Sensitivity of a method for the analysis of facial mobility. II. Interlandmark separation.

OBJECTIVE This study demonstrates a method of quantifying facial movements based on distortions of the skin surface. DESIGN Landmarks were identified on the faces of five healthy human subjects (2 men and 3 women; mean age, 27.6 years; range, 26 to 29 years), and the distortions were characterized by changes in the separation between 20 pairs of landmark distances during specific maximal facial animations: smile, lip purse, cheek puff, grimace, eye closure, and eye opening. Data were recorded with a video-based tracking system for a period of 3 seconds at a sampling rate of 60 Hz or frames per second. For each subject, we analyzed the change in the separation of 20 pairs of landmarks, of which the majority were bilaterally symmetrical and functionally active. RESULTS Characteristic patterns of movement emerged for each animation. We found that smiling involved movements of the lateral orbital, circumoral, and chin regions; grimacing involved the inner orbital, lateral orbital, lateral nasal, and upper-lip regions; eye closure involved the inner orbital, lateral orbital, and, to a lesser degree, lateral nasal regions; eye opening involved the inner and lateral orbital regions; cheek puffing involved the cheek and lower-lip regions; and the lip purse animation involved the nasolabial, cheek, commissure, and lip regions. CONCLUSION This measurement of distortion provided a quantitative estimate of facial movement, and this approach is especially applicable to patients with unilateral problems in which the patient can serve as his or her own control.