The most obvious sign of a squint is eyes that look in different directions.
Most often, one eye turns inwards (convergent squint) or outwards (divergent squint). In rarer cases, it may turn up or down (vertical squint).
They can either be apparent at all times (constant), or only be apparent at certain times (intermittent). Minor squints are not always obvious.
Squints can also cause blurred vision or double vision, but babies and young children may not realise there is a problem.
Babies and young children
It is quite normal for the eyes of newborn babies to "cross" occasionally, particularly when they are tired. However, you should speak to your doctor if you notice this happening to your child after three months of age.
If your child looks at you with one eye closed or with their head turned to one side, it may mean that they are experiencing double vision and could be a sign that they have a squint. If this happens repeatedly, take your child to see your doctor as soon as possible.
If a squint is left untreated, lazy eye (amblyopia) can develop. The vision in the affected eye gradually deteriorates because the brain ignores the weaker message being sent from that eye. A lazy eye can be treated up until about six or seven years of age, but it is important that it is treated as soon as possible.
As with squints, a lazy eye may cause blurred or double vision in children but it may not be detected until their first sight test. This is usually at around four or five years of age.
The exact cause of a squint is not always known. In most cases, babies are born with a squint or develop one because of a problem with their vision.
If a baby is born with the condition, it is called a congenital squint. Squints that develop later are called acquired squints.
Acquired squints are sometimes caused by the eye's inability to focus light that passes through the lens. This is known as a refractive error. Types of refractive errors include:
- short-sightedness (myopia) – a sight problem that affects your ability to see distant objects
- long-sightedness (hyperopia) – a sight problem that affects your ability to see close-up objects
- astigmatism – where the cornea at the front of the eye is unevenly curved, which causes blurred vision
If a child has a refractive error, their eye may turn inwards or outwards as it attempts to focus. Squints caused by refractive errors usually develop in children aged two years or older. They tend to be most common in children who are long-sighted.
Although most squints are congenital or caused by refractive errors, in rare cases they are the result of:
- childhood illnesses, for example viral infections such as measles, although it is possible these illnesses simply accelerate a squint that would have developed anyway
- some genetic conditions, such as Down's syndrome
- hydrocephalus, which is caused by a build-up of fluid in the brain
- other eye problems, such as abnormal development of the muscles that move the eye, or a problem with the retina (the layer of light-sensitive nerve cells at the back of the eye)
Some things may increase the risk of a child having a squint, including:
- having a family history of squints, lazy eye (amblyopia) or needing glasses
- having a condition that affects the nervous system, such as cerebral palsy
- being born early (prematurely) or with a low birth weight
Squints are often detected in children during routine eye checks.
These are usually carried out:
- at birth or by the time your baby is 14 days old
- at around six to eight weeks of age
- before your child starts primary school or during their first year
However, if any of these checks do not happen or if you are concerned about your or your child's vision, speak to your doctor.
After an initial assessment, you may be referred to an orthoptist. An orthoptist is an eye specialist trained to assess problems relating to eye movements and how the eyes work together.
Different tests can be used to help diagnose a squint and assess the level of vision. These will vary according to your age, but may include:
- looking at a light
- matching letters and pictures
- reading a letter chart
- looking at visual targets at different distances, first with one eye covered and then the other
Other tests may also be needed to determine whether glasses are needed.
The light-sensitive layer at the back of the eye (retina) and the nerve that carries visual messages to the brain (optic nerve) will also be examined to make sure there are no other problems.
In most cases, eye drops will be used to widen the pupils before the eyes are examined. This will make it easier for the ophthalmologist to study the back of the eyes.
It is important that a squint is treated as soon as possible after being detected.
If it is not treated, vision problems, such as those caused by a lazy eye (amblyopia), are likely to get worse or could become permanent.
Treatment is most effective in very young children.
Several types of treatment are available for squints, including:
- eye exercises
- botulinum toxin injections
- corrective surgery
These are described below.
Glasses are one of the most common treatments for squints. They can be used to correct the vision problems (refractive errors) that may be causing the squint, such as:
Children's glasses will have plastic rather than glass lenses to reduce the risk of possible injury. Your child will usually need to wear their glasses all the time.
In some cases, it may be possible to treat a squint using special eye exercises that help the eyes work together.
Botulinum toxin injection
Botulinum toxin may be a treatment option for some types of squint.
It can be injected into one of the muscles that move the eye. The injection temporarily weakens the injected muscle, allowing the eyes to realign.
The effects of botulinum toxin usually last around three months. After this time, the eyes may stay in position or they may go back out of alignment and require further treatment.
Children will usually be given medication to help them relax (a sedative) before having the botulinum toxin injection.
Botulinum toxin injections can cause temporary side effects such as:
- a droopy eyelid (ptosis)
- the eye "drifting" slightly, so it appears as if one eye is looking up
- double vision
- some bleeding over the white part of the eye
If treatment doesn't work, surgery may be recommended. Surgery can be used to:
- improve the alignment of the eyes (and therefore their appearance)
- help the eyes work together
Read more about squint surgery.
A squint is a condition where the eyes point in different directions.
One eye may turn inwards, outwards, upwards or downwards while the other eye looks forward. The medical name for a squint is strabismus.
Squints can also cause:
- blurred vision
- double vision
- lazy eye (amblyopia) – when the brain starts to ignore signals coming from the eye with the squint
Read more about symptoms of a squint.
When to see a doctor
Squints are common and affect about 1 in 20 children. They usually develop before a child is five years of age, but can appear later.
Up to around three months of age, many babies occasionally squint as their vision develops. This is normal and nothing to worry about.
If your child still has a squint after this age, you should see your doctor. Your doctor may refer you to a specialist called an orthoptist for some tests.
Many squints are detected during routine eye checks carried out at certain stages in your child's development.
Read more about diagnosing squints.
Why do squints happen?
It is not always apparent what causes a squint.
Some babies are born with a squint (called a congenital squint) and some develop it later (acquired squint).
Read more about the causes of squint.
How are squints treated?
Most squints need to be treated as soon as possible to improve the chances of successful treatment.
Common treatments include glasses and eye exercises. If your child has a lazy eye, they may need to wear an eye patch to improve the vision in the affected eye.
If these treatments aren't successful, corrective surgery will most likely be required. This involves moving the muscles that control the movement of the eye.
Risks from surgery are rare, although sometimes more than one operation will be needed.
Occasionally, squints corrected during childhood reappear in adulthood. You should visit your doctor as soon as possible if you develop a new squint.
Read more about how squints are treated.
Recovering from surgery
It can take several weeks to fully recover from corrective squint surgery.
During this time, the eye may feel painful or itchy for a short time and you may have temporary double vision.
If other treatments are unsuccessful, surgery may be needed to correct a squint.
Surgery can be used to:
- improve the alignment of the eyes (and therefore their appearance)
- help the eyes work together
Surgery involves moving the muscles attached to the outside of the eye to a new position. It may be necessary to operate on both eyes to balance them, even if the squint is only in one eye.
The operation is carried out under general anaesthetic and usually takes less than an hour to perform. It is often carried out as a day case, so your child can go home the same day.
You may be able to accompany your child to the operating theatre and stay with them until they have been given the anaesthetic. A nurse will be with your child throughout the procedure.
During the operation, your child's eye will be kept open using an instrument called a lid speculum. The ophthalmologist (eye care specialist) will detach one part of the muscle connected to your child's eye and will either move it backwards to weaken the pulling effect, or shorten it to increase the pulling effect. Once the correction has been made, the muscles will be sewn back into place using dissolvable stitches.
Risks of surgery
As with any kind of operation, there is a risk that problems will arise due to surgery to fix a squint.
If you or your child are having surgery for a squint, ask your ophthalmologist (eye care specialist) to discuss possible risks with you before the operation.
Risks of eye surgery include:
- The possibility of further surgery, which is sometimes needed if the squint is severe.
- The eye may remain red for a long time after the operation. This is rare, but it may be caused by scar tissue forming on the surface of the eye.
- Double vision may occur after the operation. This usually resolves after a week or so.
- The squint may recur and another operation may be needed.
- One of the eye muscles may slip after the operation, although this is very rare. This makes the eye point inwards or outwards (depending on which muscle has slipped) and can impair eye movement. It may need to be operated on again.
- In rare cases, the inside of the eye can be damaged during surgery.
- An infection may develop after the operation. This is possible with any type of surgery. In the case of eye surgery, eye drops or ointment can be used to reduce the risk.
One study that looked at squint surgery for adults estimated that around one in five people may need more than one operation to treat their squint successfully. Double vision occurred in less than 1 in 100 cases. This usually either improves with time, or it can be treated with further surgery, for example.
In children, it is more common to need another operation to correct the squint, particularly if the first operation was carried out when the child was very young. Some studies have found that around 6 out of 10 children who have squint surgery at about one year of age need to have another operation at some point.
Other complications in children are usually rare, but you should ask your ophthalmologist for more information.
Recovering from surgery
It can take several weeks to fully recover from corrective eye surgery. After surgery, you or your child may have a sore eye for a few days. The pain can be treated using simple painkillers, such as paracetamol. Children under 16 years of age should not be given aspirin. If the pain does not improve, speak to your eye care specialist or visit your doctor.
Following eye surgery, a pad may be put over the affected eye, which will usually be removed before you or your child are discharged from hospital. There is no need to wear a patch or bandage at home and you can return to daily activities, such as reading, as soon as you feel able to. The aim is to get the eyes working normally as quickly as possible.
Your care team will be able to give you more specific advice about returning home after an eye operation, but some general tips include:
- you or your child may not feel like eating, but you should drink water at regular intervals
- the stitches can take up to six weeks to dissolve and it may feel like there is a bit of grit in the eye or the eye may be itchy – try not to rub it
- avoid washing your hair for a few days and try not to get any soap or shampoo in the eye
- your child should not play in sand or use face paint for two weeks after the operation
- you or your child will need to go back to your eye care specialist for regular follow-up visits
- if you or your child wore glasses before the operation, it is likely that you will still need to wear them after the procedure
Returning to school or work
Your child should be able to return to school or nursery about a week after surgery. If you have had surgery, you should also be able to return to work after about a week.
After surgery, you or your child should avoid playing sports for around two weeks. You may need to avoid contact sports, such as rugby, for up to a month. Swimming should be avoided for at least a month after the operation.
If you have had surgery to correct a squint and you drive, you should ask your surgeon when you can drive again. You should not drive if you have double vision.