Optimization of a Novel Automated, Low Cost, Three-Dimensional Photogrammetry System (PHACE).

Introduction: Clinical tools are neither standardized nor ubiquitous to monitor volumetric or morphological changes in the periorbital region and ocular adnexa due to pathology such as oculofacial trauma, thyroid eye disease, and the natural aging process. We have developed a low-cost, three dimensionally printed otogrammetry for utomated ar (PHACE) system to evaluate three-dimensional (3D) measurements of periocular and adnexal tissue.

Methods: The PHACE system uses two Google Pixel 3 smartphones attached to automatic rotating platforms to image a subject's face through a cutout board patterned with registration marks. Photographs of faces were taken from many perspectives by the cameras placed on the rotating platform. Faces were imaged with and without 3D printed hemispheric phantom lesions (black domes) affixed on the forehead above the brow. Images were rendered into 3D models in Metashape (Agisoft, St. Petersburg, Russia) and then processed and analyzed in CloudCompare (CC) and Autodesk's Meshmixer. The 3D printed hemispheres affixed to the face were then quantified within Meshmixer and compared to their known volumes. Finally, we compared digital exophthalmometry measurements with results from a standard Hertel exophthalmometer in a subject with and without an orbital prosthesis.

Results: Quantification of 3D printed phantom volumes using optimized stereophotogrammetry demonstrated a 2.5% error for a 244μL phantom, and 7.6% error for a 27.5μL phantom. Digital exophthalmometry measurements differed by 0.72mm from a standard exophthalmometer.

Conclusion: We demonstrated an optimized workflow using our custom apparatus to analyze and quantify oculofacial volumetric and dimensions changes with a resolution of 244μL. This apparatus is a low-cost tool that can be used in clinical settings to objectively monitor volumetric and morphological changes in periorbital anatomy.