Schlemm's canal and adjacent structures in glaucomatous patients

Lipid peroxidation in open-angle glaucoma

UV-spectrophotometry and fluorescent analysis were used to study lipid extracts from lenses, aqueous humour and blocks containing trabecular and Schlemms canal tissues, obtained from 49 eyes of patients with primary open-angle glaucoma (POAG). Accumulation of the primary, secondary, and end products of lipid peroxidation (LPO) (diene and triene conjugates, Schiff's bases) was noted in the studied extracts. Significant differences in the levels of all the mentioned LPO products in comparison with the control were observed. The data may be considered as an evidence of LPO participation in destruction of the trabecule and Schlemm's canal in POAG.

Pressure effects on flow channels in the lining endothelium of Schlemm's canal. A quantitative study by transmission electron microscopy

A quantitative investigation, using transmission electron microscopy, was conducted to determine the relative incidence of nuclei, giant vacuoles and their pores, non-vacuolar transcellular channels and minipores in the endothelium lining the trabecular aspect of Schlemm's canal at various levels of intraocular pressure in the range 0--50 mmHg. The eyes of twelve rhesus monkeys were used and prior to intracameral fixation, the intraocular pressure was maintained at the appropriate level for one hour. The results obtained from a single section analysis showed that the incidence of giant vacuoles, vacuolar and non-vacuolar transcellular channels and minipores could be related to pressure. An analysis of serial reconstructions of samples of the vacuoles indicated that vacuolar transcellular channels became more numerous and more enlarged as pressure was increased. We concluded that the transcellular pore system serves as a major outflow route for aqueous humour.

Pressure-induced changes in the ultrastructure of the endothelium lining Schlemm's canal

In a transmission electron microscopic investigation of the endothelium lining Schlemm's canal subjected to graded levels of intraocular pressure (0 to 50 mm Hg for one hour), there was an increase in the number of vacuolar structures with the increase in pressure (range, 8 to 30 mm Hg). At 0 mm Hg, giant vacuoles were absent, while at 50 mm Hg their numbers were less than at 22 and 30 mm Hg. Vacuoles were invaginations either from the meshwork or from the canal surface of the endothelium. A few were transcellular channels that possibly served as a pressure-sensitive outflow system. In addition, the numbers of nonvacuolar transcellular channels and minipores increased with an increase in pressure while the numbers of pinocytotic and micropinocytotic vesicles decreased. The changes were not accompanied by alterations in organelles associated either with protein or energy production. At 50 mm Hg, breaches in the endothelium lining the trabecular wall were obvious and aqueous outflow was considered to be by nonphysiologic routes.

Pressure gradient changes on the trabecular meshwork of monkeys

The cellular lining of the inner wall of Schlemm's canal was anatomically different at different pressure levels. When the anterior chamber pressure rose above that of the canal, there was a marked increase in the number and size of the vacuoles present. At the same time the canal became smaller. When Schlemm's canal pressure exceeded that of the anterior chamber, the vacuoles decreased in size and number, and the canal enlarged. These findings were independent of postmortem artifacts.