Amblyopia refers to diminished vision in either one or both eyes, for which no cause can be discovered upon examination of the eye. Amblyopia is the medical term used when the vision in one of the eyes is reduced because the eye and the brain are not working together properly. The eye itself looks normal, but it is not being used normally because the brain is favoring the other eye. This condition is also sometimes called lazy eye.
Lazy eye is a common non-medical term used to describe amblyopia because the eye with poorer vision does not seem to be doing its job of seeing. Amblyopia is the most common cause of impaired vision in childhood. It affects approximately two or three out of every 100 children. Vision is a combination of the clarity of the images of the eyes (visual acuity) and the processing of those images by the brain. If the images produced by the two eyes are substantially different, the brain may not be able to fuse the images. Instead of seeing two different images or double vision (diplopia), the brain suppresses the blurrier image. This suppression can lead to amblyopia. During the first few years of life, preferring one eye over the other may lead to poor visual development in the blurrier eye. Unless it is treated successfully in early childhood, amblyopia usually persists into adulthood and is the most frequent cause of monocular (one eye) visual impairment among children.
The prevalence of amblyopia is difficult to assess, with estimates ranging from 1.0 to 3.5 percent in healthy children to 4.0 to 5.3 percent in children with other vision problems. It is seen in similar numbers in both sexes and in all races.