Riboflavin-UV--a crosslinking for fixation of biosynthetic corneal collagen implants.

Purpose: To evaluate riboflavin-UV-A crosslinking as an alternative suture-free fixation method for biosynthetic corneal collagen implants.

Methods: A range of cell-free corneal implants consisting of recombinant human collagen type III were examined. In vitro, the implants were crosslinked with different riboflavin solutions and irradiations.

Functional fabrication of recombinant human collagen-phosphorylcholine hydrogels for regenerative medicine applications.

The implant-host interface is a critical element in guiding tissue or organ regeneration. We previously developed hydrogels comprising interpenetrating networks of recombinant human collagen type III and 2-methacryloyloxyethyl phosphorylcholine (RHCIII-MPC) as substitutes for the corneal extracellular matrix that promote endogenous regeneration of corneal tissue. To render them functional for clinical application, we have now optimized their composition and thereby enhanced their mechanical properties.

Precision, morphology, and histology of corneal flap cuts using a 200-kHz femtosecond laser.

Purpose: Laser-assisted in situ keratomileusis (LASIK) requires precise corneal flap cutting. Especially the creation of thin flaps has recently gained importance for thin-flap LASIK. Currently, there is a trend towards faster femtosecond lasers that can produce flaps in a short period of time.

Repeated transchoroidal implantation and explantation of compound subretinal prostheses: an exploratory study in rabbits.

Purpose: For human trials with retinal prostheses it is mandatory to develop procedures to safely explant and possibly reimplant the devices. This prompted us to investigate in a small exploratory study the safety of repeated transchoroidal implantation and explantation procedures of complex subretinal devices in laboratory animals.

Methods: Repeated transchoroidal surgery was performed in four rabbits.

Effect of 3 excimer laser ablation frequencies (200 Hz, 500 Hz, 1000 Hz) on the cornea using a 1000 Hz scanning-spot excimer laser.

Purpose: To evaluate the possible side effects on human and porcine cadaver eyes induced by excimer laser ablation with 3 ablation frequencies.

Setting: Augenklinik, Klinikum rechts der Isar, Technische Universitaet Muenchen, Munich, Germany.

Methods: Central epithelial abrasion was performed on porcine and human donor eyes.

Epi-laser in situ keratomileusis: comparative evaluation of epithelial separation with 3 microkeratomes.

Purpose: To evaluate the cleavage plane, corneal cytoarchitecture, and cell vitality of separated corneal epithelial sheets created with 3 commonly used microkeratomes.

Setting: Laboratories of the Regensburg University Medical Center, Regensburg, Germany.

Methods: Mechanical separation of the epithelial layer in 10 porcine eyes and 2 human eyes was performed with 3 different microkeratomes (Amadeus II, Zyoptix XP, Epivision).

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.

Light-induced decomposition of indocyanine green.

Purpose: To investigate the light-induced decomposition of indocyanine green (ICG) and to test the cytotoxicity of light-induced ICG decomposition products.

Methods: ICG in solution was irradiated with laser light, solar light, or surgical endolight. The light-induced decomposition of ICG was analyzed by high-performance liquid chromatography (HPLC) and mass spectrometry.

Intrinsic tissue fluorescence in an organotypic perfusion culture of the porcine ocular fundus exposed to blue light and free radicals.

Background: A wide variety of pathological pathways may result in age-related macular degeneration. Because of its complexity, there is no comprehensive model of the disease yet. One key feature is the accumulation of the autofluorescent pigment lipofuscin in the retinal pigment epithelium (RPE).

Maintenance of adult porcine retina and retinal pigment epithelium in perfusion culture: characterisation of an organotypic in vitro model.

The purpose of this study was to characterise an ex-vivo adult porcine retina-retinal pigment epithelium (RPE) perfusion organ culture model. Fresh porcine full-thickness retina-RPE-choroid tissue samples were clamped into tissue carriers and mounted in two-compartment containers. The retinal and choroidal sides were continuously perfused with culture medium.

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.

Ascorbic acid modulates proliferation and extracellular matrix accumulation of hyalocytes.

Ascorbic acid is known to influence proliferation and functional properties of several cell types and is therefore widely used in tissue engineering. In this study, the effect of ascorbic acid on the proliferation and functional properties of hyalocytes was evaluated. Hyalocytes were cultured with different amounts of ascorbic acid in classical two-dimensional (2-D) cultures and a three-dimensional (3-D) pellet culture system.

Safety testing of indocyanine green in an ex vivo porcine retina model.

Purpose: To assess retinal toxicity of indocyanine green (ICG) in a porcine ex vivo perfusion organ culture model, and to measure intraretinal penetration of ICG applied to the retinal surface.

Methods: The retinal surface of fresh porcine retinal tissue was exposed to ICG 0.1% and 1% dissolved in glucose 5% for 1 and 30 minutes with and without concomitant illumination.

Histological evidence for revascularisation of an autologous retinal pigment epithelium--choroid graft in the pig.

Background: Translocation of a free autologous graft consisting of retinal pigment epithelium (RPE), Bruch's membrane, choriocapillaris and choroid in patients with exudative age-related macular degeneration is currently being evaluated in clinical practice. Angiographic studies in these patients suggest that their grafts become revascularised.

Aim: To investigate the histological evidence of revascularisation of the graft in a porcine model.

Perfluorohexylethan (O62) as ocular endotamponade in complex vitreoretinal surgery.

Purpose: To investigate the safety and performance of perfluorohexylethan (O62), a partially fluorinated alkane, as an intraoperative tool and heavy ocular endotamponade in complex vitreoretinal surgery.

Patients And Methods: In a prospective clinical study, O62 was used as a postoperative ocular endotamponade in 11 eyes of 11 patients after pars plana vitrectomy for the following inferior pathologic conditions, proliferative vitreoretinopathy (n = 8), rhegmatogenous retinal redetachment with inferior tears (n = 1), and inferior giant tear (n = 2). The median duration of the O62 tamponade was 43 days (range, 17-55 days), and the median follow-up period after removal of the tamponade was 16 months.

Subretinal electrical stimulation of the rabbit retina with acutely implanted electrode arrays.

Background: Subretinal implants intend to replace photoreceptor function in patients suffering from degenerative retinal disease by topically applying electrical stimuli from the subretinal space. This study intended to prove the feasibility of a newly developed transchoroidal surgery and, furthermore, of a subretinal electrode array, which closely resembles envisioned human implants to electrically stimulate the visual system in rabbits.

Methods: Five rabbits (ten eyes) were implanted with a 4x2-electrode array via a transchoroidal access to the subretinal space.

Cellular and nerve regeneration within a biosynthetic extracellular matrix for corneal transplantation.

Our objective was to determine whether key properties of extracellular matrix (ECM) macromolecules can be replicated within tissue-engineered biosynthetic matrices to influence cellular properties and behavior. To achieve this, hydrated collagen and N-isopropylacrylamide copolymer-based ECMs were fabricated and tested on a corneal model. The structural and immunological simplicity of the cornea and importance of its extensive innervation for optimal functioning makes it an ideal test model.

Clinical findings on the use of long-term heavy tamponades (semifluorinated alkanes and their oligomers) in complicated retinal detachment surgery.

Background: Heavy tamponades for pathologies in the lower part of the retina are a new development, and different tamponades have recently come into clinical use: semifluorinated alkanes (F(6)H(6), F(6)H(8)) and their oligomers (OL62HV).

Method: Nine patients had been operated on using F(6)H(8) (n=5) and by OL62HV (n=4). In all cases the reasons for using the tamponades were complicated retinal detachments in the lower part.

RPE in perfusion tissue culture and its response to laser application. Preliminary report.

Purpose: To study the effects of conventional laser application on the retinal pigment epithelium (RPE) in a perfusion tissue culture model of porcine retinal pigment epithelium without overlying neurosensory retina.

Methods: RPE with underlying choroid was prepared from enucleated porcine eyes and fixed in a holding ring (Minusheet). Specimens were then placed in two-compartment tissue culture containers (MinuCell & Minutissue, Bad Abbach, Germany) and were cultured during continuous perfusion with culture medium at both sides of the entire specimen, the upper RPE and the lower choroid (12 specimens out of 6 eyes).

Outflow facilities through Descemet's membrane in rabbits.

Background: The outflow pathway in viscocanalostomy, a new procedure in glaucoma surgery, is unclear; however, outflow through Descemet's membrane has been postulated. This study evaluates outflow rates through Descemet's membrane at different IOP levels in rabbits.

Methods: 51 Descemet's membranes without endothelium from enucleated rabbit eyes were installed in a double-ring system, the Minuth sheet.

Biostability of micro-photodiode arrays for subretinal implantation.

Micro-photodiode arrays based on semiconductor chip technology are being developed to replace degenerated photoreceptor cells in the retina. Electric current is generated in tiny micro-photodiodes and delivered to the adjacent tissue by micro-electrodes. One of the main requirements of a sub-retinal implantable device is long-term stability versus corrosion in vivo (biostability).