Amblyopia is an early childhood condition where the child's vision does not develop properly. It usually occurs in one eye, but it can occur in both eyes. Sometimes referred to as lazy eye, amblyopia affects about one in 25 children.
A baby is able to see as soon as it is born, and vision continues to develop up until around the age of seven or eight. After this, no further development occurs until sight deteriorates with age, or after eye injury or disease.
Light rays travel through the lens at the front of the eye, and form images on the retina, which is a light-sensitive surface at the back of the eye. The retina sends messages to the brain so that it recognises the objects we are seeing.
During early childhood it is important that clear images are formed in the eye and are sent to the brain, so that the child's vision develops normally. If there is a problem with this development, it may result in impaired vision (amblyopia).
There are a number of different eye disorders that can cause amblyopia including:
Strabismic amblyopia is the most common cause of lazy eye. The condition involves a squint (strabismus) in one eye, which is noticeable because the eyes look in different directions. For example, one eye may look straight ahead and the other may look inwards, outwards, up, or down. To avoid double vision, the brain ignores the signals from the eye with a squint, and only sees images from the normal eye. As the affected eye is not being used, over time the squinting eye will become lazy.
Anisometropic amblyopia is where a refractive error (poor focussing of light) occurs due to short-sightedness (myopia), long-sightedness (hypermetropia), or astigmatism (where the surface of the lens is uneven, causing blurred vision) and there is a difference of refraction in each eye. Usually, both eyes are affected to the same degree.
However, in anisometropic amblyopia, a child who has hypermetropia, for example, will be more long-sighted in one eye compared with the other. As a result, their brain will ignore the signals from the eye that has the biggest refractive error (is most long-sighted) and, as a result, amblyopia may develop in this eye.
Ametropic amblyopia is a reduction in the vision of both eyes. It usually occurs when a child has large, uncorrected refractive errors. The image that is produced on the retina, at the back of the eye, is constantly blurred as a result of undetected long-sightedness or astigmatism.
Stimulus deprivation amblyopia is the rarest form of amblyopia, but it is often the most severe. It is caused when one or both eyes are prevented from seeing and become lazy due to:
Stimulus deprivation amblyopia can also be caused by an injury or surgery to the eye.
Ideally, amblyopia needs to be diagnosed and treated as early as possible, preferably before the age of six. However, it can be difficult to know if a child has a lazy eye because they often do not realise there is anything wrong with their vision. Therefore, it is often not diagnosed until your child has their first eye test.
In the UK, children are usually given a routine eye examination before they start school. This means that if a child has amblyopia, it is possible to diagnose and treat the condition before it is too late.
If, from the results of your child's eye test, the eye specialist (ophthalmologist) suspects a lazy eye, a full eye examination will be carried out in order to make a firm diagnosis. Each eye will be tested separately to see if there is any serious long or short sightedness. Afterwards, both eyes will be tested together to see if there is a squint.
The structure of your child's eyes may also be examined to determine whether there are any abnormalities, such as astigmatism.
If your child has amblyopia they do not receive and send clear images. This means that your child is unable to focus properly with one of their eyes. However, the other eye will often make up for the problems in the affected eye, resulting in the affected eye becoming lazy.
Also, a child may not notice that there is a problem. Therefore, a lazy eye is often not diagnosed until the child has their first eye test.
As the affected eye is not able to send clear, sharp images to the brain, the main symptom of a lazy eye is blurred or double vision. Although, there are usually no physical symptoms of a lazy eye, some children may have a noticeable squint, a droopy eyelid or a cataract (clouding of the lens of the eye).
The younger the child is when a lazy eye is diagnosed, the more successful treatment is likely to be. If treatment is started after the age of eight, it is unlikely to be as successful.
The two main treatment options for amblyopia are:
Vision problems, such as long or short sightedness, can be corrected using glasses. However, you may not realise that your child has a vision problem unless their sight is tested. For example, if your child has anisometropia, the sight in one eye will be good and will become the main source of vision, but amblyopia may develop in the eye that is not being used. Cataracts can be removed to treat blurred and distorted vision.
A number of different treatments options can be used in order to make the affected eye work. These include: