subject: Binocular Vision, Stereo Vision - Why We Have One View of the World When We Have Two Eyes [print this page] Binocular Vision, Stereo Vision - Why We Have One View of the World When We Have Two Eyes
This ability to use two eyes to see an object as one is known aptly, as the binocular vision. What if we can see with only one eye? What will the world seem to us?
Indeed, having two eyes is better than one. They provide us stereo vision and depth perception. In laymen terms, it refers to the ability to see images as solid objects in 3-dimension and this in turn, helps us judge the depth, contrast and distance of things in our surrounding.
Separated by a nose and approximately a little more than two inches apart, each of our eyes views the same object from different angle or from a different perspective.
For instance, when you hold up an apple and look at it with just your right eye, the image will be different from the one you see with only your left. Not only that, you will notice that the position of the apple seems to have shifted, relative to the background. The apple will seem to be more to the left side when you look with your right eye, and conversely more to the right side when you look with your left.
Yet, when the two images are sent from our eyes to the brain, it processes the two as one.
There is a region in the back of the cerebral cortex called the visual cortex, where the brain processes vision. The neurons from the retina communicate over synaptic connections with neurons in the visual cortex, and these cortical neurons are either "monocular" or "binocular". For most people, the majority of neurons in the visual cortex are binocular and so they respond to nerve impulses to light coming from both eyes.
As the image of the apple from both eyes merged as one, it seems to us to be sharply-defined, detailed and depth-filled. You can see the light and shadow cast on the apple. It does not look flat.
However, there are some people who are not so lucky. People born with lazy eye or crossed eyes usually have to rely on using their better eye to look around. They cannot see normally through the two eyes together. The neurons in their visual cortex respond to either the left or right eye. This means a loss in the binocular vision.
Without binocular vision, they will find it difficult to watch 3-D movies. They will not enjoy any ball games as they find it hard to focus their eyes on the ball.
However, the good news is binocular vision can be improved with vision therapy. We should not let our vision problem from living a normal carefree life.
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