What causes a lazy eye?

A child’s visual system develops from birth until about eight years of age. During this time the eyes learn to communicate with the brain. The optic nerves that connect the eyes to the brain gradually mature. This development is a vital part of achieving good vision. Eye problems during the first eight years of life can affect this development and cause a lazy eye, or Amblyopia.

Children who have one eye which is more long-sighted or more short-sighted than the other eye may develop a lazy eye, when the brain learns to ignore the eye with blurry vision, resulting in a lack of development in that eye. This happens because the brain needs to be able to combine the two images coming from the two eyes, into one, but if one image is blurry, the brain can’t fuse them. The easy solution becomes ignoring it.

A squint (a turn in one eye) is the other main cause of a lazy eye. The vision from the eye with the squint may be ignored by the brain, affecting the development of the visual system. So squints and lazy eyes are closely linked and are often found together.