Monitoring of Cerebral Oxygen Saturation in Interhospital Transport of Patients Receiving Extracorporeal Membrane Oxygenation.

Extracorporeal membrane oxygenation (ECMO) in acute respiratory distress syndrome (ARDS) is used to achieve oxygenation and protect lung ventilation. Near infrared spectroscopy (NIRS) measures cerebral regional tissue oxygenation (rSO 2 ) and may contribute to patient safety during interhospital transport under ECMO support. We evaluated 16 adult ARDS patients undergoing interhospital ECMO transport by measuring cerebral rSO 2 before and after initiation of ECMO support and continuously during transport. To compare peripheral oxygen saturation (SpO 2 ) measurement with rSO 2 , both parameters were analyzed. NIRS monitoring for initiation of ECMO and interhospital transport under ECMO support was feasible, and there was no significant difference in the percentage of achievable valid measurements over time between cerebral rSO 2 (88.4% [95% confidence interval {CI}, 81.3-95.0%]) and standard SpO 2 monitoring 91.7% (95% CI, 86.1-94.2%), p = 0.68. No change in cerebral rSO 2 was observed before 77% (73.5-81%) (median [interquartile range {IQR}]) and after initiation of ECMO support 78% (75-81%), p = 0.2. NIRS for cerebral rSO 2 measurement is feasible during ECMO initiation and interhospital transport. Achievement of valid measurements of cerebral rSO 2 was not superior to SpO 2 . In distinct patients ( e.g. , shock), measurement of cerebral rSO 2 may contribute to improvement of patient safety during interhospital ECMO transport.

The efficacy of corneal cross-linking shows a sudden decrease with very high intensity UV light and short treatment time.

PURPOSE: Standard treatment in cases of progressive keratectasia is UV-triggered corneal cross-linking. For irradiances larger than 10 mW/cm(2) and treatment times below 10 minutes, the scientific proof of a biomechanical strengthening effect is insufficient. The authors investigated the biomechanical strengthening of ex vivo corneal tissue treated with irradiances between 3 mW/cm(2) and 90 mW/cm(2) and illumination times from 30 minutes to 1 minute, respectively. METHODS: A total of 100 porcine eyes received riboflavin + UV treatment (constant irradiation dose of 5.4 J/cm(2)) with different intensities and illumination times and were randomly assigned into 10 groups. A control group (80 eyes) was not irradiated but underwent the same treatment otherwise. Young's modulus at 10% strain was determined for each strip after uniaxial stress-strain measurement. A Kruskal-Wallis test was used for statistical analysis. RESULTS: A statistically significant difference (α = 0.01) was found between the median value of Young's modulus of the treatment groups up to 45 mW/cm(2) (illumination times from 30 minutes to 2 minutes) compared with the control group. There was no statistically significant difference between the treatment groups from 50 mW/cm(2) up to 90 mW/cm(2) (illumination times of less than 2 minutes) and the control group. CONCLUSIONS: The ex vivo results of corneal cross-linking performed in porcine corneas show that the Bunsen-Roscoe reciprocity law is only valid for illumination intensities up to 40 to 50 mW/cm(2) and illumination times of more than 2 minutes. Further experiments are necessary to validate these results for in vivo human corneal tissue. Additionally, safety aspects at high intensities must be investigated.

Riboflavin/ultraviolet a crosslinking of the paracentral cornea.

PURPOSE: The depth of corneal crosslinking (CXL) does not seem homogeneous within the treatment area but shows a reduction toward the periphery of the cornea. This study was undertaken to investigate this reduction effect and to look for possible solutions. METHODS: Ten corneas were investigated by means of an optical coherence tomography system (SS-100; Tomey, Nagoya, Japan) 1 month after standard CXL (epithelium off, 0.1% riboflavin for 30 minutes, ultraviolet A radiation 365 nm, 3 mW/cm). The depth of the demarcation line was measured as a function of the radial distance from the apex. These curves were compared with a theoretical curve derived from a standard model of photopolymerization. RESULTS: The CXL depth 3 mm away from the center decreases on average to 65% of the central depth (range: 52%-78%). Polymerization theory predicts this decay, however, underestimates the effect. CONCLUSIONS: The intended depth of CXL using current light sources is achieved only within the central area of the cornea. To provide CXL to the peripheral cornea, the ultraviolet beam either should have an improved intensity profile or may have to be decentered.

Initial surface temperature of PMMA plates used for daily laser calibration affects the predictability of corneal refractive surgery.

PURPOSE: To investigate the relevance of initial temperature of the polymethylmethacrylate (PMMA) plates used as a target for photoablation during calibration of excimer lasers performed in daily clinical routine. METHODS: An experimental argon fluoride excimer laser with a repetition rate of 1050 Hz, a radiant exposure of 500 mJ/cm², and single pulse energy of 2.1 mJ was used for photoablation of PMMA plates. The initial plate temperature varied from 10.1°C to 75.7°C. The initial temperature was measured with an infrared camera and the central ablation depth of a myopic ablation of -9.00 diopters (D) with an optical zone of 6.5 mm was measured by means of a surface profiling system. RESULTS: The ablation depth increased linearly from 73.9 to 96.3 µm within a temperature increase from 10.1°C to 75.7°C (increase rate of 0.3192 µm/K). The linear correlation was found to be significant (P<.05) with a coefficient of determination of R²=0.95. Based on these results and assuming a standard room temperature of 20°C, optimal plate temperature was calculated to be 15°C to 25°C to maintain an ablation within 0.25 D. CONCLUSIONS: The temperature of PMMA plates for clinical laser calibration should be controlled ideally within a range of approximately ±5°C, to avoid visually significant refractive error due to calibration error. Further experimental investigations are required to determine the influence of different initial corneal temperatures on the refractive outcome.

Optimization model for UV-riboflavin corneal cross-linking.

PURPOSE: To develop a theoretical model for riboflavin ultraviolet-A cross-linking treatment that can predict the increase in stiffness of the corneal tissue as a function of the ultraviolet intensity and riboflavin concentration distribution, as well as the treatment time. METHODS: A theoretical model for calculating the increase in corneal cross-linking (polymerization rate) was derived using Fick's second law of diffusion, Lambert-Beer's law of light absorption, and a photopolymerization rate equation. Stress-strain experiments to determine Young's modulus at 5% strain were performed on 43 sets of paired porcine corneal strips at different intensities (3-7 mW/cm²) and different riboflavin concentrations (0.0%-0.5%). The experimental results for Young's modulus increase were correlated with the simulated polymerization increase to determine a relationship between the model and the experimental data. RESULTS: This model allows the calculation of the one-dimensional spatial and temporal intensity and concentration distribution. The total absorbed radiant exposure, defined by intensity, concentration distribution, and treatment time, shows a linear correlation with the measured stiffness increase from which a threshold value of 1.7 J/cm² can be determined. The relative stiffness increase shows a linear correlation with the theoretical polymer increase per depth of tissue, as calculated by the model. CONCLUSIONS: This theoretical model predicts the spatial distribution of increased stiffness by corneal cross-linking and, as such, can be used to customize treatment, according to the patient's corneal thickness and medical indication.

Optical ray tracing-guided laser in situ keratomileusis for moderate to high myopic astigmatism.

PURPOSE: To assess the efficacy, safety, and predictability of an individualized laser in situ keratomileusis (LASIK) ablation profile based on an optical ray-tracing algorithm to treat moderate to high myopic astigmatism. SETTING: Ophthalmology centers in Zurich, Switzerland; Dublin, Ireland; and, Cologne, Germany. DESIGN: Multicenter clinical trail. METHODS: This 3-center study enrolled eyes with a manifest refraction sphere ranging from 0.50 to -10.25 diopters (D) and/or astigmatism ranging from 0.00 to -4.50 D. The intended outcome was plano in most eyes, undercorrection of 0.50 D in 1 eye, and undercorrection of 0.25 D in 2 eyes. Refractive outcomes were analyzed preoperatively and postoperatively at 1 day and 1 and 3 months. RESULTS: The study enrolled 127 eyes (71 patients). The mean manifest refraction was -5.92 D ± 1.72 (SD). By 3 months postoperatively, 15 eyes had been lost to follow-up and 1 eye was excluded from analysis because of early retreatment. Of the remaining 111 eyes, 93 (83.8%) had an uncorrected distance visual acuity (UDVA) of 20/20 or better. The mean manifest refraction spherical equivalent (MRSE) in all eyes was 0.03 ± 0.30 D. In 97 (87.4%), the MRSE was within ±0.50 D and in 107 (96.4%), within ±1.00 D. No eye lost 2 or more lines of corrected distance visual acuity. CONCLUSIONS: The new optical ray-tracing algorithm for individualized LASIK ablation profiles to treat moderate to high myopic astigmatism was efficacious, safe, and predictable. The UDVA in eyes with high myopic astigmatism was better than in those treated with wavefront-guided LASIK.

Equivalence of biomechanical changes induced by rapid and standard corneal cross-linking, using riboflavin and ultraviolet radiation.

PURPOSE: Ultraviolet (UV) corneal cross-linking is an accepted method for treating corneal ecstatic disorders. The authors evaluated whether a rapid treatment protocol (higher intensity and shorter irradiation time) could achieve the same increase in corneal stiffness as the currently used standard protocol. METHODS: Stress-strain measurements were performed on porcine corneal strips. The corneas (n = 72) were cut into three strips, each randomly receiving a different treatment: rapid (10 mW/cm(2), 9 minutes), standard (3 mW/cm(2), 30 minutes), or no (control, 0 mW/cm(2)) irradiation. After irradiation, the Young's modulus of each strip was determined. The results of the stress-strain measurements were analyzed statistically. RESULTS: Statistical analysis showed that, after irradiation, the median value of Young's modulus from both active treatment groups (rapid, 3.83 N/mm(2); standard, 3.88 N/mm(2)) was significantly higher (P < 0.05) than that of the control group (2.91 N/mm(2)). Treatment increased Young's modulus by a factor of 1.3. However, there was no significant difference (P = 0.43) between the rapid and standard groups in the median of Young's modulus. CONCLUSIONS: Rapid UV cross-linking treatment can be regarded as equivalent to the standard procedure in terms of increase in corneal stiffness. The new rapid protocol shortens the treatment duration by more than two thirds, from 30 to 9 minutes. The safety of the higher intensities must be addressed in further clinical studies.

Effect of air-flow on the evaluation of refractive surgery ablation patterns.

An Allegretto Eye-Q laser platform (Wavelight GmbH, Erlangen, Germany) was used to study the effect of air-flow speed on the ablation of artificial polymer corneas used for testing refractive surgery patterns. Flat samples of two materials (PMMA and Filofocon A) were ablated at four different air flow conditions. The shape and profile of the ablated surfaces were measured with a precise non-contact optical surface profilometer. Significant asymmetries in the measured profiles were found when the ablation was performed with the clinical air aspiration system, and also without air flow. Increasing air-flow produced deeper ablations, improved symmetry, and increased the repeatability of the ablation pattern. Shielding of the laser pulse by the plume of smoke during the ablation of plastic samples reduced the central ablation depth by more than 40% with no-air flow, 30% with clinical air aspiration, and 5% with 1.15 m/s air flow. A simple model based on non-inertial dragging of the particles by air flow predicts no central shielding with 2.3 m/s air flow, and accurately predicts (within 2 µm) the decrease of central ablation depth by shielding. The shielding effects for PMMA and Filofocon A were similar despite the differences in the ablation properties of the materials and the different full-shielding transmission coefficient, which is related to the number of particles ejected and their associated optical behavior. Air flow is a key factor in the evaluation of ablation patterns in refractive surgery using plastic models, as significant shielding effects are found with typical air-flow levels used under clinical conditions. Shielding effects can be avoided by tuning the air flow to the laser repetition rate.

Femtosecond lentotomy: generating gliding planes inside the crystalline lens to regain accommodation ability.

Based on Helmholtz Theory for accommodation the increasing sclerosis of lens nucleus and cortex is the main cause for the developments of presbyopia. Existing therapies, however, do not reverse the stiffness of the crystalline lens and thus do not regain real accommodation ability. A new approach to restore the flexibility of the lens could be realized by photodisruption using ultrafast laser pulses. This process, known as fs-lentotomy, was used to create micro-incisions which act as gliding planes inside the crystalline lens without opening the eye globe.

Interaction dynamics of spatially separated cavitation bubbles in water.

We present a high-speed photographic analysis of the interaction of cavitation bubbles generated in two spatially separated regions by femtosecond laser-induced optical breakdown in water. Depending on the relative energies of the femtosecond laser pulses and their spatial separation, different kinds of interactions, such as a flattening and deformation of the bubbles, asymmetric water flows, and jet formation were observed. The results presented have a strong impact on understanding and optimizing the cutting effect of modern femtosecond lasers with high repetition rates (>1 MHz).

Visualization of femtosecond laser pulse-induced microincisions inside crystalline lens tissue.

PURPOSE: To evaluate a new method for visualizing femtosecond laser pulse-induced microincisions inside crystalline lens tissue. SETTING: Laser Zentrum Hannover e.V., Hannover, Germany. METHOD: Lenses removed from porcine eyes were modified ex vivo by femtosecond laser pulses (wavelength 1040 nm, pulse duration 306 femtoseconds, pulse energy 1.0 to 2.5 microJ, repetition rate 100 kHz) to create defined planes at which lens fibers separate. The femtosecond laser pulses were delivered by a 3-dimension (3-D) scanning unit and transmitted by focusing optics (numerical aperture 0.18) into the lens tissue. Lens fiber orientation and femtosecond laser-induced microincisions were examined using a confocal laser scanning microscope (CLSM) based on a Rostock Cornea Module attached to a Heidelberg Retina Tomograph II. Optical sections were analyzed in 3-D using Amira software (version 4.1.1). RESULTS: Normal lens fibers showed a parallel pattern with diameters between 3 microm and 9 microm, depending on scanning location. Microincision visualization showed different cutting effects depending on pulse energy of the femtosecond laser. The effects ranged from altered tissue-scattering properties with all fibers intact to definite fiber separation by a wide gap. Pulse energies that were too high or overlapped too tightly produced an incomplete cutting plane due to extensive microbubble generation. CONCLUSIONS: The 3-D CLSM method permitted visualization and analysis of femtosecond laser pulse-induced microincisions inside crystalline lens tissue. Thus, 3-D CLSM may help optimize femtosecond laser-based procedures in the treatment of presbyopia.

Femtosecond laser induced flexibility change of human donor lenses.

BACKGROUND: According to the Helmholtz theory of accommodation the loss of accommodation amplitude is caused by the growing sclerosis of the crystalline lens, whereas the ciliary muscle and the lens capsule are mainly uneffected by age. A permanent treatment method for presbyopia which offers a dynamic accommodation ability is a recent field of study. The concept followed in this paper uses femtosecond laser pulses to potentially overcome the loss of deformation ability of the crystalline lens by creating gliding planes inside the lens tissue to improve its flexibility. METHODS: The aim of the study is to show that the flexibility of human donor lenses can be increased by applying tightly focused near infrared femtosecond laser pulses into the lens tissue. Thereby the tissue is separated by the photodisruption effect. A certain pattern of gliding planes is cut inside the tissue of 41 human donor lenses and the deformation ability of the lenses are compared using the Fisher spinning test before and after laser treatment. RESULTS: The laser treatment results in an increased deformation ability of the crystalline lens. The lens a-p thickness increases on average by 97 microm+/-14 microm after the treatment. The Fisher spinning test shows an increase of 16% in deformation ability of the lens at a rotational speed of 1620 rpm. CONCLUSION: The creation of gliding planes with a fs laser inside the crystalline lens tissue can change the deformation ability of the lens. This might be an indication for a possible method to treat presbyopia in future.

In vivo application and imaging of intralenticular femtosecond laser pulses for the restoration of accommodation.

PURPOSE: According to the Helmholtz theory of accommodation, one major cause of the development of presbyopia is the increasing sclerosis of the crystalline lens. One concept for regaining the elasticity of the sclerosing lens is intralenticular treatment by femtosecond laser pulses. METHODS: The feasibility of applying and imaging in vivo microincisions by femtosecond laser pulses was evaluated in five rabbit lenses with a new high repetition rate (100 kHz) femtosecond laser unit. The treated eyes were monitored using optical coherence tomography (OCT) and Scheimpflug imaging for localizing and studying the tissue effects of the incisions. The rabbits were investigated preoperatively, immediately postoperatively, and 14 days after treatment. RESULTS: The procedure, termed femtosecond-lentotomy, was successfully applied to the left lens of each rabbit. The laser microincisions within the crystalline lens were detectable with OCT and Scheimpflug imaging, which emphasizes the integral role these technologies play in targeting and characterizing postoperative tissue effects. The imaging within the lens showed a progressive fading of the incisional opacities generated by the femtosecond laser after 14 days with no detectable cataract formation. CONCLUSIONS: It is possible to create microincisions inside the crystalline lens within an acceptably short treatment time (<30 seconds). The 14-day follow-up did not show undesirable side effects, such as cataract formation, after intralenticular laser treatment.

fs-Laser induced elasticity changes to improve presbyopic lens accommodation.

BACKGROUND: According to the Helmholtz theory of accommodation, one of the major reasons for the development of presbyopia is the progressive sclerosis of the crystalline lens. However, both the ciliary muscle and the lens capsule stay active and elastic. Thus, the concept for regaining the deformation-ability of the crystalline lens is to create microincisions inside lens tissue to achieve gliding planes. METHODS: For the preparation of the microincisions, near-infrared femtosecond laser pulses are used, generating laser-induced optical breakdowns. Different cutting patterns were performed, and the elasticity regain of the lenses were measured with Fisher's spinning test for thickness determination. RESULTS: The creation of gliding planes inside lens tissue shows very good results in terms of increasing the deformation-ability. The optimization of laser parameters leads to a minimally invasive surgery with no remarkable side effects like residual gas bubbles. Furthermore, ex vivo elasticity measurements of untreated and treated pig lenses show an improvement in the flexibility of the lens. The deformation-ability increases up to 26% with a very low standard deviation (1.6%) and a high significance (p < 0.05). CONCLUSION: Generating particular cutting patterns inside lens tissue can increase the deformation-ability of the crystalline lens. Thus, it might be one possible way to treat presbyopia.