Causes of Lazy Eye
Numerous eye disorders are known to cause amblyopia (lazy eye). The main causes are:
A squint is a condition where the eyes do not work together to look in the same direction. Whilst one eye may look straight ahead, the other eye turns to point outwards, inwards, upwards or downwards. As the eyes are not aligned, they focus on different things, causing the brain to ignore the signals from one of the eyes to avoid seeing double. This means that only one eye will focus on an object. Most cases of squint occur in early childhood – the crucial time when the brain learns to see.
In some cases of squint, the vision in each eye remains normal. The eye that is used to focus will swap from time to time. As both eyes take turns doing some focusing, the visual pathways develop from both eyes. However, in many cases of squint, one eye will remain the dominant, focusing eye. The other weaker (squinting) eye is not used to focus, and the brain ignores the signals from this eye. This lack of use means that the non-dominant eye fails to develop the normal visual pathways in childhood and amblyopia develops.
Refractive Errors – Particularly Anisometropia
Refractive errors are eyesight problems caused by poor focusing of light through the eye’s lens. Refractive errors include: short sight (myopia), long sight (hypermetropia) and astigmatism.
When refractive errors occur, they generally occur in both eyes. Anisometropia can occur when there is a difference of refraction between the two eyes. In anisometropia, one eye may be myopic (short-sighted), and the other hypermetropic (long-sighted). If this difference is large, the brain cannot recognise the images coming from both eyes, and will choose to ignore one the signals. Usually the brain will select the better of the two eyes. The other eye (often the most long-sighted one) then becomes amblyopic (lazy).
Refractive errors can usually be corrected with glasses. Prescription lenses change how the lens of the eye focuses light. A parent may not realise their child has a refractive error unless their eyes are tested. This is particularly the case if the child has anisometropia. One eye’s vision might be good enough vision to get by, and without anyone realising, amblyopia may develop in the eye not being used.
Other Disorders That Prevent Clear Vision
Any disorder in a young child that prevents good vision can lead to amblyopia as the brain fails to develop the visual pathways. This is known as stimulus deprivation amblyopia. For example, acataract in the lens of an eye or a scarred cornea can stop light getting to the back of the eye. Even a droopy eyelid can cause amblyopia if it covers enough of the eye to prevent it seeing properly.
About 1 in 25 children develop some level of amblyopia (lazy eye). It is the most common condition treated by paediatric ophthalmologists (eye surgeons).
Diagnosis Of Lazy Eye
Amblyopia can be diagnosed by examining the eyes and testing vision. Depending on the age of the child, there are different techniques are used to test vision. Children with a known squint are monitored carefully to see if amblyopia develops.
Children in the UK are usually offered a routine preschool vision check. One of the main reasons for this is to detect amblyopia whilst it is still treatable. However, even if your child has had their eyes checked in the past, tell your doctor if you suspect that vision in one or both eyes has become poor.
A baby or child with a suspected amblyopia is usually referred to an orthoptist, an eye care professional specialising in the diagnosis and management of binocular vision problems. The orthoptist will assess and manage children with squint and amblyopia. If necessary, they will refer a child to an ophthalmologist for further assessment and treatment.
If you have permanent amblyopia, you do not see properly out of one eye. The range of visual impairment can vary. Although you can see well enough out of one eye to get by, it is always best to have two fully functioning eyes.
Some of the problems that are associated with amblyopia include a poor sense of depth when looking at objects and trouble judging distances. You are unable do some jobs if you have good vision in only one eye. If you only have good vision in one eye, you have a risk of severe sight problems if you have an injury or disease of the good eye later in life. So, treatment is usually always advised if it is likely to restore vision.
Treatment Of Lazy Eye
Correcting The Underlying Eye Disorders
Refractive errors such as short or long sight can be corrected with prescription glasses. Improvement in eyesight after being fitted with glasses can take 4 -6 months. Cataracts can be treated with an operation.
Making The Affected Eye Work
The main treatment for amblyopia involves restricting the use of the good eye. This then forces the affected eye to work. If this is done early enough in childhood, the visual development will usually improve, often up to a normal level.
This treatment, know as eye patching involves using a patch to cover the good eye, forcing the amblyopic (lazy) eye to see. Eye patches are soft, with sticky edges that fix them to the skin surrounding the eyelids.
The length of treatment with an eye patch dependents on the age of the child and the severity of the amblyopia. Treatment is continued until either the vision is normal, or until there is no further improvement. Usually check ups would be scheduled for every three months. If the vision is normal or stable for six months, use of the eye patch may be discontinued. If your child has had cataracts, full-time eye patching may be recommended up to the age of seven years. Short breaks are needed over this time to prevent the good eye, which is under the patch, from becoming amblyopic due to disuse. It may take several weeks or several months for eye patching to be successful. On average, patches should be worn for between 2 and 6 hours per day. In some severe cases they may have to be worn for most of the day.
Your child will be followed up usually until around eight years of age. This is to make sure that the treated eye is still working properly, and does not become amblyopic again. Sometimes, further patch treatment is needed before the vision pathways in the brain are set and cannot be changed.
Other treatments for amblyopia include eye drops and glasses. Eye drops may be used to blur the vision in the good eye instead of an eye patch. This can be useful if a child feels self conscious about wearing a patch. Once drops are put in a child’s eye, the child can’t change the blurring of vision; but will simply wear off over several hours. You might have to put the drops in your child’s eye each day, though sometimes it can be done just at weekends. The eye drops used to blur the vision usually contain a medicine called atropine. This can occasionally cause side-effects such as eye irritation, reddening of the skin, a fast heartbeat (tachycardia) and hyperactivity.
Another option is to be fitted with glasses with one frosted lens to prevent the good eye from seeing clearly. One problem with this method is that the child may look around the lens, defeating the object of preventing the eye from seeing.
Vision therapy can be used as a supplement treatment to maintain the progress achieved by eye patching. This involves playing visually demanding games with a child to work the affected eye even harder. Your child should do close-up activities when wearing a patch. Activities such as drawing, reading and school work all involve a lot of detail and work the eye well.
As a rule, the younger a child is treated, the quicker the vision is likely to improve, and the better the chance of restoring full normal vision. If treatment is started before the age of about 6-7 years then there is a very good chance of restoring normal vision. If treatment is started when a child is older it is still possible to gain some improvement in vision, but full normal vision is unlikely to be achieved.
About 1 in 4 children develop a recurrence of amblyopia once treatment is stopped.
The risk is higher if patching is stopped suddenly, and is the reason for careful monitoring.
For this reason, it is very important to follow the advice given to you by an orthoptist or ophthalmologist carefully. The most common reason for a failed treatment is because the patch has not been worn correctly or for long enough. As your child grows older, their vision pathways will become fully developed. Once this happens, it is impossible to change, so early patching is essential.
Hard work and persistence with treatment can reward the child with the long-term benefit of good vision. Something that they will come to appreciate long after the treatment is over. But, it can be difficult to persuade a young child to wear an eye patch. The patch may be annoying, and they are likely to try and take it off. From a child’s perspective, you are temporarily making their sight worse whilst they are wearing the patch. You have covered their good eye which sees well and are forcing them to the other eye which is much weaker. This can be very difficult for a young child to understand. Rewards, such as stickers or star charts, or making a game out of it are some techniques that can be used to encourage them to wear their patch. It is normally easier to patch a baby’s eye, as they are less able to remove it. If you are struggling to get your child to wear the patch properly, your ophthalmologist or orthoptist may suggest using drops or another method to make the amblyopic eye work.
If other treatments are unsuccessful, surgery may be necessary to correct a squint. Surgery will help to improve the alignment of the eyes and help the eyes work together.
Surgery involves moving the muscles attached to the outside of the eye to a new position. It may be necessary to operate on both eyes to balance them, even if the squint is only in one eye.
The operation is carried out under general anaesthetic and usually takes less than an hour to perform. It is often carried out as a day case, so your child can go home the same day. You may be able to accompany your child to the operating theatre and stay with them until they have been given the anaesthetic. A nurse will be with your child throughout the procedure.
During the operation, your child’s eye will be kept open using an instrument called a lid speculum. The Ophthalmologist will detach one part of the muscle connected to your child’s eye and will either move it backwards to weaken the pulling effect, or shorten it to increase the pulling effect. Once the correction has been made, the muscles will be sewn back into place using dissolvable stitches.
As with any kind of operation, there is a risk that problems will arise due to surgery to fix a squint.
If you or your child are having surgery for a squint, ask your Consultant to discuss possible risks with you before the operation.
Risks of eye surgery include:
- The possibility of further surgery, which is sometimes needed if the squint is severe.
- The eye may remain red for a long time after the operation. This is rare, but it may be caused by scar tissue forming on the surface of the eye.
- Double vision may occur after the operation. This usually resolves after a week or so.
- The squint may recur and another operation may be needed.
- One of the eye muscles may slip after the operation, although this is very rare. This makes the eye point inwards or outwards (depending on which muscle has slipped) and can impair eye movement. It may need to be operated on again.
- In rare cases, the inside of the eye can be damaged during surgery.
- An infection may develop after the operation. This is possible with any type of surgery. In the case of eye surgery, eye drops or ointment can be used to reduce the risk.
One study that looked at squint surgery for adults estimated that around one in five people may need more than one operation to treat their squint successfully. Double vision occurred in less than 1 in 100 cases. This usually either improves with time, or it can be treated with further surgery, for example.
In children, it is more common to need another operation to correct the squint, particularly if the first operation was carried out when the child was very young. Some studies have found that around 6 out of 10 children who have squint surgery at about one year of age need to have another operation at some point.
Other complications in children are usually rare, but you should ask your ophthalmologist for more information.
It can take several weeks to fully recover from corrective eye surgery. After surgery, you or your child may have a sore eye for a few days. The pain can be treated using simple painkillers, such as paracetamol. Children under 16 years of age should not be given aspirin. If the pain does not improve, speak to your eye care specialist or visit your GP.
Following eye surgery, a pad may be put over the affected eye, which will usually be removed before you or your child are discharged from hospital. There is no need to wear a patch or bandage at home and you can return to daily activities, such as reading, as soon as you feel able to. The aim is to get the eyes working normally as quickly as possible.
Your care team will be able to give you more specific advice about returning home after an eye operation, but some general tips include:
- you or your child may not feel like eating, but you should drink water at regular intervals
- the stitches can take up to six weeks to dissolve and it may feel like there is a bit of grit in the eye or the eye may be itchy – try not to rub it
- avoid washing your hair for a few days and try not to get any soap or shampoo in the eye
- your child should not play in sand or use face paint for two weeks after the operation
- you or your child will need to go back to your eye care specialist for regular follow-up visits
- if you or your child wore glasses before the operation, it is likely that you will still need to wear them after the procedure
Returning To School Or Work
Your child should be able to return to school or nursery about a week after surgery. If you have had surgery, you should also be able to return to work after about a week.
After surgery, you or your child should avoid playing sports for around two weeks. You may need to avoid contact sports, such as rugby, for up to a month. Swimming should be avoided for at least a month after the operation.
If you have had surgery to correct a squint and you drive, you should ask your surgeon when you can drive again. You should not drive if you have double vision.
Our Appointments Team have a dedicated and caring approach to finding you the earliest appointment possible with the best specialist.
If you do not have a GP, then we have an in-house private GP practice that you can use. Alternatively we can suggest the most appropriate course of action for you to take, given your location and individual circumstance.
If you have medical insurance (e.g. Bupa, Axa PPP, Norwich Union), you will need to contact your insurer to get authorisation for any treatment and, in most cases, you will require a referral letter from your GP.