Childhood squint (strabismus)

Squint, also called strabismus, is an eye condition where the eyes do not look in the same direction as each other. This means that while one eye looks forwards to focus on an object, the other eye turns either inwards, outwards, upwards or downwards and do not work together as a pair all the time.

Most squints occur in young children. Sometimes when a child has a squint, the sight in the eye which turns may be weaker (this is called a “lazy eye”).

What causes childhood squint?

There are many different types of squint. For some children there will not be a particular cause for their squint. This is known as “idiopathic”, meaning there is an unknown cause.

Some common causes of squint can include:

  • Refractive errors (focusing problems)
    • Long-sightedness in children may cause a squint to develop where the eye turns in (esotropia).
    • Short Sightedness and astigmatism may cause the eyes to turn out (exotropia)
  • Eye conditions: Other eye conditions such as congenital cataract or retinal or optic nerve conditions can cause an eye to have poor vision. This can also cause a squint to develop in this eye.
  • Eye muscle problems: Some squints only occur when the eyes are looking in certain directions. These are an eye movement problem and don’t affect vision in the same way as other squints because the eyes are usually straight most of the time. Brown’s syndrome and Duane’s retraction syndrome are examples of eye conditions which can cause a squint only when looking in certain directions.

What are the risk factors for squint?

There are some risk factors that can increase the chances of a child developing a squint:

  1. Family history: Some types of squints can run in families, so if a parent has had a squint or needed glasses from an early age, there may be an increased chance that their child may also be affected.
  2. Prematurity or low birth weight: Children that are born early (before 32 weeks) may be at more risk of developing a squint. Babies with low birth weights are also more at risk of developing a squint.
  3. Other conditions: Children with conditions such as cerebral palsy and Down’s syndrome may also be more prone to develop a squint.

Squints can be constant or intermittent

What are some of the different types of squint?

Some common types of childhood squint include:

  1. Congenital or infantile esotropia: This is an inward turning squint which normally develops in the first six months of life. There is no known underlying cause
  2. Accommodative esotropia: This type of squint is caused by long-sightedness (hypermetropia) which causes an inward turning squint. The squint can be improved or removed by wearing glasses.
  3. Non-accommodative esotropia: This type of inward turning squint usually develops in children between 2-5 years old, and is a squint which isn’t improved by wearing any glasses.
  4. Intermittent distance exotropia: This is an outward turning squint which comes and goes, usually being more apparent when a child is looking at things into the distance. Commonly, parents may notice that the eye turns out when the child is tired, daydreaming or in bright sunlight. A child may also close or rub one eye when they are out in bright sunlight.

How can a squint affect vision?

If your child develops a squint it means each eye is looking in a different direction and their eyes are sending different pictures to the brain. Their brain finds it difficult to merge the two pictures into one clear image because the pictures are so different. This means their eyes have stopped working together and would ordinarily, in an adult, cause double vision. However, as your child’s visual system is still developing the brain can easily adapt to stop this double vision by ignoring the image coming from the eye with the squint. They will use only the vision from their better/straight eye. The brain “switching off” the vision from the squinting eye is called “suppression” and this may cause the vision in that eye to become poor because it is not being used.

Children can easily adapt to using one eye and it may not be obvious from how they are acting that they have any problems with their eyes and vision. This may only be detected by having your child’s eye tested by an eye health professional.

Timing of a squint

When your child is born their eyes and brains do not work well together. Over the first few months you may notice your baby’s eyes appear to squint or move separately from each other every now and again. This is normal and usually should get better by around two months and should be gone by the time they reache four months.

More commonly a squint will develop a little later in your child’s life often between the ages of 18 months and four years old. If you notice that your child appears to have a squint, it’s important to have this checked.

What is the outlook for children with squint?

The treatments for squint and amblyopia are generally very effective if the squint is detected and treated early. In these cases, most children will have good vision in each eye in the long-term.

If a squint or amblyopia is not picked up before the age of 7/8 years old then it can have a permanent effect on the vision in one eye. The level of vision in this eye will vary between individuals and some may retain a reasonable level of sight. Most people who have had a squint or lazy eye since childhood that wasn’t successfully treated are totally adapted to having poorer vision in one eye and it doesn’t cause them any problems day to day.

Poor vision in one eye can reduce depth perception which can cause difficulties with judging distances as well as activities such as catching a ball, or navigating steps. However, children with a lazy eye are totally adapted to this and their brain finds other ways of judging distances so these difficulties are generally not a problem. If your child has a squint or lazy eye, they won’t be able to fully see the 3D effects in 3D films.

In the future, even if they have reduced vision in one eye your child would still be able to drive a car as long as the vision in their remaining eye is unaffected by other eye conditions and meets the driving standard. Some professions, such as being a pilot, police officer, some professional drivers, or some areas of the forces require a certain level of vision to be reached in both eyes and both eyes working together. Keeping this in mind can help you and your child plan their career choice for the future.

11 year old girl with left eye exotropia

4 year old girl with right eye hypotropia, seen clearly when asked to look up.