What is the minimal perceptible change for the dimensional alteration of facial structures in the frontal view?

Abstract

BackgroundA better understanding of the perceptibility of dimensional changes in facial structures is of interest to all involved in facial esthetics. PurposeWe aimed to determine the minimal perceptible change (MPC) in the dimensional alterations of the facial structures in the frontal view and the influential factors. Study design, setting, sampleThis cross-sectional study was conducted on individuals accompanying the patients at the outpatient department of a tertiary care hospital and students in art and science. Those with impaired cognition, craniofacial anomalies, history of esthetic facial surgeries and health professionals working on facial esthetics were excluded. Independent variablesThe observers assessed the frontal photographs of two models and their modifications. The independent variables were the anatomic structure modified (mouth, nose, ears, eyes), the percentage change (5, 10, 15%), and the type of modification (magnification or reduction). Outcome VariablesThe outcome variables were the MPC (perceived by at least 50% of the observers) and the perceptibility of changes (Yes/No) CovariatesThe age of the observer, the sex of the observer and the model were the covariates. AnalysisThe inter-group differences in perceptibility of changes and the influence of independent variables and covariates were analyzed with Chi-square / Cochran's Q test and generalized estimating equations, respectively, with statistical significance set at p<.05. ResultsThe sample comprised 110 males and 110 females, aged 23.9 ± 5.8 years. The MPC was 5% for the mouth, nose, and eyes and 15% for the ears. The changes in the nose [OR=0.68(0.56-0.83), p<.001], ears [OR=0.29(0.24-0.36), p<.001], and eyes [OR=0.78(0.64-0.95), p=.015] were less perceptible than the mouth. The perceptibility was higher in female than male observers [OR= 1.37(1.11-1.69), p=.003] and reduction than magnification [OR=1.11(1.00-1.23) p=.036]. Compared to a 5% change, the perceptibility was higher for 10 and 15% [OR= 2.00(1.76-2.27), 3.33(2.84-3.91), respectively, p<.001]. Conclusions and RelevanceThe MPC was 5% for the mouth, nose, and eyes and 15% for the ears. The perceptibility of change was influenced by the structure, the extent and type of modification and the observer's sex. These findings may be of use to all professionals involved in esthetic facial corrections.