The ultrastructure of the extracellular components of the trabecular meshwork in the human eye

Contractile cells in the human scleral spur

The scleral spur in 37 human (age 17-87 years) and six cynomolgus monkey eyes (2-4 years) was investigated. Serial meridional and tangential sections were studied with ultrastructural and immunocytochemical methods. The bundles of the ciliary muscle do not enter the scleral spur, but their tendons, which consist of elastic fibres join the elastic fibres in the scleral spur. Within the scleral spur a population of circularly oriented and spindle-shaped cells is found. In contrast to the ciliary muscle cells, the scleral spur cells form no bundles, but are loosely aggregated. They have long cytoplasmic processes and are connected to each other by adherens-type and gap junctions. They stain intensely for alpha-smooth muscle actin, myosin and vimentin. In contrast to the ciliary muscle cells, they do not stain for desmin. Ultrastructurally, the scleral spur cells contain abundant thin (actin) filaments, but do not otherwise show the typical ultrastructural features of ciliary muscle cells. The scleral spur cells do not express a complete basal lamina. They form individual tendinous connections with the elastic fibres in the scleral spur, which are continuous with the elastic fibres of the trabecular meshwork. The scleral spur cells are in close contact with nerve terminals containing small agranular (30-60 nm) and large granular (65-110 nm) vesicles but also with terminals containing small granular (30-60 nm) vesicles which are regarded as typical for adrenergic terminals. We conclude that the scleral spur cells are contractile myofibroblasts. Their contraction might influence the rate of the aqueous outflow.

Immunomicroscopical study of type VI collagen in the trabecular meshwork of normal and glaucomatous eyes

Cross-strained fiber bundles called long-spacing collagen or curly collagen occur in normal eyes in the trabecular meshwork. It can be seen in the basement membrane of the trabecular lamellae, in the sheath of the elastic-like fibers and underneath the inner wall of Schlemm's canal, where it forms part of the so called plaque material. The amount of this long-spacing collagen increases with age and is significantly more pronounced in glaucomatous eyes. Using immunohistochemical and immuno-electronmicroscopic methods, we have been able to show that type VI collagen is present in the aggregates called long-spacing collagen.

Aqueous outflow in the beagle. II. Postnatal morphologic development of the iridocorneal angle: corneoscleral trabecular meshwork and angular aqueous plexus

The morphology and postnatal ontogeny of the major pathway for aqueous outflow in the canine eye has been examined. Normal canine chamber angles of the Beagle at one day, one through ten weeks, three, four and six months, and one and two years of age were used. Angle tissue was prepared and examined by standard techniques for light and electron microscopy. At birth the corneoscleral trabecular meshwork largely consisted of spongy mesenchyme. By the end of the first month the corneoscleral trabecular meshwork developed into a series of longitudinally oriented sheets anteriorly covered by the peripheral extremity of the corneal endothelium. The angular aqueous plexus (trabecular veins), which was formed at birth, was continually separated from the corneoscleral meshwork by an endothelial lining. Transcellular channels interconnected the trabecular veins and the corneoscleral trabecular meshwork. The corneoscleral trabecular meshwork and angular aqueous plexus in the canine angle are similar topographically, structurally and ultrastructurally to that described in other nonprimate and primate angles.

[Banded filamentous associates in the intra- and extracellular space in connection with collagen degradation (author's transl)]

Banded fibrous associates are described in the extracellular space of connective tissue from human endometrium, Ehlers-Danlos syndrome and of tendon rupture. In the cases of morbus Dupuytren these associates are also found as intracellular inclusions. The banded structures are interpreted as states of an enzymatically induced degradation of collagen in correlation with Type-III collagen.

Pressure effects on the distribution of extracellular materials in the rhesus monkey outflow apparatus

An electron-microscopic investigation was conducted to determine the distribution of extracellular materials in the rhesus monkey outflow apparatus at various maintained levels of intraocular pressure. Intraocular pressure was maintained at either 0,8, 15, 22, 30, or 50 mm Hg, by an intracameral needle attached to a reservoir system for a period of 1 h. Thereafter the eyes were fixed either by intracameral perfusion of glutaraldehyde at the appropriate pressure level, or by carotid perfusion of the fixative, or by rapid enucleation and immersion fixation. The electron-dense cationic stains, colloidal thorium and colloidal iron were used to indicate the presence of carbohydrate-rich extracellular materials in the drainage tissues. In the control tissue (15 mm Hg), heavy concentrations of stain were detected within the cores of the trabeculae and in the extracellular spaces of the endothelial meshwork. With pressure elevation there was a progressive decrease in the surface staining on the meshwork cells, an increase in staining intensity within the trabecular cores, and a 'washout' of extracellular materials from the spaces of the endothelial meshwork. The washout was thought to occur via giant vacuoles up to 30 mm Hg, but at 50 mm Hg the process was accelerated by loss of association between the cells of the canal endothelial monolayer. Over the entire pressure range 0 to 50 mm Hg, there was an increase in the staining on the apical surface of the canal endothelium which was associated with a decrease in the incidence of micropinosomes.