Squint

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 your child is young or a baby. However, it is possible to develop a squint in adulthood. It affects approximately one in 20 children.
 
About squint
Symptoms of squint
Complications of squint
Causes of squint
Diagnosis of squint
Treatment for squint 
 

About squint

Squint is a condition that causes one eye to look in a different direction to the other when focusing on an object. It is 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) and become more noticeable when he or she is tired or unwell.
 
There are two main types of squint: concomitant squint and inconcomitant squint.
 

Concomitant

A concomitant squint, also called a non-paralytic squint, is when the angle of the squint is the same in every direction your child looks. Both eyes are able to move well and all the muscles controlling their movement are working properly. However, the two eyes are always misaligned to the same extent.
 
The direction of a squint can be as follows:
 

• esotropia, also know as a convergent squint, when the eye turns inward – this is the most common type of squint
• exotropia, also known as a divergent squint, when the eye turns outward – this can be more obvious
• hypertropia, where the affected eye turns upward
   
• hypotropia, where the affected eye turns downward

 
With esotropia and exotropia there may also be some upward or downward movement of the squinting eye. It is possible for the angle of the squint to appear greater in either upward gaze (referred to as an V pattern) or downward gaze (referred to as a A pattern). This is the case for half of all children with an concomitant squint.

 
Inconcomitant squint

An inconcomitant 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 they look in the other direction the eyes are misaligned. This type of squint can develop in adults too.
 
This type of squint happens when one of the muscles that control eye movement is either paralysed or its movement has become restricted. Paralysis of the muscles happens because the nerve impulses to the muscles have been interrupted (your child may be born with this or develop it).
 

Pseudostrabismus

This is when the eyes appear to be crossed but are in fact correctly aligned. This is sometimes due to a fold of skin at the inner corner of the eye.

 
Symptoms of squint

A squint can be quite obvious, so you will probably notice that your child’s eyes don’t always look in the same direction. The squint may be obvious all the time or you may only see it intermittently (for example when your child is tired or unwell).
 
If your child can see well out of both eyes, he or she may move their head into odd positions to look at an object to compensate for the eyes not being correctly aligned.
 
An older child may also notice that their eyesight isn’t as good out of one eye.


 

Complications of squint

If a squint is left untreated, there is a risk that your child’s binocular single vision (BSV) may not develop properly. BSV helps your child to see the world three dimensionally. When you look 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 you to interpret depth (this is called stereopsis). BSV develops during childhood. If the eyes are not correctly aligned 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 one clear picture is perceived. The eye that is ignored is called a lazy eye. It can lead to vision being lost completely in the affected eye.
 
A lazy eye develops in one in three children with a squint. It is most common in infants who develop an esotropia squint. The older your child gets, the more difficult it is to reverse – a lazy eye is usually permanent by the age of seven or eight.
 
With a lazy eye your child will still be able to see the world in three dimensions, but their depth perception may be reduced. This may not be an immediate concern. However, it can cause problems when doing some sports and, in later life, may make certain careers impossible (for example, pilot). Also, reliance on one good eye could lead to serious sight problems if vision in it is affected.
 

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 is often not known, but they are usually related to muscle and nerve problems around the eye. A squint can also be associated with severe short-sightedness or long-sightedness.
 
Acquired squints can be caused by a head injury or disorders affecting the brain (eg cerebral palsy), nervous system (eg multiple sclerosis) or the eyes (eg cataract). They can also be associated with other conditions such Down's syndrome, thyroid disease or diabetes.
 

Diagnosis of squint

If you child has a squint, it's important to get a diagnosis as early as possible, otherwise there is a risk of permanent damage to their 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). A diagnosis will be made if your child’s eyes are misaligned when he or she is aged three months or over.
 
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 heath, including eye surgery.
 
Your child's orthoptist or ophthalmologist will ask about his or her medical history as well as test their vision and carry out a thorough examination of both eyes.
 

Treatment for squint

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

Glasses

Glasses will be prescribed if you child's sight is poor because he or she either long-sighted or short-sighted or astigmatic. This will improve his or her vision and may also straighten the eye affected by the squint.
 

Occlusion

Occlusion is used if your child has developed a lazy eye. It involves putting a patch over his or her good eye so that the 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. Sometimes eye drops or special glasses are used instead of a patch to blur the vision in your child's good eye and make the lazy eye work harder.
 
There is a risk that the good eye may become lazy if it is covered up too much or for too long. Your orthoptist or ophthalmologist will monitor your child’s progress carefully and adjust treatment accordingly, but it is 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 and your doctor may consider other approaches if this treatment proves too difficult or isn’t working.
 
However, there is a risk that the good eye may become lazy if it is covered up too much for too long. It's important to follow the instructions given by your child's ophthalmologist or optometrist carefully to make sure this doesn't happen.
 
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 which are designed to encourage the eyes to work together.
 

Botulinum toxin

If you child's squint is caused by problems with eye muscles, a very small amount of botulinum toxin 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.
 

Surgery

An operation can be carried out to straighten your child's eye so that his or her eyes are properly aligned. The operation will also improve the cosmetic look of your child’s eye. The aim of surgery is to weaken any muscles that are overworking while strengthening the other muscles around the eye. The type of operation your child has will depend on the cause and severity of their squint.
 
Surgical correction for a squint it usually carried out as a day case. This means that your child will be able to go home the same day. The operation is carried out under general anaesthesia, so your child will be asleep during the procedure.
 
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 their vision is good beforehand.