Skin phototesting using a divergent ultraviolet B beam : development and evaluation on a normal material

Abstract: The phototesting method proposed provokes the skin by means of a divergent UVB beam. The beam divergence is induced by an optical plano-concave !ens placed at the opening of the light guide which directs the light from the UV lamp to the skin. The relationship between the dose administration and the following skin response could be fully exploited by the introduction of adapted dosimetry and skin assessment techniques and procedures. Two-dimensional maps of the irradiance field were plotted by use of a specially built scanning detector unit. The beam divergence thus resulted in an irradiance (dose) field with a profile consisting of 20 sampled irradiance (dose) values, administered to the skin <luring one single illumination. Skin reaction diameter was measured both visually and by laser Doppler perfusion imaging (LDPI). This diameter was then directly translated to an MED value by utilisation of the mm for mm correspondence between skin response and irradiance field.Phototesting based on the divergent UVB beam was evaluated on 20 healthy volunteers. The method proved its potential to determine an MED with a single provocation. No systematic difference could be seen between assessment methods (LDPI and visual assessment). The 95% confidence interval for the mean difference between LDPI and visual diameters was calculated to (-0.8, 2.0). Exploiting the characteristic symmetry in both LDPI and dosimetry data allowed the generation of dose-response information for each subject.The divergent beam phototesting protocol has shown sufficient promise to warrant further improvement of the technical pre-requisites, the extension of the clinical material to patients with known light sensitivity and the investigation of the technique' s use in basic research.