In normal vision, both eyes look at the same object. The images seen by the two eyes are fused into a single picture by the brain. If the eyes do not point at the same object, the image seen by each eye is different and cannot be fused. The result is double vision. Possibly because of a defect in the muscles which control the movement of the eyes or in the control of these muscles through the nerves and brain.
Double vision can be extremely discomforting.
The brain acts to alleviate the discomfort by suppressing, or blanking out, one of the images. In young children, if this suppression persists over a continued length of time, it can lead to an impairment of the development of the visual system. The suppressed eye may get to the point where it is unable to see well, no matter how good the spectacle or contact lens correction. Doctors call this condition amblyopia. Treatment of double vision consists of eye exercises, surgical straightening of the eye, special prism eyeglasses or a combination of the three.