Anderson, 1981  Title: The optics of human skin.
Authors: Anderson RR, Parrish JA
Journal: J Invest Dermatol 1981 Jul;77(1):13-9
PMID: 7252245, UI: 81240972
Affiliated institution:
Cited in: Williams, Lin, Dierickx
An integrated review of the transfer of optical
radiation into human skin is presented, aimed at developing useful
models for photomedicine. The component chromophores of epidermis
and stratum corneum in general determine the attenuation of radiation
in these layers, moreso than does optical scattering. Epidermal
thickness and melanization are important factors for UV wavelengths
less than 300 nm, whereas the attenuation of UVA (320-400 nm)
and visible radiation is primarily via melanin. The selective
penetration of all optical wavelengths into psoriatic skin can
be maximized by application of clear lipophilic liquids, which
decrease regular reflectance by a refractive-index matching mechanism.
Sensitivity to wavelengths less than 320 nm can be enhanced by
prolonged aqueous bathing, which extracts urocanic acid and other
diffusible epidermal chromophores. Optical properties of the dermis
are modelled using the Kubelka-Munk approach, and calculations
of scattering and absorption coefficients are presented. This
simple approach allows estimates of the penetration of radiation
in vivo using noninvasive measurements of cutaneous spectral remittance
(diffuse reflectance). Although the blood chromophores Hb, HbO2,
and bilirubin determine dermal absorption of wavelengths longer
than 320 nm, scattering by collagen fibers largely determines
the depths to which these wavelengths penetrate the dermis, and
profoundly modifies skin colors. An optical "window"
exists between 600 and 1300 nm, which offers the possibility of
treating large tissue volumes with certain long-wavelength photosensitizers.
Moreover, whenever photosensitized action spectra extend across
the near UV and/or visible spectrum, judicious choice of wavelengths
allows some selection of the tissue layers directly affected.
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