Sight is the elementary product of each eye.
Vision is the highest order product of the brain, dependent on the precise teaming of both eyes. This teaming is called Binocularity . Each eye perceives a separate and distinct image that must be interpreted by the brain as one image so that the brain can in turn coordinate body movements and spatial orientation. This teaming must be precise for the brain to fuse the images - no slack is allowed. Often, because the precision is so critical, when the two eyes do not work as a perfect team, the brain receives conflicting messages creating confusion.