Amblyopia or lazy eye is a condition which affects children when the vision in one eye doesn’t develop properly. This means the child cannot see as clearly out of one of their eyes and relies more heavily on their ‘good’ eye. It is estimated between 1 in 30 and 1 in 50 children will develop a lazy eye, which is usually diagnosed around the age of 4.
Amblyopia is caused when the normal development of the eye is disrupted. If this happens as the child’s eye develops the signals sent to the brain can become disrupted and this affects the quality of the images interpreted by the brain. Over time the brain starts to ignore the poor quality images from the weaker eye and relies more heavily on the better eye.
The development of the child’s eye may be disrupted by common conditions such as a squint or refractive errors.
A squint is a common eye condition which causes one eye to look straight while the other looks off to the left, right, up or down. This affects approximately 1 in 20 children and means the brain receives two different images it cannot combine properly. In adults this leads to double vision, while in children the brain ignores the images sent from the eye with the squint which leads to a lazy eye. Some babies are born with a squint, but older children can develop a squint due to a refractive error in the eye.
Refractive errors are when the light rays entering the eye aren’t focused properly at the back of the eye, leading to blurred vision. This is due to the structure of the eye not developing properly. Refractive errors that may lead to a lazy eye are long-sightedness (hyperopia), short-sightedness (myopia) or astigmatism.
Long-sightedness occurs when the eye develops too short so the lens of the eye is unable to focus the light correctly at the back of the eye (retina). This means the patient is unable to focus on close up objects but may be able to see objects in the distance clearer.
Short-sightedness occurs when the eye develops too long so the lens of the eye is unable to focus the light correctly at the back of the eye (retina). This means the patient is unable to focus on distant objects, but can see close up objects clearly.
Astigmatism refers to the shape of the cornea not developing correctly, leading to distorted and blurred vision.
These refractive errors can cause the brain to rely on the signals from one eye over the other, leading to a lazy eye.
Less common eye conditions which may lead to a lazy eye include childhood cataracts, a droopy eyelid (ptosis), or an eye disease which affects the cornea.
A lazy eye often doesn’t have any symptoms and children are often unaware that there is anything wrong with their vision or are unable to explain what’s wrong. Older children may notice difficulty reading, writing or drawing and may complain that they cannot see as clearly through one eye.
You may notice one of your child’s eyes looks different from the other however this is likely due to another condition which may lead to a lazy eye, such as a squint, refractive error or childhood cataracts (see above).
One way to check your child’s eyes for a lazy eye at home is by covering each eye, one at a time, with your hand. If they have a lazy eye they might not mind you covering it, but then object to you covering the good eye. If they push your hand away from one eye but not the other it may be a sign that they can see better out of one than the other, and you should take them for an eye test to check for a lazy eye.
Lazy eyes are normally diagnosed during routine eye tests before parents realise there is a problem. Children should have their eyes tests as soon as they are old enough, which is usually around 3.5 years old. It is difficult to treat a lazy eye after 4.5 years old so it is important to have an eye test done as early as possible. If you are concerned about your child’s eyesight visit your GP who can refer you to an eye specialist (ophthalmologist) for testing if necessary.
Most of the time it is possible to treat a lazy eye which is generally done in two steps, but this can vary based on the underlying cause of the lazy eye and how severe it is. If the underlying problem is a refractive error or squint it is usually corrected with glasses to focus the eye properly; which often helps to correct a squint as well. Glasses need to be worn continuously and checked regularly to ensure they are working properly and the prescription hasn’t changed. Your child may complain that they can see better without their glasses, this is because their eyes are used to working hard to focus and now they struggle to allow the glasses to focus for them. It is important to monitor them and ensure they wear their glasses consistently. In some cases glasses are enough to correct a lazy eye alone, but if not a second step of treatment is used.
Then the child is encouraged to use the affected eye again which can either be done by covering the stronger eye with an eye patch or with eye drops to temporarily impair the vision in the stronger eye. This is usually done for a few hours a day for several weeks, and the child should be encouraged to do close up activities such as reading or drawing to encourage the development of their lazy eye.
This treatment is generally affective but can take several months to be completely effective.
If the child has childhood cataracts which are affecting their vision it may be necessary to undergo surgery as soon as possible to remove the affected lens and replace it with a new one. Glasses may also need to be used after surgery depending on the other eye conditions your child may have.
It is possible for adults to develop amblyopia usually due to changes in their vision such as cataracts, which makes the vision in the affected eye much worse. Cataracts are when the lens of the eye becomes cloudy with age, distorting the vision and potentially leading to a lazy eye. Cataracts are treated with surgery to remove and replace the cloudy lens.
If your child has childhood cataracts which are affecting their vision and may be slowing down or stopping the normal development of the eye, surgery is usually recommended. This means the surgeon will make a small incision in the cornea, remove the affected lens and may replace it with a new artificial lens, before closing the incision with stitches which gradually dissolve. It is more common however in the case of small children to not insert and artificial lens and instead have the child wear contact lenses or glasses to allow the eye to focus. This results in clearer vision and allows the eye to develop properly.
Cataract surgery is generally successful with a low risk of complications. The most common risk is called posterior capsule opacification (PCO) a condition which affects the artificial lens implant (if used) and causes it to go cloudy.
Another risk is glaucoma which is when pressure builds in the eye which, if left untreated, can cause irreversible damage. Although there are some possible complications they can generally be treated with medication or further surgery.
Under the supervision of your optician one method of treatment for amblyopia is to exercise the effected eye in order to strengthen it. This involves the use of either an eye patch over the stronger eye or eye drops into the stronger eye which encourages the use of the lazy eye. This is usually done for a few hours per day and it is important to spend this time doing close up work such as reading to exercise the eye properly.
Whether glasses alone are enough to correct a lazy eye depends on the underlying cause and the severity of the condition. Glasses can correct amblyopia in some patients as the prescription lens helps correct some underlying causes of the lazy eye, for example a refractive error. Sometimes a second stage of treatment is needed to strengthen the lazy eye such as eye drops or an eye patch, which encourages the brain to make more use of the lazy eye. However if the underlying cause is a condition that cannot be corrected by glasses such as childhood cataracts or damage to the cornea other treatment may be necessary such as corrective surgery.
Strabismus or a squint is an eye condition which causes the eyes to point in different directions which is most common in young children but can also affect adults. If you have a squint one of your eyes may look up, down, left or right while the other looks straight. The cause of strabismus is not always known but in children they are often caused by other eye conditions such as myopia (short-sightedness), hyperopia (long-sightedness) or an astigmatism (which affects the shape of the cornea).
A lazy eye however is usually as a result of a refractive error or astigmatism and means one eye is weaker than the other, causing blurred vision in that eye. Amblyopia and strabismus may be related as the patient may have an underlying eye condition causing them, but they are not the same condition and do not have the same symptoms.
A lazy eye is when one eye is weaker than the other and so the brain begins to ignore the images sent from this eye and relies more heavily on the stronger eye. It is still possible to see out of the lazy eye and this is usually done with glasses or contact lenses, however without this treatment the signals from this eye will continue to be ignored and not used. A lazy eye does not mean blindness in one eye and is easily treatable in early childhood.