Corneal Stromal Filler Injection as a Novel Approach to Correct Presbyopia-An Ex Vivo Pilot Study.

Purpose: To evaluate the ex vivo feasibility of corneal stromal filler injection to create bifocality to correct presbyopia by flattening the central posterior corneal surface and thus increase refractive power. Methods: Femtosecond laser-assisted corneal stromal pockets of varying diameters close to the posterior corneal curvature were cut into rabbit eyes ex vivo. Subsequently, hyaluronic acid was injected to flatten the central posterior curvature. Refractive parameters were determined using perioperatively acquired three-dimensional optical coherence tomography (OCT) scans. Using micrometer-resolution OCT, corneal endothelial cell morphology and density were evaluated. Results: Following filler injection into the corneal stromal pockets, a fair volume-dependent increase of central refractive power up to 4 diopters (dpt) was observed. Unremarkable refractive changes of the peripheral posterior (3 mm, 0.20 ± 0.11 dpt; 2 mm, 0.11 ± 0.10 dpt) and the anterior corneal curvature (3 mm, 0.20 ± 0.34 dpt; 2 mm, 0.33 ± 0.31 dpt) occurred. Only negligible changes in astigmatism were observed. Different sizes of optical zones could be established. Furthermore, no alterations of corneal endothelial morphology or endothelial cell density (2831 ± 356 cells/mm2 vs. 2734 ± 292 cells/mm2; P = 0.552) due to the adjacent laser treatment were observed. Conclusions: The ex vivo investigations proved the principle of injecting a filler material into femtosecond laser-created corneal stromal pockets close to the posterior corneal curvature as an efficacious, individually adjustable, and novel approach to correct presbyopia without ablating corneal tissue. Translational Relevance: Due to the aging population worldwide, presbyopia is an increasing problem; thus, our study may encourage further exploration to extend the treatment spectrum of clinically used femtosecond laser systems to correct presbyopia.

Refractive Changes After Corneal Stromal Filler Injection for the Correction of Hyperopia.

PURPOSE: To evaluate a new non-ablative and adjustable procedure for laser ablative refractive corneal surgery in hyperopia using the injection of a biocompatible liquid filler material into a stromal pocket. METHODS: A total of 120 stromal pockets were created using a clinical femtosecond laser system in 96 rabbit corneoscleral discs and 24 whole globes. Pockets were cut at a depth of 120 or 250 µm below the epithelial surface. Hyaluronic acid was injected manually into the pocket. To determine the refractive changes, three-dimensional optical coherence tomography images and a specifically developed picture recognition Matlab (The Mathworks) routine were used. RESULTS: After injection, a steepening of the anterior and flattening of the posterior corneal surface was observed, which led to hyperopic correction. The two main factors determining the amount of correction were the pocket depth and the injected volume. After the pocket was homogeneously filled, an initial refractive increase was observed, followed by a linear relation between the injected volume and the refraction increase. CONCLUSIONS: This possible clinical protocol for controlled refraction correction of hyperopia suggests a potential readjustable clinical application. [J Refract Surg. 2020;36(6):406-414.].

First Assessment of a Carbon Monoxide Laser and a Thulium Fiber Laser for Fractional Ablation of Skin.

BACKGROUND AND OBJECTIVES: A recent generation of 5,500 nm wavelength carbon monoxide (CO) lasers could serve as a novel tool for applications in medicine and surgery. At this wavelength, the optical penetration depth is about three times higher than that of the 10,600 nm wavelength carbon dioxide (CO2 ) laser. As the amount of ablation and coagulation is strongly influenced by the wavelength, we anticipated that CO lasers would provide extended coagulation zones, which could be beneficial for several medical applications, such as tissue tightening effects after laser skin resurfacing. Until now, the 1,940 nm wavelength thulium fiber (Tm:fiber) laser is primarily known as a non-ablative laser with an optical penetration depth that is eight times higher than that of the CO2 laser. The advantage of lasers with shorter wavelengths is the ability to create smaller spot sizes, which has a determining influence on the ablation outcome. In this study, the ablation and coagulation characteristics of a novel CO laser and a high power Tm:fiber laser were investigated to evaluate their potential application for fractional ablation of the skin. STUDY DESIGN/MATERIALS AND METHODS: Laser-tissue exposures were performed using a novel CO laser, a modified, pulse-width-modulated CO2 laser, and a Tm:fiber laser. We used discarded ex vivo human skin obtained from abdominoplasty as tissue samples. Similar exposure parameters, such as spot size (108-120 µm), pulse duration (2 milliseconds), and pulse energy (~10-200 mJ) were adjusted for the different laser systems with comparable temporal pulse structures. Laser effects were quantified by histology. RESULTS: At radiant exposures 10-fold higher than the ablation threshold, the CO laser ablation depth was almost two times deeper than that of the CO2 laser. At 40-fold of the ablation threshold, the CO laser ablation was 47% deeper. The ablation craters produced by the CO laser exhibited about two times larger coagulation zones when compared with the CO2 laser. In contrast, the Tm:fiber laser exhibited superficial ablation craters with massive thermal damage. CONCLUSIONS: The tissue ablation using the Tm:fiber laser was very superficial in contrast to the CO laser and the CO2 laser. However, higher etch depths should be obtainable when the radiant exposure is increased by using higher pulse energies and/or smaller spot sizes. At radiant exposures normalized to the ablation threshold, the CO laser was capable of generating deeper ablation craters with extended coagulation zones compared with the CO2 laser, which is possibly desirable depending on the clinical goal. The effect of deep ablation combined with additional thermal damage on dermal remodeling needs to be further confirmed with in vivo studies. Lasers Surg. Med. © 2020 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

Correction of hyperopia by intrastromal cutting and liquid filler injection.

Correction of hyperopia requires an increase of the refractive power by steepening of the corneal surface. Present refractive surgical techniques based on corneal ablation (LASIK) or intrastromal lenticule extraction (SMILE) are problematic due to epithelial regrowth. Recently, it was shown that correction of low hyperopia can be achieved by implanting intracorneal inlays or allogeneic lenticules. We demonstrate a steepening of the anterior corneal surface after injection of a transparent, liquid filler material into a laser-dissected intrastromal pocket. We performed the study on ex-vivo porcine eyes. The increase of the refractive power was evaluated by optical coherence tomography (OCT). For a circular pocket, injection of 1 µl filler material increased the refractive power by +4.5 diopters. An astigmatism correction is possible when ellipsoidal intrastromal pockets are created. Injection of 2 µl filler material into an ellipsoidal pocket increased the refractive power by +10.9 dpt on the short and +5.1 dpt on the long axis. OCT will enable to monitor the refractive change during filler injection and is thus a promising technique for real-time dosimetry.

Selective retina therapy: toward an optically controlled automatic dosing.

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.

Assessment of skin lesions produced by focused, tunable, mid-infrared chalcogenide laser radiation.

BACKGROUND: Traditionally, fractional laser treatments are performed with focused laser sources operating at a fixed wavelength. Using a tunable laser in the mid-infrared wavelength range, wavelength-dependent absorption properties on the ablation process and thermal damage formation were assessed with the goal to obtain customizable tissue ablations to provide guidance in finding optimized laser exposure parameters for clinical applications. METHODS: Laser tissue experiments were carried out on full thickness ex vivo human abdominal skin using a mid-infrared tunable chromium-doped zinc selenide/sulfide chalcogenide laser. The laser has two independent channels: a continuous wave (CW) output channel which covers a spectrum ranging from 2.4 µm to 3.0 µm with up to 9.2 W output power, and a pulsed output channel which ranges from 2.35 µm to 2.95 µm. The maximum pulse energy of the pulsed channel goes up to 2.8 mJ at 100 Hz to 1,000 Hz repetition rate with wavelength-dependent pulse durations of 4-7 ns. RESULTS: Total ablation depth, ablation efficiency, and coagulation zone thickness were highly correlated to wavelength, pulse width, and pulse energy. Using the same total radiant exposure at 2.85 µm wavelength resulted in 10-times smaller coagulation zones and 5-times deeper ablation craters for one hundred 6 ns pulses compared to one 100 ms pulse. For a fixed pulse duration of 6 ns and a total radiant exposure of 2.25 kJ/cm2 the ablation depth increased with longer wavelengths. CONCLUSION: The tunable laser system provides a useful research tool to investigate specific laser parameters such as wavelength on lesion shape, ablation depth and thermal tissue damage. It also allows for customization of the characteristics of laser lesions and therefore facilitates the selection of suitable laser parameters for optimized fractional laser treatments. Lasers Surg. Med. 50:961-972, 2018.© 2018 Wiley Periodicals, Inc.

Interface Bonding With Corneal Crosslinking (CXL) After LASIK Ex Vivo.

Purpose: Interface bonding with corneal crosslinking (CXL) after LASIK using two different photosensitizers was studied ex vivo. Methods: A LASIK flap was created in enucleated rabbit eyes using a femtosecond laser. After the dissection, CXL was performed to seal the interface. In one group interface CXL was performed using rose bengal and green light, whereas in a second group riboflavin and UV-A light was used. In both groups irradiance, radiant exposure, dye concentration, and imbibition time was varied. In a control group, LASIK only was performed. After the procedures, the maximal shear-force required to separate the flap from the stroma was measured. Additionally, corneal transmission spectra were recorded. Results: Optimized parameters for rose bengal/green-light bonding lead to a 2.1-fold increase in shear-force compared with untreated control eyes (P < 0.01). The optimal parameter combination was: irradiance of 180 mW/cm2 for 14 minutes (total radiant exposure 150 J/cm2), rose bengal concentration 0.1%, and an imbibition time of 2 minutes. Optimized riboflavin/UV-A light parameters were 0.5% for 2 minutes with a radiant exposure of 8.1 J/cm2 obtained by an irradiance of 30 mW/cm2 for 4.5 minutes. These optimized parameters lead to a 2-fold increase compared with untreated control eyes (P < 0.01). Optical transmission experiments suggest safety for more posterior structures. Conclusions: Based on ex-vivo results, interface bonding after LASIK using crosslinking with either rose bengal or riboflavin increases the adhesion between flap and stromal bed. In vivo trials are needed to evaluate the temporal evolution of the effect.

Power-controlled temperature guided retinal laser therapy.

Laser photocoagulation has been a treatment method for retinal diseases for decades. Recently, studies have demonstrated therapeutic benefits for subvisible effects. A treatment mode based on an automatic feedback algorithm to reliably generate subvisible and visible irradiations within a constant irradiation time is introduced. The method uses a site-individual adaptation of the laser power by monitoring the retinal temperature rise during the treatment using optoacoustics. This provides feedback to adjust the therapy laser power during the irradiation. The technique was demonstrated on rabbits in vivo using a 532-nm continuous wave Nd:YAG laser. The temperature measurement was performed with 523-nm Q-switched Nd:YLF laser pulses with 75-ns pulse duration at 1-kHz repetition rate. The beam diameter on the fundus was 200 µm for both lasers, respectively. The aim temperatures ranged from 50°C to 75°C in 11 eyes of 7 rabbits. The results showed ophthalmoscopically invisible effects below 55°C with therapy laser powers over a wide range. The standard deviation for the measured temperatures ranged from 2.1°C for an aim temperature of 50°C to 4.7°C for 75°C. The ED50 temperature value for ophthalmoscopically visible lesions in rabbits was determined as 65.3°C. The introduced method can be used for retinal irradiations with adjustable temperature elevations.

Biomedical optics centers: forty years of multidisciplinary clinical translation for improving human health.

Despite widespread government and public interest, there are significant barriers to translating basic science discoveries into clinical practice. Biophotonics and biomedical optics technologies can be used to overcome many of these hurdles, due, in part, to offering new portable, bedside, and accessible devices. The current JBO special issue highlights promising activities and examples of translational biophotonics from leading laboratories around the world. We identify common essential features of successful clinical translation by examining the origins and activities of three major international academic affiliated centers with beginnings traceable to the mid-late 1970s: The Wellman Center for Photomedicine (Mass General Hospital, USA), the Beckman Laser Institute and Medical Clinic (University of California, Irvine, USA), and the Medical Laser Center Lübeck at the University of Lübeck, Germany. Major factors driving the success of these programs include visionary founders and leadership, multidisciplinary research and training activities in light-based therapies and diagnostics, diverse funding portfolios, and a thriving entrepreneurial culture that tolerates risk. We provide a brief review of how these three programs emerged and highlight critical phases and lessons learned. Based on these observations, we identify pathways for encouraging the growth and formation of similar programs in order to more rapidly and effectively expand the impact of biophotonics and biomedical optics on human health.

Polyacrylamide gel substrates that simulate the mechanical stiffness of normal and malignant neuronal tissues increase protoporphyin IX synthesis in glioma cells.

Protoporphyrin IX (PPIX) produced following the administration of exogenous 5d-aminolevulinic acid is clinically approved for photodynamic therapy and fluorescence-guided resection in various jurisdictions around the world. For both applications, quantification of PPIX forms the basis for accurate therapeutic dose calculation and identification of malignant tissues for resection. While it is well established that the PPIX synthesis and accumulation rates are subject to the cell's biochemical microenvironment, the effect of the physical microenvironment, such as matrix stiffness, has received little attention to date. Here we studied the proliferation rate and PPIX synthesis and accumulation in two glioma cell lines U373 and U118 cultured under five different substrate conditions, including the conventional tissue culture plastic and polyacrylamide gels that simulated tissue stiffness of normal brain (1 kPa) and glioblastoma tumors (12 kPa). We found that the proliferation rate increased with substrate stiffness for both cell lines, but not in a linear fashion. PPIX concentration was significantly higher in cells cultured on tissue-simulating gels than on the much stiffer tissue culture plastic for both cell lines. These findings, albeit preliminary, suggest that the physical microenvironment might be an important determinant of tumor aggressiveness and PPIX synthesis in glioma cells.

Light-Controlled Delivery of Monoclonal Antibodies for Targeted Photoinactivation of Ki-67.

The selective inhibition of intracellular and nuclear molecules such as Ki-67 holds great promise for the treatment of cancer and other diseases. However, the choice of the target protein and the intracellular delivery of the functional agent remain crucial challenges. Main hurdles are (a) an effective delivery into cells, (b) endosomal escape of the delivered agents, and (c) an effective, externally triggered destruction of cells. Here we show a light-controlled two-step approach for selective cellular delivery and cell elimination of proliferating cells. Three different cell-penetrating nano constructs, including liposomes, conjugates with the nuclear localization sequence (NLS), and conjugates with the cell penetrating peptide Pep-1, delivered the light activatable antibody conjugate TuBB-9-FITC, which targets the proliferation associated protein Ki-67. HeLa cells were treated with the photosensitizer benzoporphyrin monoacid derivative (BPD) and the antibody constructs. In the first optically controlled step, activation of BPD at 690 nm triggered a controlled endosomal escape of the TuBB-9-FITC constructs. In more than 75% of Ki-67 positive, irradiated cells TuBB-9-FITC antibodies relocated within 24 h from cytoplasmic organelles to the cell nucleus and bound to Ki-67. After a second light irradiation at 490 nm, which activated FITC, cell viability decreased to approximately 13%. Our study shows an effective targeting strategy, which uses light-controlled endosomal escape and the light inactivation of Ki-67 for cell elimination. The fact that liposomal or peptide-assisted delivery give similar results leads to the additional conclusion that an effective mechanism for endosomal escape leaves greater variability for the choice of the delivery agent.

Selective retina therapy (SRT) for clinically significant diabetic macular edema.

PURPOSE: To test selective retina therapy (SRT) as a treatment of clinically significant diabetic macular edema (DME). METHODS: Prospective two-center interventional uncontrolled phase II pilot study. Thirty-nine eyes of 39 patients with previously untreated non-ischemic DME were treated with focal laser treatment using a Q-switched frequency doubled Nd:YLF laser which selectively affects the retinal pigment epithelium while sparing the photoreceptor layer. Optoacoustic measurements, fundus fluorescein angiography (FFA), and funduscopy were used to determine the individual threshold of RPE damage of each patient. The pulse energy was adjusted to apply angiographically visible but funduscopically invisible effects. Optoacoustic measurements were correlated with funduscopy and FFA. Follow-up examinations at 3 and 6 months post-treatment included best-corrected ETDRS visual acuity (BCVA), FFA, fundus photography, and retinal thickness measured by optical coherence tomography. The primary outcome measure was change of BCVA. Other outcome measures were change of retinal thickness, presence of hard exudates, leakage in FFA, accuracy of optoacoustic measurements, and correlation of BCVA with change of anatomical and systemic parameters. RESULTS: Mean BCVA improved from 43.7 letters (standard deviation, SD=9.1) at baseline to 46.1 letters (SD=10.5) at the 6-month follow-up (p=0.02). BCVA improved (>5 letters) or remained stable (+/-5 letters) in 84% of eyes. Thirteen percent of eyes improved by > or =10 letters, while 16% of eyes lost more than 5 letters. There was no severe loss of vision (> or =15 letters). Overall, retinal thickness, hard exudates, and leakage in FFA did not change significantly (p> 0.05), while improvement of BCVA correlated with a reduction of hard exudates (p=0.01) and central retinal thickness (p=0.01). Specificity and sensitivity of detecting the angiographic visible threshold of RPE damage by optoacoustic measurements were 86% and 70% respectively. No adverse effects or pain were noted during or after treatment. Conclusions Functional and anatomical improvement or stabilization was observed in most patients. SRT appears to be safe. Optoacoustic measurements accurately detect the individual threshold of RPE damage. A randomized trial is required to further test efficacy and safety of SRT as a treatment of clinically significant diabetic macular edema (DME).

Effects on choroidal neovascularization after anti-VEGF Upload using intravitreal ranibizumab, as determined by spectral domain-optical coherence tomography.

PURPOSE: It is unclear whether anti-VEGF monotherapy in age-related macular degeneration (AMD) achieves morphologic CNV regression or only stops further CNV growth. In this study, spectral domain-optical coherence tomography (SD-OCT) was used to image CNV structure before and after anti-VEGF treatment. METHODS: Out of 107 consecutive patients, a prospective CNV evaluation was possible in 78 of them. Newly diagnosed CNV (classic CNV: n = 16; occult CNV: n = 54; minimal classic CNV: n = 8) due to AMD was imaged before and 4 weeks after anti-VEGF upload in three intravitreal injections of ranibizumab. Qualitative (structural changes) and quantitative measurements (diameter and thickness) of the CNV were obtained from the OCT images. RESULTS: Classic CNV components were observed above the RPE/photoreceptor complex, whereas occult CNVs stayed below. Of all postoperative OCTs, 59% revealed complete dry retinal structures, 27% showed reduced edema, and 14% showed edema remaining unchanged. Mean macular thickness decreased significantly from 427 to 303 microm (P = 0.000). Qualitatively, overall CNV architecture appeared to be unchanged in 78%, was reduced in thickness in 18%, and became larger in 4%. Quantitatively, in all CNV subtypes, the diameter of the CNV lesions (preoperative, 2813 microm; postoperative, 2804 microm) did not change after treatment (classic CNV: P = 0.390; occult CNV: P = 0.405, minimal classic CNV: P = 0.092) independent of postoperative retinal edema. The overall thickness of the lesion, however, was reduced from 205 to 175 microm (P = 0.000). Thickness reduction was significantly enhanced especially in CNV with classic components (n = 24; 252 to 197 microm; P = 0.000; reduction, 22%), whereas reduction was smaller but also significant in occult CNV (183 to 164 microm; P = 0.003; reduction, 10%). CONCLUSIONS: With SD-OCT, CNV size can be two-dimensionally determined and followed up after intravitreal anti-VEGF treatment. In only 4% of CNV was enlargement observed, whereas in 78%, CNV architecture appeared qualitatively unchanged, independent of retinal edema. Quantitative measurements underlined stable CNV diameters for all subtypes but revealed significant reduction of thickness especially for classic CNV components. In this series, ranibizumab monotherapy was able to morphologically stop further CNV growth but, in most patients, did not lead to a major regression of CNV, especially of its occult components.

Selective retina therapy (SRT) of chronic subfoveal fluid after surgery of rhegmatogenous retinal detachment: three case reports.

BACKGROUND: Shallow subfoveal fluid accumulation after successful surgery for retinal detachment can be the reason for compromised visual acuity. To date, therapeutical options to tackle this problem have not been established. Selective retina therapy (SRT) is a new laser technology that uses a train of mus-laser pulses to selectively damage retinal pigment epithelial (RPE) cells while sparing retinal structures. METHODS: We treated three patients with chronic subfoveal fluid accumulation after retinal detachment surgery. The median period between retinal surgery and SRT treatment was 7 months. For SRT, we used a prototype frequency-doubled, Q-switched Nd:YLF laser (lambda = 527 nm). Each laser exposition contained 30 pulses (t = 1,7 micros, 100 Hz, E = 100-400 microJ). Two of the three patients were treated subfoveally. OCT III (optical coherence tomography) examinations were performed to evaluate changes in subretinal fluid accumulation. RESULTS: In all three patients, we observed complete resolution of subfoveal fluid within 1-5 months. Follow-up has been 16 months to 2 years. Visual acuity improved in all patients. In one patient, cystoid macular edema developed 3 months after treatment. Additional SRT treatments were not necessary. CONCLUSION: SRT is a safe treatment. Visual acuity improved after SRT, even in subfoveal irradiations. SRT is an option to support subretinal fluid reabsorption. In this situation where no other therapeutical options are established, SRT may be a beneficial treatment for chronic subfoveal fluid accumulation after retinal detachment surgery.

Clinical evaluation of experimentally induced choroidal neovascularizations in pigmented rabbits by subretinal injection of lipid hydroperoxide and consecutive preliminary photodynamic treatment with Tookad.

PURPOSE: Up to date several approaches have been undertaken to achieve an 'easy-to-handle' animal model of choroidal neovascularizations (CNVs) in rabbits; however, so far in none of the studies could healthy retinal tissue be maintained, which is mandatory to further investigate the effects of photodynamic therapy (PDT) or anti-vascular-endothelial-growth-factor treatments. It was our aim to reevaluate and verify the method of inducing experimental CNVs in rabbits using subretinally injected linoleic acid hydroperoxide (LHP) as proposed by Tamai et al. and to use it for experimental PDT. MATERIAL AND METHODS: In 33 eyes of Chinchilla breed rabbits LHP of two different concentrations (25 and 100 microg/50 microl) was injected into the subretinal space via a transvitreal approach under guidance of an operation microscope. Ophthalmoscopic and angiographic examinations were performed on days 3, 7, 14 and 28 after surgery. Preliminary PDT with different experimental parameter sets was performed in 3 eyes using the new photosensitizer Tookad. RESULTS: Using LHP in the higher concentration, an angiographically determined CNV induction was observed in 27% of all injection sites (n = 34) on days 14 and 28 revealing early well-demarcated and progressive leakage. No CNV was detected at the lower LHP concentration (60 injection sites). Subretinal CNV was verified histologically revealing vessel formation above the retinal pigment epithelium level. Herein, a significant damage to the outer retinal layers was always observed; however, the general structure of the choriocapillary layer was maintained. Tookad PDT was clinically able to completely stop leakage in 1 case and reduce leakage in 2 cases. Histologically the choriocapillary layer was occluded. CONCLUSION: Subretinal injection of LHP induces angiographically well-demarcated classic CNVs in rabbits; however, the CNV rate was low, and histology revealed severe damage of the outer retinal layers but not of the choriocapillary layer, which is important for studying PDT interactions. Preliminary experimental PDT could clinically stop or reduce leakage from angiographic CNV. Due to the small CNV rate and the significant collateral retinal tissue damage, this model seems to be only of partial suitability for investigating new treatment modalities in CNV.

Investigation of selective retina treatment (SRT) by means of 8 ns laser pulses in a rabbit model.

BACKGROUND: It has been shown that selective retina treatment (SRT) using a train of 1.7 microseconds laser pulses allows selective damage of the retinal pigment epithelium (RPE) while sparing the adjacent photoreceptors and thus avoiding laser scotoma. It was the purpose of this work to investigate SRT laser effects with Q-switched pulses of only 8 nanoseconds in duration by evaluating the angiographic and ophthalmoscopic damage thresholds and the damage range by histology in a rabbit model. MATERIALS AND METHODS: A flash lamp pumped frequency doubled (532 nm) Nd:YAG laser with 8 nanoseconds pulse duration was used. In total 210 laser lesions, each calculated to be 102 microm in diameter on retina, were applied through a slit lamp onto the fundus of six eyes of Chinchilla Bastard rabbits. The rabbits were irradiated with increasing energies with single pulses and a train of 10 laser pulses at 10 Hz. After treatment fundus photography and angiography were performed to determine the damage thresholds (ED(50)-probability of RPE cell damage and neurosensory retinal damage) as well as the safety range between both thresholds (ratio of angiographic ED(86) vs. ophthalmoscopic ED(14)). Selected histology was taken for single and repetitive pulse lesions after treatment. RESULTS: Angiographic and ophthalmoscopic ED(50)-thresholds decreased with increasing number of pulses. For single pulse application ophthalmoscopic and angiographic ED(50) were determined to 365 and 144 mJ/cm(2), respectively. Regarding 10 pulses 266 and 72 mJ/cm(2) were found. No retinal hemorrhages or disruptions were observed for both sets of parameters. The therapeutic window between angiographic and ophthalmoscopic threshold revealed a factor of 3.1 for single pulses and 2.3 for repetitive pulse irradiation. The safety range respectively had a factor of 0.8 (single pulses) and 1.7 (10 pulses). Histologic examination of laser lesions with single and repetitive pulses at radiant exposures within the therapeutic window-292 and 213 mJ/cm(2) respectively-revealed damaged RPE, intact Bruch's membrane and choriocapillaries. Photoreceptors were partly spared but also damaged to various extents. CONCLUSIONS: Short laser pulses of 8 nanoseconds pulse duration can damage the RPE without retinal hemorrhage or disruption. Selective damage of the RPE without affecting the photoreceptors can only rarely be achieved due to the small safety range. Thus, so far microsecond laser pulses for SRT seems favorable compared to nanosecond pulses in order to prevent unintentional photoreceptor damage.

[Selective Retina Therapy (SRT)]. / Selektive Retina-Therapie (SRT).

Selective Retina Therapy (SRT) is a new and very gentle laser method developed at the Medical Laser Center Lübeck. It is currently investigated clinically in order to treat retinal disorders associated with a decreased function of the retinal pigment epithelium (RPE). SRT is designed to selectively effect the RPE while sparing the neural retina and the photoreceptors as well as the chorioidea. Aim of the therapy is the rejuvenation of the RPE in the treated areas, which should ideally lead to a long term metabolic increase at the chorio-retinal junction. In contrast to conventional laser photocoagulation, which is associated with a complete thermal necrosis of the treated site, SRT completely retains full vision. This paper reviews the methods and mechanisms behind selective RPE effects and reports the first clinical results. An online dosimetry technique to visualize the ophthalmoscopically invisible effects is introduced.

Filtering bleb evaluation with slit-lamp-adapted 1310-nm optical coherence tomography.

PURPOSE: Investigation of slit-lamp-adapted 1310-nm optical coherence tomography (OCT) as an in vivo imaging device in the postoperative course of glaucoma surgery. METHODS: Postoperative images of filtering blebs and deep sclerectomies and their healing processes were qualitatively evaluated with a slit-lamp-adapted anterior segment OCT (AS-OCT; Heidelberg Engineering, Heidelberg, Germany) in 28 patients. Ophthalmologic examinations included slit-lamp examination, applanation tonometry, and slit-lamp photography. The OCT scans were qualitatively correlated with the morphologic and functional outcome of the filtering bleb. RESULTS: 1310-nm OCT was able to demonstrate the internal structure and the dimensions of filtering blebs, as well as the scleral flap and the deep sclerectomy location including Descemet membrane. Functioning filtering blebs showed a low OCT signal, small fluid-filled cysts, superficial microcystic layer, and a slack internal texture. High internal reflectivity indicated an earlier scarring of the filtering bleb. Nonfunctioning filtering blebs delivered a high OCT signal, no or few cysts, and a dense internal texture. These different OCT patterns correlated with the clinical outcome. CONCLUSIONS: Slit-lamp-adapted 1310-nm OCT allowed the noncontact observation and documentation of the postoperative healing course of filtering blebs after glaucoma surgery. Internal structures of the filtering bleb and deep sclerectomies could be visualized. Functioning and dysfunctioning filtering blebs delivered different OCT pattern and correlated with the clinical outcome. This could be a new way to assess the postoperative healing process with the possibility of earlier intervention in cases of impending scarring.

Noninvasive optoacoustic online retinal temperature determination during continuous-wave laser irradiation.

The therapeutic effect of most retinal laser treatments is initiated by a transient temperature increase. Although crucial to the effectiveness of the treatment, the temperature course is not exactly known due to individually different tissue properties. We develop an optoacoustic method to determine the retinal temperature increase in real time during continuous-wave (cw) laser irradiation, and perform temperature calculations to interpret the results exemplary for transpupillary thermotherapy (TTT). Porcine globes ex vivo and rabbit eyes in vivo are irradiated with a diode laser (lambda=810 nm, P< or =3 W, phi=2 mm) for 60 s. Simultaneously, pulses from a N2-laser pumped dye laser (lambda=500 nm, tau=3.5 ns, E approximately 5 microJ) are applied on the retina. Following its absorption, an ultrasonic pressure wave is emitted, which is detected by a transducer embedded in a contact lens. Using the previously measured temperature-dependent Gruneisen coefficient of chorioretinal tissue, a temperature raise in porcine eyes of 5.8 degrees C(Wcm2) after 60 s is observed and confirmed by simultaneous measurements with an inserted thermocouple. In a rabbit, we find 1.4 degrees C(Wcm2) with, and 2.2 degrees C(Wcm2) without perfusion at the same location. Coagulation of the rabbit's retina occurs at DeltaT=21 degrees C after 40 s. In conclusion, this optoacoustic method seems feasible for an in vivo real-time determination of temperature, opening the possibility for feedback control retinal laser treatments.

Photoablation of inner limiting membrane and inner retinal layers using the Erbium:YAG-laser: an in vitro study.

BACKGROUND AND OBJECTIVES: To explore the potential of Er:YAG-laser irradiation for precise and tractionless retinal tissue and inner limiting membrane ablation. MATERIALS AND METHODS: We used free-running Er:YAG-laser irradiation (lambda = 2.94 microm) transmitted either through a 10 cm long low-OH-quartz fiber or a 2 m long sapphire fiber that produced a more homogenous light distribution at the fiber tip. Retinal ablation in porcine retinal explants was performed under air or perfluorodecaline (PFD). Ablation depth was evaluated by optical coherence tomography (OCT) and from histologic sections. RESULTS: A radiant exposure of 5.0 J/cm(2) delivered through a low-OH-quartz fiber and PFD caused a complete transsection of the neurosensory retina. Radiant exposures between 3.5 and 2.0 J/cm(2) resulted in marked variations of ablation depth and adjacent thermal damage. By contrast, laser pulses of 4.0 and 3.0 J/cm(2) transmitted through the sapphire fiber produced more homogenous defect patterns and less thermal damage. Close to the ablation threshold, with 1.0-2.0 J/cm(2), ablation was limited to a 10-20 microm thin layer of the neural retina. CONCLUSIONS: We achieved in vitro ablation of inner retinal layers, but could not produce selective and reproducible ILM removal.