There can be little doubt how important our eyes are to us. It can be seen in the way we use the word everyday. There is “eye of the storm”,”apple of my eye”, “I have my eye on you”, “for your eyes only” and the list goes one endlessly. The tongue is to taste as the eye is to vision but unlike the tongue, the eye is an organ. We all know somethings about the eye but other things we think we know are not true.
First, the eyes are not round like golf balls. If they were they would get knocked out of our head much more often. The eye is a good bit bigger at the back but that is really one of the least interesting thing about it. What is much more interesting is that we see upside down. After the image passes through the lens it projects onto the back of the eye. At that point the image is upside down. The optic nerve picks up on the signal through rods and cones and electrochemically sends the information to the brain where it is turned back right side up.
The iris, the colored part of the eye, is what the eye uses to control the amount of incoming light. This is need because it has a static contrast ratio. In terms of a camera lens it is 6 ½ fstops. Because we can see in variable amounts of light it can range from f/8.3 in dim areas but can contract in the brightest to f2.1.
Between the rods and cones, we see both light and color, however seeing in dim light is on in black and white. Once it is bight enough we can see up to 10,000,000 shades of color. The eyes are also very sensitive to light. In absolute darkness, even the light of a candle can be noticed for miles. The key is absolute darkness and that means even star light or light pollution from 1,000′s of mile away means it is not absolute darkness. Except for deep caves, it is not found in nature.
Despite the fact that we have a field of view of up to 90% in some directions we can only truly focus on about 2 degrees. More than that we have to move our eyes. The area of sharp focus is known as the fovea and is one of the most important part of vision.