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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.
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.
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.
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.
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.
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.
By combining a description of the coupled solute and water flows through the in vivo cornea with a set of appropriate mechanical equilibrium conditions, it is possible to calculate directly the corneal thickness, given the corneal temperature, the state of the aqueous and tears, the swelling pressure-hydration relation of the corneal stroma, and the transport properties of the corneal membranes. Active transport of ions or water by the corneal epithelium or endothelium, or both, are explicitly included. When published parameters are inserted into the formulation, the normal corneal thickness is recovered, and the corneal potential, anteriorly directed water flux, and stromal salt content are in reasonable to quantitative agreement with experiment. The analysis yields a simple physical explanation of the stromal imbibition pressure and the opposing forces which cause the cornea to assume its normal thickness.
A case of 'black cornea', occurring 6 years after commencement of a therapy with adrenaline derivative eye drops, is reported. Enucleation was performed because of suspected malignant melanoma. The eye was sent to our laboratory for histopathological examination. The clinical and histopathological findings are described, and the pathogenesis of the 'black cornea' is discussed.
Cornea cells were isolated from bovine corneae after collagenase treatment. Subcellular fragments were fractionated by density gradient centrifugation. The density gradient run was monitored by determination of the marker enzyme activities for mitochondria, plasma membranes, lysosomes and endoplasmatic reticulum, of the enzyme activities involved in keratan sulfate synthesis and of the protein content. The fractions were further investigated by electron microscopy. Two membrane fractions with keratan sulfate-synthesizing activity (UDP-N-acetylglucosamine:keratan-N-acetylglucosaminyl-transferase, UDPgalactose:keratan galactosyltransferase and keratan sulfotransferase) were detected: a heavy fraction separated from the other organells investigated and a light fraction exhibiting the same density as plasma membranes. The activities of the three enzymes were found in the same density gradient fractions with a similar distribution pattern between the fractions, which suggests a joint localization of these 3 enzymes at the same intracellular sites.
Distribution and principal characteristics of (Na+K+)-activated ATPase in human cornea were investigated. (Na+K+)-ATPase was present in both epithelium and endothelium, whereas the corneal stroma did not exhibit significant enzyme activity. In homogenates specific activity of the (Na+K+)-ATPase was 2.3-fold higher in endothelium than in epithelium. Calculation of total enzyme activity revealed a 6.1-fold higher content of (Na+K+)-ATPase in the epithelium. In the epithelium a 7-fold enrichment of (Na+K+)-ATPase compared to the homogenate was obtained in the 150-1500 X gav fraction. Maximum enrichment in the endothelium was 3.5-fold and was achieved in the 1500-2500 X gav fraction. Both fractions showed, however, the same specific activity. The pH-optimum of (Na+K+)-ATPase in the 150-1500 X gav fraction ranged from 8.0-8.2 in both epithelium and endothelium. In the epithelial 150-1500 X gav fraction the apparent Km-values were 4.0 mM for Na+, 2.8 mM for K+ and 0.12 mM for Mg2+ - ATP in equimolar concentrations. The inhibition constant of epithelial (Na+K+)-ATPase for ouabain was determined as Ki = 3.3 X 10(-7) M. The present data support the view that control of corneal hydration in man is a function of both endothelium and epithelium.
The shaping of swollen, abnormally hydrated donor corneal tissue on the cryolathe for use in keratorefractive surgery yields lenticules of insufficiently predictable dioptric powers. The irregular nature of this abnormal hydration precludes the use of mathematical compensating factors. To improve control over the shape of the lenticule, we have developed a cornea press which restores normal hydration and dimensions to the donor tissue by mechanical dehydration.
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We studied the effect of azlocillin, mezlocillin and sisomicin in concentrations of 1, 2.5 and 5% on the regeneration of stromal corneal wounds in rabbits following subconjunctival injections and treatment with eye drops. Concentrations of the antibiotics were also determined in corneal tissue and in aqueous humor and compared with that of penicillin G-potassium. Together with azlocillin, sisomicin proved to be the most effective and the safest. Mezlocillin only inhibited wound regeneration slightly and thus mezlocillin appears to be inferior to the other two antibiotics investigated in the local treatment of the eye.
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