Some people have big ears, others have small ones; some people have long noses, others have short ones. And of course, some folks have ears and noses that are just about medium. But did you know that some people, including children, have “long eyeballs,” while others have “short eyeballs”? When the eyeball is longer than normal instead of being round in shape, people are nearsighted, and when their eyeballs are shorter than normal, they are farsighted. In other words, a nearsighted person has an eyeball that is a little bit egg-shaped, while a farsighted person has an eyeball that is flatter than the round shape of the perfect eyeball. Look at the drawings on page 32 and you will see the differences between the shapes of the normal eyeball, the nearsighted eyeball, and the farsighted eyeball.
The eye is very much like a camera. The round, black part in the center of the eye is called the pupil. It gets bigger in the dark to let more light into the eye, and it gets smaller in a bright light. The diaphragm of a camera works the same way. it is regulated so that the opening is larger in dim light and smaller in bright light.
The colored portion of the eye is called the iris and it is composed of a muscle that contracts and relaxes. When the iris muscle contracts, the pupil gets smaller; and when it relaxes, the pupil gets larger. You can see that for yourself very easily. Turn off the light in your room, so it is not very bright. Next, hold a flashlight in your hand or, if you don’t have a flashlight, hold your hand on the chain of a lamp. Now, ask your mother to sit close to you so you can stare into her eyes. Finally, flash the light into her eyes—or pull the chain on the lamp—and as you look into her eyes, you will see her pupil immediately get smaller.
Just like a camera, the eye has a lens through which the light passes. The purpose of the lens is to focus the light on the retina in the back of the eye. When it is focused properly, we see things clearly; when it doesn’t focus properly, things look all blurred and unclear. Doctors always compare the retina of the eye to the film in a camera. it is the place where the light finally strikes and is turned into something we can see.
In a nearsighted person, since the eyeball is too long, the light focuses in front of the retina, and in a farsighted person, because the eyeball is too short, the light focuses beyond the retina. As a result, nearsighted and farsighted people can’t see as clearly as those with perfectly shaped eyeballs. However, we are pretty lucky because we can correct nearsightedness and farsightedness very easily with eyeglasses. All we have to do is to have our eyes tested by an eye doctor and, in a jiffy, he can tell us exactly what kind of glasses we need to make our sight normal.
Most children don’t have to wear their eyeglasses all the time even if they are nearsighted or farsighted. A great many boys and girls will need the glasses only when they read, or watch television, or go to the movies. And nearsighted and farsighted youngsters can use their eyes just as much as those who don’t wear glasses. Eyes are not weak just because they require eyeglasses!