Objective assessment of the severity of unilateral facial palsy using OKAO Vision® facial image analysis software

Abstract

Conclusion: Severity of ipsilateral facial palsy (UFP) can be assessed objectively by use of OKAO Vision®. Facial symmetry percentage (FSP) values were well correlated with the results by two conventional grading systems. Objectives: To introduce the basic principle of facial motion analysis using OKAO Vision®, to represent the data measured in patients with UFP, and to show the correlation between the severity of facial palsy assessed by this method and conventional systems. Methods: Two independent facial motions, closing the eyes and grinning, were recorded with a video camera. By comparing the movement distances between right and left sides, the eye symmetry ratio (ESR) and grin symmetry ratio (GSR) were obtained. The degree of UFP was assessed by FSP, which was calculated by the formula: FSP = (ESR + GSR)/2 × 100 (%). FSP was measured in 12 normal volunteers and in 30 patients with UFP. Results: In patients with UFP, varying degrees of FSP were noted corresponding to the grade of facial palsy. The severity of facial palsy assessed by FSP was closely correlated with the Yanagihara score (r = 0.88, p < 0.05) and was inversely related to the House–Brackmann grade (r = –0.90, p < 0.05).

Keywords::

• Symmetrical facial movement
• degree of facial palsy
• facial recognition
• facial feature extraction

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.