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.
How do our eyes work?
When light enters the front of the eye through the pupil, the muscles inside the eye squeeze or relax to help the lens focus the image onto the retina.
The eyes themselves are moved by muscles, which allow us to look up, down and from side to side without moving our head. There are six muscles attached to the eye in pairs, each of which can move the eye in one direction.
Normally, both eyes work together to form picture on the retina which is then interpreted by the brain. As each eye sees a slightly different picture, the resulting image is in three-dimensions (binocular vision). This allows us to work out which object is nearer or further away (depth of vision).
How is it diagnosed?
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.
Many parents also notice that their child is squinting and take him or her to the GP. Again, if the GP suspects that your child has a squint, you will be referred 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.
What causes squints?
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.
How common are squints, and whom do they affect?
Squints are quite common in children, affecting around two to three per cent of children. Squints can affect anyone - they do not affect boys more than girls, or one race more than another.
How are squints treated?
There are several methods of treating a squint. The aim of all methods of treatment is to align the eyes so that they look normal and work properly. Non-surgical methods like glasses or patches are tried first.
An operation is only considered if these methods do not correct the squint.
The squint operation
What happens before the operation?
The operation is usually carried out as a day case, which means your child will have the operation and go home later the same day. Occasionally, children have to stay in overnight if they feel sick after the operation or have a medical condition that requires monitoring overnight after an anaesthetic.
You will have received information about how to prepare your child in your admission letter. Your child should not have had anything to eat or drink beforehand from the time set out in the letter. It is important to follow these instructions - otherwise your child’s operation may need to be delayed or even cancelled.
On the day your child comes into hospital for the operation, the surgeon will explain about the operation in more detail, discuss any worries you might have and ask you to sign a consent form giving your permission for the operation.
An anaesthetist will also see you to explain about your child’s anaesthetic in more detail. If your child has any medical problems, such as allergies, please tell the doctors.
You will be able to go with your child to the operating theatre and stay until he or she has been given the anaesthetic.
What does the operation involve?
The squint operation is carried out under a general anaesthetic and usually takes between 30 minutes and two hours.
The eye surgeon moves the muscles connected to the eye so that they are strengthened or weakened. This stops the muscles pulling the eye out of alignment. The number of muscles the surgeon moves depends on the type of squint your child has.
In some cases the surgery performed is done using adjustable sutures. This is usually only used in older children. Your surgeon will explain if it is appropriate for your child and what it entails.
Are there any risks?
Over two hundred squint operations are carried out each year by our experienced eye surgeons at Great Ormond Street Hospital, and the risk of complications is very small. However, you should be aware of the following:
- Every anaesthetic carries a risk, but this is very small. Your child’s anaesthetist is a doctor who is trained to deal with any complications and all children are fully monitored throughout the operation. After an anaesthetic, your child may feel sick. Your child may also have a headache, sore throat or feel dizzy. These side effects are usually short-lived.
- There is a risk of more marked bleeding which affects around one in 30 children and the ‘white’ of the eye is always red at the site of the muscle operation. The bleeding is not severe, and usually shows up as a red mark on the white of the eye or a bruise underneath the eye. This usually clears up without the need for any further treatment.
- Infection is a risk with any operation. Signs of infection include redness, swelling and oozing. These usually show up on the first to third day after the operation. It is quite normal for your child’s eye to be sticky first thing in the morning after getting up, but oozing that continues throughout the day may be a sign of infection. These signs of infection are easily treated with a course of antibiotics and very rarely cause any long-term problems. In one in 20,000 cases, the infection can get into the eye, needing urgent treatment.
- Despite careful measurements before and during the operation, there is always a chance that the muscles will be overstrengthened or overweakened by the operation. This is rarely serious enough to need a second operation in a short time, but further operations may be needed later in childhood in up to one third of children.
- On rare occasions, one of the eye muscles slips after the operation. This will make the eye point outwards or inwards (depending on the muscle that has slipped) and not move fully. If this happens, your child may need a further operation under general anaesthetic, usually straightaway.
- There is a very small chance that the retina of the eye will be damaged during the operation. The eye surgeon can see whether this has happened and treat it during the same operation. This will not leave any mark outside the eye, but usually leaves a tiny scar on the retina. This does not usually affect your child’s vision.
What happens after the operation?
You will be able to go to the recovery room to be with your child when he or she wakes up. Your child will come back to the ward to wake up fully from the anaesthetic. Their eyes will probably appear quite red to begin with, but this settles down in time.
Your child will have been given pain-relieving medications during the operation, but these will begin to wear off. Your child will need to have regular pain relief for at least three days, in the form of eye drops and paracetamol.
Some of our surgeons use cold compresses for 24-48 hours after the operation to reduce swelling. You will be instructed as to what to do if necessary. We will give you the medications to take home with you.
For instructions on how to put in eye drops, please see our leaflet.
As well as the medications, distracting your child by playing games, watching TV or reading together can also help to keep your child’s mind off the pain.
Your child may feel quite sick for the first 24 hours. This is due to the combination of having had an eye operation and an anaesthetic. This will usually pass, but some children may need some anti-sickness medications.
You and your child will be able to leave the ward as soon as the anaesthetic has worn off and your child has had a drink. The surgeon will also check that your child is fine to return home.
When you go home
You should encourage, but not force, your child to drink. As long as your child is drinking, it does not matter if they do not feel like eating for the first couple of days.
They may complain about having double vision. This is a normal side effect of any eye operation and will not last long.
Your child will have some tiny stitches in his or her eye. These stitches can take up to six weeks to dissolve. They may make your child feel like there is a piece of grit in his or her eye, but try to stop any rubbing as this will make it feel worse.
Your child should stay away from school or nursery until they are comfortable but should avoid swimming for a couple of weeks after the operation.
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.