The first wheel slows down before the other hits the mud and the cart will change direction. The cornea of the eye is curved so that only light rays entering on the line of a radius are not bent. Light travels slower in the cornea than in air and therefore the cornea is a major influence in focusing the light. Behind the cornea is a space called the anterior chamber . It is filled with fluid called aqueous humor secreted by glands in the ciliary body and drained by the canal of Schlemm into the nasal passages.
Light passes through the opening in the iris called the pupil .
Light then passes through the lens which is composed of collagen and which slows light a little bit more. The lens has a minor effect on focusing, but it can change shape and thus focus objects at different distances. The lens is stretched and made thin by a ligament . This ligament is attached to the sclera at an angle and the ciliary muscle is also attached to it so that when the muscle contracts, tension on the ligament is relieved and the elasticity of the lens makes it more round. The more round the lens, the more it focuses light originating closer to the eye.