Experimental verification of subthreshold laser therapy using conventional pattern scan laser

PURPOSE Leading-edge therapeutic laser technologies are not available at every medical facility; therefore, alternative approaches incorporating novel advances in digital and laser technology into more readily available conventional methods have generated significant research interest. Using a rabbit model, this study investigated whether the algorithm used in the Endpoint Management (EM) software system of the latest devices could enable subthreshold laser treatment in conventional retinal tissue laser therapy systems. MATERIALS AND METHODS Two types of devices were used, the PASCAL Streamline 577 and the MC 500-Vixi™, and the laser method was classified into three categories: EM; single-shot using PASCAL with arbitrary energy settings (PSS-SDM); and MC500-VixiTM (VX-SDM), which were performed in eight eyes from four Dutch-Belted rabbits. In EM, 100 mW (100%) was set as a landmark, and the laser energy parameters were gradually decreased to 80%, 60%, 50%, 40%, 30%, 20%, and 10%, using a 2 × 3 square pattern. In PSS-SDM and VX-SDM, as control, the laser energy was gradually decreased to 100, 80, 60, 50, 40, 30, 20, and 10 mW. The laser settings were fixed at 200 μm, 20 ms, and a wavelength of 577 μm. To identify and compare the extent of tissue damage at each spot size, optical coherence tomography (OCT) and histological findings were used to construct a three-dimensional histopathology image using a confocal laser scanning fluorescence microscope. RESULTS The spot size at 50% setting on EM was 7183 μm2; PSS-SDM required 50 mW (5503 μm2) to 60 mW (10279 μm2) and VX-SDM required 50 mW (7423 μm2) to create the approximate spot size. Furthermore, at 50 mW of PSS-SDM and VX-SDM, the extent of tissue damage in all three methods was generally in accord with the outer nuclear layer by OCT and inner nuclear layer by histopathological imaging. CONCLUSION These findings suggest that it may be possible to perform subthreshold laser therapy using approximations from the EM algorithm.