Squint (Strabismus) in children

A squint occurs when the eyes do not look in the same direction. Usually when one eye is looking straight ahead the other eye is pointing inwards, outwards, up or down.
Most squints occur in young children and problems arise firstly if the child stops using the affected eye to see with and secondly if the appearance of the squint causes the child difficulties.
If the child stops using the affected eye to see with, this can lead to visual loss called amblyopia which can become permanent unless treated in childhood. Amblyopia is usually treated by patching the good eye to force the affected eye to see.
If the appearance of the squint is unacceptable, surgery may be required to try and realign the eyes.

What causes a squint?
What problems can be caused by a squint in a child?
How do you know if your child has a squint?
How are squints treated?
Surgery for squint in children

What causes a squint?
The movement of each eye is controlled by six different muscles that pull the eyes in various directions.
A squint develops when the eye muscles do not work in a balanced way and the eyes do not move correctly together.
Approximately 1 in 20 children over the age of 20 months have a squint.
There are a number of reasons why children develop squint:

Congenital squints of unknown cause
Congenital means that the child is born with a squint, or it develops within 6 months of age. In the majority of cases the exact cause is unknown and in most cases one eye turns inward. This is called a Congenital Esotropia (or an infantile esotropia).
This is a common type of squint and tends to run in families, although not always.
In some cases the eye may turn outwards in which case it is called a Congenital Exotropia.

Squint related to refractive errors
Refractive errors include short sight (myopia), long sight (hypermetropia) and astigmatism. When a child has a refractive error and they try to focus clearly, one of the eyes may turn in the wrong direction and they can sometimes develop a squint. This type of squint tends to develop in children over the age of two years, particularly in children who are long sighted. The squint most commonly involves one eye turning in (an esotropia).
Wearing glasses to correct the long sight will often correct the squint.

Other causes
The majority of children who develop a squint are otherwise healthy and have one of the above types of squint.
In some cases children may have a squint as part of another medical condition, commonly a genetic or brain condition, for example children with cerebral palsy, hydrocephalus or an injury to the brain.

What problems can be caused by a squint in a child?

Ambylopia
Ambylopia is sometimes called a ‘lazy eye’. It is a condition in which the vision in an eye is poor because of lack of use of the eye early in childhood.
The visual loss of ambylopia is permanent if not treated before the age of about seven years and after that cannot be corrected with the use of glasses.
In order to understand ambylopia it is helpful to understand how vision normally develops.
When a baby is born, although it can see, its visual system is not fully developed. The visual system (eyes and parts of the brain that interpret vision) continues to develop and mature until the age of about 7 years. In order to mature properly, the brain needs signals from the eyes about what they can see. If for any reason a young child does not use one or both of its eyes properly, then vision will not be learnt properly and it will develop poor vision, ambylopia. Essentially, ambylopia is a developmental problem of the brain and visual pathways, rather than the eye itself.
A squint is a common cause of ambylopia because the brain ignores the signals from the eye that turns in the wrong direction. As a result of this the visual system related to this eye fails to develop properly and it becomes an amblyopic eye with poor vision.
There are also other causes of ambylopia.

The cosmetic appearance of the squint
A squint can be a cosmetic problem as often people may notice the eye ‘wandering’. It is possible to correct a squint by operating on the muscles around the eye to try and realign them so that they work more effectively together and the eye does not ‘wander’.

Impaired depth perception
In eyes that work normally together, both eyes look and focus on the same spot, this is called binocular vision. The brain is able to combine the images seen from each eye to form a three-dimensional image and gives us the ability to perceive depth.
If a child has a squint, and the eyes do not point in the same direction, the brain learns to ignore the image from the squinting eye so that the child does not notice double vision from seeing two images. However if the eyes are not looking at the same point, then the child will not develop binocular vision and will not have a good sense of depth when looking at objects.
As adults they may not notice much problem from this as they will adapt, but some jobs do require good depth perception and they may be excluded from a small number of professions, those usually involving work with a microscope and very fine vision such as airline pilots. Eye doctors also require very fine vision!

How do you know if your child has a squint?
Firstly all newborn infants should have their eyes checked at birth and at a 6 to 8 week review to look for any evidence of a squint or other eye problems.
It is essential that all children have a pre-school eye check aged 4-5 years to check their vision and specifically look for a squint.
Obviously if your think your child has a squint you should take them to see an Ophthalmologist for a review.

How are squints treated?
Squints are treated with a combination of the following measures:
• If the child has a refractive error (is long or short sighted) they will usually be given glasses to try and improve the vision.
• If they appear to have some visual loss (ambylopia) in one eye, then the doctor will try to treat this, usually by getting the child to use a patch over the good eye for some hours every day to encourage the ‘lazy eye’ to work harder and improve the vision (a process known as patching).
• Surgery may be required to improve the appearance of the squint and in some cases may help the eyes work together and give some binocular vision.

Surgery for squint in children
In many cases an operation is needed to try and improve the cosmetic appearance of the eyes. Sometimes surgery can help give some degree of binocular vision, although this is often difficult.
The exact nature of the surgery depends on the type of squint, but in general it involves altering the position of one or more muscles where they attach onto the eye.
Squint surgery will usually reduce the amount of squint although sometimes more than one surgery may be needed. Sometimes even after successful surgery the squint can return years later and further surgery can be considered.
The surgery needs to be performed under general anaesthetic.