A theoretical and experimental study of light absorption and scattering by in vivo skin.

A theoretical treatment has been developed for the optical properties of a layered structure which absorbs and scatters light. This theory predicts that the logarithm of the inverse of reflectance (LIR) of the surface should be a useful parameter for the examination of that structure. This approach has been applied to a study of skin in vivo. An instrument was constructed for use in clinical situations to measure the LIR spectrum of skin over the visible region of the spectrum (450-760 nm). The contributions to the observed spectra made by pigments and the skin structure were deduced by reference to the theoretical model. Numerical indices were used to quantify the changes in skin haemoglobin content following the application of vasoconstricting preparations. The indices also provided a means of measuring erythema and melanin pigmentation induced in the skin by exposure to ultraviolet radiation. The assessments made using this instrument were more reproducible and sensitive than judgments made by eye.