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PubMed1984

Elastic and related fibres in the normal cornea and limbus of the domestic cat.

The presence of elastic and related fibres in the corneal and limbal tissue of the domestic cat is described. Various ages of animal from birth to maturity were studied by light and electron microscopy. Oxytalan fibres were present throughout the new-born kitten cornea. They were seen in greatest concentration both at the junction of the posterior limiting lamina with the inner substantia propria and beneath the peripheral anterior epithelium. With increasing maturity, oxytalan fibres disappeared from all but the most peripheral parts of the cornea where some of the, by now, thicker oxytalan fibres had matured into elaunin. All ages of animals studied showed an abrupt increase in fibre thickness and numbers at the corneal limbus. Oxytalan fibres predominated in the newborn kitten limbus but material from adult animals showed an increased proportion of elaunin fibres. Occasional elastic fibres were also seen in the more superficial region of the adult limbus. An overall decrease in elastic fibre types with increasing maturity was most obvious in the middle limbal layers.

Aging↗
PubMed1998

Circumcorneal annulus of collagen fibrils in the human limbus.

PURPOSE: To quantify the orientation of the collagen fibrils in the human limbus and to compare it with the orientation in the cornea and the sclera. METHODS: Fibril orientation was measured from 100 synchrotron x-ray diffraction patterns collected at intervals along lines across the cornea, limbus, and sclera. RESULTS: A distinct circumcorneal annulus of collagen fibrils was revealed in the limbus. For the individual cornea investigated, the annulus was not uniform around the corneal circumference; its width, fibril angular spread, and fibril density all varied with position. The average width of the annulus was narrower in the superior sector (1.5 mm) than in the inferior sector (2.0 mm). The results from the edge of the cornea suggested that the preferentially aligned corneal fibrils bend sharply at the limbus to run circumferentially or that, together with this bending or alone, extra fibrils arising in the sclera run across this zone. In the cornea the biaxial preferred directions became more pronounced from the center of the cornea toward the limbus along the superior-inferior axis. CONCLUSIONS: The excess of circumferential fibrils in the limbus, predicted from the sharp change of curvature in the surface of the eye at the limbus, appeared to take the form of a well-defined annulus. From a consideration of the mechanics of the system it seemed probable that the purpose of this annulus was to help maintain the correct curvature of the cornea. Before further research, it was hypothesized that some refractive problems associated with an incorrect curvature of the cornea may be related in part to abnormalities of this circumcorneal annulus.

Aged↗
PubMed2003

Characterisation of WE-14 in porcine ocular tissue.

WE-14 is derived from the cell-specific posttranslational processing of chromogranin A (CgA) in subpopulations of neuroendocrine cells and neurons. Region- and site-specific chromogranin A, pancreastatin and WE-14 antisera were employed to study the generation of WE-14 in porcine ocular tissues. No chromogranin A or pancreastatin immunostaining was detected in ocular tissue. Immunohistochemistry detected WE-14 immunostaining in a network of nerve fibre bundles and nerve fibres throughout the limbus, cornea, iris and ciliary body with sparse nerve fibres detected throughout the choroid and sclera. Retinal analysis detected intense WE-14 immunostaining in large ovoid cells in the ganglion cell layer with weak immunostaining in a population of small cells in the inner nuclear layer; weak immunostaining was detected within the fibre layers in the inner plexiform layer. Quantitatively, the highest WE-14 tissue concentration was recorded in aqueous retinal and corneal extracts with lower concentrations in the sclera, choroid and anterior uveal tissues. Chromatographic profiling resolved a minor chromogranin A-like immunoreactant and a predominant immunoreactant co-eluting with synthetic human WE-14. This is the first study to demonstrate that WE-14 is generated in neuronal fibres primarily innervating the anterior chamber and in select cell populations in the retina.

Amino Acid Sequence↗
PubMed2006

Multiphoton autofluorescence and second-harmonic generation imaging of the ex vivo porcine eye.

PURPOSE: The purpose of this work was to demonstrate the use of the combined imaging modality of multiphoton autofluorescence and second-harmonic generation (SHG) microscopy in obtaining spectrally resolved morphologic features of the cornea, limbus, conjunctiva, and sclera in whole, ex vivo porcine eyes. METHODS: The 780-nm output of a femtosecond, titanium-sapphire laser was used to induce broadband autofluorescence (435-700 nm) and SHG (390 nm) from various regions of the surface of ex vivo porcine eyes. A water-immersion objective was used for convenient imaging of the curved surface of the eye. RESULTS: Multiphoton autofluorescence was useful in identifying cellular structures of the different domains of the ocular surface, and the SHG signal can be used to resolve collagen organization within the cornea stroma and sclera of ex vivo porcine eyes. CONCLUSIONS: Multiphoton autofluorescence and SHG microscopy have been demonstrated to be an effective technique for resolving, respectively, the cellular and collagen structures within the ocular surface of ex vivo porcine eyes. SHG imaging resolved the difference in structural orientations between corneal and sclera collagen fibers. Specifically, the corneal collagen is organized in a depth-dependent fashion, whereas the scleral collagen is randomly packed. Because this technique does not require histologic preparation procedures, it has the potential to be applied for in vivo studies with minimal disturbance to the eye.

Animals↗
PubMed2006

Mapping collagen organization in the human cornea: left and right eyes are structurally distinct.

PURPOSE: Aspects of the biomechanics and surface topography of fellow human corneas are known to exhibit midline symmetry, but the structural basis of these observations is poorly understood. The mechanical performance of the cornea is strongly influenced by the organization of stromal collagen fibrils. The present study was designed to examine and compare the organization of collagen fibrils in the corneal stroma of left and right eyes. METHODS: Wide-angle x-ray scattering was used to map in detail the orientation and distribution of fibrillar collagen across the cornea, limbus, and adjacent sclera of three normal human eyes, including a fellow pair, and the central 9-mm corneal region of a further four eyes. RESULTS: Fibrillar collagen in the human cornea and limbus is arranged anisotropically, and in a highly specific manner. Left and right corneas are structurally distinct. In general, the mass distribution of preferentially aligned fibrils in the cornea appears to exhibit a degree of midline symmetry between left and right eyes. CONCLUSIONS: Structural information, such as that presented herein, will enable a better understanding of corneal biomechanics and shape. Midline symmetry in the distribution of aligned, mechanically reinforcing collagen fibrils between left and right eyes may relate to the biomechanical and topographical enantiomorphism reported in the literature.

Anisotropy↗
PubMed2000

Autologous limbal transplantation in patients with unilateral corneal stem cell deficiency.

AIM: To describe a surgical technique for autologous limbal stem cell transplantation and the outcome of a series of patients with unilateral stem cell deficiency. METHODS: A report of six consecutive patients who underwent autologous limbal stem cell transplantation is presented. The primary diagnosis included alkali burn (n=3), conjunctival intraepithelial neoplasia (CIN) (n=1), recurrent pterygium (n=1), and contact lens induced keratopathy (n=1). The autologous transplanted tissue consisted of peripheral cornea, limbus, and conjunctiva obtained from the contralateral eye. Three of the above patients underwent penetrating keratoplasty in association with auto-limbal transplantation. A significant modification to established techniques was the close monitoring of conjunctival epithelial migration in the immediate postoperative period. If conjunctival epithelium threatened to migrate on to the corneal surface, it was mechanically removed at the slit lamp and prevented from crossing the limbus. This was required in three patients. RESULTS: The mean follow up was 18.8 months. The outcome was satisfactory in all cases: a stable corneal surface was restored and there was a substantial improvement in vision and symptoms. One patient had a primary failure of the corneal allograft associated with glaucoma, and 6 months later developed a retinal detachment. No complications were noted in the donor eye with the exception of one patient who developed filamentary keratitis along the edge of the donor site. CONCLUSION: Autologous limbal transplantation with corneal, limbal, and conjunctival carriers was found to be useful for ocular surface reconstruction, over a mid-term follow up, in patients with unilateral stem cell deficiency. Close monitoring of the migration of conjunctival epithelium in the immediate postoperative period, and preventing it from crossing the limbus, ensured that the corneal surface was re-epithelialised exclusively from epithelial cells derived from the transplanted limbal tissue. This approach should improve the success of this procedure.

Adult↗
PubMed1995

Surgical management of ocular surface disorders using conjunctival and stem cell allografts.

AIMS: The aim of this work was to investigate different surgical options for the repair of the ocular surface, using various extensions of the procedure of limbal stem cell allotransplantation. METHODS/RESULTS: Straightforward lamellar limbal transplantation was performed in one patient with contact lens induced limbal stem cell failure. A second patient with a neoplastic corneal lesion underwent limbal allotransplantation, followed later by a second procedure in which 360 degrees of limbus and the entire ocular surface was transplanted. A third patient who had suffered extensive chemical burns was treated by penetrating keratoplasty to restore central corneal clarity, followed later by a lamellar allograft comprising a 360 degrees annulus of peripheral cornea to repair the ocular surface. A fourth patient with long standing, chronic trachomatous eye disease underwent allotransplantation of the upper lid tarsal plate and conjunctiva, with reconstruction of the fornix. Finally, a child with Goldenhar's syndrome underwent reconstruction of the medial fornix with autologous buccal mucosa, followed by a lamellar corneal and conjunctival allograft. A stable ocular surface has been achieved in each case and there have been no obvious rejection episodes. CONCLUSION: Limbal allotransplantation can be extended to engraftment of the entire superficial cornea, limbus, conjunctiva, and tarsal plate in patients with a range of pathologies. We have described the surgical management of five cases which demonstrate the potential of the technique, but which raise questions which still need to be explored.

Adult↗
PubMed2005

[Identification of human corneal epithelial stem cells].

OBJECTIVE: To investigate the molecular markers of corneal epithelial stem cells. METHODS: The anatomy structure of corneal limbus was analyzed by histological examination. Fluorescence microscopy and laser scan confocal microscopy (LSCM) were used to evaluate the expression of un differentiation markers as p63, ABCG2, alpha6, alpha9 and beta1 integrin, alpha-enolase, EGFR, cytokeratin 19 (CK19) and CD71 in cornea-limbus sections and whole mount cornea tissue using immunohistochemistry staining. Semiquantitative RT-PCR and in situ hybridization (ISH) were used to evaluate gene expression of corneal and limbal epithelia. RESULTS: The limbal area in horizontal cut direction showed that limbal epithelial cells were as papilloma-form to correspond to the Palisades of Vogt environment. The expressions of beta1 integrin, K19, alpha-enolase and EGFR were much stronger in limbal basal cells than superficial cells. Un differentiation markers p63, ABCG2, alpha9 integrin were detected only in the basal limbal epithelial cells. LSCM and RT-PCR results showed that the protein and mRNA of p63, ABCG2 and alpha9 integrin were only detected in limbal epithelia. ISH showed that p63 mRNA only expressed in the limbal basal epithelial layer. CONCLUSIONS: The corneal limbal epithelial area is papilloma-form. Limbal stem cells have complex markers as p63 expressing in the nuclei, ABCG2 in the cytoplasm and alpha9 integrin expressing in the membrane. With these markers complex, it is easy to distinguish limbal stem cells from other epithelial cells in cornea.

Biomarkers↗
PubMed1996

Scanning electron microscopic study of episcleral arteriovenous anastomoses in the owl and cynomolgus monkey.

In the present study we have analyzed the architecture of the episcleral microvasculature in the owl and cynomolgus monkey using scanning electron microscopy of resin casts. Due to the topical pretreatment with nitroprusside the complete vasculature including segments of the aqueous humor outflow channels could be visualized. We found that 1-3 mm posterior to the limbus corneae the episcleral vessels form numerous arteriovenous anastomoses (AVA) in the size of small arterioles and venules. These AVA are also located at the collector channels near Schlemm's canal and at the episcleral venous plexus which drains the collector channels. It is assumed that the AVA might influence not only the circulation in the episcleral venous plexus but also in the aqueous humor outflow routes.

Animals↗
PubMed1996

Scanning electron-microscopic studies of the collagen architecture of the human sclera--normal and pathological findings.

The arrangement of the collagen fibrils of the human sclera was analyzed in the region of the limbus cornea, the corneoscleral trabeculum, at the zone of muscle insertion and at defined areas of the internal and external surface of the sclera. Adult eyes with no apparent pathological alterations and the sclera of a patient with staphyloma were examined by scanning electron microscopy. The investigations were performed to describe regularities in the collagen architecture in normal and pathologically altered eyes to understand pathomorphologic and pathophysiologic changes in scleral diseases.

Aged↗
PubMed2005

Inhibitory effect of triamcinolone acetonide on corneal neovascularization.

BACKGROUND: Corneal neovascularization (NV) plays an important role in the pathogenesis of corneal disorders. Recently, triamcinolone acetonide (TA) has been reported as a potential treatment for ocular angiogenesis. However, there are no reports on the inhibitory effect of TA on the corneal NV. METHODS: Triamcinolone acetonide (2 mg) was administered to four rabbits' eyes by a subconjunctival injection immediately after a basic fibroblast growth factor (bFGF)-pellet was placed into the cornea. As a control, four eyes received an injection of distilled water. Four weeks later, the inhibition of corneal NV was evaluated as the percentage ratio of the vessel invasion area to the area that was sandwiched between the pellet and the limbus cornea. To identify the characteristic appearance of new corneal vessels, the control cornea was examined by using the antibody of vascular endothelial growth factor (VEGF). To confirm TA concentration in TA-treated corneas, the TA level was measured using high-performance liquid chromatography. RESULTS: Neovascularization from the limbus to the pellet was detected in control eyes 4 weeks after the bFGF pellet implantation. TA-treated eyes demonstrated the inhibition of the neovascular response to the pellet. The severity of NV as compared between control and TA-treated eyes was statistically significant (P<0.05). Morphologically, new vessel growth was shown in the control cornea, and endothelial cells of new vessels were positively stained with the antibody of VEGF. TA concentration in TA-treated corneas at 2 weeks showed 63.5+/-42.8 microg/g (n=4, mean +/- SD), while TA was not detected in control and TA-treated corneas at 4 weeks. The level of TA was effectively maintained for at least 2 weeks after the subconjunctival injection. CONCLUSION: We have demonstrated that subconjunctival TA administration inhibited rabbit corneal NV. This agent may prove useful in the treatment of corneal angiogenic disorders.

Animals↗