# Quantifying Perceived Facial Asymmetry to Enhance Physician-Patient Communications
###### Abstract  
In cosmetic surgery, bridging the anticipation gap between the patients and the physicians can be challenging if there lacks objective and transparent information exchange during the decision-making and surgical process. Among all factors, facial symmetry is the most important for assessing facial attractiveness. The aim of this work is to promote communications between the two parties by providing a quadruple of quantitative measurements: overall asymmetry index (oAI), asymmetry vector, classification, and confidence vector, using an artificial neural network classifier to model people's perception acquired from visual questionnaires concerning facial asymmetry. The questionnaire results exhibit a Cronbach's Alpha value of 0.94 and categorize the respondents' perception of each stimulus face into perceived normal (PN), perceived asymmetrically normal (PAN), and perceived abnormal (PA) categories. The trained classifiers all overall root mean squared error < 0.01, and its result shows that the oAI is, in general, proportional to the degree of perceived asymmetry. However, there exist faces that are difficult to classify as either PN or PAN or either PAN or PA with competing confidence values. In such cases, oAI alone is not sufficient to articulate facial asymmetry. Assisting surgeon-patient conversations with the proposed asymmetry quadruple is advised to avoid or to mitigate potential medical disputes. artificial neural networks; facial asymmetry; plastic surgery; medical disputes +
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Although plastic surgery is expected to enhance one's appearance and self-esteem, there exist consequential uncertainties due to psychological and physical discomfort for the patients. Harmonious physician-patient relationships are crucial to soothe this discomfort and to promote healthcare delivery [15]. However, anticipation gaps and insufficient decision-making communications have caused medical disputes [16; 17; 18; 19]. According to the Department of Health, Taipei City, among Taipei's 415 cosmetic surgery clinics in 2016, 116 of 374 medical disputes came from aesthetic medicine [20]  
To bridge the anticipation gaps, quantitative measurements are needed to model perception of facial asymmetry. Related work and strategies in the below literature include: (1) determining how stimulus faces are collected--two-dimensional (2D) or three-dimensional (3D), real or simulated, with skin or without; (2) identifying facial landmarks automatically or semi-automatically, or maybe no landmarks; (3) defining a coordinate system and making measurements; (4) conducting questionnaire surveys to quantify perceptions of facial asymmetry; (5) computing the degree of asymmetry and classification. [PERSON] et al. employed a series of 2D images to present progressive asymmetry [21]. The results suggested that at least 3 mm of facial asymmetry on the oral commissure, brow, or both was required for the participants to notice the asymmetry. [PERSON] et al. measured the nasolabial angle on 2D facial contours to determine whether a rhinoplasty surgery was needed [22]. The results showed that 2D stimulus facial images had their constraints. [PERSON] et al. performed a similar study on facial asymmetry, though utilizing 3D images [1]. Instead of employing images from different persons, they transformed the same image by incremental soft tissue alterations. They found that the nasal structure played a crucial role in perception of symmetry, and the asymmetry of chins greatly affected the facial appearance. In clinical practices, asymmetry is usually measured by comparing bilateral facial features against the mid-sagittal plane. Quantitative studies of the face rely on the accurate positioning of facial landmarks or surface-based patches [23]. [PERSON] et al. explored the correlation of facial asymmetry between cephalometric measurements and the frontal photograph evaluation conducted by orthodontists. The result argued that there existed a discrepancy between the two [24].