Eyes
Eyes are a very complex and important sense organ. They have the greatest detection range and greatest adaptability of all the senses. By perceiving incident light we can read, see colors, observe landscapes, see distant stars and even detect danger or kindness in another person. About 300 different hues or shades of color can be discerned.
Physiologically, 70% of all our sense receptors are in our eyes. Visible light is a very small section of the Electromagnetic Spectrum. This EMS goes from extremely small gamma rays to very long waves of several hundred meters. The portion of the EMS that allows us to see is very narrow. A centimeter is one hundredth of a meter, less than half an inch. Divide the centimeter into 10 equal pieces and you get millimeters. Take one of those tiny millimeter pieces and cut it into 1000 slices and you get micrometers. If you cut it into a million slices and you get nanometers. But if you cut the millimeter into a billion slices you get picometers!!! Visible light for us has to be wavelengths between 400 and 750 nanometers, roughly 1/2000 of a millimeter. The rest of the EMS serves other purposes like radio waves, UV, X-rays, etc.
In our eyes the cornea handles refraction of light and protects the eyeball. The lens focusses images by varying the curvature and the shape of the lens. The muscles on each side vary the length of the lens from about 40 to about 70 micrometers. The shape then changes too. Professional photographers carry multiple lenses. Our eyes do it all with one lens automatically. The aqueous humor is a fluid that maintains the shape and internal pressure of the eyeball. The iris controls the amount of light entering the eye. It is like a diaphragm that regulates the size of the aperture (pupil) according to the light’s brightness. Tear ducts lubricate the eyeball with the help of the eyelids.
The retina contains photo-receptors – about 110 million rods and 6 million cones. One square millimeter on the retina contains an estimated 400,000 optical sensors. They collect and convert optical signals from visible light into chemical and subsequently electrical signals. The optic nerve sends these to the brain along a 2 mm thick nerve fiber. The decoding in the brain is another fantastically complex matter.
In addition to all the above, our eyes and face can convey feelings and detect emotions in another person. What we see also triggers a huge variety of feelings in us, good or bad.
When Darwin wrote in his book Origin of the Species, 1860’s, he had no idea just how complex the eye was yet here is what he said.
“To suppose that the eye with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest degree.”
The eye is an astounding design by a marvelous Creator!
Henry Wiebe
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