Comparison of eye and lip measurements obtained using single and stereo photogrammetry

Some of the facial distances used in Fetal Alcohol Syndrome (FAS) screening, namely palpebral fissure length, upper lip width and upper lip height, obtained using single and stereo photogrammetry, were examined. Photogrammetry as an alternative to direct measurements to obtain facial distances is less intrusive to subjects and reduces screening time, but measurements from single frontal photographs neglect depth information and may be inadequate for screening purposes. We therefore examined the role of depth in eye and lip measurements and found that depth contributed less than 1 mm to distance measurements in an idealized system where the real-world co-ordinates of points were known from three-dimensional calibration of stereo photographs. However, the differences found between measurements taken from single frontal photographs and those from stereo-photogrammetry indicated that measurements from single photographs are prone to errors.