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Ralf Brinkmann, Hossam Abbas, Christopher Kren, Veit Danicke, Dirk Theisen-Kunde, Yoko Miura, Jan Tode, Claus von der Burchard, Johann Roider; Automatic Temperature Controlled Retinal Laser Therapies. Invest. Ophthalmol. Vis. Sci. 2020;61(7):1354.
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Laser treatments at the retina lack an objective dosing control, particularly for sub visible irradiations, which become more and more popular. The laser effects vary owing to large variations of light transmission in the eye and of RPE absorption. We previously demonstrated an optoacoustic method to determine the temperature rise during laser irradiation in real-time in clinical trials. Here, we realized a first closed loop feedback control which frequently varies the laser power during irradiation in order to achieve a desired temperature rise preselected by the ophthalmologist.
We used a standard treatment laser (Carl Zeiss Meditec AG, Visulas 532s). The laser fiber was coupled to a control box containing a pulsed probe laser (Crystalaser Inc., 523 nm, 75 ns, 1 or 3 kHz) and fast attenuation optics to modify the power of the therapy laser with a frequency of 1 or 3 kHz. Both beams were transmitted by the same fiber to the laser slitlamp. The probe laser excites thermoelastic pressure waves at the retina, which become stronger with temperature rise. The pressure transients were measured by an ultrasonic transducer embedded in a contact lens. A control software calculated the required laser power in real-time in order to achieve the desired temperature rise. Experiments were performed on RPE-choroid explants form freshly enucleated pig eye, on whole pig eye globes and on Chinchilla bastard rabbits. The effects were investigated by calcein-am in vitro and by funduscopy and fluorescein angiography in vivo.
Different aim temperatures between 45°C and 70°C have been chosen for irradiation times between 50-200 ms and treatment spot diameter of 200 µm. The control circuit allowed a quick temperature increase within 10-50 ms, depending on control settings, while keeping the aim temperature constant until the end of the irradiation. Therefore, the laser power rose quickly until the aim temperature was achieved and then dropped exponentially. The ratio of the achieved temperature rise to the desired aim temperature was 100.5% ± 3.3 %.
A fast real-time feedback control scheme has been demonstrated to reliably achieve a desired preselected temperature rise at each individual retinal target site. For the first time, this allows a reliable thermal impact for visible or subvisible coagulations or for sublethal hyperthermia. This method and technique will be further investigated in a clinical pilot study in 2020.
This is a 2020 ARVO Annual Meeting abstract.
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