Abstract — Iris contains some information about human body and organ condition. Iridology is a scientific study of the iris structure to get some information that represents the condition of the various organs by examining the tissue strengths and weaknesses in the iris. With the rapid development of image processing, iridology has become more popular and reliable. In recent years, many systems that adopt iridology have been developed to diagnose a disease by analyzing a certain part of the iris or so-called Region of Interest (ROI). Typically, iris recognition systems consist of three main functions namely image pre-processing, feature extraction, and classification. This paper shows all the regions that have been studied and the accuracy of their iris recognition system.