LAZY EYE
Amblyopia is an early childhood condition where the childs 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 1 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 childs vision develops normally. If there is a problem with this development, it may result in impaired vision (amblyopia).
The better working eye is patched to stimulate the weaker eye to work
Symptoms
If your child has amblyopia she/he does 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).
There are a number of different eye disorders that can cause amblyopia including:
Strabismic Amblyopia
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
Anisometropic amblyopia is where a refractive error (spectacle power 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
Ametropic amblyopia is a reduction in the vision of both eyes. It usually occurs when a child has large, uncorrected refractive errors(spectacle power0. 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
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:
- An eye disease such as a corneal ulcer or scar,
- A congenital cataract (clouding of the lens of the eye present from birth),
- A droopy eye lid (ptosis or blepharoptosis),
- Glaucoma
Stimulus deprivation amblyopia can also be caused by an injury, or surgery, to the eye.
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