Amblyopia, sometimes called "lazy eye," is defective vision or blindness in an eye. Amblyopia happens when the eyes do not work together to develop the normal vision that fuses the image from each eye into one single image for the brain.
Sometimes both eyes cannot work together because of very poor vision in one eye. In most cases, however, the eyes are not aligned or "straight" (strabismus) and see two separate images. The result is double vision. Because the images from each eye are so different from each other, the disturbing second image is ignored by the brain. When it is not used, the "lazy eye" stops learning to see. Normal depth perception does not develop. In most cases, there is some peripheral vision but the sharper central vision is impaired.
Since the development of the eye is complete by the ages of six or seven, uncoordinated eyes in children must be treated immediately to prevent loss of sight. A child's eyes should be examined carefully at birth and there are eye tests that can be performed with very young children. Early detection and treatment are essential.