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Elementary Science Education

Concept of how the eye functions

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      Bernard Nebel

      To convey the basic way the eye functions, first demonstrate how a lens, e.g., a pocket magnifier, will cast an image of whatever is in front of it onto a piece of paper a sort short distance (one to two inches) behind it. This is the principle of the eye’s anatomy. The cornea and lens of the eye act as a single lens and cast an image of what is being looked at onto the retina at the back of eye. The retina of the eye is a bed of millions of photosensitive cells packed side by side. (Photosensitive means that the cell absorbs light and that absorbed light energy causes it to send nerve impulses according to the intensity and color of the light absorbed.) Thus each photosensitive cell in retina (a rod or cone) sends out nerve impulses according to the color and brightness of the light falling on that pixel of the image falling on it. The nerve impulses from the million or more rods and cones, each transmitting a code of impulses specifying the brightness and color of light falling in its pixel, travel down the bundle of nerves (the optic nerve) to the brain. The brain (by some mechanism not yet understood) translates these millions of nerve impulses from the eyes into our sensation of seeing. (Please relay questions that this brings up.)

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