Application of optical non-invasive methods in skin physiology:: a comparison of laser scanning microscopy and optical coherent tomography with histological analysis

Background/purpose: Optical, non-invasive methods, such as fluorescence laser scanning microscopy (LSM) and optical coherent tomography (OCT), have become efficient tools for the characterization of the skin structure in vivo, as well as real-time investigation of distribution and penetration of topically applied substances. Methods: In the present paper, the results obtained with both non-invasive methods - OCT and LSM - were compared to conventional light microscopy of histological sections. Skin structure and the distribution of topically applied particulate and non-particulate substances on the skin surface and in the epidermis were analyzed. Results: None of the methods used are suitable for the realization of all diagnostic tasks, however, each method has advantages for particular applications. Fluorescence LSM is well suited for the investigation of the upper 150 mu m of the skin as well as for the investigation of the kinetics of substances applied onto or into the epidermis. OCT can be applied for the investigation of vertical cross-sections of the skin up to a depth of 2 mm, albeit at lower resolution than achieved by LSM or conventional light microscopy. Conventional light microscopy of histological sections of biopsy specimens produces familiar high-resolution images of deeper tissue layers. However, the analysis of the kinetic processes is limited in this case. Conclusions: LSM- and OCT-measurements are efficient non-invasive tools for the characterization of morphological structures of the skin. On the one hand, the optical methods have a clear advantage in the case of kinetic measurements. On the other hand, histological investigations are characterized by a high information density and a high resolution, also in deep tissue layers. The selection of the best method for the analysis of the skin morphology depends on the target and the task of the investigation.