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During retinal laser treatment with a single microsecond laser pulse in the range of 5-50 µs, the induced optoacoutics transients are used to determine the temperature rise and microbubble formation in case of appearance.

Fluorescence Lifetime (FLT) of intrinsic fluorophores may alter under the change in metabolic state. In this study, the FLT of rabbit retina was investigated in vivo after laser irradiation using fluorescence lifetime imaging ophthalmoscopy (FLIO). The retina of the Chinchilla bastard rabbits was irradiated with a 514 nm diode laser. FLIO, fundus photography, and optical coherence tomography (OCT) were conducted 30 min and 1 to 3 weeks after treatment. After strong coagulation, the FLT at laser spots was significantly elongated immediately after irradiation, conversely shortened after more than a week. Histological examination showed eosinophilic substance and melanin clumping in subretinal space at the coagulation spots older than one week. The FLT was also elongated right around the coagulation spots, which corresponded to the discontinuous ellipsoid zone (EZ) on OCT. This EZ change was recovered after one week, and the FLT became the same level as the surroundings. In addition, there was a region around the laser spot where the FLT was temporarily shorter than the surrounding area. When weak pulse energy was applied to selectively destroy only the RPE, a shortening of the FLT was observed immediately around the laser spot within one week after irradiation. FLIO could serve as a tool to evaluate the structural and metabolic response of the retina to laser treatments.

Purpose New lasers with a continuous wave power exceeding 15 W are currently investigated for retinal therapies, promising highly localized effects at and close to the Retinal Pigment Epithelium (RPE). The goal of this work is to evaluate mechanisms and thresholds for RPE cell damage by means of pulse durations up to 50 µs. Methods A diode laser with a wavelength of 514 nm, a power of 15 W, and adjustable pulse durations between 2 µs and 50 µs was used. Porcine RPE-choroidal explants (ex vivo) and chinchilla bastard rabbits (in vivo) were irradiated to determine threshold radiant exposures for RPE damage \({\bar H_{Cell}}\) by calcein vitality staining and fluorescence angiography, respectively. Thresholds for microbubble formation (MBF) \({\bar H_{MBF}}\) were evaluated by time-resolved optoacoustics. Exemplary histologies support the findings. Results \({\bar H_{{{MBF}}}}\) is significantly higher than \({\bar H_{Cell}}\) at pulse durations ≥ 5 µs (P < 0.05) ex vivo, while at 2 µs, no statistically significant difference was found. The ratios between \({\bar H_{{{MBF}}}}\) and \({\bar H_{Cell}}\) increase with pulse duration from 1.07 to 1.48 ex vivo and 1.1 to 1.6 in vivo, for 5.2 and 50 µs. Conclusions Cellular damage with and without MBF related disintegration are both present and very likely to play a role for pulse durations ≥ 5 µs. With the lower µs pulses, selective RPE disruption might be possible, while higher values allow achieving spatially limited thermal effects without MBF. However, both modi require a very accurate real-time dosing control in order to avoid extended retinal disintegration in this power range.

Selective Laser Trabeculoplasty (SLT) is a treatment option for open-angle glaucoma, however, it lacks an instant evidence for successful irradiation. So far ophthalmologists use the visible appearance of permanent champagne like bubbles as an indicator for appropriate pulse energy. We hypothesize that micro bubbles, which take place far below the appearance of macro bubbles already trigger the therapeutic benefit. Here we present two techniques for real-time detection of the onset of micro bubbles. The trabecular meshwork of freshly enucleated porcine eye globes was irradiated, in contrast to conventional SLT, with a series of 15 pulses with a pulse duration of 1.7 μs and with increasing energy at a repetition rate of 100 Hz per each spot of 200 μm in diameter. Both observation methods, an optoacoustic and an optical, are equally capable of detecting micro bubble nucleation, with sensitivities over 0.83 and specificities over 0.89. We demonstrated an accurate method for detection of micro bubble formation in SLT. In case that the therapeutically demanded pressure reduction is already achieved with these micro bubbles, which needs to be proved clinically, then the methods presented here can be used in a feedback loop controlling the laser irradiation. This will unburden the clinicians from any dosing during SLT.

This paper describes the further investigation into the capabilities of the already established noncontact optoacoustic method to measure temperature profiles in cell cultures during controlled heating. The technic is scalable in spatial and temporal resolution. The intra and extracellular medium is heated by a thulium laser (wavelength 1.94 µm; power up to 25W). With a second Q-switched thulium laser (2.01 µm; up to 3 mJ) the sample medium temperature is simultaneously probed in the dish (20 mm diameter) via the photoacoustic effect. The pressure waves emitted due to the thermoelastic expansion of water are measured with an ultrasonic hydrophone at the side of the dish. The amplitudes of the waves are temperature dependent and are used to calculate the temperature/time course at 10 locations. Temperatures of up to 70°C with a heating power of up to 25 W after 5 s were measured, as well as lateral temperature profiles over time. Measurements in water show temperature fluctuations likely due to thermal convection and water circulation. Since measurements in agar do not show similar temperature fluctuations, this theory seems to be confirmed. In conclusion opto-acoustics can serve as a real-time non-contact technique to determine temperature changes in cell and organ cultures as well as in vivo and during hyperthermia based therapies.

Objective/Purpose: In order to study the effects of hyperthermia and other temperature-related effects on cells and tissues, determining the precise time/temperature course is crucial. Here we present a non-contact optoacoustic technique, which provides temperatures during heating of cultured cells with scalable temporal and spatial resolution. Methods: A thulium laser (1.94 µm) with a maximum power of 15 W quickly and efficiently heats cells in a culture dish because of low penetration depth (1/e penetration depths of 78 µm) of the radiation in water. A repetitively Q-switched holmium laser (2.1 µm) is used simultaneously to probe temperatures at different locations in the dish by using the photoacoustic effect. Due to thermoelastic expansion of water, pressure waves are emitted and measured with an ultrasonic hydrophone at the side of the dish. The amplitudes of the waves are temperature dependent and can be used to calculate the temperature/time course at any location of probing. Results: We measured temperatures of up to 55 °C with a heating power of 6 W after 10 s, and subsequent lateral temperature profiles over time. Within this profile, temperature fluctuations were found, likely owing to thermal convection and water circulation. By using cultured retinal pigment epithelial cells, it is shown that the probe laser pulses alone cause no biological damage, while immediate cell damage occurs when heating for 10 s at temperatures exceeding 45 °C. Conclusions: This method shows great potential not only as a noninvasive, non-contact method to determine temperature/time responses of cells in culture, but also for complex tissue and other materials.

Selective retina therapy (SRT) targets the retinal pigment epithelium (RPE) with pulsed laser irradiation by inducing microbubble formation (MBF) at the intracellular melanin granula, which leads to selective cell disruption. The following wound healing process rejuvenates the chorio-retinal junction. Pulse energy thresholds for selective RPE effects vary intra- and interindividually. We present the evaluation of an algorithm that processes backscattered treatment light to detect MBF as an indicator of RPE cell damage since these RPE lesions are invisible during treatment. Eleven patients with central serous chorioretinopathy and four with diabetic macula edema were treated with a SRT system, which uses a wavelength of 527 nm, a repetition rate of 100 Hz, and a pulse duration of 1.7 μs. Fifteen laser pulses with stepwise increasing pulse energy were applied per treatment spot. Overall, 4626 pulses were used for algorithm parameter optimization and testing. Sensitivity and specificity were the metrics maximized through an automatic optimization process. Data were verified by fluorescein angiography. A sensitivity of 1 and a specificity of 0.93 were achieved. The method introduced in this paper can be used for guidance or automatization of microbubble-related treatments like SRT or selective laser trabeculoplasty.

Selective retina therapy (SRT) is an ophthalmological laser technique, targeting the retinal pigment epithelium (RPE) with repetitive microsecond laser pulses, while causing no thermal damage to the neural retina, the photoreceptors as well as the choroid. The RPE cells get damaged mechanically by microbubbles originating, at the intracellular melanosomes. Beneficial effects of SRT on Central Serous Retinopathy (CSR) and Diabetic Macula Edema (DME) have already been shown. Variations in the transmission of the anterior eye media and pigmentation variation of RPE yield in intra- and inter- individual thresholds of the pulse energy required for selective RPE damage. Those selective RPE lesions are not visible. Thus, dosimetry-systems, designed to detect microbubbles as an indicator for RPE cell damage, are demanded elements to facilitate SRT application. Therefore, a technique based on the evaluation of backscattered treatment light has been developed. Data of 127 spots, acquired during 10 clinical treatments of CSR patients, were assigned to a RPE cell damage class, validated by fluorescence angiography (FLA). An algorithm has been designed to match the FLA based information. A sensitivity of 0.9 with a specificity close to 1 is achieved. The data can be processed within microseconds. Thus, the process can be implemented in existing SRT lasers with an automatic pulse wise increasing energy and an automatic irradiation ceasing ability to enable automated treatment close above threshold to prevent adverse effects caused by too high pulse energy. Alternatively, a guidance procedure, informing the treating clinician about the adequacy of the actual settings, is possible.

Photocoagulation is a treatment modality for several retinal diseases. Intra- and inter-individual variations of the retinal absorption as well as ocular transmission and light scattering makes it impossible to achieve a uniform effective exposure with one set of laser parameters. To guarantee a uniform damage throughout the therapy a real-time control is highly requested. Here, an approach to realize a real-time optical feedback using dynamic speckle analysis in-vivo 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 633 nm diode laser and analyzed by a CMOS camera with a frame rate up to 1 kHz. An algorithm is presented that can discriminate between different categories of retinal pigment epithelial damage ex-vivo in enucleated porcine eyes and that seems to be robust to noise in-vivo. Tissue changes in rabbits during retinal coagulation could be observed for different lesion strengths. This algorithm can run 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.

Background The purpose of the study was to evaluate the safety and selectivity of the retinal pigment epithelium lesions by using automatic energy ramping and dosimetry technique for selective retina therapy and to investigate the healing response. Methods Ten eyes of Chinchilla Bastard rabbits were treated with an automatic dosage controlled selective retina therapy laser (frequency doubled Q-switched Nd:YLF, wavelength: 527 nm, pulse duration: 1.7 μs, repetition rate: 100 Hz, pulse energy: linear increasing from pulse to pulse up to shut down – maximal 110 μJ, max. number of pulses in a burst: 30, retinal spot diameter: 133 μm). After treatment, fundus photography, optical coherence tomography and fluorescein angiography were performed at three time points from 1 h to 3 weeks. Histological analysis was performed. Results A total of 381 selective retina therapy laser spots were tested (range 13–104 μJ).Typical fundus photographs obtained at 1 h after irradiation showed that 379 out of 381 lesions produced by selective retina therapy were not visible ophthalmoscopically and the lesions could be detected by angiography only. Optical coherence tomography images revealed that the structure of photoreceptors was preserved, but a disrupted retinal pigment epithelium layer was observed as was expected. By 3 weeks, histology showed selective retinal pigment epithelium damage without any effect on the inner retina and focal proliferation of the retinal pigment epithelium layer. Conclusions Automatically controlled selective retina therapy is a significant improvement in this innovative treatment. It could be demonstrated that the non-contact, reflectometric technique with a controlled pulse energy ramp is safe and selective.

Purpose Selective laser trabeculoplasty (SLT) is a treatment option for open-angle glaucoma; however, it lacks an instant evidence for successful irradiation. So far ophthalmologists use the visible appearance of permanent champagnelike bubbles (macro bubbles) as an indicator for appropriate pulse energy. We hypothesize that micro bubbles, which start energetically far below the appearance of macro bubbles, already trigger the therapeutic benefit. Here we present two methods to capture the onset of these micro bubbles. Methods The trabecular meshwork of freshly enucleated porcine eye globes was irradiated with a series of 15 pulses with a pulse duration of 1.7 μs and with increasing energy at a repetition rate of 100 Hz per each spot of 200 μm in diameter. An optical and an optoacoustic method have been developed and appropriate algorithms investigated towards the real-time detection of the onset of micro bubbles. Results Both observation methods are capable of detecting micro bubble nucleation. Threshold radiant exposures were found at 310 ± 137 mJ/cm2. By combination of both methods a sensitivity and specificity of 0.96 was reached. Conclusions In case that the therapeutically demanded pressure reduction is already achieved with these micro bubbles, which needs to be proven clinically, then the methods presented here can be used in an automatic feedback loop controlling the laser irradiation. This will unburden the clinicians from any dosing during SLT. Translational Relevance Automatic real-time pulse energy dosing based on the formation of micro bubbles in SLT significantly improves and facilitates the treatment for the physician.

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.

Kurzfassung Mittels Selektiven Laserschmelzen hergestellte, konturbezogen temperierte Werkzeugkerne bieten beim Spritzgießen bedeutende Einsparpotenziale durch reduzierte Durchlaufzeiten. Dies konnte bei einem führenden Automobilzulieferer praktisch nachgewiesen werden. Davon ausgehend wurde eine spezifische Konstruktionsrichtlinie für Spritzgießund Druckgusswerkzeuge mit der neuen Temperiermöglichkeit erarbeitet. Aufbauend auf den gemachten positiven Erfahrungen erfolgt die Erprobung konturbezogen temperierter Werkzeugkerne für ein Druckgusswerkzeug.

Selective retina therapy (SRT) stimulates retinal pigment epithelium (RPE) cell migration and proliferation into irradiated areas. The objective of this study was to evaluate the efficacy and safety of SRT in Korean patients with clinically significant diabetic macular edema (DME). Prospective non-randomized interventional case series study. Twenty-three eyes of 21 patients with clinically significant DME were treated with SRT and followed for 6 months. Patients underwent an evaluation of best corrected visual acuity (BCVA) in Early Treatment Diabetic Retinopathy Study (ETDRS) letters. Microperimetry was employed to measure macular sensitivity within the central 10° field, and the central macular thickness (CMT) and maximum macular thickness (MMT) were measured. An improvement in BCVA of one to two ETDRS lines was observed in 41.2 % of patients and an improvement of greater than two lines in 29.4 %. Although there was no significant change in CMT (P > 0.05), MMT decreased from 465.8 ± 87.4 μm to 434.3 ± 83.9 μm (P = 0.006), and mean macular sensitivity increased from 20.8 ± 3.4dB to 22.5 ± 3.5dB (P = 0.02). The gains in BCVA and improvement in macular sensitivity demonstrated that SRT may be used as an effective and safe treatment modality in Korean patients with clinically significant DME.

Laser coagulation of the retina is an established treatment for several retinal diseases. The absorbed laser energy and thus the induced thermal damage varies with the transmittance and scattering properties of the anterior eye media and with the pigmentation of the fundus. The temperature plays the most important role in the coagulation process. An established approach to measure a mean retinal temperature rise is optoacoustics, however it provides limited information on the coagulation. Phase sensitive OCT potentially offers a three dimensional temporally resolved temperature distribution but is very sensitive to slightest movements which are clinically hard to avoid. We develop an optical technique able to monitor and quantify thermally and coagulation induced tissue movements (expansions and contractions) and changes in the tissue structure by dynamic laser speckle analysis (LSA) offering a 2D map of the affected area. A frequency doubled Nd:YAG laser (532nm) is used for photocoagulation. Enucleated porcine eyes are used as targets. The spot is 100μm. A Helium Neon laser (HeNe) is used for illumination. The backscattered light of a HeNe is captured with a camera and the speckle pattern is analyzed. A Q-switched Nd:YLF laser is used for simultaneous temperature measurements with the optoacoustic approach. Radial tissue movements in the micrometer regime have been observed. The signals evaluation by optical flow algorithms and generalized differences tuned out to be able to distinguish between regions with and without immediate cell damage. Both approaches have shown a sensitivity of 93% and a specificity above 99% at their optimal threshold.

The purpose of the study was to evaluate the safety and selectivity of the retinal pigment epithelium lesions by using automatic energy ramping and dosimetry technique for selective retina therapy and to investigate the healing response.Ten eyes of Chinchilla Bastard rabbits were treated with an automatic dosage controlled selective retina therapy laser (frequency doubled Q-switched Nd:YLF, wavelength: 527 nm, pulse duration: 1.7 μs, repetition rate: 100 Hz, pulse energy: linear increasing from pulse to pulse up to shut down - maximal 110 μJ, max. number of pulses in a burst: 30, retinal spot diameter: 133 μm). After treatment, fundus photography, optical coherence tomography and fluorescein angiography were performed at three time points from 1 h to 3 weeks. Histological analysis was performed.A total of 381 selective retina therapy laser spots were tested (range 13-104 μJ).Typical fundus photographs obtained at 1 h after irradiation showed that 379 out of 381 lesions produced by selective retina therapy were not visible ophthalmoscopically and the lesions could be detected by angiography only. Optical coherence tomography images revealed that the structure of photoreceptors was preserved, but a disrupted retinal pigment epithelium layer was observed as was expected. By 3 weeks, histology showed selective retinal pigment epithelium damage without any effect on the inner retina and focal proliferation of the retinal pigment epithelium layer.Automatically controlled selective retina therapy is a significant improvement in this innovative treatment. It could be demonstrated that the non-contact, reflectometric technique with a controlled pulse energy ramp is safe and selective.

Selective Retina Therapy (SRT) targets the Retinal Pigment Epithelium (RPE) without effecting neighboring layers as the photoreceptors or the choroid. SRT related RPE defects are ophthalmoscopically invisible. Owing to this invisibility and the variation of the threshold radiant exposure for RPE damage the treating physician does not know whether the treatment was successful or not. Thus measurement techniques enabling a correct dosing are a demanded element in SRT devices. The acquired signal can be used for monitoring or automatic irradiation control. Existing monitoring techniques are based on the detection of micro-bubbles. These bubbles are the origin of RPE cell damage for pulse durations in the ns and µs time regime 5µs. The detection can be performed by optical or acoustical approaches. Monitoring based on an acoustical approach has already been used to study the beneficial effects of SRT on diabetic macula edema and central serous retinopathy. We have developed a first real time feedback technique able to detect micro-bubble induced characteristics in the backscattered laser light fast enough to cease the laser irradiation within a burst. Therefore the laser energy within a burst of at most 30 pulses is increased linearly with every pulse. The laser irradiation is ceased as soon as micro-bubbles are detected. With this automatic approach it was possible to observe invisible lesions, an intact photoreceptor layer and a reconstruction of the RPE within one week.

We evaluated visual outcomes, changes of maximum macular thickness (MMT) and subretinal fluid (SRF), and safety in patients with chronic central serous chorioretinopathy (CSC) after treatment with selective retina therapy (SRT). Retrospective cohort study of patients with chronic CSC presenting to a university-based hospital from January 2014 through January 2015 was conducted. A total of 12 eyes of 12 patients with chronic CSC lasting for at least 3 months was recruited. The follow-up period ranged from 3 to 12 months. Following evaluation of test spots at temporal arcades, SRT (Q-switched neodymium-doped yttrium lithium fluoride [Nd:YLF] laser; wavelength, 527 nm, pulse duration, 1.7 microsececond) was applied to the surrounding areas of leakage observed on fluorescein angiogram and/or pigment epithelial detachment (PED). Changes in best-correct visual acuity (BCVA), MMT, and SRF and macular sensitivity (MS) by microperimetry (MP) were evaluated. Eyes received treatment in a mean of 3.83 spots at the pulse energy of 65 to 90 μJ. Mean BCVA (logMAR) improved from 0.23 ± 0.12 at baseline to 0.14 ± 0.13 at 3 months. MMT decreased from 341.4 ± 85.5 μm at baseline to 236.0 ± 57.9 μm at 3 months. SRF completely resolved in 75% (9 eyes) at 3 months. Large PEDs (2 eyes) were flattened at 3 months. Retreatment was performed in 4 eyes. MP showed no evidence of scotoma around SRT-treated lesions. SRT treatment targeting the surrounding area of leakage point showed favorable visual and structural outcomes in chronic CSC patients without the risk of scotoma.