Noninvasive Determination of Epidermal and Stratum Corneum Thickness in vivo Using Two-Photon Microscopy and Optical Coherence Tomography: Impact of Body Area, Age, and Gender.

BACKGROUND: High-resolution images of the epidermis are important to understand the transdermal penetration and changes in epidermal components. Both ex vivo and in vivo technologies are available to picture the epidermal thickness (ET). So far, the illustration of the stratum corneum (SC) has not been possible without artifacts. OBJECTIVE: Precision in vivo measurement of the ET and SC, duly considering the impact of location on the body, age, and gender. METHODS: In this pilot study on 20 skin-healthy subjects aged 18-66 years, the ET was imaged by two-photon microscopy (2PM) and optical coherence tomography (OCT), and the SC by using 2PM at five different body sites. RESULTS: On solar-exposed body areas, both the epidermis and SC are thicker compared to solar-protected areas (p < 0.05), the epidermis at the gluteal region being the thickest (p < 0.05). The ET decreases with age (p < 0.05). Males show a thicker epidermis than females (p < 0.05). CONCLUSION: 2PM provides a noninvasive method for imaging the epidermis and especially the SC in vivo and is optimally suited for the application of histological criteria.

Impact of Body Site, Age, and Gender on the Collagen/Elastin Index by Noninvasive in vivo Vertical Two-Photon Microscopy.

BACKGROUND/AIMS: Extrinsic and intrinsic skin aging is subject to constant remodeling and degradation processes, primarily in components of the extracellular matrix. While collagen fibers thin out during the aging process, the amorphous elastin fibers accumulate. These are essential formative components of the dermis. So far, these processes have been detected in vertical histological sections of invasive biopsies and recently in noninvasive horizontal scans. METHODS: In this pilot study, a modified noninvasive 2-photon microscope was applied to measure the collagen/elastin index of skin in vivo. The obtained images permit an immediate vertical survey and allow a conclusion on the dermal composition at once. The collagen/elastin index was quantified by the second harmonic to autofluorescence aging index of dermis (SAAID) depending on volunteers' age (18-66 years), gender, and body area. RESULTS: The highest SAAID was measured at the volar forearm as compared to the abdominal SAAID, which was significantly lower (p < 0.05). The gluteal region showed the significantly lowest SAAID (p < 0.05). The SAAID in female skin was higher compared to male skin and decreased with increasing age. CONCLUSION: These effects are to be considered in subsequent studies to be able to specifically detect and evaluate influences.

Body regions have an impact on the collagen/elastin index of the skin measured by non-invasive in vivo vertical two-photon microscopy.

It is known that the collagen and elastin fibre structures are changing with age. There is little knowledge about the influence of body area as these investigations have been limited for ethical reasons, so far. Thus, modified non-invasive two-photon microscopy was used providing vertical optical sections of second harmonic generation and autofluorescence to calculate the collagen-to-elastin ratio and its alterations depending on the investigated body site in vivo. The results of this study indicate that the impact of different body areas could be higher than the influence of age and should be considered in future studies.