A squint (strabismus) is a condition where the eyes point in different directions. 

Squints are common and affect around one in 20 children. They usually develop before five years of age, but can appear later.

Signs and symptoms of a squint

One of your child's eyes may turn inwards, outwards, upwards or downwards, while the other eye looks forward. Squints may not be constant, and a minor squint isn't always obvious.

A squint can cause blurred or double vision, but children may not realise there's a problem.

Left untreated, lazy eye (amblyopia) can develop. This is when the brain starts to ignore signals coming from the eye with the squint.

When to see a doctor

It's quite normal for the eyes of newborn babies to "cross" occasionally, particularly when they're tired. However, 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 they're experiencing double vision and could be a sign they have a squint. If this happens repeatedly, take your child to see your GP as soon as possible.

They may refer you to a specialist called an orthoptist, for 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?

The exact cause of a squint isn't always known. Some babies are born with a squint (congenital squint) and some develop it later (acquired squint).

Acquired squints are often caused by the eye attempting to overcome a vision problem – known as refractive errors. Types of refractive errors include:

• short-sightedness (myopia) – the ability to see distant objects is reduced
• long-sightedness (hyperopia) – the ability to see close-up objects is reduced
• astigmatism – where the cornea at the front of the eye is unevenly curved, which causes blurred vision

In rare cases, a squint may be the result of:

• childhood illnesses – such as measles
• some genetic conditions – such as Down's syndrome or cerebral palsy
• hydrocephalus – caused by a build-up of fluid in the brain
• other eye problems affecting the muscles or the retina (the layer of light-sensitive nerve cells at the back of the eye)

A child's risk of having a squint is increased if there's a family history of eye problems, if they're born prematurely or with a low birth weight.

How are squints treated?

To be most successful and avoid long-term problems, most squints should be treated as soon as possible. Treatment is most effective in very young children.

Several types of treatment are available for squints, including:

• Glasses – worn constantly to correct vision problems (refractive errors). Children are usually given plastic lenses instead of glass.
• Eye exercises – in some cases, special eye exercises may help the eyes to work together.
• Botulinum toxin injections into one of the eye muscles – the injection weakens the muscle, allowing the eyes to realign for around three months. The eyes may stay in position or may need further treatment. Children will usually be given a sedative before the 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 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 (occlusion).

Squint surgery

If other treatments aren't successful, surgery will probably be required. This involves moving the muscles that control the movement of the eye to improve their alignment and help the eyes work together.

Risks from surgery are rare, although sometimes more than one operation will be needed.

Recovering from surgery

It can take several weeks to fully recover from corrective squint surgery.

The eye may feel painful or itchy for a short time afterwards, and you may have temporary double vision.

Read more about squint surgery.

Occasionally, squints corrected during childhood reappear in adulthood. You should visit your GP as soon as possible if you develop a new squint.