In its physical structure and action, the eye is similar to a camera and is controlled by similar rules. The cornea is transparent and, normally, has a plus spherical curvature. It is the rigid lens of the eye which bends rays of light entering the eye. Like the camera, the eye has a shutter to control the light. It is called the iris. It works automatically -- like the camera, it has a film, for forming images, which covers the retina.
The retina is like a flower emerging from the stem. It is composed of innumerable rods and cones emerging from the stem. The stem is composed of a bundle or bundles of nerves which are directly connected to the brain. The stem is called the optic nerve. It is the optic nerve with the rods and cones which is the main factor in seeing.
The eye can see objects only in front and in a limited space. In order to see sideways, without turning the head, the eyes themselves must turn. For turning and moving purposes the eyes are supplied with six sets of muscles. Fourr of them to turn the eyes inward, outward, upward, and downward. The other two musles are for oblique and rotation purposes. It is important to emphasize that the muscles which move the eye for direction are located outside the eye ball.