The eye can be compared to a camera. The front section is composed of two natural lenses: the cornea, which is in front of the iris and the lens, which lies behind it.
The iris gives the eye its unique colour and acts as a diaphragm by controlling the amount of light that penetrates the eye through the pupil opening (black circle in the centre). The pupil contracts in bright light and dilates in dim light.
The cornea is a rounded window. Its curve gives it the ability to focus, similar to how a camera lens works.