The cornea is responsible for protecting the eye and for refracting incoming light rays.
The pupil is merely an opening that allows light to enter into the eye. Its black color is attributed to the fact that light is not able to exit the eye through the pupil.
The iris acts to control the size of the pupil. In bright light, the iris is dilated in such a way as to reduce the size of the pupil and limit the amount of entering light. In dim light, the iris adjusts its size as to maximize the size of the pupil and increase the amount of incoming light.
The crystalline lens is a fibrous, jelly-like material that serves to fine tune the vision process by adjusting its shape and therefore the focal length of the system.
The ciliary muscles relax and contract to change the shape of the lens.
The retina contains rods and cones which detect the intensity and frequency of incoming light and, in turn, send nerve impulses to the brain.