In vivo measurements of epidermal thickness by reflectance mode confocal microscopy to assess cellular proliferation induced by topical agents

Using a reflectance mode confocal scanning laser microscope (rCSLM), a noninvasive technique to monitor epidermal thickness in vivo is presented. The modality is characterized by the collection of the reflectance profile from cutaneous tissues, resolved in transverse (x, y) directions at each depth (z) increment. Due to the different light scattering properties of the skin layers, each layer can be identified. The depth of each layer can then be inferred from the axial reflectance profile along the z direction. In pilot experiments an agent that induced epidermal proliferation, 12-O-tetradecanoylphorbol-13-acetate (TPA), was applied topically to the ear of a mouse. Peak-to-valley analysis of the rCSLM A-scans showed the epidermal thickness increasing from an initial 5.4 [μm] to 12.4 [μm] after 24 [hr]. Peak-to-peak analysis showed an increase from 9.1 [μm] to 21.2 [μm]. These results suggest that rCSLM imaging provides a means to study morphologic changes in the epithelium arising from inflamatory response and cell proliferation in vivo without recourse to biopsy or sacrifice of animals.