What you are seeing up close is not a camera. It is a living optical instrument assembled from collagen, crystalline protein, and pigment, refined over roughly 500 million years since the first light-sensitive patches appeared in Cambrian animals. The iris is the star of any macro shot. Its colour is not produced by blue or green pigment at all. Every human iris contains only melanin, and the visible hue is set by how much melanin sits in the anterior stroma and how that stroma scatters light: - Brown irises carry dense melanin that absorbs most incoming light - Blue irises carry very little stromal melanin, so short wavelengths are preferentially scattered back by the collagen fibres, the same Tyndall-type scattering that gives skim milk a bluish cast - Green and hazel sit in between, mixing modest melanin with scattering - The deep posterior pigment epithelium is dark in nearly every eye regardless of surface colour The radial ridges and crypts visible in close-up are the sphincte...