The problem starts when the pathways of vision in the brain don't grow strong enough. All babies are born with poor eyesight. As babies grow, their eyesight gets better.
Good eyesight needs a clear, focused image that is the same in both eyes.
If the image isn't clear in one eye, or if the image isn't the same in both eyes, the vision pathways won't develop right. In fact, the pathways may actually get worse. Anything that happens to blur the vision or cause the eyes to be crossed during childhood may cause amblyopia. For example, the image might be different in both eyes if the child has strabismus. Children who need glasses to see better, or have cataracts, a droopy eyelid, or crossed or wandering eyes may also get amblyopia.