Have you wondered why you have two eyes and why they are set close together on the front of your face? The reasons are simple and important.
Your eyes are like two small cameras. A camera catches an image of an object and records it on film. Similarly, when you look at something, each eye takes in what it sees and sends this image to the back of the eyeball. Because your eyes are set close together, they see the world from about the same height but from a little different angles. While your right eye sees an object a little to the right, your left eye sees the same object a bit to the left. Working as a team, the eyes send the images to your brain, then your brain put them together and you see a single image in the center.
Seeing in stereo (立体) means seeing with two eyes working tighter, which is called stereoscopic sight. This allows you to see the world in 3D. Seeing depth helps you to judge how far it is between you and the objects you see, and then adjust to the changing angle so that you can see something clearly when you move closer or farther away. If images are coming from a single eye, however, only height and width can be perceived. So if you see with one eye, you will get a 2D image, as in a photograph.
Now consider why your two eyes are on the front of your face. Think of other animals just like you. They are all hunting animals, like lions and tigers. This provides a field of sight about 180 degree wide, which is called binocular sight. On the other hand, animals that are hunted have eyes on the sides of the head, which provides nearly 360-degree field of sight. However, they don't have stereoscopic sight. It is difficult for them to judge how far a danger is.
With both stereoscopic and binocular sight, humans and hunting animals share the ability to see from side to side and to judge how far it is from other objects. If you think it would be great to have another kind of sight, perhaps with hundreds of tiny eyes like many insects do, think again! Each tiny insect eye sees only a tiny part. Besides, what if you needed glasses? Be glad for the eyesight that you have.
