In vivo data of epidermal thickness evaluated by optical coherence tomography: Effects of age, gender, skin type, and anatomic site

Summary

Background

The knowledge of epidermal thickness (ET) is of great significance in many areas of medical and biological research.

Objectives

We aimed to assess optical coherence tomography (OCT) in terms of precision, and to investigate the influence of several constitutional factors, such as age, gender, skin type, and anatomic site, on the mean ET using OCT in vivo.

Methods

Eighty-three subjects were studied using OCT in vivo. Intra- and inter-day repeatability measurements were performed. The mean ET was assessed in six different body sites of young (20–40 years old) and old (60–80 years old) Caucasians, respectively. An ethnic group was included into the study.

Results

OCT proved to be a precise technique in terms of repeatability and reproducibility as expressed in low coefficients of variation. Comparison of young and old Caucasians demonstrated a significant decrease of ET with age in all anatomic sites investigated. ET assessed in males and females did not significantly differ, except for forehead skin which is significantly thinner in old females than in males. ET observed in Caucasians did not significantly differ from ET measured in ethnic individuals. Anatomic sites insignificantly influenced ET on an inter-individual level. However, differences of ET between body sites on an intra-individual level are significant.

Conclusions

This was the first systematic in vivo study on ET investigating several influencing parameters of the epidermal dimension in a reasonable study sample by means of OCT. The results presented here may serve as ET reference data in a variety of clinical and experimental matters.

Introduction

The knowledge of the skin thickness is of great significance in many areas of medical and biological research. For example, to understand cutaneous reactions to biochemical or biophysical stimuli, knowledge of epidermal thickness (ET) and its dependence on factors such as gender, age, skin type, and anatomic site are important. Many authors have reported on assessment of ET in relation to various factors without drawing firm conclusions [1], [2], [3], [4], [5], [6]. These investigations have had different purposes, for example, including collection of baseline data on normal skin [4], investigation of the effect of previous sun exposure comparing different sites of the body [3], the relation between ET and pigmentation [2], or the effect of different constitutive factors [7]. Most previous in vivo studies on ET used confocal laser scanning microscopy (CM). These explorative investigations included only a few subjects [3], [4], [5], [8], and studies presenting larger samples (n > 50) have generally been based on histologic investigations either from many different parts of the body or from one anatomic site only [1], [7], [9], [10].

Histology represents the gold standard for morphological investigation of the skin, though biopsy may alter the original morphology, is non-repeatable on the same site and always requires an iatrogenic trauma. In the past decade, advances in optics, fiber as well as laser technology, have enabled the development of novel non-invasive optical biomedical imaging techniques including CM and optical coherence tomography (OCT) [11], [12], [13], [14], [15], [16]. The latter is a promising non-invasive technique capable of generating cross-sectional images of tissue microstructure. The method works analogously to an ultrasound scanner—the major difference is [17], [18], however, that ultrasound pulses are replaced by a fiber-optic Michelson interferometer with a low-coherence-length broadband light source (infrared). The corresponding short coherence length permits a spatial resolution in depth direction of less than 10 μm. The lateral resolution, typically 10–15 μm in conventional OCT, is given by the numerical aperture of the employed objective as long as single scattering prevails. Depending on the scattering properties of tissue and some accepted loss in resolution, a penetration depth of about 1 mm can be achieved using conventional OCT scanners [19], [20], [21].

OCT is particularly capable to present morphological features of the epidermis and papillary dermis. In previous studies, skin appendages including hair follicles and eccrine ducts were identified by OCT [21], [22]. In a pilot study on ET, we observed a high correlation between OCT measurements and formalin-based histology, although the agreement of both methods was not satisfactory. However, agreement between OCT and cryostat-histology has recently been documented in a large-scale method comparison study [23]. Hence, OCT may be considered a very useful tool to study ET in vivo. In the present systematic investigation, we aimed, first, to study the performance the OCT method in terms of precision, second, to investigate the influence of several constitutional factors, such as age, gender, skin type, and anatomic site, on ET using OCT in vivo.