Objective dose control is currently not possible for laser treatments at the retina. Especially in the case of subvisible irradiations, the assessment of the intended temperature effects by the visual control of the doctors is impossible. Due to the large individual differences in light transmission of the eye and absorption at the RPE, for the same laser power the achieved temperature varies at the RPE. Therefore, an opto acoustic technique to measure the temperature of the retina during laser treatment was developed and applied in a clinical study. A conventional 532 nm cw laser was used during a standard treatment. A microcontroller-based control module was optically coupled between the treatment laser and the slit lamp. This control module is able to measure and automatically control the RPE temperature rise in real time at a rate of 3 kHz and regulates the laser power in such a way that a target temperature specified by the physician is reached within several ms and kept constant until the end of the irradiation time of 100 ms. In the clinical study on patients with CSCR, a target temperature of 51°C was set. So far 7 Patients were treated. Target temperature could be reached and kept constant until the end of irradiation time of 100 ms. A wide range of applied laser power (35 to 95 mW) was used and show the need for active control during retinal laser treatment. It was demonstrated that temperature-controlled retinal laser therapy can be applied safely in patients.
The recently developed SLIDE microscope enables rapid imaging in nonlinear two-photon microscopy, where frame rates of 4 kHz are achieved. Such fast acquisition speeds coupled with the molecular specificity of fluorescence markers and the high optical resolution in the sub-μm range allow volume scan rates at 40 Hz. A commercially available Fourier Domain Mode Locked Laser system (Optores GmbH, Munich, Germany) was used as the light source emitting at 1060 nm (Bandwidth 15 nm). An electro-optical Modulator (EOM) splits the light of a single sweep duration up into 600 pulses with 30 ps pulse duration each. Each of it is then spatial separated by a diffractive grating. Only one scanner is needed for beam steering to excite the slow axis resulting to a frame rate of 4 kHz. Using a piezo driver for the objective of the microscope at a frequency of 20 Hz, a live 4D volume scan of 40 Hz with 600 x 400 x 100 voxel is possible. Until now, SLIDE systems were bulky and bound onto a fixed optical desk. The Medical Laser Centre Lübeck developed a transportable and reliable SLIDE system, so that this new and highly innovative technology can be made available to various biological laboratories in Europe. This work was conducted in the framework of the EU project “Faircharm.”
Automatic feedback temperature control has been proposed recently as a promising approach for retinal thermal laser therapy. It can regulate the retinal temperature increase to a pre-specified desired value, which can provide homogeneous temperature increase at the different irradiation sites as the feedback control can automatically set the required corresponding laser power. Therefore, we can avoid over treatment and its consequences due to the manual setting often provided by ophthalmologists in practice. However, in order to achieve successful automatic treatment, a mathematical model for the process is necessary to synthesize the feedback control algorithm. In this study, we develop a model, which can describe the dynamical relation between the temperature increase and the applied laser power at the different irradiation sites. We adopt the system identification approach, which is used to build mathematical models for dynamical systems based on experimental measurements. The identified model here can fit the rear-time data with an accuracy of about 91 ± 1.91%, which indicates its validity for effective feedback control. The control algorithm based on such models can achieve consistent irradiation time of about 50 ms in simulation
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