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Squint


Expert reviewer, Professor Simon Taylor, Consultant Ophthalmic Surgeon
Next review due October 2020

A squint is when one eye looks in a different direction from the other. While one eye looks forwards, the other may turn inwards, outwards or, less commonly, up or down.

The medical name for a squint is strabismus. It’s most common in young children but can happen at any age.

If your child has a squint, it’s recommended that it’s looked at by an eye health specialist, and the sooner the better. This is because a squint doesn’t get better on its own and, if left untreated, can lead to problems with the development of vision. After treatment, most children with squints have a good level of vision, with both eyes working together.

This information focuses on squint in childhood, but if you’re looking for information about treating squint in an adult, see our FAQ: Squint treatment in adults below.

A family in the opticians

Types of squint

Having a squint is quite common – as many as one in 20 children have one. A squint usually happens when the muscles that control eye movements are out of balance.

You may hear lots of words used to describe the different types and features of squint. These might include the following.

  • Esotropia and exotropia. Esotropia (convergent) means one eye turns inwards while the other looks forward. Exotropia (divergent) means one eye turns outwards.
  • Constant, intermittent and latent. A constant squint is there all the time; an intermittent squint comes and goes. A latent squint is one which appears only when the eye is covered.
  • Concomitant and incomitant. A concomitant (comitant) squint has the same size or angle whichever the direction the eyes are looking. With an incomitant (non-comitant) squint, the size of the squint differs depending on direction. Most children have a concomitant squint.
  • Infantile and acquired. Infantile squint starts in the first six months of life. Acquired squint starts after the first six months.

An image of a child with a convergent squint
A child with a convergent squint

You may also hear a squint described as idiopathic - this means the cause is unknown.

Some babies have the appearance of having a squint, but their eyes are actually correctly aligned. This can be due to the presence of a fold of skin at the inner corner of your child’s eye.

Another term you may come across is ‘lazy eye’. The correct medical term for this is amblyopia. This isn’t a squint, but it can happen if a squint goes untreated. It’s when one eye loses vision because the brain begins to ignore the signals from that eye. For more information, see our section: Complications of squint below.

Symptoms of squint

Some children with squint appear to have no symptoms and the condition is only picked up if they have a routine screening test. Your child will be screened for squint at birth, after about six weeks and when they start school.

It’s not unusual for a healthy baby to appear to have a squint from time to time in their first few months. However, if the squint is there all the time or carries on appearing after three months, that may mean they have a problem.

If your child has a squint, you’ll probably notice that their eyes don't always look in the same direction. This may be constant or may happen from time to time – for example, when your child is concentrating or tired. You may notice your child has a squint in a photograph. If so, show this to your child’s optician.

Other symptoms you may notice include the following.

  • Your child may move their head into odd positions to look at an object.
  • They may sometimes cover or close one eye, especially outside in sunlight.  
  • Older children may tell you that they’re seeing double or their eyesight isn't as good out of one eye.  

There’s a rare type of childhood cancer called retinoblastoma which can cause a squint. The other main symptom of retinoblastoma is that the pupil of the affected eye looks white instead of black. You might notice the white pupil in photographs taken with a flash. If your child seems to have a white pupil, they should see their optician or GP straight away. The good news is that, if treated early, retinoblastoma can be cured in nine out of 10 children.

If your child has any of these symptoms, visit your optician or GP.

Diagnosis of squint

If your child has a squint, it's important to know as early as possible so that it can be assessed and corrected. Otherwise, there’s a risk of permanent damage to their vision.

In the UK, children are screened for squint at birth, at six to eight weeks and usually again between four and five years. A squint can be diagnosed by your child’s optician (a healthcare professional who examines eyes, tests sight and dispenses glasses and contact lenses) or GP. They’ll wait until your child is at least three months old before making a diagnosis. This is because a child’s ability to use both eyes together is still developing. It’s normal for a child under three months to have an occasional squint that comes and goes.

Your optician or 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 their symptoms. They may also ask about their medical history and ask if there are any eye problems in the family. They’ll test your child’s vision and carry out a thorough examination of both eyes.

The orthoptist or ophthalmologist will be quite used to doing these tests with babies and young children. They’ll explain to you and your child what’s happening at each stage and be able to answer any questions you may have.

Treatment for squint

Treatment for a squint depends on what type it is, and its cause. It will also depend on whether or not your child is developing a lazy eye – where the vision in one eye is being lost. For more information on lazy eye, see our section: Complications of squint below.

Treatment may include glasses, patching of one eye, eye exercises and surgery. Occasionally, injection of botulinum toxin is helpful. Your child’s orthoptist or ophthalmologist will discuss with you what’s best for your child in their particular circumstances. Ideally, your child should be treated before they’re seven or eight, but treatment may still work if they’re older.

Glasses

Children with a squint are very often given glasses as the first treatment. This may be because your child has what are called refractive eyesight problems (for example, long- or short-sightedness).  They may be using their eye muscles to help them focus, which can make the eye turn in and so cause a squint. Glasses correct these problems with eyesight, letting your child see more clearly. Sometimes, glasses alone will be enough to treat a squint and help prevent a lazy eye (amblyopia). For safety, glasses will have plastic lenses.

Your child will need to see the orthoptist regularly, usually every six weeks to begin with, to check their progress.

Occlusion (eye patching)

Your child’s orthoptist may recommend occlusion (eye patching) if your child is at risk of or is already developing problems with their vision (amblyopia, lazy eye). Occlusion involves putting a patch over the good eye so that the affected (lazy) eye is forced to start working harder. Your child may need to wear the eye patch for several hours a day over many weeks or months.

An alternative to patching is to use eye drops to blur the vision in the good eye. This means your child won’t have to wear an eye patch, but the medicine in the drops may cause side-effects. The orthoptist or ophthalmologist can discuss with you whether eye drops may be an option for your child.

Your child's progress will be carefully monitored. The treatment will be adjusted to make sure the good eye doesn’t start to become ‘lazy’ itself through being covered.

Getting your child to wear a patch over their good eye can be hard work. Your child may find the patch uncomfortable and keep removing it. But if you and your child can persevere with the eye patching, it will really help them have the best possible vision in future.

Eye (orthoptic) exercises

Depending on the type of squint, your orthoptist may teach your child a series of simple eye exercises.  These may encourage the eyes to work together and improve binocular vision (for more information, see our section: Complications of squint below).

Botulinum toxin (Botox)

In some cases, squint may be treated with Botox (botulinum toxin) injections. These cause a temporary weakness in some of the muscles that move the eye. This helps the eyes to line up properly. If your child has these injections, they’ll be given a general anaesthetic and will be asleep during the procedure. The treatment usually works for a few months and may need to be repeated.

Surgery

Some children will need an operation to straighten their eyes so that they’re properly aligned. This will help to improve their binocular vision (for more information, see our section: Complications of squint below)

The aim of squint surgery is to weaken the 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 their squint.

Your child’s orthoptist or ophthalmologist will usually only recommend squint surgery if your child has already been treated with glasses and occlusion. Your child’s eyes are more likely to stay straight after surgery if the vision is good beforehand.

You can find out more about having this procedure from our topic on squint surgery.

Causes of squint

Some people are born with a squint, and some get it later on. There are lots of different types of squint, which may have different causes.

Often, we don’t know what causes a squint, but there are some things which increase the risk of having or developing one. These include:

  • other people in the family with squint
  • eyesight problems in one or both eyes, especially long-sightedness
  • genetic conditions such as Down’s syndrome
  • premature birth or a low weight at birth
  • disorders affecting the brain (such as cerebral palsy)
  • having a head injury

Complications of squint

If your child has a squint that’s not treated, it can lead to complications. The main complications are outlined here.

Problems developing binocular vision

When we look at something, both eyes pick up an image. These images are then sent to the brain where they’re merged into one image. Each image provides slightly different information about the object. This is binocular vision, and it’s what lets us see in three dimensions and judge distances.

Binocular vision develops during early childhood. If the eyes don’t face in the same direction together during this time, binocular vision can't develop properly. So if your child's squint isn’t treated, their binocular vision may never develop fully. Even with successful treatment, your child may lose some degree of binocular vision.

Lazy eye (amblyopia)

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. If the affected eye isn’t treated, it can prevent the brain developing vision for that eye. This loss of vision is often known as ‘lazy eye’ but the correct medical term is amblyopia.

Around half of children with a squint will develop a lazy eye if the squint isn’t treated. To help prevent a lazy eye, your child should ideally be treated before they’re seven, although treatment may work in older children. The earlier the treatment starts, the better the result.

Frequently asked questions

  • A latent squint is a type of squint that only occurs when one eye is covered or closed. There’s no squint when your eyes are open and being used.

    Latent squints are common; most people have one to a mild degree. It may be noticed when you’re daydreaming, or gazing into the distance.

    If you’ve had your eyes tested by an optician you may remember a test where they alternately cover one eye then the other. They watch your eyes carefully to see if they move when the cover is removed. This is called an alternating cover test, and it’s designed to pick up a latent squint if you have one.

  • No, your child won’t grow out of their squint and will need treatment to straighten their eye. If left untreated, a squint can cause permanent damage to eyesight. For more information, see our section: Complications of squint above, which talks about problems with developing binocular vision, and getting a lazy eye (amblyopia).

    It’s important to get treatment for a lazy eye as soon as possible. Treatment to straighten the eye is less urgent. Ideally, treatment of lazy eye should happen before the age of seven, although some older children may still see some improvement in their vision with treatment. In general, the sooner treatment starts, the more your child will benefit.

    Your child’s orthoptist or ophthalmologist will discuss with you the best time for any treatments they recommend for your child.

  • It's quite common for newborn babies to have a squint from time to time. This is usually nothing to be concerned about and will disappear within the first few months of life. However, if the squint is there all the time, or is still there when your infant is over three months old, talk to your optician or GP.

    If you ever notice that your baby’s pupil seems white, even just in a photograph, see your GP or an optician right away. For more information, see our section: Symptoms of squint.

  • If you develop a squint as an adult, you’ll probably notice the change in the way your eyes look in the mirror.  You may get double vision, and your eyes may feel uncomfortable – as though you have eye strain.

    If you have a squint as an adult, there’s a good chance that you’ll benefit from treatment. Treatments include glasses, prisms, eye exercises, botulinum toxin and surgery. Treatment can improve the way you look, and may also improve your binocular vision and help reduce double vision. 

    As many as four in 100 adults have a squint. You may have had it since childhood or it may have developed later.

    Treatment of your squint may help reduce symptoms of double vision if these affect you. And, although binocular vision develops during early childhood, some adults may still get some improvement in their binocular vision with treatment.

    You may want treatment for your squint because of the way you look. People with a squint often say it affects their self-esteem, social life and even their job prospects.

    Treatment of squint in adults is similar to treatment in children. Options for treatment of squint in adults includes the following.

    • Correcting eyesight (including long-sightedness and short-sightedness) with glasses.
    • Special prismatic glasses. A prism is a wedge-shaped piece of glass that bends light as it passes through. These can be attached to your glasses to help bring together the picture that each eye sees. Prisms help reduce double vision but don’t straighten the eyes.
    • Special eye exercises.
    • Injections of botulinum toxin (Botox) to weaken or paralyse some of the muscles that move your eyeball.
    • Surgery to correct the alignment of your eyes. Most people see a great improvement after one operation. Some people need a second operation. People of any age may benefit from surgery for their squint – it’s never too late.

    For more information, see our section: Treatment of squint above.

    How well your treatment works, and which treatment might be best for you may depend on what’s caused your squint. Your orthoptist or ophthalmologist will be able to talk to you about the options, risks and benefits in your particular circumstances.


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Related information

    • Strabismus. BMJ Best practice. bestpractice.bmj.com, last updated 1 April 2016
    • Strabismus (squint). PatientPlus. patient.info/patientplus, last checked 25 June 2015
    • Amblyopia. PatientPlus. patient.info/patientplus, last checked 25 June 2015
    • Examination of the eye. PatientPlus. patient.info/patientplus, last checked 5 October 2016
    • Strabismus. The MSD Manuals. www.msdmanuals.com, last full review/revision May 2016
    • Squint in children. NICE Clinical Knowledge Summaries. cks.nice.org.uk, last revised March 2016
    • Map of Medicine. Squint and amblyopia in children. International View. London: Map of Medicine; 2017 (Issue 3)
    • Guidelines for the management of strabismus in childhood. The Royal College of Ophthalmologists, 2012. www.rcophth.ac.uk
    • About retinoblastoma. Cancer Research UK. www.cancerresearchuk, last reviewed 3 July 2015
    • Childhood squint (strabismus). Royal National Institute of Blind People. www.rnib.org.uk, accessed 1 September, 2017
    • Adult strabismus. American Association for Pediatric Ophthalmology and Strabismus. aapos.org, updated November 2016
    • Kushner, BJ. The benefits, risks, and efficacy of strabismus surgery in adults. Optom Vis Sci 2014; 91(5): e102–9. doi: 10.1097/OPX.0000000000000248
  • Reviewed by Dr Kristina Routh, Freelance Health Editor, Bupa Health Content Team, October 2017
    Expert reviewer, Professor Simon Taylor, Consultant Ophthalmic Surgeon
    Next review due October 2020



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