An active contour method is presented and applied to robust iris tracking. The main strength of the method is that the contour model avoids explicit "feature" detection: contours are simply assumed to remove statistical dependencies on opposite sides of the contour. The contour model is utilized in particle filtering together with the EM algorithm. The method shows robustness to light changes and camera defocusing, and makes it possible to use off-the-shelf hardware for gaze-based interaction