Abstract: One of the goals of the eye tracking community is to build systems that allow users to move freely. In general, there is a trade-off between the field of view of an eye tracking system and the gaze estimation accuracy. We aim to study how much the field of view of an eye tracking system can be increased, while maintaining acceptable accuracy. In this paper, we investigate all the issues concerning remote eye tracking systems with large range of movement in a simulated environment and we give some guidelines that can facilitate the process of designing an eye tracker. Given a desired range of movement and a working distance, we can calculate the camera focal length and sensor size or given a certain camera, we can determine the user's range of movement. The robustness against large head movement of two gaze estimation methods based on infrared light is analyzed: an interpolation and a geometrical method. We relate the accuracy of the gaze estimation methods with the image resolution around the eye area for a certain feature detector's accuracy and provide possible combinations of pixel size and focal length for different gaze estimation accuracies. Finally, we give the gaze estimation accuracy as a function of a new defined eye error, which is independent of any design parameters.