Squint - Causes of squint

The exact cause of a squint is not always known. In most cases, babies are born with a squint or develop one because of a problem with their vision.

If a baby is born with the condition, it is called a congenital squint. Squints that develop later are called acquired squints.

Refractive errors

Acquired squints are sometimes caused by the eye's inability to focus 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 or outwards as it attempts to focus. Squints caused by refractive errors usually develop in children aged two years or older. They tend to be most common in children who are long-sighted.

Other causes

Although most squints are congenital or caused by refractive errors, in rare cases they are the result of:

• childhood illnesses, for example viral infections such as measles, although it is possible these illnesses simply accelerate a squint that would have developed anyway
• some genetic conditions, such as Down's syndrome
• hydrocephalus, which is caused by a build-up of fluid in the brain
• other 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)

Increased risk

Some things may increase the risk of a child having a squint, including:

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