The color of the iris varies widely from person to person in different parts of the world, and in some people it can be even composed of two or more different pigments. Black, light and dark brown are the most common eye colors, which are found in about three-quarters of the world's population. Iris also plays an important role in controlling the amount of light entering the eye and protects the eye from the harmful rays of the sun. Most candidates of iris implant surgery are people who suffer from aniridia (congenital absence of the iris) or iris abnormalities caused by eye diseases or injuries.