What Disorders Can Cause Amblyopia

"What disorders can cause amblyopia?

Various eye disorders can cause amblyopia. The three main causes are as follows:

Squint (strabismus)
A squint is a condition where the eyes do not look in the same direction. That is, when one eye looks straight ahead the other eye is pointing inwards, outward, up or down. As the eyes are not straight (aligned) they focus on different points or objects. Because of this, the brain ignores the signals coming from one of the eyes to avoid seeing double. So, just one eye is used to focus on objects. Most cases of squint occur in early childhood - the critical time when the brain is learning to see.
In some cases of squint, the vision in each eye remains fine. In these cases the eye that is used to focus switches from time to time. Therefore, the visual pathways develop from each eye. In many cases of squint, one eye remains the dominant focusing eye. The other 'turned' eye is not used to focus and the brain ignores the signals from this eye. This non-dominant eye then fails to develop the normal visual pathways in childhood and amblyopia develops.

Refractive errors - particularly anisometropia
Refractive errors include: short sight (myopia), long sight (hypermetropia) and astigmatism. These are conditions that are due to poor focusing of light through the lens in the eye. If you have a refractive error in one eye, often the other eye is the same. However, a situation called anisometropia means that there is a difference of refraction in the two eyes.

For example, a child may be much more longsighted on one eye compared to the other. In this situation, the brain tends to ignore the signals coming from the eye with the worst refractive error (in this case, the eye that is most longsighted). Amblyopia may then develop in this eye.

Refractive errors can usually be corrected with glasses. However, unless vision is tested, a parent or guardian may not realise that their child has a refractive error. In particular, if the child has anisometropia and one eye is 'not bad' with good enough vision to to get by with. Without anyone realising, amblyopia may be developing in the eye not being used. Therefore, Early Eye tests are recommended. Even if there are no complaints from the child.

Other disorders that prevents clear vision
Any disorder in a young child that prevents good vision can lead to amblyopia as the brain fails to learn the visual pathways. For example, a cataract in a lens of an eye or a scarred cornea stops light getting to the back of the eye. This is why it is important to remove a cataract in a child as early as possible."