Publications by authors named "Theo G Seiler"

25 Publications

  • Page 1 of 1

Oxygen Kinetics During Corneal Cross-linking With and Without Supplementary Oxygen.

Am J Ophthalmol 2021 03 21;223:368-376. Epub 2020 Nov 21.

ARTORG Center for Biomedical Engineering Research, University of Bern, Bern, Switzerland.

Purpose: To measure and simulate oxygen kinetics during corneal cross-linking at different irradiances with and without supplementary oxygen.

Design: Experimental, laboratory study.

Methods: In de-epithelialized porcine eyes, a femtosecond-laser-generated tunnel was used to place a fiber probe in corneal depths of 100, 200, and 300 μm to measure the local oxygen concentration. After riboflavin imbibition, the corneas were irradiated at 3, 9, 18, and 30 mW/cm while the oxygen concentration was measured. All experiments were performed under normoxic (21%) and hyperoxic (>95%) conditions. The obtained data were used to identify parameters of a numerical model for oxygen consumption and diffusion.

Results: The equilibrium stromal oxygen concentration under atmospheric oxygen at 3 mW/cm was 2.3% in 100 μm decreasing to <1% in 300 μm. With 9, 18, and 30 mW/cm, no oxygen was available in 200 μm, respectively, 100 μm or deeper. Using a hyperoxic environment, the concentration was 50% using 3 mW/cm in 100 μm, decreasing to 40% in 300 μm. At 9 mW/cm, the concentrations were 5%, 3%, and 1% in 100, 200 and 300 μm, respectively. Using 18 and 30 mW/cm, all oxygen was depleted at 100 μm; however, oxygen half-lives were longer at 18 mW/cm than at 30 mW/cm. The oxygen model was able to reproduce the experiments and indicated an exponential decay with increasing distance to the anterior surface.

Conclusion: Supplementary oxygen increases the oxygen availability during corneal cross-linking. At higher irradiances, supplementary oxygen is beneficial and eliminates the bottleneck of oxygen allowing a potentially more efficient cross-linking. The calibrated numerical model can quantify the spatial oxygen concentration related to different scenarios such as irradiance or environmental oxygen concentration.
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http://dx.doi.org/10.1016/j.ajo.2020.11.001DOI Listing
March 2021

Cellular Factor XIII, a Transglutaminase in Human Corneal Keratocytes.

Int J Mol Sci 2019 Nov 27;20(23). Epub 2019 Nov 27.

Division of Clinical Laboratory Science, Department of Laboratory Medicine, University of Debrecen, Faculty of General Medicine, 4032 Debrecen, Hungary.

Cellular factor XIII (cFXIII, FXIII-A), a transglutaminase, has been demonstrated in a few cell types. Its main function is to cross-link proteins by isopeptide bonds. Here, we investigated the presence of cFXIII in cells of human cornea. Tissue sections of the cornea were immunostained for FXIII-A in combination with staining for CD34 antigen or isopeptide cross-links. Isolated corneal keratocytes were also evaluated by immunofluorescent microscopy and flow cytometry. FXIII-A in the corneal stroma was quantified by Western blotting. FXIII-A mRNA was detected by RT-qPCR. The cornea of FXIII-A-deficient patients was evaluated by cornea topography. FXIII-A was detected in 68 ± 13% of CD34+ keratocytes. Their distribution in the corneal stroma was unequal; they were most abundant in the subepithelial tertile. cFXIII was of cytoplasmic localization. In the stroma, 3.64 ng cFXIII/mg protein was measured. The synthesis of cFXIII by keratocytes was confirmed by RT-qPCR. Isopeptide cross-links were detected above, but not within the corneal stroma. Slight abnormality of the cornea was detected in six out of nine FXIII-A-deficient patients. The presence of cFXIII in human keratocytes was established for the first time. cFXIII might be involved in maintaining the stability of the cornea and in the corneal wound healing process.
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http://dx.doi.org/10.3390/ijms20235963DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6928837PMC
November 2019

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

Invest Ophthalmol Vis Sci 2019 06;60(7):2563-2570

Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, United States.

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.
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http://dx.doi.org/10.1167/iovs.19-26709DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6586079PMC
June 2019

Dissatisfaction After Trifocal IOL Implantation and Its Improvement by Selective Wavefront-Guided LASIK.

J Refract Surg 2019 Jun;35(6):346-352

Purpose: To evaluate a substantially improved wavefront acquisition technique (Peramis; SCHWIND eye-tech-solutions, Kleinostheim, Germany) for selective wavefront-guided aberration correction to improve satisfaction after implantation of trifocal intraocular lenses (IOLs).

Methods: Of 213 eyes from 108 consecutive patients receiving cataract surgery with multifocal IOL implantation (FineVision; PhysIOL, Liége, Belgium), 56 eyes (26%) of 42 dissatisfied patients were treated with selective wavefront-guided laser in situ keratomileusis (LASIK) (Amaris 1050; SCHWIND eye-tech-solutions) free of cost with a follow-up of 12 months. Selective wavefront-guided ablation corrected for all aberrations except spherical aberrations to preserve the apodization and therefore to enhance the multifocal effect. The degree of satisfaction after trifocal IOL implantation, its increase after selective wavefront-guided LASIK, and the refractive error (spherical equivalent, refractive astigmatism) before and after selective wavefront-guided LASIK were evaluated.

Results: Refractive astigmatism of greater than 0.50 diopters (D) was the most frequent residual refractive error (63%), followed by myopia (45%), hyperopia (20%), and increased ocular higher order aberrations (13%). After selective wavefront-guided LASIK, the refractive target (±0.50 D) was achieved in 98% and refractive astigmatism was 0.50 D or less in 93% of the eyes operated on. The overall satisfaction score in dissatisfied patients increased from 2.1 ± 0.8 preoperatively to 3.6 ± 0.8 (out of 4). Eighty-eight percent of initially dissatisfied patients would choose this procedure again.

Conclusions: Selective wavefront-guided LASIK reduced refractive errors and significantly increased spectacle independence and satisfaction, which may lead to a better acceptance of trifocal IOLs. [J Refract Surg. 2019;35(6):346-352.].
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http://dx.doi.org/10.3928/1081597X-20190510-02DOI Listing
June 2019

Consultation Section: Refractive. June consultation #4.

J Cataract Refract Surg 2019 06;45(6):887

Zurich, Switzerland.

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http://dx.doi.org/10.1016/j.jcrs.2019.04.030DOI Listing
June 2019

Riboflavin Concentrations at the Endothelium During Corneal Cross-Linking in Humans.

Invest Ophthalmol Vis Sci 2019 05;60(6):2140-2145

JenLab GmbH, Berlin, Germany.

Purpose: To determine the riboflavin concentration in the posterior corneal stroma, Descemet's membrane, and endothelium prior to UV irradiation in corneal cross-linking (CXL) in humans.

Methods: Five human deepithelialized cadaver corneas were mounted into artificial anterior chambers. After the establishment of stable physiological hydration, two-photon imaging with a certified multiphoton tomograph was used to determine fluorescence intensity and second harmonic generation signals from collagen throughout each cornea by optical sectioning, with a step size of 2.5 μm. Afterward, 0.1% riboflavin solution was applied to the anterior corneal surface, similar to the standard CXL protocol. To determine the absolute riboflavin concentration immediately before UV irradiation, corneas were measured by two-photon imaging just at the end of the riboflavin imbibition and after riboflavin saturation.

Results: The topical application of 0.1% riboflavin results in a riboflavin concentration that decreases to 0.035% in the posterior stroma. Inside Descemet's membrane and endothelium, the concentration drops further to only approximately 0.015% at the endothelial level. Local riboflavin distribution indicates a predominantly paracellular passive diffusion of riboflavin into the anterior chamber.

Conclusion: The experimentally determined riboflavin concentration of 0.015% at the endothelium shows a substantial discrepancy of a factor of 1.7 to the previously theoretically calculated 0.025%. A lower riboflavin concentration at the endothelium may enable higher radiant exposures and further improve the efficacy of CXL.
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http://dx.doi.org/10.1167/iovs.19-26686DOI Listing
May 2019

Spatially-resolved Brillouin spectroscopy reveals biomechanical abnormalities in mild to advanced keratoconus in vivo.

Sci Rep 2019 05 16;9(1):7467. Epub 2019 May 16.

Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, MA, 02114, USA.

Mounting evidence connects the biomechanical properties of tissues to the development of eye diseases such as keratoconus, a disease in which the cornea thins and bulges into a conical shape. However, measuring biomechanical changes in vivo with sufficient sensitivity for disease detection has proven challenging. Here, we demonstrate the diagnostic potential of Brillouin light-scattering microscopy, a modality that measures longitudinal mechanical modulus in tissues with high measurement sensitivity and spatial resolution. We have performed a study of 85 human subjects (93 eyes), consisting of 47 healthy volunteers and 38 keratoconus patients at differing stages of disease, ranging from stage I to stage IV. The Brillouin data in vivo reveal increasing biomechanical inhomogeneity in the cornea with keratoconus progression and biomechanical asymmetry between the left and right eyes at the onset of keratoconus. The receiver operating characteristic analysis of the stage-I patient data indicates that mean Brillouin shift of the cone performs better than corneal thickness and maximum curvature respectively. In conjunction with morphological patterns, Brillouin microscopy may add value for diagnosis of keratoconus and potentially for screening subjects at risk of complications prior to laser eye surgeries.
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http://dx.doi.org/10.1038/s41598-019-43811-5DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6522517PMC
May 2019

Brillouin Spectroscopy of Normal and Keratoconus Corneas.

Am J Ophthalmol 2019 06 15;202:118-125. Epub 2019 Feb 15.

Wellman Center for Photomedicine - Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA.

Purpose: To investigate the age dependence of Brillouin spectroscopy of the cornea and to compare normal and keratoconus corneas.

Design: Retrospective case-control study.

Methods: Study Population: Healthy patients and patients suffering from keratoconus seen at the Institut für Refraktive und Ophthalmo-Chirurgie (IROC) between December 2016 and March 2017. Brillouin frequency shifts of patients of 2 different groups were examined with Brillouin spectroscopy perpendicular to the corneal surface. Group 1 consisted of 47 healthy eyes, whereas Group 2 included 36 eyes with keratoconus of unclear progression. Besides Brillouin examinations, corneal tomographies were acquired so that correlations and comparisons between geometric parameters and Brillouin frequency shifts could be evaluated.

Main Outcome Measures: Corneal Brillouin frequency shifts averaged over full corneal thickness.

Results: A significant correlation between age and central Brillouin frequency shift was identified (P = .011) with an increase in Brillouin frequency shift of 4 MHz per decade in normal corneas. Keratoconus corneas have a significantly reduced Brillouin frequency shift at the thinnest point compared to normal corneas (5.7072 ± 0.0214 vs 5.7236 ± 0.0146 GHz, P < .001). The Brillouin frequency shift at the point of maximum posterior elevation showed best correlation with geometry-derived keratoconus indices. The receiver operating characteristic curve analysis of Brillouin frequency shift showed substantially worse sensitivity and specificity compared to K and thinnest pachymetry for keratoconus detection.

Conclusion: Noninvasive Brillouin spectroscopy adds clinical information about the biomechanical state of the cornea perpendicular to the surface. An age-dependent stiffening of the cornea has been found and keratoconus corneas are statistically significantly different from normal corneas, but for precise differentiating of keratoconus stages (including normal corneas) the method is currently neither specific nor sensitive enough. Further development including standardized mapping and establishment of new indices may increase the potential of Brillouin spectroscopy substantially.
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http://dx.doi.org/10.1016/j.ajo.2019.02.010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6548649PMC
June 2019

Continued Long-term Flattening After Corneal Cross-linking for Keratoconus.

J Refract Surg 2018 Aug;34(8):567-570

Purpose: To report 3 cases with continued long-term flattening after corneal cross-linking (CXL) for keratoconus and to determine its prevalence.

Methods: Case series.

Results: Three eyes of three patients presented with an ongoing corneal flattening over 10 years after CXL in the absence of corneal opacities. Of the initial 433 eyes treated with CXL between 2005 to 2007, only 45 eyes completed the 10-year follow-up period, indicating a prevalence of 6.7%.

Conclusions: Besides continuous flattening due to scars and intense early flattening, a third entity of continuous flattening can be observed after CXL. Continuous long-term flattening after CXL seems to affect more patients than initially anticipated and should be considered as a late-onset complication of CXL. [J Refract Surg. 2018;34(8):567-570.].
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http://dx.doi.org/10.3928/1081597X-20180607-01DOI Listing
August 2018

The influence of hydration on different mechanical moduli of the cornea.

Graefes Arch Clin Exp Ophthalmol 2018 Sep 24;256(9):1653-1660. Epub 2018 Jul 24.

Institut für Refraktive und Ophthalmo-Chirurgie (IROC), Stockerstrasse 37, 8002 Zürich, Switzerland.

Purpose: To determine the interrelation of different elastic moduli of the cornea and to investigate their dependency on corneal hydration.

Methods: Rabbit eyes were divided into four groups. Corneas were excised and mounted into a Barron artificial anterior chamber. Various corneal hydration steady states were achieved with different dextran T-500 concentrations in the anterior chamber, as well as on the corneal anterior surface. The treatment-solutions of each group contained either 5, 10, 15, or 20% w/w dextran. Ultrasound pachymetry was used to measure central corneal thickness. Brillouin microscopy of the central cornea determined the longitudinal bulk modulus by means of Brillouin frequency shift. Subsequently, a 5-mm-wide central strip was taken for extensiometry to measure the tangential elastic modulus.

Results: The longitudinal bulk modulus was 1.2-times higher in corneas dehydrated with 20% dextran compared to those hydrated with 5% dextran. In contrast, the tangential elastic modulus increased by 4.4 times. The obtained longitudinal bulk moduli were two orders of magnitude bigger than the tangential elastic moduli. Regression analysis of longitudinal bulk modulus and tangential elastic modulus revealed a quadratic relation. The bulk modulus seemed to be independent of tension, whereas the elastic modulus was tension-dependent. Greater corneal hydration led to significantly thicker pachymetry.

Conclusion: Corneal biomechanics are highly dependent on the level of corneal hydration. Surprisingly, tangential elastic moduli were more sensitive to hydration changes than longitudinal bulk moduli. A quadratic relation was found between both moduli.
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http://dx.doi.org/10.1007/s00417-018-4069-7DOI Listing
September 2018

Effects of Corneal Hydration on Brillouin Microscopy In Vivo.

Invest Ophthalmol Vis Sci 2018 06;59(7):3020-3027

Wellman Center for Photomedicine, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, United States.

Purpose: To investigate how corneal hydration affects the Brillouin frequency of corneal stroma.

Methods: From a simple analytical model considering the volume fraction of water in corneal stroma, we derived the dependence of Brillouin frequency on hydration and hydration-induced corneal thickness variation. The Brillouin frequencies of fresh ex vivo porcine corneas were measured as their hydration was varied in dextran solution and water. Healthy volunteers (8 eyes) were scanned in vivo repeatedly over the course of 9 hours, and the diurnal variations of Brillouin frequency and central corneal thickness (CCT) were measured.

Results: The measured dependence of Brillouin frequency on hydration, both ex vivo and in vivo, agreed well with the theoretical prediction. The Brillouin frequencies of human corneas scanned immediately after waking were on average ∼25 MHz lower than their daytime average values. For stabilized corneas, the typical variation of Brillouin frequency was ± 7.2 MHz. With respect to CCT increase or swelling, the Brillouin frequency decreased with a slope of -1.06 MHz/μm in vivo.

Conclusions: The ex vivo and in vivo data agree with our theoretical model and support that the effect of corneal hydration on Brillouin frequency comes predominantly from the dependence of the tissue compressibility on the water. Corneal hydration correlates negatively with the Brillouin frequency. During daytime activities, the influence of physiological hydration changes in human corneas is < ± 10 MHz. The sensitivity to hydration may potentially be useful in detecting abnormal hydration change in patients with endothelial disorders.
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http://dx.doi.org/10.1167/iovs.18-24228DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5995485PMC
June 2018

Corneal crosslinking (CXL) with 18-mW/cm irradiance and 5.4-J/cm radiant exposure-early postoperative safety.

Graefes Arch Clin Exp Ophthalmol 2018 Aug 17;256(8):1521-1525. Epub 2018 Apr 17.

The Klinik und Poliklinik für Augenheilkunde, Klinikum rechts der Isar, Technische Universität München, Ismaningerstraße 21, 81675, Munich, Germany.

Purpose: To investigate safety of accelerated corneal crosslinking during the first postoperative month.

Methods: In this retrospective study, 76 eyes of 60 patients with verified progressive keratectasia were enrolled in this study and followed for 1 month after accelerated CXL (18 mW/cm for 5 min, radiant exposure 5.4 J/cm) (A-CXL(5*18)). Preoperatively, objective refraction, slit lamp inspection, and corneal tomography were performed. Early postoperative slit lamp examinations were performed on days 1 and 4. At 1 month, objective refraction, slit lamp inspection, and corneal tomography were performed.

Results: Gender distribution was m:f = 55:21, OD:OS was 40:36, and the average age was 26.5 ± 8.6 years at surgery. Only 71 of the 76 eyes completed the 1-month follow-up, indicating a dropout rate of 6.6%. In 7.0% (n = 5), sterile infiltrates were observed; 5.6% of eyes (n = 4) showed delayed epithelial healing (> 4 days) in 2.8% (n = 2); an infection occurred and in 1 eye (1.4%), a stromal scar was detected; no other complications, neither a loss of two or more Snellen lines at 1 month postoperatively, were observed. As a risk factor for sterile infiltrates, thin preoperative pachymetry could be identified (p = 0.027).

Conclusions: This study revealed no difference in early postoperative safety between CXL using 18 mW/cm and standard corneal CXL. Thinner preoperative pachymetry could be identified predicting a higher rate of postoperative sterile infiltrates.
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http://dx.doi.org/10.1007/s00417-018-3978-9DOI Listing
August 2018

Bridging medicine and biomedical technology: enhance translation of fundamental research to patient care.

Biomed Opt Express 2017 Dec 3;8(12):5368-5373. Epub 2017 Nov 3.

Wellman Center for Photomedicine, Massachusetts General Hospital Research Institute and Harvard Medical School, 40 Blossom Street, Boston, MA 02114, USA.

The 'Bridging medicine and biomedical technology' special all-congress session took place for the first time at the OSA Biophotonics Congress: Optics in Life Sciences in 2017 (http://www.osa.org/enus/meetings/osa_meetings/optics_in_the_life_sciences/bridging_medicine_and_biomedical_technology_specia/). The purpose was to identify key challenges the biomedical scientists in academia have to overcome to translate their discoveries into clinical practice through robust collaborations with industry and discuss best practices to facilitate and accelerate the process. Our paper is intended to complement the session by providing a deeper insight into the concept behind the structure and the content we developed.
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http://dx.doi.org/10.1364/BOE.8.005368DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5745088PMC
December 2017

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

Invest Ophthalmol Vis Sci 2017 12;58(14):6292-6298

Wellman Center for Photomedicine-Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, United States.

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.
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http://dx.doi.org/10.1167/iovs.17-22426DOI Listing
December 2017

Flexible Optical Waveguides for Uniform Periscleral Cross-Linking.

Invest Ophthalmol Vis Sci 2017 05;58(5):2596-2602

Harvard Medical School and Wellman Center for Photomedicine, Massachusetts General Hospital, Boston, Massachusetts, United States 2Harvard-MIT Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States.

Purpose: Scleral cross-linking (SXL) with a photosensitizer and light is a potential strategy to mechanically reinforce the sclera and prevent progressive axial elongation responsible for severe myopia. Current approaches for light delivery to the sclera are cumbersome, do not provide uniform illumination, and only treat a limited area of sclera. To overcome these challenges, we developed flexible optical waveguides optimized for efficient, homogeneous light delivery.

Methods: Waveguides were fabricated from polydimethylsiloxane elastomer. Blue light (445 nm) is coupled into the waveguide with an input fiber. Light delivery efficiency from the waveguide to scleral tissue was measured and fit to a theoretical model. SXL was performed on fresh porcine eyes stained with 0.5% riboflavin, using irradiances of 0, 25, and 50 mW/cm2 around the entire equator of the eye. Stiffness of scleral strips was characterized with tensiometry.

Results: Light delivery with a waveguide of tapered thickness (1.4-0.5 mm) enhanced the uniformity of light delivery, compared to a flat waveguide, achieving a coefficient of variation of less than 10%. At 8% strain, sclera cross-linked with the waveguides at 50 mW/cm2 for 30 minutes had a Young's modulus of 10.7 ± 1.0 MPa, compared to 5.9 ± 0.5 MPa for no irradiation, with no difference in stiffness between proximally and distally treated halves. The stiffness of waveguide-irradiated samples did not differ from direct irradiation at the same irradiance.

Conclusions: We developed flexible waveguides for periscleral cross-linking. We demonstrated efficient and uniform stiffening of a 5-mm-wide equatorial band of scleral tissue.
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http://dx.doi.org/10.1167/iovs.17-21559DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5433838PMC
May 2017

Comparison of Corneal Riboflavin Gradients Using Dextran and HPMC Solutions.

J Refract Surg 2016 Dec;32(12):798-802

Purpose: To determine the riboflavin concentration gradient in the anterior corneal stroma when using hydroxypropyl methylcellulose (HPMC) or dextran as the carrier agent.

Methods: Four different groups of porcine corneas (5 each) were compared regarding the riboflavin concentration in the anterior stroma. Prior to all experiments, stable hydration conditions were established for the corresponding solution. The dextran groups were treated with 0.1% riboflavin in 20% dextran for 10 and 30 minutes and the HPMC groups with 0.1% riboflavin in 1.1% HPMC for 10 and 30 minutes. After imbibition, nonlinear microscopy and consecutive image analysis were used to determine two-photon fluorescence intensities. To determine the riboflavin concentration, corneas were saturated and measured a second time by two-photon microscopy. With this measurement, a proper correction for absorption and scattering could be performed. Ultraviolet-A (UVA) transmission was measured after the application time for each group.

Results: Riboflavin concentration decreased with increasing depth and increased with longer application times in all groups. Comparing the dextran for 30 minutes and HPMC for 10 minutes groups, a significantly higher stromal riboflavin concentration was found within the most anterior 70 µm in the dextran group for 30 minutes, whereas deeper than 260 µm HPMC-assisted imbibition for 10 minutes yielded higher concentrations. In dextran-treated corneas, values obtained from pachymetry were substantially reduced, whereas HPMC-assisted imbibition led to a decent swelling. UVA transmission values were higher in dextran-assisted imbibition than in HPMC-assisted imbibition.

Conclusions: Stromal riboflavin gradients are similar when applied in dextran for 30 minutes and HPMC for 10 minutes. When using HPMC solutions, a shallower cross-linked volume is expected due to a higher corneal hydration. [J Refract Surg. 2016;32(12):798-802.].
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http://dx.doi.org/10.3928/1081597X-20160920-03DOI Listing
December 2016

Very Late-Onset Corneal Scarring After Photorefractive Keratectomy Induced by Cataract Surgery.

J Refract Surg 2016 Apr;32(4):266-8

Purpose: To report two cases with very late-onset scarring of the cornea after photorefractive keratectomy (PRK) induced by cataract surgery.

Methods: Case report and literature review.

Results: Two patients presented with a subepithelial corneal scar more than 20 years after PRK. Scarring occurred within the first few months after cataract surgery. Scar tissue was successfully removed by laser-assisted anterior lamellar keratoplasty.

Conclusions: A few cases of late-onset corneal scarring after PRK have been described in the literature following trauma or ophthalmic surgery. Due to the need for cataract surgery in an aging population with previous PRK, this might become a more common problem.
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http://dx.doi.org/10.3928/1081597X-20160121-06DOI Listing
April 2016

Customized Corneal Cross-linking: One-Year Results.

Am J Ophthalmol 2016 Jun 2;166:14-21. Epub 2016 Mar 2.

Institut für Refraktive und Ophthalmo-Chirurgie (IROC), Zürich, Switzerland.

Purpose: To compare the efficacy of customized corneal cross-linking (CXL) with standard CXL.

Design: Prospective, nonrandomized comparative clinical study.

Methods: In a prospective study at the Institut für Refraktive und Ophthalmo-Chirurgie (IROC), Zurich, Switzerland, 40 eyes of 40 patients with documented progressive primary keratoconus were treated with customized CXL (n = 20) or standard CXL (n = 20) and followed for 1 year. Customized irradiation patterns had an energy fluence of 9 mW/cm(2) and total energy levels ranging from 5.4 J/cm(2) up to 10 J/cm(2) and were centered on the maximum of the posterior float. The control group received homogenous irradiation with a fluence of 9 mW/cm(2) and a total energy of 5.4 J/cm(2). Scheimpflug tomographies, endothelium cell count, best spectacle-corrected visual acuity (BSCVA), and anterior segment optical coherence tomography (OCT) were compared preoperatively and 1 year postoperatively.

Results: Pachymetry and ΔKmax showed significant changes 1 year postoperatively within each group. Epithelial healing time, ΔKmax, and regularization index (RI) were significantly better in the customized CXL group. Two out of 19 eyes (11%) in the standard group but 7 out of 19 eyes (37%) in the customized CXL group showed a flattening of 2 or more diopters (P = .03). The RI was 5.2 ± 2.7 D in the customized group vs 4.1 ± 3.1 D in the control group (P = .03). Statistically significant correlations between RI and preoperative Kmax, preoperative pachymetry, and preoperative posterior float were found only in the customized group.

Conclusions: Customized CXL seems to be as safe as standard CXL with stronger flattening in Kmax and RI, and a faster epithelial healing period.
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http://dx.doi.org/10.1016/j.ajo.2016.02.029DOI Listing
June 2016

Superficial corneal crosslinking during laser in situ keratomileusis.

J Cataract Refract Surg 2015 Oct;41(10):2165-70

From the Institut für Refraktive und Ophthalmo-Chirurgie (T.G. Seiler, Fischinger, Koller, Derhartunian, T. Seiler), Zürich, Switzerland and the Klinik und Poliklinik für Augenheilkunde, Klinikum rechts der Isar (T.G. Seiler, Fischinger), Technische Universität München, München, Germany.

Purpose: To determine the safety of superficial corneal crosslinking after laser in situ keratomileusis (LASIK).

Setting: Institut für Refraktive und Ophthalmo-Chirurgie, Zurich, Switzerland.

Design: Prospective study.

Methods: Eyes with an ectasia risk score of 2 or higher were treated with standard LASIK (90 μm flap) for myopia correction, after which a rapid corneal crosslinking was performed in the interface (riboflavin 0.5% for 2 minutes, 9 mW/cm(2) for 5 minutes) (Group 1). The follow-up was up to 1 year. The prevalence of complications was statistically compared with that in a group of eyes matched regarding age, sex, and attempted refractive correction that were treated with standard LASIK only (Group 2).

Results: One month postoperatively, 5 eyes in Group 1 lost 1 line of corrected distance visual acuity (CDVA) compared with 1 eye in Group 2 (P < .05). One year postoperatively, all eyes regained their preoperative CDVA, indicating a complication rate of less than 5%. The refractive success was identical in both groups. Early postoperative complications such as erosions (16%), diffuse lamellar keratitis (DLK) stage 1 (38%), and DLK stage 2 (5%) were statistically significantly more frequent after superficial corneal crosslinking, leading to a statistically significantly reduced uncorrected distance visual acuity at 1 month (P < .001).

Conclusions: Based on 1-year results, superficial corneal crosslinking might be considered a safe adjunct to LASIK, with a delayed visual rehabilitation and a higher prevalence of transient side effects. It is not proved whether superficial corneal crosslinking can prevent iatrogenic keratectasia.

Financial Disclosure: No author has a financial or proprietary interest in any material or method mentioned.
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http://dx.doi.org/10.1016/j.jcrs.2015.03.020DOI Listing
October 2015

Two-Photon Fluorescence Microscopy for Determination of the Riboflavin Concentration in the Anterior Corneal Stroma When Using the Dresden Protocol.

Invest Ophthalmol Vis Sci 2015 Oct;56(11):6740-6

Laser Zentrum Hannover e.V., Hanover, Germany 5Institut für Quantenoptik, Leibniz Universität Hannover, Hanover, Germany.

Purpose: To determine the riboflavin concentration gradient in the anterior corneal stroma when using the Dresden protocol with different dextran solutions.

Methods: Three different groups of porcine corneas, five each, were compared regarding the riboflavin concentration in the anterior stroma. Before all experiments, stable hydration conditions were established for the corresponding solution. All groups were treated with 0.1% riboflavin in different dextran solutions (15%, 16%, 20%). After imbibition, two-photon microscopy was used to determine fluorescence intensity. For signal attenuation and concentration determination corneas were saturated and measured a second time by two-photon microscopy. Additionally, the distribution was calculated mathematically and compared to the empiric results.

Results: Riboflavin concentration is decreasing with depth for all dextran solutions. A nearly constant concentration could be determined over the first 75 μm. Analysis of the fit functions leads to diffusion coefficients of D = 2.97 × 10-7 cm2/s for the 15% dextran solution, D = 2.34 × 10-7 cm2/s for the 16% dextran solution, and D = 1.28 × 10-7 cm2/s for the 20% dextran solution. The riboflavin gradients of the 20% dextran group were statistically significantly different from 15% dextran starting at a depth of 220 μm and deeper (P = 0.047). The 16% dextran group differed statistically at a depth of 250 μm and deeper (P = 0.047). These results show a significant difference to those published previously.

Conclusions: With correct settings two-photon microscopy is a precise way to determine the concentration of riboflavin in cornea. The measured gradient is excellently fit by a Gaussian distribution, which comes out as a solution of Fick's second law.
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http://dx.doi.org/10.1167/iovs.15-17656DOI Listing
October 2015

Time Course of Antibiotic and Antifungal Concentrations in Corneal Organ Culture.

Cornea 2016 Jan;35(1):127-31

Departments of *Ophthalmology; and †Infectious Diseases, Inselspital, University of Bern, Bern, Switzerland.

Purpose: Contamination with bacteria and/or fungi is a serious complication in organ-cultured corneas. Hence, antibiotic and antifungal agents are added to the culture medium. The concentration of different antimicrobial and antifungal additives to the media over time has so far not been investigated in detail and is the aim of this study.

Methods: Nine human fresh corneoscleral discs were stored in corneal culture medium consisting of 2% fetal bovine serum and minimal essential medium. In addition, the culture medium contained 1200 μg/mL penicillin G, 25 μg/mL amphotericin B, 120 μg/mL streptomycin, and 100 μg/mL voriconazole. The concentration of amphotericin B used was 10 times higher than in clinical routine to facilitate its detection. The cultures were kept at 37°C for 28 days. At days 0, 7, 14, 21, and 28, samples of the culture medium were harvested for analysis of antimicrobial concentrations by liquid chromatography and electrospray ionization tandem mass spectrometry.

Results: During corneal storage, the concentration of all antibiotics and antifungal agents declined significantly. By day 28, penicillin G was reduced to 14% of the original concentration. Amphotericin B and streptomycin retained approximately 60% of the original concentration to the end of the experiment and voriconazole maintained stable concentrations after an initial decline to approximately 80% at 7 days.

Conclusions: Throughout the entire storage period, the concentrations of penicillin G, streptomycin, and voriconazole exceeded the minimum inhibitory concentrations of all common contaminants, obviating the need for a change of the medium for antimicrobial reasons. Based on the minimum inhibitory concentrations and our findings, the initial concentration of amphotericin B should be raised to 5 μg/mL.
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http://dx.doi.org/10.1097/ICO.0000000000000671DOI Listing
January 2016

Spectral behavior of second harmonic signals from organic and non-organic materials in multiphoton microscopy.

AIP Adv 2015 Aug 12;5(8):084903. Epub 2015 Mar 12.

Institute of Quantum Optics, University of Hanover , 30167 Hanover, Germany.

Multimodal nonlinear microscopy allows imaging of highly ordered biological tissue due to spectral separation of nonlinear signals. This requires certain knowledge about the spectral distribution of the different nonlinear signals. In contrast to several publications we demonstrate a factor of [Formula: see text] relating the full width at half maximum of a gaussian laser pulse spectrum to the corresponding second harmonic pulse spectrum in the spatial domain by using a simple theoretical model. Experiments on monopotassium phosphate crystals (KDP-crystals) and on porcine corneal tissue support our theoretical predictions. Furthermore, no differences in spectral width were found for epi- and trans-detection of the second harmonic signal. Overall, these results may help to build an optimized multiphoton setup for spectral separation of nonlinear signals.
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http://dx.doi.org/10.1063/1.4915134DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4513891PMC
August 2015

Intrastromal application of riboflavin for corneal crosslinking.

Invest Ophthalmol Vis Sci 2014 Jun 10;55(7):4261-5. Epub 2014 Jun 10.

The Institut für Refraktive und Ophthalmo-Chirurgie (IROC), Zürich, Switzerland.

Purpose: To experimentally evaluate the efficacy of corneal crosslinking (CXL) by injecting the photomediator riboflavin into the corneal stroma via intrastromal channels.

Methods: Five groups of pig corneas, nine each, were compared regarding stress-strain relationship and UV-absorption. Group 1 had intrastromal channels floated with riboflavin 0.5%-solution followed by UVA-irradiation (3 mW/cm(2) for 30 minutes); group 2 was handled like group 1, but were irradiated with 9 mW/cm(2) for 10 minutes; group 3 was treated according to the Dresden protocol (epi-off, 9 mW/cm(2) for 10 minutes); group 4 had the identical channel system, no riboflavin but identical irradiation; group 5 with native corneas served as a control group. The intrastromal channels were created with a femtosecond laser. The stress-strain relations were measured in corneal strips using a uniaxial material tester at strains up to 12%. The UV-transmission of the corneas was measured in groups 1, 3, and 5.

Results: The stress needed for a 10% strain was significantly increased by 82% in the corneas treated with the Dresden protocol compared with native cornea (P = 0.0005). With intrastromal application of riboflavin the significant increase was 87% (P = 0.0005) in group 1 and 64% (P = 0.007) in group 2. The channel formation alone did not alter biomechanics (P = 0.923). The corneal UVA-transmission was 2.4% after intrastromal riboflavin application, 8.9% after the treatment according to the Dresden protocol, and 57.9% in native corneas.

Conclusions: The experiments demonstrate the intrastromal application of riboflavin by means of intrastromal channels a feasible "epi-on" approach for CXL. More experimental data are needed before clinical testing.
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http://dx.doi.org/10.1167/iovs.14-14021DOI Listing
June 2014

Corneal collagen cross-linking for Terrien marginal degeneration.

J Refract Surg 2014 Jul 3;30(7):498-500. Epub 2014 Jun 3.

Purpose: To report the long-term clinical outcome of a patient diagnosed as having Terrien marginal degeneration (TMD) who was subjected to corneal collagen cross-linking (CXL) with ultraviolet-A and riboflavin in both eyes.

Methods: Topographical changes were assessed by high-resolution Scheimpflug imaging and anterior segment optical coherence tomography. Eccentric epithelium-off CXL was performed in both eyes while protecting the corneal limbus. Irradiation was performed with a fluence of 5.4 J/cm(2), using 3 mW/cm(2) for 30 minutes.

Results: Five years of postoperative follow-up showed regression of the keratometric values, a local thickening of the corneal stroma, and bilateral improvement of corrected distance visual acuity.

Conclusions: CXL may arrest progression in TMD and even reverse the catabolic process in the corneal stroma. CXL might represent an alternative therapeutic approach for the management of TMD.
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http://dx.doi.org/10.3928/1081597X-20140527-02DOI Listing
July 2014