What makes an iris scan unique?
The iris is the colored ring of muscle that opens and shuts the pupil of the eye like a camera shutter. The colored pattern of our irises is determined genetically when we're in the womb but not fully formed until we're aged about two. It comes from a pigment called melanin—more melanin gives you browner eyes and less produces bluer eyes. Although we talk about people having "blue eyes," "green eyes," "brown eyes," or whatever, in reality the color and pattern of people's eyes is extremely complex and completely unique: the patterns of one person's two eyes are quite different from each other and even genetically identical twins have different iris patterns.