Beauty Research Center, Kao Corporation, Bunka, Sumida-ku, Tokyo, Japan.
J Biomed Opt. 2013 Mar;18(3):037002. doi: 10.1117/1.JBO.18.3.037002.
We adapted the critical angle method for measuring rough surfaces under partial contact to acquire an in vivo skin refractive index (RI). Assuming that the total reflection is the simple sum of reflection from areas that are in contact and reflection from those that are not in contact, the RI can be estimated even for partial contact with a rough surface. We found that cheek skin is sufficiently soft that a sufficiently large area can be in contact and that the critical angle was detectable. The RIs of the cheeks of adult females were measured. The RI range was about 1.51 to 1.53, at a wavelength of 550 nm, without considering systematic errors. The RIs of cheeks are significantly correlated with their conductance, which corresponds to their water content. We determined the relationship between the RI and conductance within the variation of skin under normal conditions; this relationship was theoretically obtained in previous studies. In the present study, a direct in vivo measurement method was developed that enabled us to measure the RI in daily life, although this method contains errors for several reasons, including disregarding absorption.
我们采用临界角法测量部分接触下的粗糙表面，以获取活体皮肤折射率（RI）。假设全反射是接触区域反射和未接触区域反射的简单叠加，则即使在粗糙表面的部分接触下，也可以估计 RI。我们发现脸颊皮肤足够柔软，可以有足够大的面积接触，并且可以检测到临界角。测量了成年女性脸颊的 RI。在波长为 550nm 时，不考虑系统误差，RI 范围约为 1.51 至 1.53。脸颊的 RI 与它们的电导显著相关，电导对应于它们的含水量。我们在正常条件下皮肤的变化范围内确定了 RI 和电导之间的关系；这一关系在以前的研究中从理论上得到了。在本研究中，开发了一种直接的活体测量方法，使我们能够在日常生活中测量 RI，尽管由于包括忽略吸收在内的几个原因，该方法存在误差。
