Amblyopia: Introduction and Causes

Amblyopia is the medical term for a “lazy eye”. The reduced vision in an amblyopic eye occurs even though there is no structural abnormality of the eye. Amblyopia is responsible for more visual loss in childhood than all the other causes of visual loss combined.

Common causes of amblyopia include:

1. When a child develops a strabismus their brain is able to ‘turn off’ the image from one eye, preventing them from experiencing double vision. This process is known as suppression. As a consequence of suppressing the image from one eye the connections between this eye and the brain do not develop in the normal way and the vision in this eye is reduced. This is known as strabismic amblyopia, because it has arisen as a result of a strabismus.
   
   This type of amblyopia is more commonly seen in children with an esotropia (convergent strabismus) compared to children who have an exotropia known as divergent strabismus.
   
   
2. Both eyes may be significantly longsighted and or one or both eyes may have a high degree of astigmatism. These conditions can result in amblyopia because of the blurred image they produce.
   
   
3. When one eye is more long sighted, or (less commonly) short sighted than the fellow eye. The medical term for this unequal refractive error is anisometropia. This means that the more long or short sighted eye will be seeing a blurred image, compared to the fellow eye and the brain will choose to ignore this blurred image. In children with an esotropia their amblyopia is often due to a combination of their strabismus and unequal refractive error.
   
   
4. Deprivation amblyopia is caused by anything that deprives a child’s eye of visual experience. Causes of deprivation amblyopia include cataracts (cloudy lens) and a droopy eyelid (known as a ptosis).

In children who have the potential to develop stereopsis, their 3D vision will be better if they have good vision in both eyes. Perhaps the most important reason for treating amblyopia is to ensure that the vision is good enough in the amblyopic eye to enable the person to drive a car, work and live independently if they were to loose the vision in their other eye in later life.

Republished, with permission, from www.squintclinic.com.