US Patent 7810926 Lateral gaze angle estimation using relative eye separation

This invention provides for the automatic determination of a human's gaze angle. The gaze angle is assumed to be the same as the head angle (i.e., eyes looking straight ahead). It is determined by comparing the observed eye separation relative to a maximal eye separation. The gaze angle is then determined to be the inverse cosine, or arc cosine, of the ratio of these two measurements.