Elmer: There is a blue ring in Amy’s eyes.
Mother: This is called the iris, which means a rainbow. You know we all like to see pretty curtains hung before windows, and such beautiful curtains you never saw as these in the eye. They are only half an inch wide, but they open or draw together around the pupil so the eye has just the right amount of light. When you are where it is very light, this wee round curtain draws up very small. If you are in a dark room, it opens wide, so the eye can have all the light there is. Sometimes these curtains are brown, gray, or blue, just the color which will match the outside of the house best.
Amy: But won’t you please tell us, mother, how we see with our eyes.
Eye showing optic nerve, cornea, pupil and iris
Mother: I will try, and perhaps we can find out some things about it. Here is a picture which may help us. You see the front of the eye bulges out like a watch crystal, and it has a strong, glassy covering, called the cornea, which lets the light through. Passing through the pupil we come to the lens, which is shaped as you see in the picture. You have seen old persons wear spec´ta-cles to help them see. The glasses in the frames are lenses; but you must not think from this that the lens in your eye is made of glass. It is because of the shape that it is called a lens. A picture of people, houses, trees, or anything else you look at, is made by the lens on the inner part of the eye, which is called the ret´i-na. It is almost wholly made up of the little branches of the nerve of sight.
Helen: And is that the way we see?
Mother: Partly. The picture passes through the clear, jelly-like substance of the eye to the back, where it is spread out, and the nerves of sight carry it into the brain, for the master to see. We may have perfect eyes, but if anything is wrong with the eye nerve, we can not see; so we really see and hear with our brain instead of our eyes and ears.
Elmer: Isn’t the eye something like the camera used to take photographs?
Mother: Yes, in some ways. One curious thing about it is that it turns its pictures upside down before they strike the nerves of sight, and in this it is like the camera.