Our eyes have functioned very crucial work. It has simple organs to focus the objects. Lens (crystalline) which provides the length adjustment (focal length for focus the object and remaining the blur) which is required to focus the objects at different distances on the retina of the eye. Generally, it works similar like camera. Focus the objects blur the background. Lots of the refraction for the light rays entering the eye at the cornea. Remember, but in outer surface of cornea.