Inter-individual Variability of the Facial Morphology During Conscious Smiling
OBJECTIVES/HYPOTHESIS To objectively measure facial motion at various facial landmarks using a video-computer interactive system. STUDY DESIGN Clinical, prospective, non-randomized. METHODS A video-computer interactive system, The Peak Motus Motion Measurement System, was used to study linear displacement at preselected facial landmarks in the normal and abnormal face. Subjects with normal facial function (n = 34) and patients with abnormal facial function (n = 26) from various etiologies were studied. The sites studied were marked with reflective beads. Of a larger repertoire of expressions, two expressions (eyes closed and closed-lip smile) were studied in all subjects. The percent asymmetry in facial displacement between the sides of the face was calculated. The sensitivity of this measurement to facial dysfunction was evaluated. The presence of synkinesis was examined by quantifying the displacement at facial sites that were remote to the sites primarily involved in a given facial expression. Test-retest reliability of the percent asymmetry measurement was evaluated with the paired t test. RESULTS The video-computer interactive approach used accurately detected and quantified gross and subtle changes in facial function. The sensitivity of the percent asymmetry measurement was 95% (both expressions) for patients with apparent facial dysfunction (House-Brackmann rating >I/VI). In patients with facial nerve dysfunction, displacement on the presumably normal side was significantly excessive in 27% to 35%, depending on the expression. With this interactive computer-video system, synkinesis was detected in 58% of the pathologic subjects during the eyes closed or closed-lip smile expressions. The paired t test indicated strong test-retest reliability (r = 0.73-0.99) of the percent asymmetry measurement. CONCLUSIONS The present report indicates that this approach to the assessment of facial motion is sensitive to facial dysfunction. This computer-video interactive system is able to quantify synkinesis. A grading system for the magnitude of synkinesis, based on the magnitude of the displacement at remote facial sites, is proposed. The common occurrence of excessive facial motion on the presumably normal side of affected individuals indicates that patients with facial paralysis often overcompensate by exaggerating the normal side in an effort to move the affected side. This system is of value in the objective measurement of normal facial function and may prove a useful tool to quantify the outcomes of various medical and surgical treatments for facial nerve dysfunction.