Binocular vision is one of the hallmarks of the human race that has bestowed on it the supremacy in the hierarchy of the animal kingdom. It is an asset with normal alignment of the two eyes, but becomes a liability when the alignment is lost.
Binocular Single Vision may be defined
as the state of simultaneous vision, which is achieved by the
coordinated use of both eyes, so that separate and slightly dissimilar
images arising in each eye are appreciated as a single image by the
process of fusion. Thus binocular vision implies fusion, the blending of
sight from the two eyes to form a single percept.