H Barry Collin

Recurrent Keratoconus After Keratoplasty

A 35-year-old woman who had undergone bilateral penetrating corneal grafts for keratoconus had keratoconus in the eye that had received a graft 16 years earlier. A second penetrating keratoplasty was performed, and the excised button was examined with light and electron microscopy. Both the light and electron microscopic findings were consistent with the clinical diagnosis of keratoconus. Keratoconus in a graft for the same disease should be added to the list of late complications of successful keratoplasties.

A comparative study of the corneal endothelium in vertebrates

Introduction: In vertebrates, a corneal endothelium is essential for the maintenance of corneal transparency in a variety of environments, including aerial, terrestrial and aquatic. Knowledge of the surface structure of the corneal endothelium may assist our understanding of this unique tissue and its evolutionary development. Except for humans and some mammals, there have been few studies of other vertebrates, particularly the unique Australian species.

Ultrastructural changes to corneal stromal cells due to ophthalmic preservatives

Abstract Normal and keratectomised rabbit corneas received drops containing preservatives over a two day period. All preservatives investigated caused some change in the morphology of the stromal keratocytes, particularly in the absence of the anterior epithelial barrier. Thimerosal (0.004%) or disodium ethylenedia‐minetetraacetate (0.1% Na2 EDTA) producted only minimum change. Chlorbutanol (0.5%) applied to intact corneas resulted in swelling of the cytoplasm and occasionally breaks in the external cell membrane, whilst in the keratectomised corneas some mitochondria showed swelling and distortion of cristae. In the normal cornea, benzalkonium chloride (0.02%, or 0.01% with 0.1% Na2 EDTA) resulted in intra and extracellular oedema and contraction of keratocytes. On removal of the superficial layers, there was extensive disruption of mitochondria, other organelles and outer cell membranes resulting in total destruction of some cells. Benzalkonium chloride should not be used on corneas with abnormalities of the epithelium —

A comparative SEM study of the vertebrate corneal epithelium

Purpose The anterior surface of the cornea of mammals, including humans, has numerous folds in the anterior epithelial cell membranes in the form of microvilli and microplicae. The role of these surface irregularities may be to increase cell-surface area and therefore aid in intra-and extracellular movement of nutritional and waste products across the cell membranes in addition to stabilizing the corneal tear film. The aim of this study was to investigate and compare the nature of these corneal-surface features in various vertebrate classes residing in different environments. Methods. The anterior corneal surfaces of various vertebrates were investigated by using field emission scanning electron microscopy. Cell areas were analyzed by using image-analysis software. Results. Representative species were examined from all the vertebrate classes, with the exception of the Cephalaspidomorphi. The mean epithelial cell density of aquatic vertebrates (17,602 ± 9,604 cells/mm2) is greater (p = 0.000018) than that of aerial and terrestrial vertebrate species, including amphibians (3,755 ± 2,067 cells/mm2). Similarly, the mean epithelial cell density for the marine vertebrates (22,553 ± 8,878 cells/mm2) is greater (p = 0.0015) than that of the freshwater and estuarine species (10,529 ± 5,341 cells/mm2). The anterior corneal surfaces of all species examined were found to show a variety of cell-surface structures. Microvilli are predominant in reptiles, birds, and mammals; microridges appear to be characteristic of the Osteichthyes; and microholes were observed only in the Chondrichthyes. Conclusion. The function of these morphologic variations in surface structure appear to be correlated with the range of ecologic environments (marine, aerial, and terrestrial) occupied by each species, corneal phylogeny, and the demands placed on the cornea to ensure clear vision.

Steroid inhibition of limbal blood and lymphatic vascular cell growth

Steroids are widely used in the prevention of corneal neovascularization in a wide range of natural and experimental situations. However, no information is available on their effect on the growth of the individual limbal blood vascular cells or of lymphatic cells involved in corneal neovascularization. In addition, tritiated thymidine labelling index is commonly used as an indicator of cell population but doubt exists as to whether it truly represents cell growth. Remote thermal cautery of the rat cornea was used to elicit corneal neovascularization. New cell growth was measured by tritiated thymidine uptake and by the number of cell nuclei per section. Cells investigated were the arteriolar, venular, capillary and lymphatic endothelial cells as well as the arteriolar and venular perivascular cells. A total of 89,320 blood vascular endothelial and perivascular cell nuclei and 12,075 lymphatic nuclei were counted. Thermal cautery elicited a significant increase in labelling index and cell population of all limbal vascular cell types. Steroid application elicited a significant short term inhibition or delay for all six cell types although this was not apparent for venular endothelial cells using labelling index as a growth indicator. At six days only the lymphatic endothelial cell population showed a significant (p < 0.001) increase associated with steroid use.

Limbal vascular response prior to corneal vascularization

Abstract In spite of claims of a significant latent period of up to 2 days between corneal injury and the beginning of corneal vascularization, there is evidence of a limbal reaction occurring only hours after injury. In this study, the central area of rat corneas was cauterized to give an injury which was remote from the limbal vessels. The resulting changes in vascular permeability were investigated. Significant emigration of neutrophil polymorphonuclear leucocytes began at 36 min and leakage of Trypan blue was discernible at about 1 hr after injury. Eosinophilic leucocytes do not appear to be involved in the response and mast cells, while not showing signs of increased degranulation, may be decreased in number over several days. The significance of these results in relation to the stimulus factors involved in these changes, and the importance of separating inflammatory and proliferative changes, are diseussed.

Ultrastructural changes to the corneal endothelium due to benzalkonium chloride

Abstract Ten normal and 20 keratectomised corneas received hourly drops of vehicle with or without benzalkonium chloride (0.02% BAC or 0.01% BAC plus 0.1% disodium ethylenediaminetetraacetate) over the daylight hours of 2 days (18 applications). When applied to the intact cornea, BAC with or without Na2EDTA caused, only slight clarification of the endothelial cytoplasm, whilst in a few mitochondria the cristae were displaced. In the keratectomised corneas receiving BAC, the majority of mitochondria of the central endothelial cells were pale and swollen or even disrupted. Many contained aggregations of membranous material either within the mitochondrion or at its outer membrane. The peripheral endothelium was much less affected than the central area of endothelium behind the keratectomy. These results suggest that BAC should not be administered to corneas in which the anterior epithelial barrier is incomplete.

Primary cilia in vertebrate corneal endothelial cells.

The presence of primary cilia in corneal endothelial cells of a range of species from six non‐mammalian vertebrate classes (Agnatha, Elasmobranchii, Amphibia, Teleostei, Reptilia and Aves) is examined by scanning and transmission electron microscopy. Our aim is to assess whether these non‐motile cilia protruding into the anterior chamber of the eye are a consistent phylogenetic feature of the corneal endothelium and if a quantitative comparison of their morphology is able to shed any new light on their function. The length (0.42–3.80 μm) and width (0.12–0.44 μm) of the primary cilia varied but were closely allied with previous studies in mammals. However, interspecific differences such as the presence of a terminal swelling in the Teleostei and Amphibia suggest there are functional differences. Approximately one‐third of the endothelial cells possess cilia but the extent of protrusion above the cell surface varies greatly, supporting a dynamic process of retraction and elongation. The absence of primary cilia in primitive vertebrates (Agnatha and Elasmobranchii) that possess other mechanisms to control corneal hydration suggests an osmoregulatory and/or chemosensory function.

Ultrastructure of lymphatic vessels in the vascularized rabbit cornea

A carbon suspension was injected into rabbit corneas vascularized as a result of silver nitrate application. Both light and electron microscopic techniques were used to study the carbon-filled corneal lymph vessels. The corneal lymphatics have a structure similar to that of lymphatic vessels in other sites. The endothelium is thin, there are no pericytes and no basement membrane and anchoring filaments are present. Hence, they are true corneal lymphatic vessels.

THE EFFECT OF OPHTHALMIC PRESERVATIVES ON THE SHAPE OF CORNEAL ENDOTHELIAL CELLS

The mean area (293.6 ± 53.6 μm2) and perimeter (65.5 ± 5.8 μm) of individual cells were determined from the photographed endothelium of a total of 54 guinea pig corneas, after staining with silver nitrate and removal of the epithelium and stroma. In addition a quantitative assessment of cell shape S (= P2/A) was calculated. The mean cell density (3406 ± 619 cells per mm2) was similar to that for young humans, and the S value (14.76 ± 0.73) was as expected for slightly irregular hexagonal and pentagonal shapes. Incubation of the corneas in glutathione‐bicarbonate‐Ringer solution for periods up to 4 h resulted in only slight changes in the endothelial cell shape (S = 15.21 ± 0.89). However, incubation with thimerosal (0.01%) for 2 h (S = 16.78 ± 1.79) or with disodium ethylenediaminetetraacetate (Na2EDTA) (0.2%) for 1 h (S = 17.20 ± 2.36) gave a marked increase in the tortuosity of the cell ‘outlines’. Longer periods of contact with Na2EDTA resulted in a rounding up and separation of endothelial cells.