THE EFFECT OF THE ILLUMINATION TIME WHEN TREATING PORT-WINE STAINS

This paper reports the electron microscopy results obtained from two p atients who were treated with 5 W of yellow (578 nm) light from a copp er vapour laser with an illumination time of 3.6 ms and a 0.3 mm spot diameter. The endpoint of treatment was transient blanching. Following treatment, erythema was observed. There was minimal damage to the epi dermis and non-vascular tissue such as the nerve fibres. There was sev ere damage to the endothelial cells of the ectatic vessels. Twenty-fou r hours after treatment, platelet activation and collagen were present , indicating that these vessels were no longer viable. Theoretical cal culations are used to determine the flow of heat within and away from a 50 mu m diameter vessel. From this, heating of the entire vessel is shown to occur with illumination times of 4 ms, with minimal heating o f the non-vascular tissue. Shorter illuminations do not heat the entir e vessel, while the use of longer illumination times will cause excess ive damage to the surrounding non-vascular tissue. Illumination times close to 4 ms must be regarded as optimal.