Squint

What is a squint?

Squints are caused by difficulty in focusing, and are a result of what are known as refractive errors, such as long-sightedness. These refractive errors may occur in one or both eyes, which interferes with the early brain development of binocular vision. This means that, because the eyes focus differently, the brain doesn't learn to use both eyes to focus together on an object. If one eye is dominant the brain may suppress the image from the weaker eye and control of that eye may be poor.

Genetic factors may be important and often there is a family history of squint or visual problems. Rarely a paralytic squint may develop, due to damage to the nerves controlling movement of the eyes, for example, by a brain tumour.

Symptoms

Some squints are obvious, with the eyes clearly looking in different directions, but minor squints may be difficult to see.

There are several different types of squint, depending on the direction followed by the gaze of the affected eye:

• Convergent squint - the abnormal eye gazes inwards
• Divergent squint - the affected eye looks outwards towards the corner of the eye
• Vertical squint - the eye gazes up or down (although this is rare)

Other symptoms may include poor vision, or blurred or double vision in the affected eye, which the child may try to deal with by spontaneously covering or closing the affected eye.

Causes and risk factors

Squints are common in babies up to the age of two months, although usually intermittent. Persistent squints after this age need to be investigated. Children with neuro-developmental delay are at increased risk of squints, as are those with motor control problems such as cerebral palsy.

It's unusual to develop a squint as an adult, but if you do it may result in double vision. New squints in adults require thorough investigation to find the cause.

Squints may sometimes be detected by shining a light on the eyes from a distance. The reflection of the light should appear in the same position in the two eyes.

One test involves asking the child to look at an object, then covering the eye that normally fixes properly on the object and watching the other eye to see if it moves to take up fixation. If it moves, there may be a squint in that eye. But some squints are only apparent to an expert.

All children are routinely screened for visual problems and squint at school entry or earlier. However, if you think your child may have a squint, talk to your doctor.

Treatment and recovery

Early treatment of squint may help the brain to develop binocular vision.

Treatment may include glasses to correct the visual problems, and patching of the normal eye to force the brain to use the affected eye. Sometimes an operation is necessary to tighten muscles around the eye.

Dr Orlena Kerek last medically reviewed this article in March 2009