Of all the various parts of the body, the eyes are among the most wonderful. They are like two big, shiny-bright, beautiful windows through which all the marvelous sights of the world are viewed. We don’t appreciate our eyes sufficiently or we would take better care of them all the time. And if you want to find out what life would be like without your eyes, ask someone to blindfold you for a little while and let you walk about your room. Then you’ll learn a little bit about how difficult life is without vision. And you’ll discover how remarkable it is that unsighted people manage to get along so well without the use of their eves.
Did you know that unsighted people develop extra-fine hearing? And that their fingers and hands develop a much better sense of touch than those of us who can see? And that their ability to smell and taste things develops better? Well, that’s because all these other senses make up for the loss of sight. In a way, unsighted people “see” with their fingers and their ears and their noses and their tongues.
To understand how we see, we must learn something about the eye’s structure and how it works. The part of the eye we see in the face is only the front of the eye. The entire eye is shaped like a ball and is called the eyeball. Most of its lies inside the head in a special bony socket called the orbit. The front of the eyeball is covered by a clear, thin tissue, the cornea. You can look through a cornea as you can a piece of clear glass. The cornea covers the iris, the colored portion of the eye. Practically all babies are born with blue-colored eyes. Some eyes stay blue permanently. Others turn brown or green or gray when the child is several months old.
There is a black-looking opening in the center of the iris in everybody’s eyes. This is called the pupil, and it is the part of the eye through which light passes. The pupil gets smaller when exposed to bright light and larger in dim light. As a result of the iris’ opening and closing, the pupil looks larger or smaller, depending on how much or how little light there is.
The white part of the eye is called the sclera, and its job is to protect the rest of the eye. We don’t see through the white portions of our eyes.
Covering the front of the eye and the insides of the eyelids-except where the cornea is located-is a tissue called the conjunctiva. It protects the eyeball from infection, and from any dust and dirt that might be flying around.
Behind the iris and pupil in the center of the eye is an elliptical lens. It is like the lens of a camera, and like
camera’s lens it lets light pass through it. The lens can change its gape, getting rounder or flatter in order to bring the light into focus.
Light passes through the cornea and pupil, then through the lens, then through the clear fluid that fills the inside of the eyeball, and, finally, hits the retina in the very back part of the eyeball.
The retina, which lines the back of the eyeball just like wallpaper lines all, is the part of the eye with which we actually see. It is like the film in a camera. Without film in a camera, it doesn’t make any difference how often we click the shutter or how little or how much light passes through the lens no picture will develop. It’s the same with our eyes. If we didn’t have a retina, no picture would result.
But this isn’t the end of the story about how we see. When light hits the retina, the retina transmits a signal along the nerve of sight-called the optic nerve-to a special part of the brain. And when that special part of the brain receives the signal, we finally fee what the eye is looking at.
Let’s go over it once more:
1. Light passes through the cornea and pupil to the lens.
2. It passes through the lens and the fluid of the eyeball to the retina.
3. The retina picks up the light impulses and passes them along to the optic nerve.
4. The optic nerve sends the signals to the brain.
5. The brain translates the signals into sight.
In many parts of this book, we discuss how smart the brain is. Just think of it. In the flash of a second, your brain translates what it sees and you say to yourself, “I see a dog,” “I see a boat,” “I see boom,” or “I see Dad.” But what happens when you see something that isn’t familiar to you? You see it, but you don’t understand it. Suppose you look through a microscope and see all sorts of strange cells and germs. You would have to say to yourself, “I see it, but it doesn’t mean anything to me.”
So it is not only important for us to see things clearly. We must study carefully and understand what we see. Most children ask questions when they don’t understand what they are seeing. That’s what helps us to grow up to be smart.
The iris of the eye. like the iris of an automatic camera, closes down in strong light and opens up in weak light to control the amount of light that enters.