The Validity of a Smartphone-Based Method for Acquiring 3D Images of the Face

Objectives. To evaluate the accuracy and reproducibility of measurements obtained using the Bellus3D Face Application on a mobile smartphone by comparing them to direct measurements on pre-marked and blank face scans. Materials and Methods. Twenty-five healthy young adults (six males and nineteen females; age range 20-30 years) were included in this prospective cross-sectional study, with the only exclusion criterion being the presence of significant facial hair interfering with the placement and visualization of landmarks. Image acquisitions were performed using an iPhone XR with the Bellus3D FaceApp face scanning application, an iOS application for smartphones. Ten single midfacial and five paired bilateral landmarks were defined and marked. Two face scans were performed on each patient, both on blank and marked faces, and distances were measured directly with calipers and digitally. Results. The random error values were 1.0 mm and 0.4 mm for the manual point placement and measurements and virtual point placement on blank faces, respectively. The two methods used (the direct method and acquisition on faces with landmarks) demonstrate relatively similar reliability (ICC > 0.8); however, a paired t-test showed that the differences between several measurements were statistically significant (p < 0.05). Regardless of the method used, there was a systematic error for various values that included the nose and mouth (p < 0.05). The measurements demonstrating the most significant differences between the methods were those that included the tip of the nose, with the mean differences being -4.4-3.3 mm. The measurements of the distances that estimate face "depth" showed the greatest consistency irrespective of the tested method (p > 0.05 and ICC > 0.8). Conclusions. The use of the Bellus3D FaceApp is precise and reproducible for certain areas of the face, but digital reconstruction errors prohibit, for the time being, the use of this technology in everyday clinical practice. The noted discrepancies were consistent and more prevalent for specific areas such as the tip of the nose. Further investigations are required to determine other sources of error and for other smartphone-based applications released for 3D face image acquisitions.