Over the past ten years, the growing emphasis on security has drawn a lot of interest in iris recognition in both academic and practical settings. Due to its high accuracy, reliability, and uniqueness, iris recognition is becoming increasingly popular in the fields of access control, electronic commerce, and border security. The iris is the best potent identification and verification feature when compared to extra biometric modalities because the human iris does not change throughout the course of a person's lifetime. Feature extraction, segmentation, template matching and normalization are the first four steps of iris recognition. These preprocessing techniques used by different researchers for iris segmentation are the focus of this review paper.