How exactly are the eyes designed to give us depth perception?  First, both eyes must have normal or near normal vision to work together.  Glasses or contact lenses may be needed to obtain normal, or 20/20 vision.  Then, the eyes must be aligned in the skull so that they are facing in the same direction and are close enough together that each eye's peripheral vision, or side vision, overlaps considerably with that of the other.  If we cover one eye and then the other when looking at an object, we can tell that each eye is seeing the same object just a little differently.  As we cover and uncover each eye, it is as if each object moves a little to the right or to the left.  Therefore, each eye receives a slightly different image that is sent to the brain for processing.

The ability of the brain to process or blend these two similar images is called fusion. The brain must be able to maintain the blending of these images into one image as the eyes move together in various directions.  High-level fusion develops completely during childhood, usually between the ages of 5 and 9.
As you can see from reading about eye anatomy, there are many structures that are necessary to give us vision.  The human visual system is designed to give us depth perception, which means that we can tell which objects are in front of or behind other objects.  Depth perception is useful for doing simple tasks, such as pouring a cup of coffee or driving a car, and is even more important in tasks that require detailed eye-hand coordination, such as performing surgery.
Our two eyes provide peripheral vision, allowing us to see in 3 dimensions.
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