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Squint

Page last reviewed: 13/07/2011

A squint is a condition where your eyes look in different directions. One eye turns inwards, outwards, upwards or downwards while the other eye looks forwards. The medical name for a squint is strabismus.

The misalignment of the eyes can be caused by a problem with the eye muscles or by an uncorrected vision problem, such as short-sightedness or long-sightedness.  

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 they 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 visit your GP.

It is very important that a squint is picked up and treated as early as possible to avoid vision problems developing. If a squint is identified when a child is young, there is a good chance that it will be successfully treated.

How does a squint affect vision?

In young children, a squint can cause:

  • blurred vision
  • double vision
  • lazy eye (amblyopia)

If your child has a squint, their eyes are no longer working together and they may see two images (double vision) instead of one. To avoid double vision, your child's brain ignores the signals from the eye with the squint and only recognises images from the normal eye. As the squinting eye is not being used, it eventually becomes 'lazy'.

In older children, a squint may cause double vision but not result in a lazy eye. This is because their vision has fully developed and their brain is unable to ignore signals from the eye with the squint.

If the vision in the eye that squints is poor, your child may have to wear a patch over their other eye to encourage the vision to develop.

Can adults get a squint?

Occasionally, squints that have been corrected during childhood reappear in adulthood. Squints that affect adults may cause double vision because the brain has been trained to collect images from both eyes.
 
You should visit your GP as soon as possible if you develop a new squint. They may refer you to an ophthalmologist (eye care specialist) who will carry out an examination to identify the cause.

Squints may cause a cosmetic problem in adults if the condition was not treated when they were young. In such cases, the appearance of a squint can lead to low self-esteem.

Types of squint

There are four different types of squint depending on the direction in which the eye turns. They are:

  • esotropia - where the eye turns inwards
  • exotropia - where the eye turns outwards
  • hypertropia - where the eye turns upwards
  • hypotropia - where the eye turns downwards

Hypertropia and hypotropia are less common than esotropia and exotropia.

Squints can also be:

  • apparent at all times (constant), or
  • only apparent at certain times (intermittent).

The cause, severity and direction of a squint will vary from person to person.

How the eyes work

Light enters the eye through the cornea and lens. These are transparent layers that cover the front of the eye.

The light passes to the retina, which is a layer of light-sensitive tissue at the back of the eye. The retina converts the light into electrical signals.

The optic nerve at the back of the eye transmits the electrical signals to the brain, where they are converted into an image.

Each eye works independently of the other, creating its own, slightly different image. However, you only see one image because the brain controls the eye muscles so that both eyes point at the object you are looking at. The brain joins the images that are produced by each eye together into a single image.

Page last reviewed: 13/07/2011

The most obvious sign of a squint is one eye that does not look straight ahead but turns inwards, outwards, upwards or downwards. Minor squints may be less obvious.

Squints can cause blurred vision or double vision, but babies and young children may not realise that 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. Speak to your GP 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 GP as soon as possible.

Lazy eye

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.

Page last reviewed: 13/07/2011

Congenital squints

The cause of a squint is not always known. Squints sometimes run in families and a baby can be born with the condition. This is called a congenital squint.

Squints are also sometimes the result of childhood illnesses, or other sight-related problems, such as refractive errors.

Refractive errors

Squints are sometimes caused by the eye's inability to focus the 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 as it attempts to focus. Squints that are caused by refractive errors usually develop in children who are two years of age or over. They tend to be most common in children who are long-sighted.

Other causes

Although most squints are congenital (inherited from a family member) or caused by refractive errors, they can occasionally be the result of:

  • childhood illnesses, for example viral infections such as measles
  • some genetic conditions, such as Noonan syndrome
  • a brain condition, such as hydrocephalus, where there is a build-up of fluid in the brain
  • 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)

Risk factors

Some factors that may increase the risk of a child having a squint include:

  • having a family history of squints or lazy eye (amblyopia)
  • having a condition that affects the nervous system, such as cerebral palsy
  • being born early (prematurely) or with a low birth weight

Page last reviewed: 13/07/2011

Visit your GP if you notice that your baby or child has a squint, or if you develop a squint. The earlier a squint is identified and diagnosed, the greater the chance of successfully treating it and restoring vision to normal.

Your GP may refer you or your child to an orthoptist. An orthoptist is an eye specialist trained to assess problems relating to eye movements and how the eyes work together.

Routine eye checks

Routine eye checks are carried out:

  • at birth
  • at around six to eight weeks of age
  • during their first year of school

However, if any of these checks do not happen, or if you are concerned about your child's vision, speak to your GP. Sight tests are free for children under 16 years of age.

Sight tests

Your child will have a number of different tests that can help diagnose a squint and assess their level of vision. The type of tests that your child has will depend on their age, but may include:

  • looking at a light
  • matching letters and pictures
  • reading a letter chart
  • looking at visual targets, such as a toy, at different distances, first with one eye covered and then the other

If a squint is suspected, your GP may refer your child to an orthoptist or an ophthalmologist (a specialist in eye conditions and their treatments) for further examination.

Your child may have other tests to determine whether they need glasses, such as looking at letters or colours with different lenses in front of their eyes.

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 that there are no other problems with them.

In some cases, your child's pupils may be widened first using eye drops. This will make it easier for the ophthalmologist to examine the back of your child's eyes.

Your eye care team

If you or your child have a squint, there are three types of eye care professionals who may be involved with your care. They are listed below.

  • Optometristscarry out sight tests and prescribe glasses. They can also detect eye conditions.
  • Orthoptists are specially trained to assess problems relating to eye movements and how the eyes work together.
  • Ophthalmologists  specialise in eye conditions and their treatments. They also carry out any surgery that may be needed.

Page last reviewed: 13/07/2011

It is very 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:

  • glasses
  • an eye patch
  • botulinum toxin injections
  • eye exercises
  • corrective surgery

These are described below.

Glasses

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:

  • short-sightedness (myopia)
  • long-sightedness (hyperopia)
  • having an unevenly curved cornea (astigmatism) 

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.

Eye patch

If your child has a lazy eye, they may need to wear a patch over their 'good' eye to encourage the eye with the squint to work harder. This will not correct the squint, but it can improve the vision in the lazy eye.

The patch may need to be worn for a few hours a day for several weeks. Eye patches are most effective if they are worn before a child is seven or eight years of age.

Botulinum toxin injection

Botulinum toxin is a poison that in very small doses can be used to treat a range of different health conditions. 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 their realigned position or they may go back out of alignment and require further treatment. 

Botulinum toxin may be a treatment option for some types of squint, such as those that are caused by a problem with the nerves around the eye, or in babies under one year of age.

Children will usually be given medication to help them relax (a sedative) before having the botulinum toxin injection. 

After the injection, your child may experience some temporary side effects such as:

  • a droopy eyelid (ptosis)
  • their eye 'drifting' slightly so that it appears as if one eye is looking up
  • double vision
  • some bleeding over the white part of their eye

Eye exercises

In some cases, it may be possible to treat a squint using special eye exercises that help the eyes work together.

Surgery

If none of the above treatments work, surgery may be a possible treatment option. Surgery can be used to:

  • improve the alignment of the eyes and therefore their appearance
  • help the eyes work together

The procedure

Surgery to correct a squint 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 effectively, even if the squint is only in one eye.

As corrective squint surgery usually takes less than an hour to perform, the procedure is often carried out as a day case, so your child will be able to go home the same day. The operation is usually carried out under general anaesthetic, which means that your child will be asleep throughout the procedure.

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 that is 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.

There is very little chance that your child's eyesight will be damaged during the operation because the part of the eye responsible for focusing is not touched.

Eye drops

For a short time after the operation, your child will need to use eye drops. The nurse will show you how to use them before you leave the hospital.

The eye drops will help your child's eye to heal and prevent infection. They will need to be used three or four times a day, for up to four weeks after the operation. 

After surgery

Surgery to correct a squint does not usually hurt, although your child's eye may feel slightly uncomfortable afterwards.

Following surgery, the white part of your child's eye will be red. This is quite normal and it should pass after a few days.

Page last reviewed: 13/07/2011

There are risks associated with any kind of surgery. If you or your child are having surgery for a squint, ask your ophthalmologist (eye care specialist) to discuss the possible risks with you before the operation.

The risks of eye surgery are listed below.

  • Further surgery is sometimes needed to correct the squint, particularly if it is a severe squint.
  • The eye may remain red for a long time after the operation. This is rare, but it may be due to scar tissue forming on the surface of the eye.
  • Double vision may occur after the operation. This usually resolves itself after a week or so.
  • The squint may reoccur 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 very 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 and 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 fewer than 1 in 100 cases. This usually either improves with time, or it can be treated, for example, with further surgery. 

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.

Page last reviewed: 13/07/2011

After having corrective eye 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. If the pain does not improve, speak to your eye care specialist or visit your GP.

Children under 16 years of age should not be given aspirin.

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 or your child will be able to return to daily activities, such as reading, as soon as you (or they) feel able to. The aim is to get the eyes working normally as quickly as possible.

Advice after eye surgery

Follow the advice outlined below when you or your child return home after having an eye operation.

  • You or your child may not feel like eating, but drink water at regular intervals.
  • You or your child may have double vision, but this will usually resolve itself over the course of a few weeks.
  • 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 getting any soap or shampoo in the eye for two weeks.
  • 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 after a week or two. If you have had surgery, you should be able to return to work after a week or two.

Sports

After surgery, you or your child should avoid playing sports for around two weeks. You may need to avoid contact sports, such as football, for up to a month. Swimming should be avoided for at least a month after the operation.

Driving

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.

Content provided by NHS Choices www.nhs.uk and adapted for Ireland by the Health A-Z.

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