Comparative analysis of intrinsic skin aging between Caucasian and Asian subjects by slide‐free in vivo harmonic generation microscopy

Abstract

Phenotypical and functional differences in the intrinsic skin aging process of individuals between Caucasians and Asians have generated considerable interest in dermatology and cosmetic industry. Most of the studies focused on the stratum corneum, and in some other studies inter-individual differences overwhelms the racial difference. None of the studies comparatively analyzes the difference from the histopathological point of view. Here we report our harmonic generation microscopy study to analyze the difference of intrinsic aging between Caucasian and Asian skin from a histopathological point of view. As a result, the cellular and nuclear areas of basal cells in Caucasian subjects were found to increase at the same rate as the Asian subjects, ideal for scoring age. The maximum thickness of the viable epidermis, the dermal papilla (DP) volume per unit area and the depth of the DP zone in Caucasians were found to decrease at faster rates than those in Asians. K E Y W O R D SAsian, Caucasian, dermal papillae, harmonic generation microscopy, in vivo imaging, intrinsic aging, race, viable epidermis

Slide-free clinical imaging of melanin with absolute quantities using label-free third-harmonic-generation enhancement-ratio microscopy

“…Extensive studies and discussions have been conducted and previously published to address this concern, especially for the 1230-1260 nm based femtosecond THG microscopy with an average power on the order of 100 mW [22,34,[46][47][48][49][50]. No evidence of photodamage can be found either in clinical trials [22,32,34,35,[51][52][53][54][55] or studies on animal models [22,[47][48][49][50]. This is attributed to the low photon energy (∼1eV) of the adopted excitation light, which avoids the linear melanin absorption [22] and significantly increases the multi-photon ionization threshold [34], when compared with femtosecond excitation light with a higher photon energy.…”

A Study on Applying Slide-Free Label-Free Harmonic Generation Microscopy For Noninvasive Assessment of Melasma Treatments With Histopathological Parameters

“…With the same mechanism, absolute quantities of melanin of keratinocytes in human skin can be noninvasively measured by using third harmonic generation enhancementratio microscopy [15]. Combining THG with second harmonic generation (SHG) microscopy, Liao et al pointed out that some structural variables, including the thickness of dermal papilla zone (DPZ) [16,17] and the size of keratinocytes [17,18], have a statistically significant relationship with intrinsic skin aging. Similarly, Kapsokalyvas et al used in vivo SHG microscopy to measure and characterize the dermal papilla length, corresponding to DPZ thickness, in psoriatic and healthy skin as well [19].…”

Investigating the optical clearing effects of 50% glycerol in ex vivo human skin by harmonic generation microscopy

“…With a laser repetition rate of 105 MHz, the corresponding pulse energy was 0.95 nJ per pulse, with a maximum pulse fluence of 0.18 J/cm 2 at the focal spot and a corresponding scanning power density of 181 W/cm 2 at the sample plane. Under the same experimental conditions, pervious clinical studies indicated that the nonlinear photodamage for 1260-nm is far below the threshold to cause the DNA damage and can be negligible [42][43][44][45][46][47][48]54 . After HGM imaging of the same imaging condition, previous in vivo clinical studies reported that there was no erythema, pigmentation, crust, or vesicular formation, nor does the volunteer feels heat or discomfort [42][43][44][45][46][47][48]54 .…”

“…In this article, we report our OC study on ex vivo human skin with 50% glycerol application by harmonic generation microscopy (HGM). By adopting a femtosecond excitation light 40 located at the skin penetration window around 1300 nm 41 , HGM has been confirmed to be a noninvasive histopathology imaging tool for the differential diagnosis of various skin lesions [42][43][44][45][46] , the study of skin aging 10,47,48 , and other clinical tissues [49][50][51][52] . For comparison purpose, we applied 100% or 50% glycerol by immersion or topical application on human skin to observe if the OC effect varied.…”

“…The 2D pixel size is 460 nm, which is close to the previously measured lateral resolution in live human skin 72 . The average power of the laser after the objective was 100 mW, same as previous in vivo clinical trials [42][43][44][45][46][47][48]54 . With a laser repetition rate of 105 MHz, the corresponding pulse energy was 0.95 nJ per pulse, with a maximum pulse fluence of 0.18 J/cm 2 at the focal spot and a corresponding scanning power density of 181 W/cm 2 at the sample plane.…”