Impact of left ventricular end-diastolic pressure as a marker for diastolic dysfunction on long-term outcomes in patients undergoing transcatheter aortic valve replacement

OBJECTIVE

The aim of this study was to investigate the proportion of elevated left ventricular end-diastolic pressure (LVEDP) as an indicator of diastolic function after transcatheter aortic valve replacement (TAVR) and its implication in predicting long-term mortality.

METHODS

We analyzed retrospectively collected data on 3328 patients with severe aortic stenosis undergoing TAVR in our institution between July 2009 and June 2021. Patients were stratified into two groups based on invasive post-procedural LVEDP measurements: normal (<15 mmHg) vs. elevated (≥15 mmHg) LVEDP.

RESULTS

Mean age of the patients was 81.6 years, and 53.3% were female. Elevated post-procedural LVEDP was identified in 2408 (72.3%) patients. The 5-year mortality rates were higher in the group with elevated LVEDP compared with the group with normal LVEDP (27.4% vs. 8.3%, p = 0.01; hazard ratio [HR] 1.22, 95% CI 1.05-1.41). A multivariate model revealed the following independent predictors of mortality after TAVR: post-procedural elevated LVEDP (HR 1.24, 95% CI 1.01-1.53), pre-procedural significant tricuspid regurgitation (HR 1.24, 95% CI 1.02-1.52) and pulmonary hypertension (PH) (HR 1.53, 95% CI 1.26-1.86). In the present study, a significant paravalvular leak after TAVR was not associated with higher mortality (HR 1.45, 95% CI-0.95-2.19, p = 0.75).

CONCLUSION

Elevated post-procedural LVEDP in patients who undergo TAVR is an independent predictor of all-cause mortality. Furthermore, PH and tricuspid regurgitation were also identified as predictors of mortality. These data confirm that diastolic dysfunction is an important predictor of mortality in TAVR and should be considered to guide procedure timing, favoring an early interventional approach and management in aortic stenosis patients.

Fluorescence-guided laser lithotripsy: Estimation of the potential effectiveness and safety increase based on first clinical data

In clinically approved laser lithotripsy systems, there is no automatic monitoring of fiber position to date. We investigated whether detecting stone autofluorescence, excited by a green aiming beam, is possible via the fiber during fragmentation by continuously recording the fluorescence signal in 12 ureterosopic lithotripsy procedures. We estimated which threshold the fluorescence signal's amplitude exceeds before laser pulses with visible stone removal by retrospective inspection of the endoscope's video data. For all procedures, blocking the laser when the fluorescence amplitude is below a threshold corresponding to the signal's baseline plus its range (maximum - minimum value) would have been appropriate to suppress ineffective pulses - the energy input could have been reduced by a mean of 14% (1-29%) without changing the operation time. Ablation of the PTFE coating of the guidewire could have been prevented 3 times and cutting of a wire of the retrieval basket 2 times. This article is protected by copyright. All rights reserved.

Energy Compression and Stabilization of Laser-Plasma Accelerators

Laser-plasma accelerators outperform current radio frequency technology in acceleration strength by orders of magnitude. Yet, enabling them to deliver competitive beam quality for demanding applications, particularly in terms of energy spread and stability, remains a major challenge. In this Letter, we propose to combine bunch decompression and active plasma dechirping for drastically improving the energy profile and stability of beams from laser-plasma accelerators. Realistic start-to-end simulations demonstrate the potential of these postacceleration phase-space manipulations for simultaneously reducing an initial energy spread and energy jitter of ∼1-2% to ≲0.1%, closing the beam-quality gap to conventional acceleration schemes.

Compact Multistage Plasma-Based Accelerator Design for Correlated Energy Spread Compensation

The extreme electromagnetic fields sustained by plasma-based accelerators could drastically reduce the size and cost of future accelerator facilities. However, they are also an inherent source of correlated energy spread in the produced beams, which severely limits the usability of these devices. We propose here to split the acceleration process into two plasma stages joined by a magnetic chicane in which the energy correlation induced in the first stage is inverted such that it can be naturally compensated in the second. Simulations of a particular 1.5-m-long setup show that 5.5 GeV beams with relative energy spreads of 1.2×10^{-3} (total) and 2.8×10^{-4} (slice) could be achieved while preserving a submicron emittance. This is at least one order of magnitude below the current state of the art and would enable applications such as compact free-electron lasers.

Observation of the Self-Modulation Instability via Time-Resolved Measurements

Self-modulation of an electron beam in a plasma has been observed. The propagation of a long (several plasma wavelengths) electron bunch in an overdense plasma resulted in the production of multiple bunches via the self-modulation instability. Using a combination of a radio-frequency deflector and a dipole spectrometer, the time and energy structure of the self-modulated beam was measured. The longitudinal phase space measurement showed the modulation of a long electron bunch into three bunches with an approximately 200  keV/c amplitude momentum modulation. Demonstrating this effect is a breakthrough for proton-driven plasma accelerator schemes aiming to utilize the same physical effect.

Indikationsstellung für die zerebrale Angiographie. Entwicklung eines Bayes-Programms zur Entsclieidungsliilfe

Die Anwendung der zerebralen Angiographie bei Patienten mit raumfordernden oder vaskulären Hirnprozessen ist mit einer Reihe von Risiken verbunden. Es wurde ehi Bayes-Programm entwickelt, das den Arzt bei der Indikationsstellung zur zerebralen Angiographie unterstützen soll. In das Programm gehen nur Daten ein, die vor einer Angiographie relativ leicht erhoben werden können. Das Programm basiert auf der Auswertung von 328 Krankengeschichten von Fällen mit abschließend überprüfter Diagnose. Reklassifikationsergebnisse sowie weitere Daten über die Klassifikationsleistung demonstrieren die mögliche Verbesserung der Indikationsentscheidungen.

Chirp Mitigation of Plasma-Accelerated Beams by a Modulated Plasma Density

Plasma-based accelerators offer the possibility to drive future compact light sources and high-energy physics applications. Achieving good beam quality, especially a small beam energy spread, is still one of the major challenges. Here, we propose to use a periodically modulated plasma density to shape the longitudinal fields acting on an electron bunch in the linear wakefield regime. With simulations, we demonstrate an on-average flat accelerating field that maintains a small beam energy spread.

Resection of calcified aortic heart leaflets in vitro by Q-switched 2 µm microsecond laser radiation

BACKGROUND

Transcatheter aortic valve implantation (TAVI) can result in paravalvular leakage and stent deformation in the presence of severe calcification. This study was undertaken to determine the efficacy of laser-assisted resection of calcific aortic valve leaflets as a method to minimize the effects of calcium on perivalvular leakage during TAVI.

METHODS

A Q-switched Tm:YAG laser emitting at a wavelength of 2.01 μm was used to evaluate the cutting efficiency on highly calcified human aortic leaflets in vitro (N = 10). A pulse energy of 4.3 mJ, a pulse duration of 0.8-1 μs, and a repetition rate of 1 kHz were used. The radiation was transmitted via a 200 µm core diameter quartz fiber. Resection was performed in a fiber-tissue contact mode on water-covered samples in a dish. The remnant particles were analyzed with respect to quantity and size by light microscopy.

RESULTS

A resection rate of 40.4 ± 22.2 mg/min on highly calcified aortic leaflets was achieved. This corresponds to a cutting speed of approximately 1 cm/min; a laser dissection time of 3 min per leaflet is expected. The majority of the remnant particles (85.4%) were <6 μm in diameter, with only 0.1% exceeding 300 μm.

CONCLUSIONS

The Q-switched Tm:YAG laser system showed promising results in cutting calcified aortic valves, by transmitting sufficient energy through a small flexible fiber. Catheter-based removal of aortic valve calcification may help to improve TAVI technology.

Implantation Doping and Stimulated Emission of Er3+ in LinbO3:Ti Optical Waveguides

We have implanted Nd and Er ions into x- and z-cut LiNbC3 single crystals and investigated the recrystallization of the host and the rare earth solubility and diffusion. The diffusion is substitutional, fastest parallel to c-axis and characterized by an activation energy of 3.6 eV. Optical fluorescence experiments of Er3+ in a waveguide configuration show stimulated emission and amplification at 1.53, 1.55 and 1.56 μm wavelength.

MeV Ion Implantation of Er into LiNbO3

The incorporation of Er into LiNbO3 is of great interest for fabricating waveguide lasers and amplifiers. We compare Er diffusion data with the results of Er implantation, performed at 3.6 MeV energy. Even after annealing for 4h at 1060°C, the resulting Er profiles display very good matching to the optical modes. The results of a theoretical gain estimate are presented.

[Basic principles and clinical application of retinal laser therapy]

The scientific background of laser photocoagulation of the ocular fundus was studied extensively by several investigators in the 1970 s and 1980 s. The basic principles were successfully resolved during that time and clinical consequences for proper application of the laser photocoagulation for various diseases were deduced. The present paper gives an overview about the physical basics of laser-tissue interactions during and after retinal laser treatment and the particular laser strategies in the treatment of different retinal diseases. Thus, it addresses the issue of the impact on tissue of laser parameters as wavelength, spot size, pulse duration and laser power. Additionally, the different biological tissue reactions after laser treatment are presented, such as, e. g., for retinopexia or macular treatments as well as for diabetic retinopathies. Specific laser strategies such as the selective laser treatment of the RPE (SRT) or the transpupillary thermotherapy (TTT) are presented and discussed.

Numerical modelling of conductive and convective heat transfers in retinal laser applications

The control of the temperature increase is an important issue in retinal laser treatments. Within the fundus of the eye heat, generated by absorption of light, is transmitted by diffusion in the retinal pigment epithelium and in the choroid and lost by convection due to the choroidal blood flow. The temperature can be spatially and temporally determined by solving the heat equation. In a former analytical model this was achieved by assuming uniform convection for the whole fundus of the eye. A numerical method avoiding this unrealistic assumption by considering convective heat transfer only in the choroid is used here to solve the heat equation. Numerical results are compared with experimental results obtained by using a novel method of noninvasive optoacoustic retinal temperature measurements in rabbits. Assuming global convection the perfusion coefficient was evaluated to 0.07 s(-1), whereas a value of 0.32 s(-1)--much closer to values found in the literature (between 0.28 and 0.30 s(-1))--was obtained when choroidal convection was assumed, showing the advantage of the numerical method. The modelling of retinal laser treatment is thus improved and could be considered in the future to optimize treatments by calculating retinal temperature increases under various tissues and laser properties.

Selective retina therapy in patients with central serous chorioretinopathy

BACKGROUND

Central serous chorioretinopathy (CSC) is a disease with a localized breakdown of the outer blood-retinal barrier located within the retinal pigment epithelium (RPE) causing subretinal fluid accumulation. Selective retina therapy (SRT) is a new, minimally invasive laser technology that has been designed to selectively target the RPE. SRT spares retinal tissue.

METHODS

Twenty-seven eyes of 27 patients with active CSC were treated with SRT using a pulsed double-Q-switched Nd-YLF prototype laser (lambda=527 nm, t=1.7 micros). At baseline, best-corrected visual acuity was determined and fluorescein angiography and optical coherence tomography were performed. The patients were followed for up to 3 months.

RESULTS

After 4 weeks 85.2% of patients showed complete resolution of subretinal fluid and in 96.3% there was no leakage visible on fluorescein angiography. After 3 months 100% of patients demonstrated no subretinal fluid and 100% of patients had no leakage activity on fluorescein angiography. Visual acuity, 20/40 at baseline, improved to 20/28 after 4 weeks and to 20/20 after 3 months.

CONCLUSION

SRT is a safe and effective treatment for active CSC. Especially if the RPE leak is located close to the fovea, SRT is the favoured therapeutic option. We recommend earlier treatment of patients with acute CSC in order to prevent development of chronic changes due to CSC with irreversible anatomical and functional damage. SRT might be considered as a first-line treatment for active CSC.

[Selective retina therapy in patients with diabetic maculopathy]

Selective Retina Therapy (SRT) is a new laser treatment that selectively targets the retinal pigmen epithelium (RPE). In this study, we treated 39 patients presenting with nonischemic, focal and focal-diffuse diabetic maculopathy with SRT. In the main. the results indicate that SRT had stabilizing effects on visual acuity, angiographic leakage, lipid exudation, and foveal retinal thickness. SRT is safe and is especially useful for treating pathologies that are located close to the fovea, which cannot be treated with conventional argon laser photocoagulation.

[Selective retina therapy in central serous chorioretinopathy with detachment of the pigmentary epithelium]

BACKGROUND

Selective Retina Therapy (SRT) is a new and innovative laser treatment modality that selectively treats the retinal pigmentary epithelium while sparing the photoreceptors. This therapeutic concept appears to be particularly suitable for treating patients with acute or chronic central serous chorioretinopathy (CSC). We present preliminary results obtained in five patients who had CSC associated with pigmentary epithelium detachment (PED) and serous subretinal fluid (SRF) and who were treated with SRT.

METHODS

This case series was made up of five male patients (mean age 47 years) with chronic CSC and SRF resulting from PED. Examinations performed before and at 1 month and 3 months after the treatment were: BCVA, FLA, OCT (Zeiss OCT III). For SRT, confluent treatment of the PED (area of leakage) was carried out using a pulsed frequency-doubled, Q-switched Nd-YLF prototype laser (lambda=527 nm, t= 1.7 s, 100 Hz, energy = 150-250 J).

RESULTS

Best corrected visual acuity at baseline was 0.53, while after 4 weeks it was 0.56 and after 12 weeks, 0.5. At baseline leakage was seen at the PED on fluorescein angiography in all patients. After 4 weeks leakage activity was no longer noted on angiography in 4 of 5 patients. OCT at baseline showed SRF at the edge of the PED in all patients, but in 4 of the 5 patients this was no longer detectable after 4 weeks.

CONCLUSION

SRT is a safe and effective treatment for patients with CSC in which PED has caused SRF. Not a single case of rip syndrome was observed in this study, even though the PED was treated confluently. Since SRT spares the photoreceptors it is particularly suitable for the treatment of CSC, especially when the origin of leakage is located close to the fovea. The results indicate that SRT leads to reconstruction of the outer blood-retina barrier.

Selektive Retinatherapie

Selective retina therapy (SRT) is currently under evaluation, as a new and very subtle laser method, for the treatment of retinal disorders associated with a degradation of the retinal pigmentary epithelium (RPE). SRT makes it possible to selectively effect the RPE, sparing the adjacent neural retina with the photoreceptors and also the choroid below the RPE. In the best case, the therapy leads to regeneration of the RPE and a long-term metabolic increase at the chorio-retinal junction. In contrast to conventional laser photocoagulation, which is associated with complete thermal necrosis of and around the treated site, absolutely no scotoma occurs in SRT. This paper reviews the methods and mechanisms behind the selective effects of the RPE. In vitro and preclinical results are used to describe the bandwidth of selective effects with respect to different irradiation settings. An optoacoustic technique is introduced to visualize effects that cannot be seen by ophthalmoscopy and to facilitate dosimetry control without recourse to angiography completes the report.

Selective retina therapy (SRT): a review on methods, techniques, preclinical and first clinical results

Selective retina therapy (SRT) is a new laser procedure for retinal diseases that are thought to be associated with a degradation of the retinal pigment epithelium (RPE). The aim of the irradiation is to selectively damage the RPE without affecting the neural retina, the photoreceptors and the choroid. Goal of the treatment is to stimulate RPE cell migration and proliferation into the irradiated areas in order to improve the metabolism at the diseased retinal sites. In a pilot study more than 150 patients with soft drusen, retinopathia centralis serosa (RCS) and macular edema were treated. The first 3-center international trial targets diabetic macular edema and branch vein occlusion. In this review, selective RPE effects are motivated and two modalities to achieve selective RPE effects will be introduced: a pulsed and a continuous wave scanning mode. The mechanism behind selective RPE-effects will be discussed reviewing in vitro results and temperature calculations. So far clinical SRT is performed by applying trains of 30 laser pulses from a Nd:YLF-Laser (527 nm, 1.7 micros, 100 Hz) to the diseased fundus areas. In the range of 450-800 mJ/cm(2) per pulse, RPE-defects in patients were proved angiographically by fluorescein or ICG-leakage. The selectivity with respect to surrounding highly sensitive tissue and the safety range of the treatment will be reviewed. With the laser parameters used neither bleeding nor scotoma, proved by microperimetry, were observed thus demonstrating no adverse effects to the choroid and the photoreceptors, respectively. During and after irradiation, it shows that the irradiated locations are ophthalmoscopically invisible, since the effects are very limited and confined to the RPE, thus a dosimetry control is demanded. We report on a non-invasive opto-acoustic on-line technique to monitor successful RPE-irradiation and compare the data to those achieved with standard angiography one-hour post treatment.

[Selective RPE laser treatment with a scanned cw laser beam in rabbits]

BACKGROUND

Selective RPE laser therapy with sparing of the neurosensory layer is possible by applying repetitive microsecond laser pulses. Macular diseases such as diabetic maculopathy, soft confluent drusen due to age-related macular degeneration or central serous chorioretinopathy were shown to be treated successfully-without concurrent laser scotoma-by this technique. It was the goal of this study to show, if selectivity could also be achieved using a conventional green cw-laser by scanning the beam across the retina during irradiation.

MATERIAL AND METHODS

A cw-laser beam at 532 nm was coupled to a slitlamp via a single mode optical fiber. The spot (18 microm) was scanned across the retina of Dutch-belted rabbits through a contact lens using a two-dimensional acusto-optical deflector. The scan-field was 300 microm x 300 microm in size and consisted of six separate scan lines. The scanning speed was adjusted so as to produce 5 micros exposure at each absorber in the center of the scan line. The entire scan pattern was applied 100 times at each site at a frame rate of 100 Hz. Dose response curve was measured by variation of the laser power. ED(50)-thresholds for RPE damage were calculated by fluorescein angiographic leakage in irradiated areas after exposure to different laser intensities. The extent of selectivity was examined by light microscopy.

RESULTS

Clinically the selective laser-induced RPE defect was demonstrated by fluorescein angiographic leakage and concurrent absence of ophthalmoscopic visibility. The angiographic ED(50)-damage threshold was 161 mJ/cm(2) (66 mW). Ophthalmoscopic visibility was not noticed even with the maximum available radiant exposure of 438 mJ/cm(2) (180 mW). Thus the safety range between angiographic and ophthalmoscopic thresholds had a factor of at least 2.7. First histological examinations revealed selective RPE destruction with intact photoreceptors for irradiation at laser power levels 2 times above angiographic threshold.

CONCLUSION

Selective RPE targeting is feasible with a conventional green cw-laser when scanning the focused laser beam across the fundus with a speed such that every point in exposed RPE is irradiated for duration of 5 micros.

[Fundus autofluorescence after selective RPE laser treatment]

BACKGROUND

The selective RPE laser treatment is a new technique which selectively damages the RPE and avoids adverse effects to the neural retina. A problem is the ophthalmoscopically non-visibility of the laser lesions. The aim of the study was to investigate whether fundus autofluorescence (AF), which is derived from the lipofuscin contained by the RPE cells, is changed due to the RPE damage, and thus may be used for non-invasive treatment control.

METHODS

A total of 26 patients with macular diseases, i.e. diabetic maculopathy (DMP), soft drusen maculopathy (AMD) and central serous retinopathy (CSR), were treated with repetitive short laser pulses (800 ns) from a green Nd:YAG laser (parameters: 532 nm, 100 and 50 pulses at 500 and 125 Hz, retinal spot diameter 200 micrometer, pulse energies 70-175 microJ). AF was excited by 488 nm and detected by a barrier filter at 500 nm (HRA, Heidelberg engineering). Patients were examined by ophthalmoscopy, fluorescein angiography and autofluorescence measurements at various times after treatment (i.e. 1 h, 1 and 6 weeks, 3, 6 and 12 months).

RESULTS

None of the laser lesions was ophthalmoscopically visible during treatment although fluorescein angiography showed leakage of the irradiated areas. Identification of the lesions was possible by AF imaging showing an intensity decay in the irradiated area in 22 out of 26 patients, predominantly in patients with CSR and AMD. Lesions could be identified as hypoautofluorescent spots 1 h after treatment. During follow-up the laser spots became hyperautofluorescent. In patients with DMP some AF images were less helpful due to diffuse edema and larger retinal thickness.

CONCLUSION

Imaging of non-visible selective RPE laser effects can be achieved by AF measurements predominantly in patients without retinal edema. Thus AF may replace invasive fluorescein angiography in many cases to verify therapeutic laser success.

Autofluorescence imaging after selective RPE laser treatment in macular diseases and clinical outcome: a pilot study

AIM

Selective retinal pigment epithelium (RPE) laser treatment is a new technique which selectively damages the RPE while sparing the neural retina. One difficulty is the inability to visualise the laser lesions. The aim of the study was to investigate whether fundus autofluorescence (AF) is changed because of the RPE damage, and thus might be used for treatment control. Additionally, the clinical course of patients with various macular diseases was evaluated.

METHODS

26 patients with macular diseases (diabetic maculopathy (DMP), soft drusen maculopathy (AMD), and central serous retinopathy (CSR)) were treated and followed up for at least 6 months. Treatment was performed with a train of repetitive short laser pulses (800 ns) of a frequency doubled Nd:YAG laser (parameters: 532 nm, 50 and 500 pulses at 100 and 500 Hz, retinal spot diameter 200 micro m, pulse energies 75-175 micro J). AF was excited by 488 nm and detected by a barrier filter at 500 nm (HRA, Heidelberg Engineering, Germany). Patients were examined by ophthalmoscopy, fluorescein angiography, and autofluorescence measurements at various times after treatment (10 minutes, 1 hour, 1 and 6 weeks, 3, 6, and 12 months).

RESULTS

Fluorescein angiography showed leakage from the irradiated areas for about 1 week after treatment. None of the laser lesions was ophthalmoscopically visible during treatment. Identification of the lesions was possible by AF imaging showing an intensity decay in the irradiated area in 22 out of 26 patients, predominantly in patients with CSR and AMD. Lesions could be identified 10 minutes after treatment as hypoautofluorescent spots, which were more pronounced 1 hour later. During follow up the laser spots became hyperautofluorescent. In patients with DMP some AF images were less helpful because of diffuse oedema and larger retinal thickness. In these cases ICG angiography was able to confirm therapeutic success very well. Most of the patients have had benefit from the treatment, with best results obtained for CSR patients.

CONCLUSION

Imaging of non-visible selective RPE laser effects can be achieved by AF measurements predominantly in patients without retinal oedema. Therefore, AF may replace invasive fluorescein angiography in many cases to verify therapeutic laser success. Selective laser treatment has the potential to improve the prognosis of macular diseases without the risk of laser scotomas.

The value of radiation therapy in the management of aggressive non-Hodgkin's lymphomas

Even though chemotherapy plays a major role in the treatment of aggressive non-Hodgkin's lymphomas, the high radiosensitivity of the lymphatic lesions has established radiotherapy as an important component in the management of the disease in localized stages. Nevertheless, the treatment strategies with regard to the stage-adopted indications for radiotherapy, the treatment volume, and the dose remain controversial. This article reviews the available data concerning combined-modality treatment in localized stages and treatment of bulky lesions and residual lymphomas after chemotherapy with emphasis on the role of radiation therapy.

Generation of GW radiation pulses from a VUV free-electron laser operating in the femtosecond regime

Experimental results are presented from vacuum-ultraviolet free-electron laser (FEL) operating in the self-amplified spontaneous emission (SASE) mode. The generation of ultrashort radiation pulses became possible due to specific tailoring of the bunch charge distribution. A complete characterization of the linear and nonlinear modes of the SASE FEL operation was performed. At saturation the FEL produces ultrashort pulses (30-100 fs FWHM) with a peak radiation power in the GW level and with full transverse coherence. The wavelength was tuned in the range of 95-105 nm.

Origin of retinal pigment epithelium cell damage by pulsed laser irradiance in the nanosecond to microsecond time regimen

BACKGROUND AND OBJECTIVE

Selective photodamage of the retinal pigment epithelium (RPE) is a new technique to treat a variety of retinal diseases without causing adverse effects to surrounding tissues such as the neural retina including the photoreceptors and the choroid. In this study, the mechanism of cell damage after laser irradiation was investigated.

STUDY DESIGN/MATERIALS AND METHODS

Single porcine RPE-melanosomes and RPE cells were irradiated with a Nd:YLF laser (wavelength lambda = 527 nm, adjustable pulse duration tau = 250 nsec-3 microsec) and a Nd:YAG laser (lambda = 532 nm, tau = 8 nsec). Fast flash photography was applied to observe vaporization at melanosomes in suspension. A fluorescence viability assay was used to probe the cells vitality.

RESULTS

The threshold radiant exposures for vaporization around individual melanosomes and for ED50 cell damage are similar at 8-nsec pulse duration. Both thresholds increase with pulse duration; however, the ED50 cell damage radiant exposure is 40% lower at 3 microsec. Temperature calculations to model the onset of vaporization around the melanosomes are in good agreement with the experimental results when assuming a surface temperature of 150 degrees C to initiate vaporization and a homogeneous melanosome absorption coefficient of 8,000 cm(-1). Increasing the number of pulses delivered to RPE cells at a repetition rate of 500 Hz, the ED50 value decreases for all pulse durations. However, the behavior does not obey scaling laws such as the N 1/4 equation.

CONCLUSION

The origin of RPE cell damage for single pulse irradiation up to pulse durations of 3 microsec can be described by a damage mechanism in which microbubbles around the melanosomes cause a rupture of the cell structure. The threshold radiant exposure for RPE damage decreases with increasing number of pulses applied.

Beam-profile modulation of thulium laser radiation applied with multimode fibers and its effect on the threshold fluence to vaporize water

The threshold fluences at which vaporization is initiated at the tip of a multimode fiber that is submerged in water were investigated when free-running and Q-switched thulium laser pulses (lambda = 2.01 microm) were applied with different pulse energies. We focused on the quantification of temporal and spatial fluence modulations of the beam profile at the tip of a 400-microm fiber. The spatial and the temporal fluence peaks over the average fluence were measured to as high as 1.5 and 4 in the Q-switched mode, respectively, and 2.5 and 40 in the free-running mode, respectively. The fluence peaks significantly influence the vaporization process. An increase in the threshold fluence with increasing pulse energy was found for the Q-switched mode, but there was a decrease for the free-running mode. Pressure transients of the order of 1 kbar and temperatures higher than 200 degrees C were calculated for a 30-mJ Q-switched laser pulse at the onset of vaporization. Collecting all the data allowed us to trace the thermodynamic path of rapid heating and vaporization in a phase diagram of water.

Corneal Endothelial Cell Damage After Experimental Diode Laser Thermal Keratoplasty

PURPOSE

To evaluate the safety of diode laser thermal keratoplasty (LTK) with respect to corneal endothelial cell damage.

METHODS

In an in vitro animal model system, porcine eyes were irradiated with a continuously emitting laser diode at wavelengths (lambda) of 1.85 or 1.87 microm, corresponding to an absorption coefficient (micro(a)) of 1.1 or 2.0 mm(-1). Different irradiation and application parameters were tested serially. To determine the temperature threshold for endothelial damage, corneal buttons were analyzed separately in a waterbath experiment. The endothelial damage was assessed after trypan blue and alizarin red supravital staining under light microscopy.

RESULTS

The thresholds for the 50% probability of thermal damage (ED50) were determined at corneal temperatures of 65 degrees C for a 10-second water-bath immersion, and 59 degrees C for 60 seconds. Coagulations that reached the deeper stromal layers revealed severe endothelial cellular alterations and areas of exposed Descemet's membrane. The thermally induced changes were dependent on laser power and the absorption coefficient (wavelength). Mean diameter of total endothelial cell damage was 245 +/- 154 microm (range, 0 to 594 microm) for an absorption coefficient of 1.1 mm(-1). The maximal lateral extent of endothelial cell damage induced by the laser exposure was 594 microm in diameter. Increasing the absorption coefficient decreased the penetration depth of the laser irradiation, creating a greater temperature rise within the corneal stroma and significantly less endothelial damage (P < .01), when the same laser power was applied. The calculated total area of damage for the paracentral human corneal endothelium ranged from 1.8% to 13.6%.

CONCLUSION

Data obtained in this in vitro study were transferred to an endothelial cell damage nomogram, demonstrating that appropriate parameter improvements can minimize the adverse effects to the corneal endothelium. However, model adjustment to the human cornea indicates the potential for endothelial cell damage after diode laser thermal keratoplasty, and should be considered when performing this elective procedure.

Thermal and biomechanical parameters of porcine cornea

PURPOSE

New methods in refractive surgery require a considerable understanding of the material "cornea" and are often studied by theoretical modeling in order to gain insight into the procedure and an optimized approach to the technique. The quality of these models is highly dependent on the preciseness of its input parameters. Porcine cornea often is used as a model in preclinical studies because of its similarity to man and its availability.

METHODS

The important physical parameters for biomechanical deformation, heat conduction, and collagen denaturation kinetics have been determined for porcine cornea. Experimental methods include densitometry, calorimetry, turbidimetry, tensile tests, stress relaxation, and hydrothermal isometric tension measurements.

RESULTS

The density of porcine cornea was measured as p = 1062+/-5 kg/m3, the heat capacity gave c = 3.74+/-0.05 J/gK. The stress-strain relation for corneal strips is represented by a third order approximation where the secant modulus yields about Esec approximately equal to 0.4 MPa for small strains less than 2%. The normalized stress relaxation is described by an exponential fit over time. The denaturation process of cornea is characterized by specific temperatures which can be related to the change of the mechanical properties. Denaturation kinetics are described according to the model of Arrhenius yielding the activation energy deltaEa = 106 kJ/mol and the phase transition entropy deltaS = 39 J/(mol x K).

CONCLUSIONS

The established set of parameters characterizes the porcine cornea in a reliable way that creates a basis for corneal models. It furthermore gives direct hints of how to treat cornea in certain refractive techniques.

Influence of temperature and time on thermally induced forces in corneal collagen and the effect on laser thermokeratoplasty

PURPOSE

To investigate thermomechanical aspects of corneal collagen denaturation as a function of temperature and time and the effect of the induced forces on refractive changes with laser thermokeratoplasty (LTK).

SETTING

Medical Laser Center Lübeck, Lübeck, Germany.

METHODS

In a material-test setup, porcine corneal strips were denatured in paraffin oil at various constant temperatures for 10 and 500 seconds, and the temporal course of the contractive forces was studied under isometric conditions. Typical LTK lesions were performed in porcine eyes in vitro with a continuous-wave infrared laser diode at a wavelength of 1.87 microm for 10 and 60 seconds. The laser power was chosen to achieve comparable denatured volumes at both irradiation times. The refractive changes were measured and analyzed by histologic evaluations and temperature calculations.

RESULTS

The time course of the induced forces was characterized by a maximal force, which increased almost linearly with temperature, and a residual lower force. After 500 seconds of heating, the highest force was achieved with a temperature of 75 degrees C. With a limited heating period of only 10 seconds, the forces steadily increased with temperature over the entire observation period. Laser thermokeratoplasty produced less refractive change after 10 seconds of irradiation than after 60 seconds, although the laser power was 25% higher in the short heating period. Polarization light microscopy of LTK lesions revealed different stages of thermal damage.

CONCLUSION

The course of the contractive forces during and after heating is a complicated function of the spatial time/temperature profile. Laser thermokeratoplasty lesions produced with 2 irradiation times showed different stages of denaturation and induced refractive change.

Subthreshold (retinal pigment epithelium) photocoagulation in macular diseases: a pilot study

BACKGROUND

Subthreshold (retinal pigment epithelium) photocoagulation is a new photocoagulation method, which treats the retinal pigment epithelium (RPE) and avoids damage to the neural retina. The initial results in this prospective pilot study on various macular diseases are presented.

METHODS

12 patients with diabetic maculopathy (group I), 10 with soft drusen (group II), and four with central serous retinopathy (CSR) (group III) were treated and followed up for 1 year. Treatment was achieved using a train of repetitive short laser pulses (1.7 micros) of a green Nd:YLF laser (parameters: 527 nm, 100 and 500 pulses, repetition rate: 500 Hz, spot size: 160 microm, energies: 70-100 microJ). Laser energy was based on the visibility of test lesions on fluorescein angiography (50-130 microJ). Patients were examined at various times by ophthalmoscopy, fluorescein and ICG angiography, and infrared imaging.

RESULTS

After 6 months hard exudates disappeared in six out of nine patients in group I and leakage disappeared in six out of 12 diabetic patients. In group II drusen were less in seven out of 10 patients. In group III serous detachment disappeared in three out of four cases. Visual acuity was stable in all cases. None of the laser lesions was clinically visible immediately. After 1 day most lesions were visible as yellowish RPE depigmentation. After 3 months some of the lesions were visible as hyperpigmented areas but most were not. Fluorescein angiography showed leakage only in the first week. Infrared imaging showed that most lesions can be visualised in groups I and II after a period longer than 1 week as hyperreflective areas.

CONCLUSION

This study showed that subthreshold (RPE) photocoagulation is effective in some cases of diabetic maculopathy, drusens, and in CSR. Visibility of laser burns is not always necessary in the treatment of macular diseases presented here. Infrared imaging is an effective and non-invasive way of visualising subthreshold (RPE) laser burns.