Until now, most research on iris recognition has been focused on recognition algorithms and iris camera systems. There has been little research into fake iris detection, although recently its importance has been greatly emphasized. Fake iris detection refers to the process of detecting and defeating fake iris images. In this work, we propose a new method of defeating fake iris attacks using Purkinje images based on gaze position. Our research presents the following four improvements over previous works. First, we calculate the theoretical positions and distances between the Purkinje images based on the 3-D human eye model. Second, by using these positions and distances (which changed according to gaze positions), we design a more robust way of detecting fake irises. Third, since it is not necessary to align the center of the user's eyeball with the optical axis of the camera, the proposed method can be used in practical iris systems. Fourth, by activating the illumination infrared-light-emitting diode (IR-LED), the distance-measuring IR-LED and the Purkinje IR-LED alternatively, we obtain accurate positions for the Purkinje images according to the user's gaze position. Experimental results show that the false rejection rate (FRR) is 0.2% and the false acceptance rate (FAR) is 0.2%.