  The use of eye-tracking techniques is becoming rapidly extended because of
its relevance for acquiring information about cognition and behavior. Recent
studies indicate that a correct characterization of the motion of the pupil
inside the eyeball is needed, because this motion influences the eye-tracking
results. In this work we face this problem and we develop a model that
reproduces several findings of recent experiments on saccadic movements. In
particular, the dependence of the amplitude and period of the post saccadic
oscillations on the saccade size, as well as that of the peak velocity. Our
results suggest that post saccadic oscillations could obey mainly to inertial
phenomena experimented by the inner part of the iris when the eyeball rotates.
