Algorithm and software for field distortion correction in a commercial SD-OCT for corneal curvature assessment.

Accurate assessment of corneal curvatures using frequency domain optical coherence tomography (OCT) with galvanometer scanners remains challenging due to the well-known scan field distortion. This paper presents an algorithm and software for correcting the distortion using only two simple measurements in which a readily available standard sphere is positioned in different depths in front of the OCT scanner. This offers a highly accessible and easily reproducible method for the field distortion correction (FDC). The correction was validated by measuring different spherical phantoms and conducting corneal curvature measurements of ex vivo porcine corneas using a commercial spectral-domain OCT system and a clinically approved swept-source OCT as a reference instrument. Thus, the error in radius measurements of spherical phantoms was reduced by >90% and astigmatism by >80% using FDC. In explanted porcine eyes, the error in astigmatism measurements with the Telesto was reduced by 75% for power and 70% for angle. The best fitting sphere radius was determined up to a deviation of 0.4% from the Anterion. This paper describes a correction algorithm for OCT immanent distortion that is applicable to any scanning OCT setup and enables precise corneal curvature measurements. The MATLAB software for the FDC is publicly available on GitHub.

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.

Simple approach for aberration-corrected OCT imaging of the human retina.

Aberration-corrected imaging of human photoreceptor cells, whether hardware or software based, presently requires a complex and expensive setup. Here we use a simple and inexpensive off-axis full-field time-domain optical coherence tomography (OCT) approach to acquire volumetric data of an in vivo human retina. Full volumetric data are recorded in 1.3 s. After computationally correcting for aberrations, single photoreceptor cells were visualized. In addition, the numerical correction of ametropia is demonstrated. Our implementation of full-field optical coherence tomography combines a low technical complexity with the possibility for computational image correction.

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.

In-vivo retinal imaging with off-axis full-field time-domain optical coherence tomography.

With a simple setup, mainly composed of a low coherence light source and a camera, full-field optical coherence tomography (FF-OCT) allows volumetric tissue imaging. However, fringe washout constrains its use in retinal imaging. Here, we present a novel motion-insensitive approach to FF-OCT, which introduces path-length differences between the reference and the sample light in neighboring pixels using an off-axis reference beam. The temporal carrier frequency in scanned time-domain OCT is replaced by a spatial carrier frequency. Volumetric in-vivo FF-OCT measurements of the human retina were acquired in only 1.3 s, comparable to the acquisition times of current clinically used OCT devices.

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.

Algorithms for optoacoustically controlled selective retina therapy (SRT).

OBJECTIVES: Selective Retina Therapy (SRT) uses microbubble formation (MBF) to target retinal pigment epithelium (RPE) cells selectively while sparing the neural retina and the choroid. Intra- and inter-individual variations of RPE pigmentation makes frequent radiant exposure adaption necessary. Since selective RPE cell disintegration is ophthalmoscopically non-visible, MBF detection techniques are useful to control adequate radiant exposures. It was the purpose of this study to evaluate optoacoustically based MBF detection algorithms. METHODS: Fifteen patients suffering from central serous chorioretinopathy and diabetic macula edema were treated with a SRT laser using a wavelength of 527 nm, a pulse duration of 1.7 µs and a pulse energy ramp (15 pulses, 100 Hz repetition rate). An ultrasonic transducer for MBF detection was embedded in a contact lens. RPE damage was verified with fluorescence angiography. RESULTS: An algorithm to detect MBF as an indicator for RPE cell damage was evaluated. Overall, 4646 irradiations were used for algorithm optimization and testing. The tested algorithms were superior to a baseline model. A sensitivity/specificity pair of 0.96/1 was achieved. The few false algorithmic decisions were caused by unevaluable signals. CONCLUSIONS: The algorithm can be used for guidance or automatization of microbubble related treatments like SRT or selective laser trabeculoplasty (SLT).

Advances in Imaging of Subbasal Corneal Nerves With Micro-Optical Coherence Tomography.

Purpose: To investigate the most peripheral corneal nerve plexus using high-resolution micro-optical coherence tomography (µOCT) imaging and to assess µOCT's clinical potential as a screening tool for corneal and systemic diseases. Methods: An experimental high-resolution (1.5 × 1.5 × 1 µm) µOCT setup was applied for three-dimensional imaging of the subbasal nerve plexus in nonhuman primates (NHPs) and swine within 3 hours postmortem. Morphologic features of subbasal nerves in µOCT were compared to ß3 tubulin-stained fluorescence confocal microscopy (FCM). Parameters such as nerve density, nerve distribution, and imaging repeatability were evaluated, using semiautomatic image analysis in form of a custom corneal surface segmentation algorithm and NeuronJ. Results: Swine and NHP corneas showed the species-specific nerve morphology in both imaging modalities. Most fibers showed a linear course, forming a highly parallel pattern, converging in a vortex with overall nerve densities varying between 9.51 and 24.24 mm/mm2. The repeatability of nerve density quantification of the µOCT scans as approximately 88% in multiple image recordings of the same cornea. Conclusions: Compared to the current gold standard of FCM, µOCT's larger field of view of currently 1 × 1 mm increases the conclusiveness of density measurements, which, coupled with µOCT's feature of not requiring direct contact, shows promise for future clinical application. The nerve density quantification may be relevant for screening for systemic disease (e.g., peripheral neuropathy). Translational Relevance: Technological advances in OCT technology may enable a quick assessment of corneal nerve density, which could be valuable evaluating ophthalmic and systemic peripheral innervation.

Investigations on Retinal Pigment Epithelial Damage at Laser Irradiation in the Lower Microsecond Time Regime.

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

Selective retina therapy (SRT) in patients with geographic atrophy due to age-related macular degeneration.

BACKGROUND: For geographic atrophy (GA) due to age-related macular degeneration (AMD) there is so far no approved treatment option. Usually, increased autofluorescence (AF) levels of different patterns adjacent to the atrophic area indicate lipofuscin-laden retinal pigment epithelium (RPE) cells at a high risk for apoptosis. Herein, SRT was used to selectively treat these cells to stimulate RPE proliferation, in order to reduce or ideally stop further growth of the atrophic area. MATERIAL AND METHODS: Six eyes of six patients with bilateral equally pronounced GA were treated by SRT, while the fellow eye served as control. Irradiation was performed using a prototype SRT laser (Medical Laser Center Lübeck, Nd:YLF laser; 527 nm; 200 ns/1.7 micros pulse duration; 30 repetitive pulses at 100 Hz). Test lesions with increasing energies were applied at the lower vessel arcade to determine the individual angiographic and ophthalmoscopic threshold radiant exposures. Treatment was then performed in the area of increased AF adjacent to the GA using energies between both thresholds. The GA progression rates of treated and fellow eyes were evaluated. RESULTS: After a 1-year follow-up, a progression of the atrophic area was observed in the treated eyes (0.7-8.0 mm(2)/yr, mean 3.0 mm(2)/yr; 46%/yr) whereas the progression rates of the fellow eyes were insignificantly lower (0.46-4.04 mm(2)/yr, mean 1.9 mm(2)/yr; 30%/yr; p = 0.134). The progression rate in the treated eyes of two patients increased significantly, while in the other four patients, the progression rates were nearly the same between both eyes. Moreover, one of these two eyes showed an unexpected RPE reaction after treatment, since all laser lesions led to RPE atrophy and thus an accelerated enlargement of the GA occurred. CONCLUSION: SRT in the hyperautofluorescent areas of GA was not able to stop or slow down the progression of GA. However, modified treatment strategies might be more promising, e.g. placing the spots outside the hyperautofluorescent areas where RPE apoptosis is postulated. Moreover, SRT studies on GA might be more successfully performed on specific subgroups of GA, based on autofluorescence and other findings.

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).

Micro-optical coherence tomography for high-resolution morphologic imaging of cellular and nerval corneal micro-structures.

We demonstrate the highest resolution (1.5×1.5×1 µm) micrometer optical coherence tomography (µOCT) imaging of the morphologic micro-structure of excised swine and non-human primate corneas. Besides epithelial, stromal, and endothelial cell morphology, this report focuses on investigating the most peripheral corneal nerve fibers, the nerve fibers of the subbasal plexus (SBP). Alterations of SBP nerve density and composition are reportedly linked to major neurologic disorders, such as diabetic neuropathy, potentially indicating earliest onsets of denervation. Here, the fine, hyperreflective, epithelial nerve structures located just above Bowman's membrane, are i) visualized using our µOCT prototype, ii) validated by comparison to fluorescence confocal microscopy (including selective immunohistochemical staining), and iii) segmented using state-of-the-art image processing. Here, we also introduce polarization sensitive (PS) µOCT imaging, demonstrating, to the best of our knowledge, the highest resolution corneal PS-OCT scans reported to date.

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.

Stromal Nerve Imaging and Tracking Using Micro-Optical Coherence Tomography.

Purpose: To image, track and map the nerve fiber distribution in excised rabbit corneas over the entire stromal thickness using micro-optical coherence tomography (µOCT) to develop a screening tool for early peripheral neuropathy. Methods: Excised rabbit corneas were consecutively imaged by a custom-designed µOCT prototype and a commercial laser scanning fluorescence confocal microscope. The µOCT images with a field of view of approximately 1 × 1 mm were recorded with axial and transverse resolutions of approximately 1 µm and approximately 4 µm, respectively. In the volumetric µOCT image data, network maps of hyper-reflective, branched structures traversing different stromal compartments were segmented using semiautomatic image processing algorithms. Furthermore, the same corneas received ßIII-tubulin antibody immunostaining before digital confocal microscopy, and a comparison between µOCT image data and immunohistochemistry analysis was performed to validate the nerval origin of the tracked network structures. Results: Semiautomatic tracing of the nerves with a high range of different thicknesses was possible through the whole corneal volumes, creating a skeleton of the traced nerves. There was a good conformity between the hyper-reflective structures in the µOCT data and the stained nerval structures in the immunohistochemistry data. Conclusions: This article demonstrates nerval imaging and tracking as well as a spatial correlation between µOCT and a fluorescence corneal nerve standard for larger nerves throughout the full thickness of the cornea ex vivo. Translational Relevance: Owing to its advantageous properties, µOCT may become useful as a noncontact method for assessing nerval structures in humans to screen for early peripheral neuropathy.

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.].

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.

Optimization-based vessel segmentation pipeline for robust quantification of capillary networks in skin with optical coherence tomography angiography.

Optical coherence tomography angiography (OCTA) provides in-vivo images of microvascular perfusion in high resolution. For its application to basic and clinical research, an automatic and robust quantification of the capillary architecture is mandatory. Only this makes it possible to reliably analyze large amounts of image data, to establish biomarkers, and to monitor disease developments. However, due to its optical properties, OCTA images of skin often suffer from a poor signal-to-noise ratio and contain imaging artifacts. Previous work on automatic vessel segmentation in OCTA mostly focuses on retinal and cerebral vasculature. Its applicability to skin and, furthermore, its robustness against imaging artifacts had not been systematically evaluated. We propose a segmentation method that improves the quality of vascular quantification in OCTA images even if corrupted by imaging artifacts. Both the combination of image processing methods and the choice of their parameters are systematically optimized to match the manual labeling of an expert for OCTA images of skin. The efficacy of this optimization-based vessel segmentation is further demonstrated on sample images as well as by a reduced error of derived quantitative vascular network characteristics.

Selective Equatorial Sclera Crosslinking in the Orbit Using a Metal-Coated Polymer Waveguide.

Purpose: Photochemical crosslinking of the sclera is an emerging technique that may prevent excessive eye elongation in pathologic myopia by stiffening the scleral tissue. To overcome the challenge of uniform light delivery in an anatomically restricted space, we previously introduced the use of flexible polymer waveguides. We presently demonstrate advanced waveguides that are optimized to deliver light selectively to equatorial sclera in the intact orbit. Methods: Our waveguides consist of a polydimethylsiloxane cladding and a polyurethane core, coupled to an optical fiber. A reflective silver coating deposited on the top and side surfaces of the waveguide prevents light leakage to nontarget, periorbital tissue. Postmortem rabbits were used to test the feasibility of in situ equatorial sclera crosslinking. Tensometry measurements were performed on ex vivo rabbit eyes to confirm a biomechanical stiffening effect. Results: Metal-coated waveguides enabled efficient light delivery to the entire circumference of the equatorial sclera with minimal light leakage to the periorbital tissues. Blue light was delivered to the intact orbit with a coefficient of variation in intensity of 22%, resulting in a 45 ± 11% bleaching of riboflavin fluorescence. A 2-fold increase in the Young's modulus at 5% strain (increase of 92% P < 0.05, at 25 J/cm2) was achieved for ex vivo crosslinked eyes. Conclusions: Flexible polymer waveguides with reflective, biocompatible surfaces are useful for sclera crosslinking to achieve targeted light delivery. We anticipate that our demonstrated procedure will be applicable to sclera crosslinking in live animal models and, potentially, humans in vivo.

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.

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.