Strabismus and amblyopia in children (squint and lazy eye)

This means that while one eye looks forwards to focus on an object, the other eye turns either inwards, outwards, upwards or downwards. The eyes do not work together as a pair all the time.

Most strabismus develops in young children. Strabismus can also develop in adults, but an adult will develop strabismus for different reasons than a child will. This information will focus on childhood strabismus.

For the purpose of this information, we will refer to the medical terms, strabismus for squint and amblyopia for lazy eye.

For further information on this topic, please download the full factsheet by clicking the link.

Most people have eyes that work together as a pair. When you look at an object your eyes will be pointing in the same direction and focusing at the same point. Your brain will receive similar but slightly different pictures from each eye so it can join them together to allow you to have binocular and three-dimensional (3D) vision. This allows you to have depth perception (also known as stereopsis) and to judge how far away things are.

The movement of each eye is controlled by six muscles that move your eyeball in different directions. The muscles for one eye also work and coordinate with the muscles from your other eye so that they can work together.

When you are born, your eyes and brain must learn to work together. As you grow you use your eyes to collect information which is sent to the brain to process and this builds up a connection between them. This connection between the eyes and the brain is known as the visual pathway.

The visual pathway develops throughout your childhood and up to the age of about eight years old. During this time, it’s important that your eyes send clear and similar images to your brain. The eyes and brain use your visual experiences to improve their coordination and allow your visual pathway to develop as fully as possible. This allows a good level of vision to develop in each eye separately as well as allowing the two eyes to work together as a pair to allow you to see in 3D.

After the age of about eight years old, the visual pathways and the "seeing" parts of the brain are nearly fully formed and are difficult to change. Therefore, it’s important to treat childhood vision problems before this age.

Strabismus is common and affects around three per hundred children in the UK (not far off an average of one child in every class of 30).

Strabismus is where one of your eyes points in a different direction from the other eye. This may be more noticeable when a child focuses on a small object, is tired or feeling unwell, although in some children the strabismus is noticeable when they are not focusing directly on something.

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 gets better by around two months and should be gone by the time they reach four months. If this isn't the case, you should speak to your GP or health visitor about a referral for a full assessment with your hospital eye department.

More commonly strabismus 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 strabismus, it’s important to have this checked by an optometrist (also known as an optician) as soon as possible. Children are entitled to a free NHS eye test. Your optometrist may be able to correct the strabismus (for example with glasses). If your optometrist cannot correct it, they will then be able to refer your child to the hospital eye clinic to be seen by an orthoptist (a professional who investigates and manages strabismus).

Your child’s strabismus may be described in different ways by the professionals looking after your child’s eyes. Some of the words you may hear will have particular meanings when used to describe the strabismus. The strabismus may be described depending on:

• When it can be seen: constant, if it is visible all the time, and intermittent if it comes and goes.
• The strabismus may be described as refractive if it is caused by a focusing problem and non-refractive if it isn't.
• Which eye appears to be affected: either left or right, or alternating, where the strabismus can alternate from one eye to the other.
• Which way the eye turns: if the turn is inwards it is called a convergent strabismus or esotropia, if the turn is outwards it is called a divergent strabismus or exotropia, if the turn is upwards it is called a hypertropia, if the turn is downwards it is called a hypotropia.

This means that your child's squint can be carefully categorised by the professionals involved and they may describe your child’s strabismus using a mixture of these words, for example, an “intermittent convergent squint”. Knowing the nature of your child's squint and labelling it as accurately as possible can help to decide how it can be dealt with.

Some common types of childhood strabismus include:

• Congenital or infantile esotropia. This is an inward turning strabismus which normally develops in the first six months of life.
• Accommodative esotropia. This type of strabismus is caused by long-sightedness (hypermetropia) which causes an inward turning strabismus. The strabismus can be improved or removed by wearing glasses.
• Non-accommodative esotropia. This type of inward turning squint usually develops in children between two and five years old, and is a strabismus which isn’t improved by wearing any glasses.
• Intermittent distance exotropia. This is an outward turning strabismus which comes and goes, usually being more apparent when a child is looking at things in 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.

The aims of treatment for strabismus in childhood are to make sure that the vision in each eye develops normally, thereby preventing the development of amblyopia and to help the two eyes work together so that binocular and 3D vision can develop as well as possible. For treatment to be successful, it needs to be given before the visual pathway finishes developing (ideally before the age of about eight years).

Some of the most common ways that squint can be treated include:

• Glasses
• Occlusion therapy (patching)
• Exercises
• Surgery

For more detailed information on the treatments for strabismus, please download the full factsheet in the link above.

If your child develops strabismus, 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 strabismus. They will use only the vision from their better/straight eye. The brain "switching off" the vision from the eye with strabismus 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.

Amblyopia (lazy eye) is a condition that can develop during childhood when one eye does not send a good clear image to the brain. This could be because of a strabismus or an inability to focus clearly. As the brain finds it difficult to fuse together the images from the better eye and the weaker eye, it learns to ignore the blurred image from the weaker eye over time. This means the visual pathway of the weaker eye won’t develop very well and the vision in that eye will be blurred even when your child is wearing the correct glasses. An eye which has amblyopia can be called an amblyopic eye or may be referred to as a "lazy" eye. Although the vision is not clear, the eye may still be completely healthy in many cases.

Strabismus may be noticed by parents, relatives, friends or your health visitor or GP. Routine checks to detect eye problems in babies and children are usually done at the new-born examination and at the six to eight week review. There should also be a routine eye screening for when children start school (at the age of between four and five years old) to ensure that their vision is good and that their eyes work together.

This screening is usually managed and sometimes carried out by professionals known as orthoptists, who detect and help manage any treatment needed for strabismus. Unfortunately, this screening may not happen in some parts of the country and if you are in any doubt about whether your child's vision has been checked, you should ask at your child's school or nursery.

If you are concerned about your child's eyes at any age before this check because you have noticed a squint or other symptoms, then you should discuss this with an optometrist or your child’s GP or health visitor and ask to be referred to an orthoptist.

• Orthoptists are usually based in the eye clinic at the hospital and are recommended to carry out or manage the children's screening service at four to five years old. They are experts in how the two eyes work together (known as binocular vision) and this includes strabismus, double vision and amblyopia. If your child is suspected to have any of these conditions, they are usually one of the first professionals they will see if they are referred to the hospital. Orthoptists are extremely skilled in testing vision in young children, diagnosing strabismus, prescribing patching therapy and any eye exercises that may help. Most hospital appointments about your child’s strabismus will be with an orthoptist.
• Ophthalmologists are hospital-based eye doctors. Their job is to diagnose eye conditions and perform any treatment or surgery that may be needed. If your child has been referred to the hospital for a strabismus, they may see an ophthalmologist to check the health of their eyes and make sure there is no underlying eye condition causing the strabismus.
• Optometrists (also known as opticians) are experts at testing your vision and prescribing glasses. They are also qualified to detect eye conditions or problems, including strabismus and binocular vision problems. If your child is prescribed glasses to help treat their strabismus then you may see an optometrist in the community or at the hospital to supply your child’s glasses. Optometrists can also manage some types of squint.
• Dispensing opticians are qualified in the dispensing and fitting of spectacles and can give professional advice about suitable frames and lenses for children. They usually work in community optical practices and in some hospital eye clinics.

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 strabismus or amblyopia is not picked up before the age of about eight years old, it is less likely that treatment will be as effective as if the problem is treated earlier. 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 strabismus or amblyopia since childhood that hasn’t been 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 strabismus or amblyopia, 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 if 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 roles in the forces require a certain level of vision to be reached in both eyes and for both eyes to be working together. Keeping this in mind can help you and your child plan their career choice for the future. You can ask your orthoptist or optometrist for more information about certain jobs and whether your child may be affected by this.

Sometimes adults who have had squint surgery as a child may need to have further surgery later in life to straighten the eyes again.

It’s completely natural to be worried when your child is diagnosed with strabismus or amblyopia, particularly if you haven’t noticed any problems with their eyes. It can be reassuring to know that prompt diagnosis and assessment of these conditions usually means that they can be dealt with and often treated successfully.

Children whose treatment isn’t as successful may have poor sight in one eye. This may not cause them any problems throughout their life as many people adjust very well to poor vision in one eye only. However, it’s important that someone with good vision in only one eye should have regular eye examinations with an optometrist to make sure that the eye they rely on is healthy. An optometrist will be able to give you advice on how often your child should have their eyes tested.