An eye tracking system configured to: receive a plurality of right eye images of a right eye of a user; receive a plurality of left eye images of a left eye of a user, each left eye image corresponding to a right eye image in the plurality of right eye images; detect a pupil and determine an associated pupil signal, for each of the plurality of right eye images and each of the plurality of left eye images; calculate a right eye pupil variation of the pupil signals for the plurality of right eye images and a left eye pupil variation of the pupil signals for the plurality of left eye images; and determine a right eye weighting and a left eye weighting based on the right eye pupil variation and the left eye pupil variation. For one or more right eye images and one or more corresponding left eye images, the eye tracking system can: determine at least one right eye gaze signal based on the right eye image and at least one left eye gaze signal based on the corresponding left eye image; and calculate a combined gaze signal from a weighted sum of the right eye gaze signal and the left eye gaze signal using the right eye weighting and the left eye weighting.