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At least 37 records · Page 2Linked to original sources

PubMed1981

Secondary lens formation from the cornea following implantation of larval tissues between the inner and outer corneas of Xenopus laevis tadpoles.

Secondary lens formation from the cornea of larval Xenopus laevis has been used as a measure of the lens-inducing capacities of various larval Xenopus tissues. The experimental design employed involved implantation of selected body tissues between the inner and outer cornea of stage-50 tadpole eyes, in such a way that the integrity of the inner cornea and eye cup was not disrupted. Implantation of retina, pituitary, limb blastema or limb bud resulted in secondary lens formation from the outer cornea. Such lenses were similar in appearance to stage-5 lens regenerates described by Freeman (1963). No secondary lenses were observed in eyes receiving either heart or hind brain implants or in eyes which underwent corneal separation but which received no implant. It is concluded that the retina is the natural source of a stimulatory factor which initiates and maintains corneal transformation to lens during lens regeneration following lensectomy. Influences emanating from pituitary, limb blastema and limb bud, but apparently not from heart or hind brain, are able to act on cornea in a way similar to the retinal factor. Furthermore, our findings support the contention that in the normal eye, the inner cornea is a barrier to the passage of retinal factor and so maintains the single lens structure of the eye. When this barrier is by-passed by lens-inducing tissue, as in the present experimental design, lens formation from the cornea is able to take place. Electronmicroscopical studies have shown that the inner cornea, in the stage-50 tadpole eye, consists of a dense meshwork of collagen fibrils and a basal layer of cohesive elongated mesenchymal cells well suited for this barrier function.

Animals↗

PubMed1986

Aqueous to cornea fluorescein distribution ratio in normal and swollen cornea.

Intravitreal sodium fluorescein was used to simulate equilibrium fluorescein kinetics, thereby allowing simple measurement of the aqueous to cornea fluorescein distribution ratio. Two groups of rabbit corneas were studied: normal corneas and corneas wounded by freezing. The aqueous to cornea fluorescein distribution ratio was approximately 0.4, was not significantly different in groups of normal or wounded eyes and little variability was noted. In addition, a comparison of in vivo and in vitro measurements of corneal fluorescein concentration in wounded eyes suggests that in vivo protein-bound fluorescein in the cornea fluoresces less efficiently than free fluorescein.

Animals↗

PubMed2002

Cornea procurement from very old donors: post organ culture cornea outcome and recipient graft outcome.

AIM: To study the suitability of corneas from very old donors for graft after banking and their clinical and endothelial outcomes in recipients. METHODS: 419 corneas stored in organ culture were divided into group 1, donors under 85 years (330 corneas) and group 2, "very old" donors aged 85 years and over (89 corneas). Endothelial cell density (ECD) before and after organ culture, discard rate before and after storage, and clinical and endothelial outcomes of the 196 penetrating keratoplasties (PKP) (158 in group 1 and 38 in group 2) were compared in a prospective longitudinal study. RESULTS: Initial ECD was lower in group 2 than in group 1 and elimination for low ECD was more frequent in group 2 (respectively 38% v 20.2%, p=0.001). At the end of storage, because very old corneas lost fewer ECs than younger ones (respectively 4.2% v 9.5%, p=0.022), ECD was comparable between the two groups. The corneas of very old donors had a poorer macroscopic appearance at procurement and during surgery. Despite this, in grafted patients, overall graft survival in groups 1 and 2 (respectively 87.4% v 80.6%, p=0.197), visual acuity, and ECD did not differ at completion of the study (mean follow up 25 months). CONCLUSION: This study suggests that endothelial cell count during banking ensures that functional and cellular results of PKPs are not dramatically influenced by very old donor age. Considering Europe's ageing population, the very elderly should not be deemed off limits for corneal procurement.

Adolescent↗

PubMed1997

Cornea refractive changes after clear cornea phacoemulsification with foldable intraocular lens.

BACKGROUND: Clear cornea incision for phacoemulsification is the current trend of cataract surgery, with the benefits of small incision, quick rehabilitation and stable wound architecture. In our Oriental eyes with small palpebral fissure the cornea curvature is easily affected by the tight lid compression. Evaluation of the postoperative cornea topographic change after this procedure in our patient is thus necessary. METHODS: Forty eyes with simple cataract were enrolled in this study. Among them 22 were right eyes and 18 were left eyes. All of them were through temporal clear cornea incision. A 2.65 mm length incision for phacoemulsification then enlarged to 3.5 mm for foldable intraocular lens implantation. The wound remained self-healing without suture. Color topographies were taken before and then one and three months after surgery. Palpebral fissures were measured before surgery. RESULTS: Induced cornea astigmatism measured as 0.30 +/- 0.35 diopter in the first postoperative month, and 0.50 +/- 0.43 diopter in the third postoperative month. All the induced astigmatism was toward the incision axis and with the rule shifting. CONCLUSIONS: Tolerable with-the-rule astigmatism shifting around 0.5 diopter was noted postoperatively via temporal clear cornea phacoemulsification with foldable intraocular lens implantation in our patients.

Aged↗

PubMed1996

Conjunctival epithelial cells can resurface denuded cornea, but do not transdifferentiate to express cornea-specific keratin 12 following removal of limbal epithelium in mouse.

Limbal stem cell deficiency contributes to recurrent corneal epithelial defects. We examined whether the conjunctival epithelium can transdifferentiate to corneal epithelium following surgically induced limbal stem cell deficiency. Mice were anesthetized by intraperitoneal injection of sodium pentobarbital. Partial or total epithelial removal was produced with a no. 69 Beaver blade under a dissecting microscope. The wounds were allowed to heal for 0-28 days, and the mice were examined every other day to evaluate re-epithelialization. Corneas were then subjected to histological, immunohistochemical studies and Western blot analysis with epitope-specific anti-keratin 12 antibodies. Partial epithelial defects re-epithelialized within 2 days and were normal in appearance and expressed cornea-specific keratin 12. In eyes with limbal deficiency, re-epithelialization progressed more slowly and was characterized by opacification; epithelial closure usually occurred by the 7th day. This epithelium differed from normal corneal epithelium in basic morphology, cell shape, and the presence of goblet cells at 2 weeks after injury. The epithelium at the center of injured corneas with total defect at 4 weeks had cornealike morphology and was devoid of goblet cells. These epithelial cells derived from conjunctiva did not express the cornea-specific keratin 12 as determined by immunohistochemistry, Western blot analysis and in situ hybridization. As evidenced by differences in morphology and the expression of cornea-specific keratin 12, conjunctival transdifferentiation does not occur in conjunctical overgrowth after the removal of limbal epithelium.

Amino Acid Sequence↗

PubMed1997

Comparison of astigmatism after penetrating keratoplasty by experienced cornea surgeons and cornea fellows.

PURPOSE: We compared surgically induced astigmatism after penetrating keratoplasty performed by supervised cornea fellows and experienced cornea surgeons. METHODS: Data were collected by retrospective chart review of 166 cases (166 eyes) of penetrating keratoplasty: 63 performed by two cornea surgeons and 103 by four cornea fellows. Astigmatism was calculated using scalar and vector methods. Vector analysis was performed on 109 of 166 eyes. Two techniques were compared: intraoperative keratometry and suture adjustment and the torque-antitorque running suture technique with no intraoperative keratometry or suture adjustment. RESULTS: Mean surgically induced scalar astigmatism changed from preoperative astigmatism by 3.27 diopters (fellows) and 2.94 diopters (attending surgeons). In 109 cases, surgically induced vector cylinder changed from peroperative astigmatism by 4.21 diopters at 98 degrees (fellows) and 4.25 diopters at 114 degrees (surgeons). Surgically induced vector astigmatism changed from preoperative astigmatism by 4.67 diopters at 93 degrees in the first 6 months (fellows) and by 3.79 diopters at 103 degrees in the second 6 months. Analysis of x-axis and y-axis components of the surgically induced vector cylinder showed that the majority of the astigmatism was induced in the y-axis and that this difference was significant (P < .001) in all comparisons, independent of technique or surgeon group. CONCLUSIONS: Penetrating keratoplasty performed by supervised cornea fellows resulted in similar rates of surgically induced vector astigmatism, surface asymmetry, and surface regularity as that by experienced surgeons. Fellows induced significantly more with-the-rule astigmatism, but this tendency decreased with further training. Penetrating keratoplasty astigmatic outcomes were not significantly different whether or not intraopertive keratometry and suture adjustment were utilized. This study supports the concept that increased experience with corneal transplantation improves the outcome of penetrating keratoplasty by using the criterion of postoperative astigmatism as a measures.

Astigmatism↗

PubMed1997

Morphological and morphometric aspects of primate cornea: a comparative study with human cornea.

Morphological and morphometric features of the cornea of 13 species of primates have been studied in order to determine possible morphological differences between them. The existence of relationships between different morphometric corneal variables was also examined to establish which variables best defined and characterized the cornea. The present aim is to determine which primate cornea resembles that of the human being most with a view to possible future clinical and experimental studies. The results obtained revealed that all the cornea under study presented similar morphological features. The relationship between total corneal thickness and corneal epithelial thickness was determined as well as the relationship between epithelial thickness, the number of epithelial layers and the number of epithelial cells. However, the morphological pattern of Bowman's membrane and corneal endothelium differed in the species studied. Finally, the study indicates that the chimpanzee and the gorilla are the species with a corneal morphometry which is closest to that of the human cornea.

Animals↗

PubMed2005

Biocompatibility of a nonpenetrating synthetic cornea in vascularized rabbit corneas.

PURPOSE: This study was designed to assess feasibility and biocompatibility of a lamellar, nonperforating supraDescemetic Synthetic Cornea (sDSC) implanted in rabbit eyes after a corneal injury. METHODS: Corneal vascularization and scarring was induced in the right eye of 15 rabbits by application of 1-heptanol and complete surgical removal of the limbus. An sDSC (7-mm diameter, 450-microm-thick optical zone, 100-microm-thick outer flange) was implanted after 45 +/- 5 days. The keratoprostheses were implanted with their central optic part positioned on a completely exposed Descemet's membrane (DM) while the outer flange was located in deep stroma. Three different materials were tested: hydrophobic PMMA (n = 5) and hydrophilic HEMA-MMA (n = 5) and HEMA-NVP (n = 5) with a water content of 34% and 75%, respectively. The corneal surface was covered with a conjunctiva-Tenon flap. Central flap trephination was performed after 63 +/- 7 days. DM vascularization and scarring was assessed and graded after flap opening and weekly thereafter. RESULTS: In all 15 consecutive cases implantation could be completed successfully without perforation of DM. Repair of the conjunctival flap had to be performed in five rabbits. Four months postoperatively, the flaps were opened. Four of five corneas (80%) with a PMMA implant and three of five (60%) with a HEMA-NVP75 implant had retained their original transparency. The others had developed significant neovascularization in the Descemet-sDSC optic interface. All corneas (100%) that received an sDSC made of HEMA-MMA34 displayed a completely clear DM without any vessels or scarring. DM was found firmly attached to the posterior surface of the optic. CONCLUSION: Implantation of a nonperforating synthetic cornea on top of an exposed DM is feasible. HEMA-MMA34 showed the most promising results. Because opening of the anterior chamber is not required, a lamellar supraDescemetic Synthetic Cornea would theoretically reduce some of the risks attributed to penetrating keratoprostheses.

Animals↗

PubMed2006

Altered expression of type XIII collagen in keratoconus and scarred human cornea: Increased expression in scarred cornea is associated with myofibroblast transformation.

PURPOSE: Type XIII collagen (ColXIII) is a transmembrane protein thought to be involved in cell-cell and cell-matrix interactions. We report here on its presence in the normal human cornea and compare the results for keratoconus and scarred corneas. METHODS: Immunohistochemistry and in situ hybridization were applied to human corneal samples obtained by penetrating keratoplasty. RESULTS: In the normal human cornea, ColXIII was immunolocalized to the corneal epithelial cells, and to a lesser degree to the stromal keratocytes. The keratoconus cases showed otherwise similar results, but in areas containing Bowman membrane disruptions showed thinned epithelial cells reduced immunostaining for ColXIII, whereas occasionally pronounced immunoreactivity was seen in the stromal keratocytes. The corneal scar samples contained highly increased ColXIII immunostaining by stromal cells in the fibrotic foci, whereas the peripheral areas showed less intense immunostaining. In situ hybridization confirmed that the corneal epithelium and keratocytes actively synthesize the transcript. Immunostaining with alphaSMA revealed that a substantial proportion of the ColXIII mRNA-expressing cells in the stromal scar tissues was myofibroblasts and that these areas lack CD34 immunoreactivity. CONCLUSIONS: The results indicate that ColXIII, which is predominantly confined to the basal corneal cells in the normal cornea, may have a role in the adhesion of corneal epithelial cells to each other and to the underlying basement membrane. Additionally, highly increased expression in scarred corneas suggests that it participates in the corneal wound healing process.

Actins↗

PubMed1983

Studies on the cornea. X. Incorporation of 14C-glucosamine into glycosaminoglycans and glycoproteins of elasmobranch corneas, extractability of these components and morphological effects of such extractions.

Incorporation of 14C-glucosamine into dogfish (Squalus acanthias) corneas occurs primarily in the glycosaminoglycans (GAG) and glycoproteins (GP) extractable with elasmobranch Ringer's solution but the rate at which this component can be extracted varies inversely with the age (size) of the fish. Whereas this fraction represents only one-fourth of the total hexosamine (Hex-N) it contains nearly three-fourths of the newly incorporated 14C-glucosamine. The CaCl2-extractable HexN contains only 13% of the incorporated radioactivity. Collagen-associated GAG in both soluble and insoluble collagen fractions contain keratan sulfate, dermatan sulfate and chondroitin-4-sulfate, with the GAG associated with the salt-insoluble collagen having only half the radioactivity of those associated with the soluble fraction. However, the specific activities of both the salt-insoluble and the salt-soluble fractions were very low, suggesting that the GAG-GP which are tightly bound to collagen may have a high degree of stability. Partially de-epithelialized corneas incorporated 14C-glucosamine at rates ranging from 22% to 58% of the efficiency of intact corneas, suggesting a possibly significant role of the epithelium in the biosynthesis of GAG-GP in the adult dogfish. Morphologic results exactly paralleled those previously reported by us for the bovine cornea with the exception that the effects of CaCl2 extraction of GAG-GP were not evident on the collagen fibers until the second to fifth sequential CaCl2 extraction. The morphologic findings, therefore, exactly parallel the analytic findings which show that a significant portion of the collagen and collagen-associated GAG-GP of the dogfish cornea remains after the double extraction. How much of this remaining material represents sutural fibers and their associated GAG-GP is yet to be determined.

Animals↗

PubMed2002

[Protection of cornea against proteolytic damage. Experimental study of procyanidolic oligomers (PCO) on bovine cornea].

AIM OF THE STUDY: The purpose of this work was the development of an antiprotease treatment for the cornea and later for other ocular tissues. Indeed, many proteases participate in various ocular pathologies and no really effective treatments are currently available. METHODS: We worked on bovine corneas in organ cultures, incubated in the presence and absence of bacterial collagenase. We used procyanidolic oligomers from grape seeds (PCO) as the antiproteolytic agent, added to the cultures in two different concentrations. RESULTS: The corneas incubated in the presence of collagenase were quickly attacked and their degradation was practically complete after 24 hours. With the low concentration used (0.066 mg/ml), proteolysis was only slightly inhibited. With the higher concentration of PCO (1 mg/ml), the collagenolysis was completely prevented and the corneas were completely preserved. CONCLUSION: These results show that the protective effect of the PCO against proteolytic attack, demonstrated previously on other tissues, proved to be effective also for the cornea in vitro. An adequate method of administration in clinical practice must now be developed in order to obtain an effective clinical antiproteolytic treatment.

Animals↗

PubMed1991

Excimer-laser-induced fluorescence of rabbit cornea: radiometric measurement through the cornea.

The laser-induced fluorescence spectrum of rabbit cornea irradiated at ablative intensities was measured. This system directly measured the radiant exposure of fluorescence transmitted through the cornea when the anterior surface of the cornea was irradiated by an ArF excimer laser. Evidence of changing spectral characteristics as a function of total laser dose suggests photochemical changes in the cornea may be occurring. Results are compared with previous data of laser-induced fluorescence in other models and detection schemes.

Animals↗

PubMed2005

How the cornea heals: cornea-specific repair mechanisms affecting surgical outcomes.

In mammals, penetrating injuries typically heal by deposition of fibrotic "repair tissue" that fills and seals wounds but does not restore normal function. Excessive deposition of fibrotic repair tissue can lead to pathologies involving excessive scarring and contracture. In the cornea, fibrotic repair presents special challenges affecting both clarity and shape of the cornea. With the increasing popularity of surgical techniques that alter corneal refractive errors, understanding of cornea repair mechanisms has acquired new significance. The cornea has unique anatomic, cellular, molecular, and functional features that lead to important mechanistic differences in the process of repair in comparison with what occurs in skin and other organs. Moreover, corneal function calls for special outcomes. This review addresses these features from the viewpoint of the authors' research on factors of importance to understanding and improving surgical outcomes.

Animals↗

PubMed1962

Studies on the cornea. II. The uptake and transport of colloidal particles by the living rabbit cornea in vitro.

In vitro studies of the transport of colloidal particles by the cornea were carried out on intact corneas of adult rabbits in a chamber described by Donn, Maurice, and Mills (2) in which the epithelial or the endothelial surface of the cornea was exposed to thorium dioxide or saccharated iron oxide under various conditions. These studies confirmed the results of previous work in vivo and allowed modification of the experimental conditions. Particles are pinocytosed at the apical surface of the corneal endothelium and carried around the terminal bar in membrane-bounded vesicles. Basal to the terminal bar these vesicles fuse with the lateral cell margin and their contents are released into the intercellular space, in which they appear to be carried by a one-way flow down to Descemet's membrane and the corneal stroma. Indications that the endothelial transport is an active process are presented by the different pathways of transport into or out of the corneal stroma, as well as by the approximately 70 per cent reduction in transport activity at low temperatures.

Animals↗

PubMed1988

MHC class I and class II antigen expression in normal human corneas and in corneas from cases of herpetic keratitis.

The expression of HLA class I and class II antigens in corneas from normal donors and patients with quiescent herpetic keratitis was investigated using specific monoclonal antibodies. Keratocytes from diseased corneas showed aberrant expression of HLA class I and class II (DR, DP and DQ) antigens. The expression of HLA antigens in these corneas was not associated with immune cell infiltrates or viral antigens.

Adult↗

PubMed1996

[A specular microscopic study on irradiated rabbit corneas--report I. Early injury of the cornea].

To evaluate the effects of ionizing radiation on the cornea, one eye of healthy mature albino rabbits (n = 5) was irradiated with 20 Gy of X-rays (250 kV, 12 mA). Corneal observation was done with a slit-lamp biomicroscope and a specular microscope before irradiation, and follow-up observations were done at one week and 4 weeks after irradiation. Specular microscopic photographs were analyzed with a digitizer. Although slit-lamp biomicroscopy did not show any abnormal findings in the cornea, specular microscopy revealed a significant enlargement of the mean cell area of the superficial corneal epithelium at 4 weeks after irradiation. There were no significant changes in the corneal endothelium during this study. These results strongly suggest that high doses of X-ray irradiation could induce corneal epithelial injury at the early phase, even when by slit-lamp biomicroscopy shows no abnormal findings in the cornea.

Animals↗

PubMed2000

Immunobiology of xenogeneic cornea grafts in mouse eyes. II. Immunogenicity of xenogeneic cornea tissue grafts implanted in anterior chamber of mouse eyes.

BACKGROUND: Xenogeneic corneal fragments (guinea pig) are highly resistant to immune rejection in the anterior chamber of mouse eyes. Because guinea pigs and mice are discordant (i.e., mouse serum normally contains guinea pig reactive xenoantibodies), we wished to determine the extent to which xenogeneic corneal fragments placed intraocularly in normal and specifically sensitized mice activated xenoreactive T and B cells. METHODS: Guinea pig corneas, deprived surgically of epithelium, were cut into fragments and inserted into the anterior chamber of eyes of BALB/c mice, adjacent to the central cornea of the recipient. Antibody (immunoglobulin [Ig]M, IgG) and delayed type hypersensitivity (DTH) immune responses of recipient mice to guinea pig xenoantigens were assessed. The fate of xenogeneic cornea implants was assessed in mice immunized systemically to guinea pig antigens. RESULTS: Guinea pig spleen cells and corneal fragments implanted s.c. induced within 2 weeks of immunization both DTH and IgG antibodies to guinea pig xenoantigens. By contrast, xenogeneic corneal fragments implanted in the anterior chamber of mouse eyes evoked no change in recipient humoral immune status and induced mild guinea pig-specific DTH only after 5 weeks. Presensitization of mice to guinea pig xenoantigens failed to increase the proportion of grafts that were regarded as rejected, but the onset of rejection in failed grafts occurred earlier than in unsensitized recipients. Active systemic immunization of mice bearing intracameral guinea pig corneal fragments failed to curtail the grafts' survival. Guinea pig corneal fragments implanted in the anterior chamber of normal mice failed to induce anterior chamber-associated immune deviation. CONCLUSIONS: Xenogeneic corneal fragments implanted in the anterior chamber of eyes of normal mice display strikingly reduced immunogenicity, and an inability to induce anterior chamber-associated immune deviation. These properties are discussed in terms of the vulnerability of guinea pig corneal tissue to immune rejection within the eye.

Animals↗

PubMed1984

Energy dispersive x-ray analysis of the cornea. Application to paraffin sections of normal and diseased corneas.

The distribution of chemical elements in the normal human cornea was studied by energy dispersive x-ray analysis and scanning electron microscopy of routinely prepared paraffin sections. Calcium, phosphorus, and sulfur were consistently present in quantities above background and varied in concentration regionally. Analysis of fresh-frozen tissue, an approximation of the in vivo state, gave a similar elemental profile to paraffin sections, except for the loss of diffusable electrolytes in the latter. After fixation, S was the most abundant element and was highest in Descemet's membrane. Corneas with granular, lattice, macular, and Fuchs' endothelial dystrophies, band keratopathy, and spheroidal degeneration were also examined. Characteristic patterns of abnormal S and Ca distribution were found in each of the dystrophies. The relative proportions of Ca, P, and S gave diagnostic profiles for distinguishing band keratopathy and spheroidal degeneration.

Adolescent↗