The iris is the coloured part of the eye. A circular muscle in the iris controls the amount of light entering the eye through the pupil, the black area in the centre of the iris.

The cornea is the outer clear, round structure that covers the iris and the pupil. The cornea directs light rays into the eye and helps focus them on the light-sensitive retina at the back of the eye, providing sharp, clear vision.

The lens is located behind the iris and is normally clear. Light passes through the pupil to the lens. Small muscles attached to the lens can make the lens change shape, allowing the eyes to focus on near or far objects.