THE ELASTIC TISSUE OF PRIMATE TRABECULAR MESHWORK; A HISTOLOGIC AND ELECTRON MICROSCOPIC STUDY.
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Anatomy↗
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[Glucocorticoids upregulate transepithelial electrical resistance and expression of tight junction-related protein in human trabecular meshwork cells].
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Cells, Cultured↗
Synthesis of glycoconjugates by trabecular meshwork of glaucomatous corneoscleral explants.
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Adult↗
Ethacrynic acid: outflow effects and toxicity in human trabecular meshwork in perfusion organ culture.
The effect of ethacrynic acid, a potential outflow agent for the treatment of glaucoma, was studied in a series of 25 pairs of human eyes in perfusion organ culture. Concentrations varied from 0.01 mM to 2.4 mM and were used in single or repetitive doses. Intraocular pressure was continuously recorded for up to two weeks after exposure. Eyes were then fixed and the meshwork examined histologically. Ethacrynic acid in single doses of 0.05 mM, 0.3 mM, and 0.6 mM increased facility of outflow at least 40% when compared with fellow control eyes. The duration of effect was approximately 18 hours, during which time the intraocular pressure gradually returned to baseline. Histologic examination revealed dose related effects on the trabecular cells, ranging from clumping of nuclear chromatin in some eyes to cellular swelling, disruption of cytoplasmic membranes, and cell necrosis in other eyes at concentrations of 0.1 mM and higher. No recovery or reversal of these changes was noted with time, even two weeks after a single exposure to the drug. Although ethacrynic acid is effective in temporarily lowering intraocular pressure in the human eye, a low therapeutic index may limit its clinical usefulness.
Adult↗
Morphology of the trabecular meshwork and inner-wall endothelium after cationized ferritin perfusion in the monkey eye.
Nine eyes of five cynomolgus monkeys were perfused through the anterior chamber with cationized ferritin (CF) at normal and increased intraocular pressure. After perfusion with glutaraldehyde, the morphologic appearance of the endothelial lining of Schlemm's canal (SC) and of the adjacent regions was analyzed using tangential and sagittal serial sections. The CF, which binds to negatively charged surfaces, was observed to be adherent to the free surfaces of trabecular cell membranes and to accumulate in the cribriform layer underlining the endothelial lining of SC. Tangential sections of the inner-wall endothelium demonstrated that separations of the adjacent cell membranes occur between the tight junctions forming openings or lacunae and bent, tunnel-like channels that represent continuous paracellular pathways. Complete staining of these inner-wall paracellular pathways with CF were observed indicating that the adjoining membranes are negatively charged and that the perfused fluid had passed through these intercellular channels. These paracellular pathways appeared enlarged and were more easily identified at elevated perfusion pressure. In general, intracytoplasmic vacuoles demonstrated heavy staining with CF on their luminal surface but only faint staining on the adluminal (cribriform-facing) surface. Apparent giant vacuoles were observed to be often not real intracellular vacuoles but rather dilatations of the paracellular spaces. This study demonstrates that there are paracellular routes through the inner-wall endothelium by which high molecular-weight substances such as ferritin and macrophages can leave the anterior chamber. Probably there are both transcytoplasmic and paracellular mechanisms of aqueous outflow that may vary under different conditions of pressure or flow.
Animals↗
Trabecular meshwork and uveoscleral outflow models.
PURPOSE: To describe current laboratory models used to study aqueous outflow. Because development of primary open angle glaucoma (POAG) is rare in animals, no animal model of POAG is available for laboratory study on the pathogenesis of this condition. This review will discuss the alternative models used in the laboratory to study aqueous outflow. METHODS: This is a brief review of published techniques, with commentary upon advantages and limitations of each. RESULTS: Whole eyes and anterior segments are useful in assessing aqueous outflow resistance and anatomical changes in the meshwork. They have a limited duration of viability. Cell cultures are less expensive, easier to obtain, provide more cells than in intact meshwork, and are excellent in studying cellular physiology. The artificial environment of cell culture, however, including the plastic dish or artificial substrate and also the requirement of serum supplements, may limit applicability. Modern understanding of cells, their interaction with the extracellular matrix, and sensitivity to the composition of culture media suggest that these laboratory models should be updated to more closely mimic the in vivo situation. CONCLUSION: Outflow models are a useful beginning in the study of cellular physiology, cell-extracellular matrix interactions, and reactions of the whole meshwork. All have limitations, however; the development of an animal model of human POAG would be an ideal solution to many of the current limitations.
Animals↗
Human trabecular meshwork cells express the ciliary neurotrophic factor (cntf) tripartite receptor complex.
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Blotting, Western↗
Morphology of the trabecular meshwork within monkey (Macaca speciosa) eyes after irradiation with the free-running Nd:YAG laser.
The long-term tissue response of monkey eyes to trabeculoplasty produced at the chamber angle by neodymium:YAG (Nd:YAG) laser (thermal mode) was investigated. Four weeks after irradiation, a monolayer of corneal-like endothelial cells extended over the trabeculum in impact zones, with partial occlusion of intertrabecular spaces; this condition persisted at all subsequent stages of observation (viz, up to 13 weeks). Both primary and secondary degeneration of trabecular endothelial cells occurred predominantly at the posterior border of the juxtacanalicular tissue, and continued throughout the observation period. Lysis and degradation of collagen fibrils were also prominent in this region, and collagen-phagocytosing cells could be seen at all stages. Although activated fibroblasts were marked in this zone, regeneration processes were, in general, less marked than those of degeneration. The significance of these findings in relation to the mechanism by which trabeculoplasty works is discussed.
Animals↗
[Cell-to-cell interactions between iris and trabecular meshwork in primary open-angle glaucoma].
Pathomorphological study of the ocular draining system in the presence of an ischemic iris was carried out in patients with primary open-angle glaucoma (POAG). A total of 173 biopsy specimens of the sclera and iris were collected during anti-glaucoma operations in 115 patients aged 32-90 years. The specimens were stained for amyloid with Congo red, thioflavin, and toluidine blue at pH 4.6 and 5.8 for detecting glycosaminoglycanes. The specimens were examined by histochemical and electron microscopic methods. Morphological changes in the trabecular system in POAG are due to abnormalities in the iridal microcirculatory bed. The status of the trabecular system during the initial and advanced stages of glaucoma depends on the severity of involvement of iridal arterioles, capillaries, and venules, modulating the biochemical processes in the anterior segment of the eye. Endotheliocyte and collagen matrix pathology and subsequent degradation of the trabecular system are closely related to dystrophic processes in the iris (release of plasma protein from the vessels and melanin granules into anterior chamber humor, cytotoxic effects of degradation products on adjacent tissues). The detected changes imply the use of drugs improving blood supply to the eye at the microcirculatory level and antihypoxants and antioxidants in local and total-systems therapy of patients with POAG.
Adult↗
Isolated amyloidosis of anterior uvea and trabecular meshwork.
Amyloid deposition in the iris is rare, scanty and associated with systemic disease. We present a case of isolated localized heavy amyloid infiltration of the iris and describe a new hillock-pattern feature visualized using scanning electron microscopy.
Aged↗
[Histopathological features of the trabecular meshwork in a case of presumed bilateral Chandler syndrome].
BACKGROUND: We describe a patient who had notable decrease in the number of corneal endothelial cells in both eyes and developed open angle glaucoma without evident iris atrophy and peripheral anterior synechia. CASE: A 74-year-old woman. The trabeculectomized angle tissue and iris tissue of her left eye were observed under light and transmission electron microscopy. From Schwalbe's line to the anterior chamber angle, degenerated endothelium-like cells were observed and overgrowth of layers of collagen fiber with varied cycles and basement membrane-like material were noticed. In addition, the morphology of intra-trabecular space was atrophic and occlusive with marked degeneration and exfoliation of endothelial cells in the trabecular space. On the side of the anterior chamber, degenerated endothelium-like cells were observed, the morphology of which was considered to result from abnormal metabolic function in corneal endothelium. Overgrowth of basement membrane-like material onto iridic tissue was not observed. CONCLUSION: Although slit lamp examination revealed no obvious abnormality, the result of histological examination suggested that this was a case of Chandler's syndrome in a broad sense or was in the early stage of this disease. We also discussed differential diagnosis from other diseases.
Aged↗
Dexamethasone treatment decreases hyaluronan-formation by primate trabecular meshwork cells in vitro.
The functional significance of Hyaluronan (HA) present in the cribriform layer of Schlemm's canal is not known. It may contribute to the actual outflow resistance but the relatively inert molecule might also be necessary to prevent adherence of larger molecules to the cribriform network. Thus HA might rather prevent an increase in outflow resistance. It is well known that treatment with Dexamethasone (DM) in a number of patients leads to an increase in intraocular pressure presumably due to an increase in outflow resistance. To clarify whether an imbalance in HA formation might be involved in these changes we have treated confluent cultures of human trabecular cells as well as control cell lines (ciliary muscle cells, scleral fibroblasts) with 500 nM DM for 24 hr or 12 days and have measured HA-synthesis using incorporation assays with 0.05 m D-[6-3H] Glucosamine hydrochloride. In all six cell lines investigated there was a significant decrease in HA-synthesis following short and long term treatment with DM when compared with the untreated controls. This reaction of trabecular cells to DM treatment is different from the DM effect reported on the synthesis of many other components of the extracellular matrix like fibronectin and elastin which increase after DM treatment. If the DM-effect seen in cell cultures plays a role in vivo decreased formation in HA could result in impaired function of the outflow pathways.
Animals↗
Argon laser photocoagulation of the trabecular meshwork in open-angle glaucoma.
Argon laser photocoagulation is an effective surgical modality in the management of open-angle glaucoma. Twenty-two eyes with open-angle glaucoma were treated. Approximately 50 burns of 50 micron spot size were applied to the anterior trabeculum over the inferior 180 degrees of the angle. An average pressure drop of 6.1 mmHg was achieved. Complications were minimal, a transient postoperative pressure rise being the most potentially hazardous.
Adult↗
[Electronmicroscopic studies of the trabecular meshwork in corticosteroid glaucoma].
The tissue specimen of a 41-year-old patient with cortisonglaucoma, obtained by trabeculectomy, was examined by electronmicroscope. There are massive depositions of band-like and linear arranged structures in the cribriform area and adjacent lamellae of the trabeculum corneosclerale. The pathways for aqueous humor of this region are almost completely obstructed by this material. That is the reason for an increased outflow resistance. The cells of this area show signs of degeneration and are reduced in their numbers. -- The cortisonglaucoma differs from all the other forms of glaucoma especially from glaucoma simplex by these characteristic deposits.
Adult↗
[Is increased outflow resistance in glaucoma simplex caused by regional differences in trabecular meshwork density? Some methodologic and morphologic considerations clarifying this question].
In 1953, Goldmann observed that outflow resistance increases in an underperfused meshwork and concluded that only continuous perfusion keeps the outflow channels open. In primary open-angle glaucoma densifications occur beneath the inner wall of Schlemm's canal. They consist of fine fibrillary material and various glycoproteins. In order to see if densifications with reduced flow exist in clinical cases three possible examination techniques are proposed. (1) Doppler ultrasound: A transmitter with a very divergent beam could be placed on the cornea and the limbus probed with a small-diameter receiver. If the meshwork is perfused radially some Doppler frequencies might be generated and rendered audible in the usual way. Over densifications without perfusion they would be absent. (2) Doppler laser: If monochromatic light were used in a gonioscope and the light returned from the angle mixed with the original, it might be possible to observe Doppler frequencies. However, present-day lasers are not sufficiently monochromatic. (3) Observation of albumin-bound fluorescein entering the chamber from the canal. The canal is filled retrogradely with blood. Gonioscopy with polarized excitant light and observation through a polarized filter.
Aqueous Humor↗
Ultrastructure of the trabecular meshwork in untreated cases of primary open-angle glaucoma (POAG).
Thirty-one trabeculectomy specimens of patients suffering from primary open-angle glaucoma (POAG) who had received no, or only minor, medication prior to surgery were ultrastructurally and quantitatively analysed. Most of the specimens revealed thickened trabeculae, increased amounts of plaque-material deposited within the cribriform layer and an abundance of long spacing (lattice) collagen. The uveal meshwork was partly deprived of cells whereas the cribriform layer often contained numerous enlarged, light cells with many small mitochondria and lysosomes but no prominent endoplasmic reticulum or Golgi complexes. The quantitation of sheath-deprived plaque material (SD plaques) in a defined area of inner and outer wall of Schlemm's canal showed no significant difference between the untreated cases studied here and the treated ones studied previously. However, both groups had significantly higher amounts of SD plaque material in the inner wall than normal controls of a similar age range.
Adult↗
Neuron-specific enolase and embryology of the trabecular meshwork of the rat eye: an immunohistochemical study.
Neuron-specific enolase (NSE) is a unique form of the glycolytic enzyme enolase found exclusively in neurons and neuroendocrine tissues. Immunohistochemical techniques in which antineuron-specific enolase antibodies are used have made it possible to map out derivatives of the neural crest in humans. By using affinity-purified antibodies against NSE, we investigated whether the contribution of the neural crest cells to the development of the anterior ocular structures in the rat is similar to that in man. We found that filtration structures in rats show morphologically striking similarities with the analogous region of the human eye. Hence, the rat eye, with certain reservations, is a suitable model for experimental studies on ocular diseases that are characterized by chamber angle anomalies or congenital glaucoma.
Animals↗
A case of Chandler's syndrome revealed by ultrastructural studies of the trabecular meshwork.
PURPOSE: To investigate ultrastructural changes in the aqueous outflow route and discuss the mechanisms associated with intraocular pressure (IOP) elevation in a patient with presumably early stage Chandler's syndrome. METHODS: A 47-year-old man underwent trabeculectomy because of elevated IOP. A specimen obtained during surgery was studied by transmission electron microscopy. RESULTS: Electron microscopy showed the presence of a monolayer composed of corneal endothelium-like cells and thick basement membrane-like material. Neovascularization was also observed in the corneoscleral trabeculum. CONCLUSIONS: Our results indicate that several mechanisms, including the formation of basement membrane-like tissue, infiltration of inflammatory cells and neovascularization, might contribute to the elevation of IOP in Chandler's syndrome. These may occur even when there is no history of conspicuous inflammatory reaction in the anterior ocular segments.
Aqueous Humor↗