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The Neodynium: Yttrium Aluminum Garnet (Nd: YAG) laser has been the most frequently used laser in correcting equine upper respiratory disorders.'4 Evaluation of this laser and several other lasers' ability to penetrate tissues is based on in vitro studies using portions of the arytenoid cartilage and the nasal septum.5 The parameters measured have routinely been the depth and width of the crater created by laser irradiation of the tissue.5 Previous studies, now considered the standard, have used a power output of 200 joules to create a measurable crater in order to make comparisons.5'6 The initial method of measurement consists of standard histological preparation followed by microscopic evaluation. This has been compared to computed tomography which has been determined to be as accurate.5'6 In a more recent study, we compared the 980nm and 810nm diode lasers producing a total power output of 20 watts, to the Nd: YAG laser.7 As demonstrated, both diode lasers can potentially be used as a substitute for the Nd: YAG laser.7 Our study also indicated that intravenous administration of indocyanine green (ICG) greatly enhanced the depth and width of crater formation in equine respiratory tissue with the laser set at 200 joules total power output.7 Intravenous administration of ICG was found to be an expensive protocol, therefore, the current study was devised to determine the penetration parameters of ICG after topical administration. The evaluation consisted of comparing depths and widths of penetration measured by computed tomography technique after ICG was topically sprayed on the tissue with solution concentrations ranging from 0. 1 % to 1%. The study's results demonstrated that topical application of ICG greater than or equal to 0.5% solution produced a depth ofpenetration significantly greater (p>0.05) than that ofthe Nd: YAG laser. The width measurements of craters created by the diode laser irradiation were found to be significantly less than those produced by the Nd: YAG laser. It was concluded that topical administration of ICG was more economical than intravenous administration.
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