Refractive index of bio-tissue and its thermal response

Although preliminary theories of light propagation in tissue have been constructed, tissue optics has not come that far and the development of methods for assessing tissue optical properties is not yet finished. On the one hand, such a situation arises from the variety and complexity of bio-tissue; on the other hand, effective research concepts and technical means are lacking. One of the most important reasons for this, in the authors' opinion, is the concept of what the refractive index of tissue is, and how to measure it in vivo and even in vitro. Unfortunately, these problems are neglected somewhat despite the fact that many researchers seem to rely on the inferred values of refractive index. However, it makes no difference whether the concept of refractive index exists or not in tissue optics. For these reasons, the main significance of the refractive index of bio-tissue, its measurement methods and its thermal properties in particular, are presented.