Decreased eyesight due to abnormal visual development. A lazy eye (amblyopia) happens when the vision of one of your eyes doesn't develop the way it should. Lazy eye (amblyopia) is reduced vision in one eye caused by abnormal visual development early in life. Lazy eye, also known as amblyopia, is an early childhood condition in which a child's eyesight does not develop as it should in one eye. Amblyopia (also called lazy eye) is a type of poor vision that happens in just 1 eye. Amblyopia is when vision in one or both eyes does not develop properly during childhood.