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Squint

Published by Bupa's Health Information Team, August 2011.

This factsheet is for parents of children who have a squint, or who would like information about it.

A squint is when one eye looks in a different direction to the other when focusing on an object.

The condition is usually diagnosed when a child is a baby or still very young. However, it’s sometimes possible to develop a squint in adulthood.

About squint

A squint is a condition that causes your eyes to look in different directions when focusing on an object. It’s also called a strabismus.

A squint happens when the muscles that control eye movements are out of balance. This means that one eye looks forward at the object in focus, whereas the other eye turns in a different direction (usually either inwards or outwards).

Your child may have a squint all the time (constant) or it may come and go (intermittent). An intermittent squint may be more noticeable when your child is tired or unwell. About five in 100 children have a squint.

There are two main types of squint: concomitant and incomitant. 

Concomitant squint

A concomitant squint is when the affected eye has a squint in every direction that your child looks. All the eye muscles are working properly, and therefore it’s also called a non-paralytic squint. With a concomitant squint your child’s eyes always face in different directions. 

Incomitant squint

An incomitant squint, also called a paralytic squint, is when the angle of your child's squint varies. For example, when your child looks in one direction there is no squint, but when he or she looks in the other direction the eyes don’t face the same way. This type of squint can develop in adults too.

An incomitant squint happens when one of the muscles that control eye movement is either paralysed or its movement has become restricted. Paralysis happens because the nerve impulses to your muscles may have been interrupted. Your child may be born with the condition or develop it after birth.

With both concomitant and incomitant squints, the direction of a squint can vary with the affected eye turning inwards, outwards, upwards or downwards.

  • An inwards squint is called esotropia, or convergent squint, and is the most common type of squint.
  • An outwards squint is called exotropia, or divergent squint, and can be more noticeable than other squints.
  • An upwards squint is called hypertropia.
  • A downwards squint is called hypotropia.

Pseudostrabismus

Pseudostrabismus is when your child’s eyes appear to be crossed but are in reality correctly aligned. This appearance is sometimes caused by a fold of skin at the inner corner of your child’s eye.

Symptoms of squint

A squint can be quite obvious, so you will probably notice if your child's eyes don't always look in the same direction. The squint may or may not be obvious all the time – for example, you may only see it when your child is tired or unwell.

Your child may move his or her head into odd positions to look at an object if he or she can see well out of both eyes. This is to compensate for the eyes not being correctly aligned. If your child can see well out of only one eye, he or she may cover the weaker eye to see better.

Older children may recognise that their eyesight isn't as good out of one eye and mention this to you. If you notice that your child has any of these symptoms, see your GP.

Complications of squint

If your child’s squint is left untreated, there is a risk that his or her binocular single vision (BSV) may not develop properly. BSV is important because it allows your child to see a single image, even though each eye will ordinarily pick up slightly different images. BSV helps your child to see the world in three dimensions.

When your child looks at something both eyes pick up an image. These images are then sent to the brain where they are turned into one image. Each image provides slightly different information about the object enabling your child to interpret depth (the ability to judge the distance between objects). BSV develops during childhood. If the eyes don’t face in the same direction together during this time, BSV can't develop properly and your child's vision may never develop fully.

Untreated squints also carry the risk of a lazy eye (amblyopia) developing. When the eyes aren't aligned, the images picked up by each eye are too different for the brain to combine into one image. To overcome this, the brain starts to ignore one of the images so that a clear picture is seen from one eye only. The eye that is ignored is called sometimes called a lazy eye. If the affected eye isn’t treated, it can prevent the brain developing vision for that eye.

One in three children with a squint will develop a lazy eye. It’s most common in children who have an esotropic squint.

Causes of squint

Your child may be born with a squint (congenital squint) or he or she may develop it later on in childhood (acquired squint). Occasionally a squint can develop in adulthood.

A squint is most commonly present from birth and can run in families. The exact cause of a squint often isn’t known, but it’s usually related to muscle and nerve problems around the eye. A squint can also be associated with severe short- or long-sightedness.

Acquired squints can be caused by a head injury or disorders affecting the brain (such as cerebral palsy), the nervous system (for example multiple sclerosis) or the eyes (such as cataracts). They can also be associated with other conditions such as Down's syndrome, thyroid disease or diabetes.

Diagnosis of squint

If your child has a squint, it's important to get a diagnosis as early as possible, otherwise there is a risk of permanent damage to his or her vision.

A squint can be diagnosed by your child's GP or optometrist (a healthcare professional who examines eyes, tests sight and dispenses glasses and contact lenses). He or she will wait until your child is at least three months old before making any diagnosis. This is because the ability to use both eyes together is still developing in babies up to three months old.

Your GP will refer your child to either an orthoptist or an ophthalmologist. An orthoptist is a health professional who specialises in eye movement problems such as squints, lazy eyes and double vision. An ophthalmologist is a doctor who specialises in eye health, including eye surgery.

Your child's orthoptist or ophthalmologist will ask about his or her symptoms as well as test his or her vision and carry out a thorough examination of both eyes. He or she may also ask about y our child’s medical history.

Treatment for squint

Treatment for a squint will depend on what is causing it and whether your child has developed a lazy eye.

Glasses

Your child may be prescribed glasses if his or her sight is poor as a result of long-sight, short-sight or an astigmatism (when the cornea at the front of the eye is not perfectly curved). This will improve your child’s vision and may also straighten the eye affected by the squint.

Occlusion

Occlusion is used if your child has developed a lazy eye. This involves putting a patch over his or her good eye so that the affected (lazy) eye is forced to start working again. Your child may need to wear the eye patch for several hours a day over many weeks or months. Your child may need to use eye drops or wear special glasses instead of a patch to blur the vision in his or her good eye and make the affected eye work harder.

There is a risk that the good eye may develop similar problems if it’s covered up too much or for too long. Your orthoptist or ophthalmologist will monitor your child's progress carefully and adjust his or her treatment accordingly, but it’s important to follow the instructions given and to report back any concerns. Getting a child to wear a patch over his or her good eye can be hard work; you may wish to ask about alternative treatments if this isn't working.

Occlusion may also be used temporarily if your child has double vision but hasn't developed a lazy eye.

Orthoptic exercises

Depending on the type of squint, your orthoptist may teach your child a series of simple exercises that are designed to encourage the eyes to work together.

Botulinum A toxin

If you child's squint is caused by problems with eye muscles, a very small amount of botulinum A toxin (eg Botox) can be injected into the muscles to paralyse them. This stops the muscles causing the squint from overworking. The treatment usually works for a couple of months and then needs to be repeated. This is a relatively new treatment option.

Surgery

Your child can have an operation to straighten his or her eyes so that they are properly aligned. The operation can also improve the cosmetic look of your child's eye. The aim of surgery is to weaken any muscles that are overworking and to strengthen the other muscles around the eye. There are different types of operation and the one your child has will depend on the cause and severity of his or her squint.

Before an operation is considered, glasses and occlusion will be used to improve your child's vision. This is because your child's eyes are more likely to stay straight after the operation if his or her vision is good beforehand.

 

For answers to frequently asked questions on this topic, see FAQs.

For sources and links to further information, see Resources.


  • This information was published by Bupa's Health Information Team and is based on reputable sources of medical evidence. It has been reviewed by appropriate medical or clinical professionals. Photos are only for illustrative purposes and do not reflect every presentation of a condition. The content is intended only for general information and does not replace the need for personal advice from a qualified health professional. For more details on how we produce our content and its sources, visit the about our health information page.

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  • Publication date: August 2011

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