Does iris structure change? Not withstanding injury or disease, the iris structure is extremely stable. So much so that iris biometrics is used at airports, banks and other high security places as one of the most accurate forms of identification. (Even more accurate than fingerprints). Why have some claimed to see structural change? One thing to consider in comparative analysis is pupil size. Larger pupils (Mydriasis) means less space for the iris. The fibres are restricted to a smaller space which means that lacunae will seem larger or more open compared to when the pupils are ideal size. In the case of Miosis, (small pupils), the fibres will be stretched into a larger space and lacuna can look quite narrow. These images are an extract from the Integrated Iridology textbook and demonstrate the impact of Mydriasis on the iris structure.