of each eye is controlled by six muscles that move your eyeball in different directions. The muscles for one eye also work and coordinate with the muscles from your other eye so that they can work together.
How does vision develop?
When you are born, your eyes and brain have to learn to work together. As you grow you use your eyes to collect information which is sent to the brain to process and this builds up a connection between them. This connection between the eyes and the brain is known as the visual pathway.
The visual pathway develops throughout your childhood and up to the age of about seven or 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 improve their coordination and allow your visual pathway to develop as fully as possible. This allows a good level of vision to develop in each eye separately as well as allowing 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 fully formed and are difficult to change. This is why it’s important to treat childhood vision problems before this age.
What causes childhood squint?
There are many different types of squint. For some children there will not be a particular cause for their squint. This is known as "idiopathic", meaning there is an unknown cause.
Some common causes of squint can include:
Refractive errors (focusing problems)
Refractive errors are very common conditions where there is a problem with the focusing power of the eye. They are usually corrected by glasses. The most common types of refractive error are:
- Hypermetropia (long-sightedness), where your eye focuses better in the distance than when looking close up, and causes the eye to work harder to see things clearer close up.
- Myopia (short-sightedness), which causes your vision to be blurry in the distance and clearer when looking at things closer up.
- Astigmatism, which can cause blurry vision up close and in the distance. It is caused by the front of the eye not being quite spherical (round). Astigmatism is very common and most people have some degree of astigmatism.
Long-sightedness in children may cause a squint to develop where the eye turns in (esotropia). Long-sightedness in children is the most common cause of esotropia.
Children's eyes have a lot of focusing power, which allows them to make the things they look at clear in the distance and up close. If your child is long-sighted their eyes will need to focus harder to make their vision clearer, particularly for close up vision. This focusing is called ‘accommodation’. When we accommodate, our eyes naturally ‘converge’ or point inwards, towards the nose. The more a child needs to accommodate, the more their eyes will converge too.
This means that if a child is long sighted and needs to accommodate to see better, this can cause their eyes to turn in too much towards one another and they may go on to develop a convergent squint (esotropia). Having glasses to correct their long sightedness allows their focusing to relax and give clearer vision. At the same time the glasses may also straighten their eyes and remove the squint because their over convergence will be relaxed too.
Other eye conditions such as congenital cataract or retinal or optic nerve conditions can cause an eye to have poor vision. This can also cause a squint to develop in this eye.
Eye muscle problems
Some squints only occur when the eyes are looking in certain directions. These are an eye movement problem and don’t affect vision in the same way as other squints because the eyes are usually straight most of the time.
Brown’s syndrome and Duane's retraction syndrome are examples of eye conditions which can cause a squint only when looking in certain directions.
Brown’s syndrome is where an eye cannot move upwards. It’s caused by one of the eye muscles that pulls the eye upwards not being able to move freely.
Duane’s retraction syndrome is where one or sometimes both eyes do not turn to the side very well and the eyelids may open and close as the eyes try to turn. It’s caused by a mis-wiring of the nerves which control certain eye muscles.
These types of squint may not require any treatment as the eyes are straight most of the time, but they may still be monitored by an ophthalmologist or orthoptist.
What are the risk factors for squint?
There are some risk factors that can increase the chances of a child developing a squint:
Some types of squints can run in families, so if a parent has had a squint or needed glasses from an early age, there may be an increased chance that their child may also be affected. The way that squints 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 a squint. Babies with low birth weights are also more at risk of developing a squint.
Children with conditions such as cerebral palsy and Down's syndrome may also be more prone to develop a squint.
How are squints described?
Your child’s squint may be described in different ways by the professionals looking after your child’s eyes. Some of the words you may hear will have particular meanings when used to describe the squint and the squint may be described depending on:
- When it can be seen: constant, if it is visible all the time, and intermittent if it comes and goes.
- Whether it is caused by a focusing problem (refractive error) such as long-sightedness: refractive if the squint is caused by a focusing problem, and non-refractive if it isn't.
- Which eye appears to be affected: either left or right, or alternating, where the squint can alternate from one eye to the other.
- How the eye turns: if the turn is inwards it is called a convergent squint or esotropia, if the turn is outwards it is called a divergent squint or exotropia, if the turn is upwards it is called a hypertropia, if the turn is downwards it is called a hypotropia.
This means that your child's squint can be carefully categorised by the professionals involved and they may describe your child’s squint using a mixture of these words, for example, an “intermittent convergent squint”. Knowing the nature of your child's squint and labelling it as accurately as possible can help to decide how it can be dealt with.
What are some of the different types of squint?
Some common types of childhood squint include:
Congenital or infantile esotropia
This is an inward turning squint which normally develops in the first six months of life. There is no known underlying cause (this is called "idiopathic").
This type of squint is caused by long-sightedness (hypermetropia) which causes an inward turning squint. The squint can be improved or removed by wearing glasses.
This type of inward turning squint usually develops in children between 2-5 years old, and is a squint which isn’t improved by wearing any glasses.
Intermittent distance exotropia
This is an outward turning squint which comes and goes, usually being more apparent when a child is looking at things into the distance. Commonly, parents may notice that the eye turns out when the child is tired, daydreaming or in bright sunlight. A child may also close or rub one eye when they are out in bright sunlight.
How can a squint affect vision?
If your child develops a squint it means each eye is looking in a different direction and their eyes are sending different pictures to the brain. Their brain finds it difficult to merge the two pictures into one clear image because the pictures are so different. This means their eyes have stopped working together and would ordinarily, in an adult, cause double vision. However, as your child's visual system is still developing the brain can easily adapt to stop this double vision by ignoring the image coming from the eye with the squint. They will use only the vision from their better/straight eye. The brain "switching off" the vision from the squinting eye is called "suppression" and this may cause the vision in that eye to become poor because it is not being used.
Children can easily adapt to using one eye and it may not be obvious from how they are acting that they have any problems with their eyes and vision. This may only be detected by having your child's eye tested by an eye health professional.
Amblyopia is caused when the visual pathway doesn't develop correctly in one eye because that eye isn’t able to send a clear image to the brain. This causes the vision to be blurred in that eye even when a child is wearing the correct glasses. An eye which has amblyopia can be called an amblyopic eye or a "lazy" eye.
A child with a squint can develop amblyopia in the eye which has the turn, because the vision in this eye is not being used by the brain.
Some children may have amblyopia, but they may not have a squint. This may be due to one or both eyes being particularly short-sighted (myopic), long-sighted (hypermetropic) and/or having a high astigmatism.
Amblyopia can lead to a permanent reduction in how well this eye can see. There are different ways to treat an amblyopic eye and treatment is more successful when vision is still developing before the age of seven or eight.
Unfortunately, amblyopia cannot be easily fixed in later life so it is very important that squints and amblyopia are picked up early and treated.
Reduced binocular vision
A squint means that the two eyes are not working together. This can reduce your child’s 3D or binocular vision. Binocular and 3D vision allows you to have depth perception (also known as stereopsis). This helps you to judge how far away things are.
Timing of a squint
When your child is born their eyes and brains do not work well together. Over the first few months you may notice your baby’s eyes appear to squint or move separately from each other every now and again. This is normal and usually should get better by around two months and should be gone by the time they reaches four months. If this isn't the case then you should speak to your GP or health visitor about a referral for a full assessment with your hospital eye department.
More commonly a squint will develop a little later in your child's life often between the ages of 18 months and four years old. If you notice that your child appears to have a squint, it’s important to have this checked by an optometrist (optician). Children are entitled to a free NHS eye test. Your optometrist or your GP would then be able to refer your child to the hospital eye clinic to be seen by an orthoptist (professionals who diagnose and manage squints).
How are squints detected?
A squint may be noticed by parents, relatives, friends or your health visitor or GP. Routine checks to detect eye problems in babies and children are usually done at the newborn examination and at the 6-8 week review. There should also be a routine eye screening for when children start school (at the age of between 4-5 years old) to ensure that their vision is good and that their eyes work together.
This screening is usually managed and sometimes carried out by professionals known as orthoptists, who detect and help manage any treatment needed for squints. Unfortunately, this screening may not happen in some parts of the country and 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 you are concerned about your child's eyes before this check, because you have noticed a squint or other symptoms, then you should discuss this with an optometrist (optician), your child’s GP or health visitor and ask to be referred to an orthoptist.
Professionals involved in looking after squint
Orthoptists are usually based in the eye clinic at the hospital and are recommended to carry out or manage the children's screening service at 4-5 years old. They are experts in how the two eyes work together (known as binocular vision) and this includes squints, double vision and amblyopia. If your child is suspected to have any of these conditions, they are usually one of the first professionals they will see if they are referred to the hospital. Orthoptists are extremely skilled in testing vision in young children, diagnosing squints, prescribing patching therapy and any eye exercises that may help. Most of your appointments about your child's squint will be with an orthoptist.
Ophthalmologists are hospital-based eye doctors. Their job is to diagnose eye conditions and perform any treatment or surgery that may be needed. If your child has been referred to the hospital for a squint, they may see an ophthalmologist to check the health of their eyes and make sure there is no underlying eye condition causing the squint.
Optometrists (also known as opticians) are experts at testing your vision and prescribing glasses. They are also qualified to detect eye conditions or problems, including squints and binocular vision problems. If your child is prescribed glasses to help treat their squint then you may see an optometrist on the high street or at the hospital to supply them. Optometrists can also manage some types of squint.
Dispensing opticians are qualified in the dispensing and fitting of spectacles and can give professional advice about suitable frames and lenses for children. They usually work in high street opticians’ practices and in some hospital optometry departments.
What tests will be done?
If your child is suspected of having a squint, they would normally be referred to an orthoptist to have the diagnosis confirmed. Sometimes an optometrist will be able to diagnose and treat your child’s squint.
The orthoptist or optometrist will measure how well your child can see, by asking them to name or match letters, pictures or shapes. There are even different ways to measure vision in babies. To check whether there is a squint present, they will check your child’s eye movements which can involve covering and uncovering each eye in turn. They will also test your child’s 3D vision (stereopsis).
The assessment for squint will also normally involve the use of eye drops. Eye drops are used to relax the focusing of your child’s eyes so their glasses prescription can be as accurate as possible.
The eye drops also make the pupils larger, so once the drops start working, your child may become sensitive to light. You could bring sunglasses or a brimmed hat or cap for your child to wear following the test just in case. Some children may also feel that their vision is blurred or fuzzy. Again this is because the drops stop the focusing mechanism working. Sometimes the drops may sting a bit when they are first put it, but this wears off within a minute or two. The effects of the eye drops usually wear off after 6-8 hours, and are fully gone within 24 hours.
Very occasionally, if another cause of squint is suspected (other than congenital squint or one related to refractive errors), a scan of the eye or brain may be needed. An orthoptist or optometrist can refer your child to an ophthalmologist for any further tests if necessary.
What are the treatments for squint?
The aims of treatment for a squint in childhood are to make sure that the vision in each eye develops normally (i.e. prevent amblyopia), and to help the two eyes work together so that binocular and 3D vision can develop as much as possible too. In order for treatment to be successful, it needs to be given before the visual pathway finishes developing (before the age of 7-8).
Most treatment for squints is on-going and it usually involves regular visits and examinations at the hospital eye clinic for a number of years. How often your child needs to be seen by the eye clinic will depend on factors such as their age, the type of squint they have, and how well a treatment is working.
How your child's squint is treated will depend on the type of squint they have. Often more than one treatment or a combination of treatments may be needed to get the best result for your child's vision.
Some of the most common ways that squint can be treated include:
- Occlusion therapy (patching)
- Botulinum toxin injections
Usually the first step in dealing with a squint is for your child to be tested to see if they need glasses. It’s important for your child to have properly prescribed glasses to give them clear vision in both eyes. This can help to prevent the squinting eye from becoming amblyopic or lazy. Most children with a squint will be prescribed with a pair of glasses that they will need to wear all the time.
You may notice when your child wears their glasses that their squint becomes less noticeable or disappears completely. This type of squint is known as an accommodative squint. When your child takes their glasses off you will notice that their squint can be seen again. This means that the glasses need to be worn to correct the squint. Many children may only need to wear glasses to treat their squint.
It’s not unusual for your child to say that they can see better without them at first. This is because they have been working their eyes so hard to focus without glasses that they find it difficult for their eye to “relax” into the glasses and let the glasses do the focusing for them. This usually settles once your child is wearing their glasses all the time. You can usually expect a follow up visit with the orthoptist or optometrist for around 6 weeks after your child has been given their first pair of glasses.
Helping your child to wear glasses
It can be difficult to get children to wear glasses. If your child isn't keen to wear their glasses, a lot of encouragement will help. Being positive about wearing glasses, making it a part of your child’s everyday routine and praising them when they wear their glasses can also help.
When choosing your child’s glasses, it may be helpful to get advice from a dispensing optician. A dispensing optician can ensure that the glasses fit correctly and are comfortable as this can help your child to wear their glasses. It’s also essential that your child is looking through the lenses of their glasses and not over the top, so the fitting of their glasses is important.
Most children with squint who need glasses need to wear them all the time. This can cause challenges at times, for example, when in the playground or when it’s raining. Most of these can be overcome with time and with learning how to care and look after the glasses. Ask your child’s optometrist or dispensing optician for more information about how to deal with situations like these.
Occlusion therapy (patching)
Occlusion therapy can’t straighten the eye, but is used to improve the level of vision in an amblyopic or lazy 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 this eye and the brain. 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, usually with the patch worn underneath their glasses, so that they can’t "peep" around the patch. Your orthoptist will let you know how often, for how long and when will be the best time for your child to wear their patch as this can vary. The patch may be worn for a few hours a day or for most of the day. When your child is wearing their patch, it’s important to encourage them to use their lazy eye by reading, colouring, watching television or playing computer games. If your child is told they need to wear their patch during school hours, it’s important to explain to your child's teacher how and when the patch should be worn.
Most children take well to wearing their patch and some may see it as a fun game. However, some children may find patching difficult because if the vision in their weaker eye is poor, they may struggle to see well when they are wearing the patch. Again, lots of encouragement with reward charts and stickers can help. Patches of different designs or colours may be available which can also encourage children to wear their patch.
It can take several weeks or months for eye patching to be successful and treatment is usually continued until the vision is normal, or no further improvement in vision is found.
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 though they don’t need to wear their patch anymore.
Sometimes eye drops are used as an alternative to a patch. Atropine drops blur the vision in your child's good eye enough so that they will start to use the other eye, just like when wearing a patch. Using drops like this doesn't work for all children and you would need to discuss this option with your orthoptist or ophthalmologist to see if it’s possible.
In some types of squint, 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 squints, and is normally used together with glasses and/or surgery.
A number of children may require an operation on the eye muscles in order to straighten the squint. This is usually needed if the squint is very pronounced and is not improved by the proper correction of glasses.
In a few children who have had a squint from a very early age, early surgery may be suggested to try and line up the eyes so that they learn to work as a pair and may give some 3D vision. This is normally planned for when a child is about a year old. In older children, surgery may be used to make the eyes look straighter. Surgery can’t improve the level of vision in a lazy 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 squint surgery are very low. The most common complication can be an over or under correction of the squint, 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 obtain the best results.
Squint surgery is usually performed under general anaesthetic which 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 usually have to stay in hospital overnight.
Botulinum toxin injection (Botox)
Some children may be offered treatment with a Botox injection. This injection weakens some of the eye muscles so that the eyes are better aligned. In children it can be carried out under general anaesthetic. It is only used in certain types of squint, and in certain cases, for example, if someone has had several squint surgeries which have not aligned the eyes properly. The effect is usually temporary but may be effective for some types of squints in children.
What is the outlook for children with squint?
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.
If a squint or amblyopia is not picked up before the age of 7/8 years old then it can have a permanent effect on the vision in one eye. The level of vision in this eye will vary between individuals and some may retain a reasonable level of sight. Most people who have had a squint or lazy eye since childhood that wasn’t 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 are totally adapted to this and their brain finds other ways of judging distances so these difficulties are generally not a problem. If your child has a squint or lazy eye, 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 would still be able to drive a car as long as the vision in their remaining 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 areas of the forces require a certain level of vision to be reached in both eyes and both eyes working together. Keeping this in mind can help you and your child plan their career choice for the future. You can ask your orthoptist or optometrist for more information about certain jobs and whether your child may be affected by this.
Sometimes adults who have had squint surgery as a child may need to have further surgery later in life to straighten the eyes again.
Currently there is no treatment to correct amblyopia in adults.
It’s completely natural to be worried when your child is diagnosed with a squint, particularly if you haven’t noticed any problems with their eyes. It can be reassuring to know that prompt diagnosis and assessment of a squint usually means that it can be dealt with so that it doesn’t cause long term changes to vision.
Most children with squints have good level of vision and both eyes working together once they have had treatment.
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.
Whether your child has just been diagnosed with a squint, or has been living with it for a while, at RNIB, we are here to help and support you through your journey.
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