Biometrics-based personal authentication systems are becoming popular with increased demand on security. A biometrics is expected to have significant amount of discriminatory information in representing uniqueness of a person. This discriminatory information about the biometric is loosely defined as the individuality. Even though some individuality studies have been carried out for fingerprints, face and handwriting, formal analysis of iris individuality has not been carried out. In this paper, we propose a partial model for iris individuality and show its usefulness in predicting the empirical performance results.