1. A method comprising: receiving glint-location data indicating a location for each of one or more glints that are reflected from an eye, wherein the glint-location data is captured by an imaging device that is associated with a head-mountable display (HMD); determining a plurality of normalized pupil locations comprising at least a first and a second normalized pupil location, wherein each normalized pupil location is determined based on the glint-location data for a different combinatoric subset of the one or more glints; determining a regression model to fit the plurality of normalized pupil locations to an expected gaze location; and performing, by a computing device, a gaze-tracking process based on the regression model.