Squints (strabismus): When a child develops a squint 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 squint.
This type of amblyopia is more commonly seen in children with an esotropia (convergent squint) compared to children who have an exotropia known as divergent squint.
High Refractive error in both eyes.
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.
Unequal refractive error: The other common cause of amblyopia is 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 squint and unequal refractive error.
Deprivation amblyopia: 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).