BSL Physics Glossary - lens - definition
You have a lens in each eye. It is made of a soft, jelly-like material. It's a converging shape. A lens can also be made out of glass or plastic. The lens can be converging or diverging in shape.
Each type of lens bends light in different ways. For a converging lens, when parallel beams of light hits the lens, the top ray bends down, the bottom ray bends up, and the middle ray continues straight on. The three bent rays cross at a point beyond the lens.
With a diverging lens when parallel rays of light hit the lens the rays are bent outwards. The middle ray, as before, continues straight on.