Squint

A squint (strabismus) occurs when the nerves and muscles controlling the eye’s movement overcompensate, which can either pull the eye inwards or outwards. In rare cases, the eye can also be pulled upwards or downwards as well. If the eye is pointing outwards, towards the side of the head, this is called exotropia or divergent. If the eye is pointing inwards, towards the nose, this is called esotropia or convergent.

To avoid double vision (diplopia), the brain can filter out the image from the eye with a squint, which can lead to that eye losing the ability to see accurately. This is called a ‘lazy eye’ or amblyopia.

Squint

What is a childhood squint?

A squint a problem when the eyes stop working together as a pair and therefore do not look in the same direction. One eye may turn inwards (most common in children), outwards or even upwards or downwards.

The medical term for squint is ‘Strabismus’.

A squint that turns inwards is called a ‘convergent squint’ or ‘esotropia’ and one that turns outwards is termed a ‘divergent squint’ or ‘exotropia’.

Diagnosis

All babies’ eyes are checked soon after birth, and then at intervals throughout childhood. The doctor examining your child may suspect that he or she may have a squint and refer you to a specialist.

There are various tests that will confirm or rule out a diagnosis of squint. The eye specialist (ophthalmologist) will watch how your child looks around the room, and ask him or her to look at a light. This will show if the light’s reflection is in the same position on each eye. Finally, the ophthalmologist will cover one eye and watch how the uncovered eye moves, then uncover it and watch both eyes moving together. You may be asked to have some medical photographs taken as well, as this can help diagnose squint and also gives a record of the progress your child makes. More sophisticated tests can be done on older children.

Causes

Squints are caused by a combination of factors including an inability to focus both eyes together and long-sightedness. If a parent had a squint, this can also increase the likelihood of a child developing squint. This may be because the child inherited the inability to focus both eyes together, or the long-sightedness or a combination of both. Squints are not usually caused by anything that happened while you were pregnant.

On rare occasions, an injury to the eye or to the head can cause problems with the muscles controlling the eye’s movements but this is very rare.

Different types of squint

Paralytic Squint: Means one of the muscle attached to the eyes is paralyzed and the eye affected may turn in/out/up/down depending on the muscle involved i.e. the eye movement is restricted in the direction of the action of the paralyzed muscle. This can be caused by direct trauma to the muscle as for e.g. injury during forceps delivery or any other injury. It may also be caused by certain nerve palsies, which in turn may be caused by peripheral neuritis or diseases of the CNS, e.g. meningitis, encephalitis etc. Treatment of paralytic squint depends on the cause and many a time paralytic squint may not be completely cured. In such cases spectacles with prisms are prescribed.

Non Paralytic Squint: A loss of coordination between the muscles of the two eyes leads to misalignment. This misalignment may be the same in all direction of gaze, or in some conditions the misalignment may be more in one direction of gaze.

In some cases there may be a false appearance of squint due to broad nasal bridge in a child. An ophthalmologist will be able to differentiate between a true squint and false squint.

How do squints affect sight?

The ability of the eyes and the brain to work together develops throughout childhood up to the age of about 8 years but particularly within the first two years of life. If a child develops a squint, the eyes stop working together and they stop developing the ability to work together correctly. Often one eye is ‘switched off’ to stop the child suffering from double vision. This may lead to a lazy eye (medical term ‘amblyopia’), meaning that the vision in the squinting eye doesn’t develop and permanent loss of sight in that eye can occur. Unfortunately this cannot be fixed in later life so it is very important that squints are picked up early and treated.

Treatment

There are number of ways in which squints can be treated, children often need more than one form of treatment.

Glasses

All children with squint need to be tested for glasses and the majority will be prescribed a pair that they will need to wear at all times, otherwise a lazy eye may develop. Many do not need other treatment. Properly prescribed glasses give clear vision in both eyes, although some children are reluctant to wear glasses and may need a lot of encouragement. They often say that they can see better without the glasses and this is because they have been working their eyes so hard to focus that they find it difficult to ‘relax’ into the glasses to let them do the focussing for them. This usually settles but needs continuous wear of glasses.

Patching (occlusion)

Children who have a lazy eye (amblyopia) often require the good eye to be covered or patched (occlusion). This is done to make the lazy eye work harder. Patching should always take place when glasses are worn (in those who need them). Some children with a slightly lazy eye do not need patching, as the lazy eye improves with spectacle correction alone.

Exercises

In some cases exercises to strengthen the ability of the eyes to work together can be useful. This type of treatment is usually helpful in older children and is commonly used in association with glasses and or surgery.

Surgery

A small number of children require an operation on the eye muscles in order to straighten the squint. This is usually needed if the squint is very pronounced and is not improved by the proper correction of glasses. Sometimes surgery is performed on very young children.

Surgery is usually performed under general anaesthetic as a day case procedure. The operation usually weakens and / or strengthens the muscles of the eye so that the eyes are better aligned. Surgery will not improve the vision in a lazy eye.

After the operation it is usually necessary to continue to use glasses. Surgery may be carried out to help the eyes work together or it may simply be used to make the eyes look straigter (but not work together as a pair).

What is the outlook for children with squints?

The outlook for children whose squints are diagnosed early is good. If a child is not diagnosed in early childhood, the ‘lazy eye’ is unlikely to develop good vision. This is also true if children do not develop binocular vision.

In almost all children who have a ‘normal’ squint, the eyes are successfully aligned in the short-term. However, up to one third of these children may need a further operation to realign their eyes during childhood. Children rarely need more than two operations.

Sources: Patient, Pediatric on Call

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