Light must penetrate the skin before it can exert therapeutic effect or offer diagnostic information. Laser radiation will penetrate some tissues better than others due to variation in tissue optical properties. Skin is a particularly difficult tissue to penetrate because of the strong scattering properties of the dermis. Fortunately, skin is a relatively thin tissue, and the shallow penetration of light is sufficient for strong interaction with the epidermis and upper dermis. The availability of the skin surface for topical irradiation makes the use of lasers in dermatology an attractive modality. This paper will discuss the basics of skin optics that are pertinent to proper dosimetry of laser irradiation in dermatology. Examples of dosimetry for wavelengths pertinent to photodynamic therapy and for laser therapy of portwine stain lesions at 577 nm wavelength are presented.
S. L. Jacques, "The role of skin optics in diagnostic and therapeutic use of lasers," Lasers in Dermatology, edited by R. W. Steiner, R. Kaufmann, M. Landthaler, O. Braun- Falco, , 1-21 (1991).