Action spectrum of vascular specific injury using pulsed irradiation.

It has been clearly demonstrated that cutaneous blood vessels will be selectively damaged by a laser whose wavelength matches one of the three absorption spectral peaks of the chromophore, oxyhemoglobin, for example, 577 nm. A restriction in the application of this wavelength for the treatment of benign cutaneous vascular tumors, such as portwine stains, has been the penetration depth of 577 nm irradiation of approximately 0.5 mm from the dermal epidermal junction (DEJ). This study was undertaken to establish whether it was possible to increase the penetration depth from 0.5 mm by changing the wavelength to beyond 577 nm in albino pig skin. Results from this study confirm that penetration depth increases from 0.5 to 1.2 mm by changing the wavelength from 577 to 585 nm at 4 J/cm2, while maintaining the same degree of vascular selectivity as that previously described after 577 nm irradiation. This occurred in spite of a mismatch in the wavelength between 585 nm and the oxyhemoglobin absorption peak of 577 nm. Unlike 585 nm irradiation and in contrast with theoretical predictions, 590 nm laser light did not penetrate as deeply as 585 nm. Not only was there a reduction in the penetration depth of the laser beam from 1.2 mm at 585 nm to 0.8 mm at 590 nm, at 4 J/cm2, but there was also a decrease in vascular selectivity in albino pig skin exposed to 590 nm irradiation.