Home About us Contact
|
Home About us Contact | ||
|
|
||
Human Cornea (human + cornea)
Selected AbstractsDiffusion and Monod kinetics to determine in vivo human corneal oxygen-consumption rate during soft contact-lens wearJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2009Mahendra Chhabra Abstract The rate of oxygen consumption is an important parameter to assess the physiology of the human cornea. Metabolism of oxygen in the cornea is influenced by contact-lens-induced hypoxia, diseases such as diabetes, surgery, and drug treatment. Therefore, estimation of in vivo corneal oxygen-consumption rate is essential for gauging adequate oxygen supply to the cornea. Phosphorescence quenching of a dye coated on the posterior of a soft contact lens provides a powerful technique to measure tear-film oxygen tension (Harvitt and Bonanno, Invest Ophthalmol Vis Sci 1996;37:1026,1036; Bonanno et al., Invest Ophthalmol Vis Sci 2002;43:371,376). Unfortunately, previous work in establishing oxygen-consumption kinetics from transient postlens tear-film oxygen tensions relies on the simplistic assumption of a constant corneal-consumption rate. A more realistic model of corneal metabolism is needed to obtain reliable oxygen-consumption kinetics. Here, physiologically relevant nonlinear Monod kinetics is adopted for describing the local oxygen-consumption rate, thus avoiding aphysical negative oxygen tensions in the cornea. We incorporate Monod kinetics in an unsteady-state reactive-diffusion model for the cornea contact-lens system to determine tear-film oxygen tension as a function of time when changing from closed-eye to open-eye condition. The model was fit to available experimental data of in vivo human postlens tear-film oxygen tension to determine the corneal oxygen-consumption rate. Reliance on corneal oxygen diffusivity and solubility data obtained from rabbits is no longer requisite. Excellent agreement is obtained between the proposed model and experiment. We calculate the spatial-averaged in vivo human maximum corneal oxygen-consumption rate as Q = 1.05 × 10,4 mL/(cm3 s). The calculated Monod constant is Km = 2.2 mmHg. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009 [source] In vitro femtosecond laser subsurface micro-disruption inside human cornea and pre-cleared scleraLASER PHYSICS LETTERS, Issue 6 2010A.A. Alekhin Abstract Micro-incisions were fabricated inside human cornea and sclera in vitro using single femtosecond laser pulses. In these experiments sclera was for the first time pre-cleared by means of a biocompatible and clinically safe (non-toxic) natural agent (refractive-index matching 40%-glucose solution in water), partially replacing water in the tissue comparing to its severe dehydration by previously used agents. Basic operational parameters of the corresponding microsurgical procedures are reported. (© 2010 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Purification, crystallization and preliminary X-ray diffraction of wild-type and mutant recombinant human transforming growth factor ,-induced protein (TGFBIp)ACTA CRYSTALLOGRAPHICA SECTION F (ELECTRONIC), Issue 3 2009Kasper Runager Transforming growth factor ,-induced protein (TGFBIp) has been linked to several corneal dystrophies as certain point mutations in the protein may give rise to a progressive accumulation of insoluble protein material in the human cornea. Little is known about the biological functions of this extracellular protein, which is expressed in various tissues throughout the human body. However, it has been found to interact with a number of extracellular matrix macromolecules such as collagens and proteoglycans. Structural information about TGFBIp might prove to be a valuable tool in the elucidation of its function and its role in corneal dystrophies caused by mutations in the TGFBI gene. A simple method for the purification of wild-type and mutant forms of recombinant human TGFBIp from human cells under native conditions is presented here. Moreover, the crystallization and preliminary X-ray analysis of TGFBIp are reported. [source] Histological changes in human cornea after cross-linking with riboflavin and ultraviolet AACTA OPHTHALMOLOGICA, Issue 2 2010Gregor WollensakArticle first published online: 23 APR 200 No abstract is available for this article. [source] Long-term biomechanical properties of rabbit cornea after photodynamic collagen crosslinkingACTA OPHTHALMOLOGICA, Issue 1 2009Gregor Wollensak Abstract. Purpose:, Photodynamic riboflavin/ultraviolet-A (UVA)-induced collagen cross-linking, which increases the biomechanical stiffness of the human cornea by about 300%, has been introduced recently as a possible treatment for progressive keratoconus. The present study was undertaken to evaluate the longterm biomechanical effects of this new cross-linking treatment as a necessary prerequisite to its clinical success. Methods:, The corneas of the left eyes of nine male rabbits were cross-linked. The contralateral eyes served as controls. After removal of the central 7 mm of the epithelium, the corneas were treated with the photosensitizer riboflavin and UVA irradiation for 30 mins with an irradiance of 3 mW/cm2 using a 370-nm UVA double diode. Groups of three animals were killed immediately after treatment and at 3 and 8 months, respectively. Biomechanical stress,strain measurements were performed using a microcomputer-controlled biomaterial tester on 4 × 10-mm corneal strips. Results:, Corneal thickness in the treated rabbit cornea was 408 ± 20 ,m. A constant and significant increase in ultimate stress (of 69.7,106.0%), Young's modulus of elasticity (of 78.4,87.4%) and a decrease in ultimate strain (of 0.57,78.4%) were found over a time period of up to 8 months after cross-linking treatment. Conclusions:, Riboflavin/UVA-induced collagen cross-linking leads to a longterm increase in biomechanical rigidity which remains stable over time. These data support our previous longterm clinical observations and give hope that this new treatment will halt progressive keratoconus definitively. [source] AER lecture: Some reflections on corneal thicknessACTA OPHTHALMOLOGICA, Issue 2007N EHLERS The corneal thickness as an object for studies was recognized in the renaissance. A value of 1 mm, representing the maximally swollen human cornea, was reported. Optical in vivo measurements were done by Blix in 1880 reporting a thickness of about 0.5 mm, the value that we today know is correct. Blix lived in "the golden age of physiologic optics". His interest was the contribution of the cornea to the optical refraction of the eye, and was thus the distance between the anterior and the posterior surface rather than the thickness of the cornea as such. A biomechanical interest in corneal thickness was initiated by the studies of tonometry, in particular Hans Goldmann's development of applanation tonometry. He predicted correctly that corneal thickness would influence the estimated pressure reading. Another physiological aspect of the cornea is its transparency. Earlier explanations by equal refractive index was revolutionized by the interference theory by David Maurice. Optical transparency required a regular fiber pattern, and thus a stabilized thickness and stromal hydration. This led to extensive interest in the permeability of the limiting layers, in particular the transport of fluid across the endothelium. The physiological concepts required a regulated or stabilized thickness. The thickness as such became interesting. The human cornea is thinner in the center than more peripherally and the central, presumably regulated central thickness (CCT) became a biometric and clinical study object. The exact individual value became of interest. Several optical and later ultrasonic principles were presented. Questions addressed were: Is CCT a life-long, age independent characteristics. Is CCT diagnostic for certain disease conditions (e.g. Macular dystrophy of Groenouw). Is CCT a useful clinical parameter to follow disease processes (e.g. progression in keratoconus or acute changes in graft rejections). Today refractive surgery has revived the interest in biomechanical and optical properties of the cornea. Modern computer technology allows for a description of the "thickness profile" of the entire cornea. This gives us access to an overwhelming amount of data, and reopen many issues of the past. We must realize, however, that what we see is the pendulum swinging back to the problems of the last century. The machinery is smarter but many of the basic questions remain to be solved. [source] Characterization of efflux proteins in human corneal epithelial cellsACTA OPHTHALMOLOGICA, Issue 2007KS VELLONEN Purpose: Corneal epithelium is the main barrier for absorption of drugs into intraocular tissues after topical administration and part of this barrier may be formed by efflux proteins which translocate molecules from the cell interior to the extracellular space. The aim of this study was to characterize the gene expression and the activity of the efflux transporters in the cell culture model of immortalized human corneal epithelial cells (HCE cells), in primary cell line (HCEpiC), and in the human corneal epithelium. Methods: The mRNA levels of MDR1, MRP1-MRP6, and BCRP were determined by the quantitative RT-PCR. Immunohistochemistry was used to study protein expression and localization of efflux transporters. Functionality of these proteins was assessed with calcein-AM efflux assay and by measuring the efflux of CDCF. Furthermore, bidirectional permeability of rhodamine 123 (Rh123) was studied. Results: The mRNA of MRP1 and MRP5 were detected in the human cornea and in both cell lines. These efflux proteins were found in the cell membranes of the human corneal epithelium. At mRNA level some efflux proteins were over-expressed in the HCE and the primary cell lines. Increased calcein retention and decreased CDCF efflux in the presence of inhibitors suggested efflux protein activity in both primary and HCE cells. Likewise, directionality in Rh123 permeability was diminished in the presence of verapamil in HCE model. Conclusions: Functionality of the efflux proteins was demonstrated in the human corneal epithelial cells. MRP1 and MRP5 proteins may have important protecting role in corneal surface by transporting molecules out from the epithelial cells. It seems that the efflux activity in the HCE model differs from that of the corneal epithelium in vivo [source] Remodelling of collagen fibrils and proteoglycans in the zebrafish cornea during developmentACTA OPHTHALMOLOGICA, Issue 2007S AKHTAR Purpose: Collagen fibrils and proteoglycans are the main components of the corneal extracellular matrix and corneal transparency depends crucially on their proper organisation. We investigated their formation and arrangement in the developing cornea of the zebrafish, a major model of vertebrate development and genetic disease. Methods: We employed thin-section electron microscopy to investigate the ultrastructure of the zebrafish cornea at different stages of development. Results: Layering of the zebrafish cornea into an epithelium, Bowman's layer, stroma and endothelium was observed by 72 hours post-fertilization. At this stage, the stroma contained orthogonally arranged collagen fibrils and small proteoglycans. The density of proteoglycans increased gradually throughout subsequent development. In the stroma of 2 week old larvae, the collagen fibrils were organized into thin lamellae for the first time and were separated by very large, randomly distributed proteoglycans. At 4 weeks, a regular arrangement of proteoglycans around the collagen fibrils was observed for the first time and the lamellae also thickened. Conclusions: This is the first report of collagen fibril and proteoglycan development in the zebrafish cornea and it directly correlates collagen fibril and proteoglycan organisation of the zebrafish cornea with that of the human cornea. The similarities between the two species, including the possession of a Bowman layer, suggest that the zebrafish could serve as a model for the genetics of human corneal development and inherited disease. [source] Corneal penetration of simultaneously applied topical levofloxacin, norfloxacin and lomefloxacin in human eyesACTA OPHTHALMOLOGICA, Issue 2 2006Masakazu Yamada Abstract. Purpose:,This study was performed to assess the corneal penetration of three topically applied fluoroquinolones (levofloxacin, norfloxacin and lomefloxacin) in corneal buttons obtained from patients undergoing penetrating keratoplasty. Methods:,Fourteen patients received three drops each of 0.5% levofloxacin, 0.3% norfloxacin and 0.3% lomefloxacin (the standard clinically available preparations) over a 30-min interval beginning 90 mins before their scheduled keratoplasty. Corneal samples obtained from excised buttons at the time of surgery were stored at , 80 ° until analysis. The concentration of the administered fluoroquinolones was measured using high-performance liquid chromatography. Results:,The mean corneal concentration of levofloxacin (4.6 ± 3.5 µg/g, mean ± standard deviation) was significantly higher than that of lomefloxacin (2.7 ± 1.8 µg/g, p = 0.0018) and norfloxacin (1.3 ± 1.2 µg/g, p = 0.00012). Conclusion:,Levofloxacin achieves a higher mean corneal concentration than norfloxacin and lomefloxacin in the human cornea. [source] Monoamine receptors in human corneal epithelium and endotheliumACTA OPHTHALMOLOGICA, Issue 1 2006Matthias Grueb Abstract. Purpose:,Monoamine receptors are found throughout the body. Reports about the presence of monoamine receptors in the human cornea are inconsistent. Methods:,Immunohistochemistry, immunofluorescence and immunoblotting were used to localize monoamine receptor sites on human corneal epithelium and endothelium. Results:,Antibodies to alpha-1, beta-1 and beta-2 adrenergic receptors and to D1-like and 5HT-7 receptors were bound in corneal epithelium. Antibodies to alpha-1, alpha-2A, beta-1 and beta-2 adrenergic receptors and to 5HT-7 receptors were bound in corneal endothelium. Conclusions:,Our data demonstrate the presence of several monoamine receptors in the human cornea. These receptors may play a role in the regulation of fluid transport or corneal homeostasis. [source] Gene therapy for diseases of the cornea , a reviewCLINICAL & EXPERIMENTAL OPHTHALMOLOGY, Issue 2 2010Keryn A Williams PhD Abstract The cornea is particularly suited to gene therapy. The cornea is readily accessible, normally transparent, and is somewhat sequestrated from the general circulation and the systemic immune system. The principle of genetic therapy for the cornea is to use an appropriate vector system to transfer a gene to the cornea itself, or to the ocular environs, or systemically, so that a transgenic protein will be expressed that will modulate congenital or acquired disease. The protein may be structural such as a collagen, or functionally active such as an enzyme, cytokine or growth factor that may modulate a pathological process. Alternatively, gene expression may be silenced by the use of modalities such as antisense oligonucleotides. Interestingly, despite a very considerable amount of work in animal models, clinical translation directed to gene therapy of the human cornea has been minimal. This is in contrast to gene therapy for monogenic inherited diseases of the retina, where promising early results of clinical trials for Leber's congenital amaurosis have already been published and a number of other trials are ongoing. [source] 3136: Donor and recipient endothelial cell populations in transplanted corneas: new insights from endothelial imagingACTA OPHTHALMOLOGICA, Issue 2010N LAGALI Purpose To elucidate the pattern of donor and recipient endothelial cell population in transplanted human corneas and investigate factors impacting this mosaic. Methods 36 corneal grafts were collected from recipients of opposite sex to the donor, at the time of re-transplantation. An endothelial sheet was harvested from each graft, and labeled by fluorescent in situ hybridization of the sex chromosomes, to identify cells as donor or recipient-derived. Images of the graft endothelium were assembled to depict the pattern of cell population of the graft, and the proportion of donor cells present was estimated. Results Endothelial cells of donor origin were found in 26 of 36 grafts, persisting up to 26 years after transplantation. The proportion of donor endothelial cells in the graft was not significantly correlated with postoperative time (P = 0.19). Endothelial images indicated a highly variable pattern of recipient cell repopulation of the graft. A tendency towards donor cell retention in transparent, successful grafts was noted; however, this feature alone was not a reliable indicator of long-term graft transparency. Recent in-vivo optical coherence tomography studies of transplanted corneas indicate a possible mechanism impacting the donor and recipient cell patterns observed on the endothelial surface. Conclusion Two-dimensional imaging of the corneal graft endothelium revealed a variable pattern and extent of donor and recipient cell population, indicating the highly dynamic nature of the corneal endothelium after transplantation. [source] 2142: Ulrastructural features of keratoconus cornea after cross-linking by riboflavin/UVAACTA OPHTHALMOLOGICA, Issue 2010S AKHTAR Purpose In the present studies we assess the effects of collagen cross-linking on ultrastructure organisation of the corneal stroma of keratoconus human corneas. Methods One normal, one keratoconus (KC) and three cross-linked keratoconus corneas were analysed. One was treated with standard cross linking (SXL) and two with trans-epithelial collagen cross linking (TEXL). Penetrating keratoplasty was performed three months after treatment. All samples were fixed in 2.5% glutaraldehyde containing cuprolinic blue in sodium acetate buffer and processed for electron microscopy. Results The structure of SXL corneas was very similar to normal corneas in their hemidesmosomes, basement membrane (BM), Bowman's layer (BW) and stromal lamellae that were not undulated. The architecture of TEXL corneas presented some differences. The BM was thick with degenerated hemidesmosomes. Bowman's layer was disorganised at some places and replaced by thin filaments forming pannus. There were thin undulating lamellae in anterior, middle and posterior stroma. The keratocytes were embedded between undulating lamellae. Large amounts of abnormal PGs were attached around collagen fibrils. The parallel running lamellae were very thin. In some parts of the anterior stroma collagen fibrils were oriented (running) in random directions instead of running parallel. There were some parts of the stroma which showed a normal appearance. Conclusion The present studies demonstrate that corneal cross-linking leads to modifications in keratocytes and in the organisation of collagen fibril. The morphological changes might be correlated to the process of increase in biomechanical stability although there are differences between stromal structures treated by standard and trans [source] Organ culture, but not hypothermic storage, facilitates the repair of the corneal endothelium following mechanical damageACTA OPHTHALMOLOGICA, Issue 4 2010Jana Nejepinska Abstract. Purpose:, To evaluate the reparative capacity of the mechanically injured endothelium of corneas stored under organ culture (OC) or hypothermic conditions. Methods:, The central endothelium of 12 pairs of human corneas with similar endothelial parameters was damaged to create a 1 mm2 lesion. One cornea from each pair was stored under OC and one under hypothermic conditions. The endothelial cell density (ECD), coefficient of variation, hexagonality and percentage of dead cells were assessed before and after damage and on days 7, 14, 21 and 28 of storage. Results:, The mean ECD of corneas subsequently stored under OC or hypothermic conditions was 2764/mm2. Immediately after damage, a denuded Descemet's membrane with a few remaining dead cells was observed at the injured area. After 7 days of storage under OC conditions, almost no dead cells were observed at the place of injury. A non-significant worsening of the qualitative parameters (polymegatism and pleomorphism) was found. After 14 days, ECD was 1933/mm2 and 2478/mm2 centrally and pericentrally, respectively. Similar values were found after 21 and 28 days of storage. The lesions with remnant dead cells persisted throughout hypothermic preservation. From day 14 the corneas became cloudy and in poor condition, while the pericentral ECD was 2523/mm2. Conclusion:, The reparative capacity of the cornea is maintained under OC but not under hypothermic conditions. For corneas containing dead endothelial cells, OC is therefore the method of choice because it may improve the quality of the stored tissue. [source] | ||||||||||