A plea for standardization of confocal microscopy and optical coherence tomography parameters to evaluate physiological and para-physiological skin conditions in cosmetic science.

BACKGROUND Non-invasive Reflectance Confocal Microscopy (RCM) and Optical Coherence Tomography (OCT) have been extended to the dermo-cosmetic field, for skin pathophysiology understanding and therapeutics monitoring. However, standardized methodology and parameters to interpret structures and changes in these settings are still lacking. OBJECTIVE to propose a validated standard methodology and a list of defined parameters for objective non-pathological skin assessments in the cosmetically sensitive cheekbone area of the face. METHODS OCT and RCM quantitative, semi-quantitative, and qualitative features were considered for assessments. Validation process included 50 sets of images divided into 2 age groups. Inter-rater reliability was explored to assess the influence of the proposed methodology. RESULTS Quantitative OCT parameters of "epidermal thickness", "density and attenuation coefficients" and "vascular density" were considered and calculated. Severity scales were developed for semi-quantitative OCT features of "disruption of collagen" and "vascular asset", while extent-scales were produced for semi-quantitative RCM "irregular honeycomb", "mottled pigmentation" and "polycyclic papillary contours". Qualitative assessment was obtained for RCM type of collagen and comparison between age-groups was performed for all features considered. Severity visual scales assistance proved excellent inter-rater agreement across all semi-quantitative and qualitative domains. CONCLUSIONS The assistance of shareable software systems allows for objective OCT quantitative parameters measurement. The use of standard reference scales, within a defined assessment methodology, offers high inter-rater reliability, and thus reproducibility for semi-quantitative and qualitative OCT and RCM parameters. Taken together, our results may represent a starting point for a standardized application of RCM and OCT in dermo-cosmetic research and practice.