So our sympathetic division of the autonomic nervous system innervates one type of smooth muscle inside the iris, known as the radial smooth muscle. And when we are inside a dark room, so under very dark conditions, the sympathetic nervous system basically contracts the radial smooth muscle, which dilates or opens up our pupil. So this iris basically contains the radial smooth muscle that contracts as a result of the sympathetic division of the autonomic nervous system and opens up our pupil. 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.