Facial asymmetry: three-dimensional analysis using laser surface scanning

Abstract

This study evaluates six different techniques with respect to their ability to quantitatively describe facial asymmetry in three dimensions. Three-dimensional facial images were acquired using a Cyberware 3030RGB laser surface scanner. Image processing was performed on a Silicon Graphics Indigo computer workstation. The following techniques for facial asymmetry analysis were developed: asymmetry in the location of anthropometric landmarks, Euclidean distance matrix analysis (EDMA), scalar measurement of the lower ciliary margin and palpebral fissure area, clearance vector mapping, and determination of the volume of asymmetry. Techniques were applied and validated in three anthropometric models: a perfectly symmetrical plastic head model and a plaster head model with and without a unilateral cheek augmentation. In each of the anthropometric test models, each analytical technique was validated by means of static anthropometric facial models and was evaluated for intraobserver and interobserver reliability. Asymmetries in the location of anthropometric landmarks can be accurately determined to within 2 mm in x, y, and z directions of the Cartesian space. EDMA is a useful technique in describing both size and shape changes of discrete areas of the face. Measurement of the lower ciliary margin and palpebral fissure area is reliable. Clearance vector mapping is especially useful in quantifying facial surface asymmetries in facial areas where anthropometric landmarks are scarce. Volume of asymmetry is potentially useful in those patients for whom the use of injections or implants of known volume may be helpful in correcting unilateral facial deficiencies.