And by opening up our pupil, that allows more light inside the eye and that allows us to see better in the dark. Now, on the other hand, if we are in a room that contains lots of light, our parasympathetic nervous system that innervates the circular muscle, the circular muscles of our iris basically contract the circular muscle and that actually decreases the size of the pupil, decreases the size of the opening, and that allows less light inside our eye. Now, the next portion that I want to discuss is the lens. So once the light hits our cornea, it basically bends and it enters the lens through our pupil. Now, once it enters the lens, from physics we know that the lens is a convex lens and a convex lens basically diverges the rays of light. So the lens of the eye is a convex lens that is used for fine tuning and focusing the light rays onto a special region at the back of the eye known as our retina.