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Why Do You Have Two Eyes?
Do You Believe That Vision Is Your Most Important Sense? Then You Need To Learn How to Protect Your EyeSight.
By: Bill Coughlin
But to have a really terrific field of view, wouldn’t you design the system to have on eye mounted on a finger like stalk atop your head to see all around? Wouldn’t it be nice to have the ability to see behind your back? The way it is now, there has to be an elaborate neck joint complex so that you can turn your head to get a reasonable near 360-degree panorama. Yet nature evolved into our present set up.
Actually, by itself, a very wide field of view is not all that beneficial. While it’s good for noticing movement and general shapes, it’s very poor for seeing details. (Try threading a needle out of the corner of your eye.)
Seeing movement is adequate for a frog since it merely triggers a reflex action to catch a fly, but for us its important to know what caused that movement. Is it a charging rhinoceros or only the shadow of a bird? To make this vital decision we must see it in detail. Learn more at http://www.protect-
Why can’t we see in detail over the entire field of view?
Very simply, the limited size of the brain.
The retinas area of detailed sight is the macula, which is about 1/20th of an inch in diameter. The flood of nerve signals from this tiny area alone keeps a large part of the brain occupied with interpreting the visual meaning. The visual cortex allocates about 35 times as much space to the fovea as the rest of the retina. If the entire retina had the sight property of the macula, the eye would have to be much bigger and the brain logarithmically larger (room-sign). Its doubtful if you could even attend to so much information.
Our vision is actually an adroit compromise. To the sides we have a reasonable field of view without much detail; at the macula we have a very limited view with marvelous detail.
It would be possible, thought, to have this arrangement with just one eye bulging out of the center of the forehead. That’s impractical because the eye would be very susceptible to injury. So the eye is placed within a bony vault for maximum protection. If you put your mind to it, you could come up with several alternate placements for the eyes – fore and aft, for instance. But there is a very distinctive advantage to frontally placed eyes with overlapping fields of view – depth perception.
Before you say, is that all? Remember that nature thinks so much of stereoscopic vision that a very elaborate system is involved to produce it.
The retina is divided almost exactly down the middle with the nerve fibers from the outer half of each eye connecting to the same side of the brain; the nerve fibers from the nasal side cross over and connect on the opposite sides of the brain. This seems like a curious arrangement, but it’s not the crossing that curious (your left hand is controlled by the right side of the brain). The nerve fibers, which don’t cross, are part of the secret of depth perception.
Because the eyes are about two and one half inches apart, each retina receives a slightly different image. You can easily prove this if you hold your fingers 8 inches in front of you nose and alternately close each eye. The position of the finger will seem to shift back and forth. Within the brain there are special cells, which match the offset images from the two eyes to yield the sense of solid depth.
That is why you have two eyes. To learn more please visit http://www.protect-
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What we feed our bodies feeds our eyes. Many of the vitamins and minerals in our bodies are found in much higher concentrations in our eyes, so a diet lacking in these vitamins and minerals can lead to vision problems as we grow older.