Optical modelling of light distributions in skin tissue following laser irradiation

A Monte-Carlo method is used to compute light distributions in a multilayer skin model for variable width finite beams. By means of a 4-layer skin model in which blood may be represented as a discrete layer, vascular lesions such as port wine stains may be studied. Light distributions and thermal profiles are simulated, representing the irradiation of a port wine stain using 577 nm and 585 nm wavelengths. Damage thresholds at 585 nm are found to substantially exceed those predicted at 577 nm, although the nature of the damage differs at the two wavelengths. Variations due to beam width are found to be unimportant if the diameter exceeds 1 mm. The predictions are compared with clinical results, and a novel 5-layer approach based on new optical parameters is adopted to account for discrepancies in epidermal temperature.