Objective: To estimate asymmetry in normal and pathological facial functions using an established computer generated objective evaluation technique.
Methods: Analysis was performed on three-dimensional (3-D) data captured using a specially designed 3-D face shape measurement system. Six healthy volunteers and six patients with Bell's palsy were analyzed for forced eye closure and grinning actions. The asymmetry was computed at locations that had the greatest effect in each action on both the left and right sides of the face, in reference to a relaxed condition. The patients' data were captured and analyzed repeatedly for a period of three days for an average interval of four weeks, and the results were compared with the Yanagihara scale.
Results: The control set of a normal sample exhibited a low standard deviation and a high correlation coefficient in both facial actions, and this contributed to a robust evaluation. The patients showed a higher standard deviation than the healthy subjects because of the larger degree of scatter of the data points in their respective data distributions. During the three clinical examinations, our proposed quantification method produced a continuous grading scheme, as opposed to the discrete scheme of the House-Brackmann grading.
Conclusion: Our proposed system shows advantages over the existing methods in that it does not rely on reference points nor does it use markers to analyze facial deformation. In addition, our estimations are very robust and accurate because our approach directly evaluates 3-D spatial variations in normal and pathological facial functions.