Why has nature endowed man with two eyes? Why not one or more?

Why has nature endowed man with two eyes? Why not one or more? The first
thing one might think trying to answer this question would be that
nature gave us a second eye as "a spare" in case the first
becomes ill or lost. The answer though, is more complicated and
certainly much more interesting.

We live in a world of three dimensions. Objects around us are not all on
the same level, and in our daily activities we interact with things
that are at a different distance from us. Whether we are walking or
driving, or just trying to touch an object, our brain, in order to
coordinate our movements, must have the information of depth.

Both our eyes produce two different images for the objects that we see and
our brain makes the fusion of these two images into a
"three-dimensional" image, an image that gives a sense of
depth. To achieve this, certain conditions must be fulfilled.

First of all, each eye individually must have good vision. If, for example,
one eye has an uncorrected refractive error (it is blurred, without
using a lens) while the other is normal or has some other
abnormality, then the two images that are "produced" by the
eyes are significantly different, even if they target the same

Even worse, if the position of the eyes (controlled by the cranial nerves
III, IV and VI, which give commands to six oculomotor muscles) is not
even in the same direction, then the two images are completely

When the brain fails to fuse the two images from both our eyes, because
they are a lot different, it is forced to repel one and make
"unusable" the eye that produces it.

Unfortunately after early childhood such problems are very difficult to correct and
the eye which is not used and was "lazy", as we say, won’t
ever recover its functionality.

It is a duty of everyone, parents, teachers, pediatricians, family or
rural doctors, to recognize as quickly as possible these signs of
problems in vision and address the specialized pediatric
ophthalmologist to determine the appropriate treatment promptly.