A system is mounted within eyewear or headwear to unobtrusively produce and track reference locations on the surface of one or both eyes of an observer. The system utilizes multiple illumination sources and/or multiple cameras to generate and observe glints from multiple directions. The use of multiple illumination sources and cameras can compensate for the complex, three-dimensional geometry of the head and anatomical variations of the head and eye region that occurs among individuals. The system continuously tracks the initial placement and any slippage of eyewear or headwear. In addition, the use of multiple illumination sources and cameras can maintain high-precision, dynamic eye tracking as an eye moves through its full physiological range. Furthermore, illumination sources placed in the normal line-of-sight of the device wearer increase the accuracy of gaze tracking by producing reference vectors that are close to the visual axis of the device wearer.
