Our eyes are constantly in motion, even during "steady" fixation. In ophthalmic systems equipped with wavefront technology, both eye and head motion potentially degrade its performance and/or increase the cost and complexity, as they induce a movement of the entrance optical pupil of the system. Here, we characterize the pupil motion in an aberrometry setting, using a custom, high-speed pupil tracker (478 Hz), and draw conclusions on design considerations of future ophthalmic systems. We also demonstrate the feasibility of tracking such motion directly with a custom-built Hartmann-Shack sensor (236 Hz) using a method that offers certain benefits over previously suggested approaches, thereby paving the way to an efficient and cost-effective approach.