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5 April 2016 Towards real time speckle controlled retinal photocoagulation
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Proceedings Volume 9693, Ophthalmic Technologies XXVI; 96931A (2016)
Event: SPIE BiOS, 2016, San Francisco, California, United States
Photocoagulation is a laser treatment widely used for the therapy of several retinal diseases. Intra- and inter-individual variations of the ocular transmission, light scattering and the retinal absorption makes it impossible to achieve a uniform effective exposure and hence a uniform damage throughout the therapy. A real-time monitoring and control of the induced damage is highly requested. Here, an approach to realize a real time optical feedback using dynamic speckle analysis is presented. A 532 nm continuous wave Nd:YAG laser is used for coagulation. During coagulation, speckle dynamics are monitored by a coherent object illumination using a 633nm HeNe laser and analyzed by a CMOS camera with a frame rate up to 1 kHz. It is obvious that a control system needs to determine whether the desired damage is achieved to shut down the system in a fraction of the exposure time. Here we use a fast and simple adaption of the generalized difference algorithm to analyze the speckle movements. This algorithm runs on a FPGA and is able to calculate a feedback value which is correlated to the thermal and coagulation induced tissue motion and thus the achieved damage. For different spot sizes (50-200 μm) and different exposure times (50-500 ms) the algorithm shows the ability to discriminate between different categories of retinal pigment epithelial damage ex-vivo in enucleated porcine eyes. Furthermore in-vivo experiments in rabbits show the ability of the system to determine tissue changes in living tissue during coagulation.
Conference Presentation
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Katharina Bliedtner, Eric Seifert, Leoni Stockmann, Lisa Effe, and Ralf Brinkmann "Towards real time speckle controlled retinal photocoagulation", Proc. SPIE 9693, Ophthalmic Technologies XXVI, 96931A (5 April 2016);

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