Methods of Non-Invasive In Vivo Optical Diagnostics in the Assessment of Structural Changes in the Skin Induced by Ultraviolet Exposure in an Experimental Model

Background: This paper demonstrates the use of optical diagnostic methods to assess the dynamic skin changes observed in acute and chronic exposure to ultraviolet (UV) radiation in vivo. Methods: Firstly, in order to initiate photoaging (chronic UV exposure), animals (n = 40) were divided into two groups: chronic UV exposure (n = 30), and control (n = 10; without irradiation). Photoaging in animals was induced by chronic repeated exposure to UVA radiation three times per week, for 12 weeks continuously, while the UV dose increased stepwise over the course of the experiment (55 minimal erythema doses (MED) in total). Laser fluorescence spectroscopy (LFS), optical tissue oximetry (OTO), laser Doppler flowmetry (LDF), and optical coherence tomography (OCT) of the shaved dorsum skin were performed regularly, once per week until the conclusion of the study. At 0, 5, and 12 weeks of the experiment, histological examination of animal tissues using hematoxylin/eosin and Masson’s trichrome staining was performed. At the second stage, erythema was induced in mice (n = 15) by acute UV exposure at high doses. The colorimetric assay of the image from a digital RGB camera was used to evaluate the erythema index. Results: The tissue content index η(collagen) of collagen was appropriate for the characterization of skin photoaging. Significant differences (p < 0.05) in η(collagen) were found between the control and photoaging groups from the 5th to the 9th week of the experiment. In addition, the rate of collagen degradation in the control group was about half that of the photoaging group. This marker allows the differentiation of photo- and chronoaging. OCT revealed the main optical layers of the skin in compliance with the histological pattern. The analysis of the RGB camera images provided visualization of the acute skin reaction to UV radiation. Conclusions: This study demonstrates the applicability of optical methods for the quantitative assessment of acute and chronic skin effects of UV exposure in vivo.