Site of Obstruction to Aqueous Outflow in Chronic Simple Glaucoma.

THE site of obstruction to aqueous outflow in chronic simple glaucoma must lie between the anterior chamber and episcleral plexus, yet opinion remains divided between those who believe that the obstruction occurs while aqueous passes through the trabecular meshwork before entering Schlemm's canal and those who believe that it occurs in the scleral plexus beyond the canal. Support is given to the latter view by the vascular changes associated with diurnal variations in intra-ocular pressure (Duke-Elder, 1955), by the infrequent appearance of blood in Schlemm's canal on gonioscopy in glaucomatous eyes, and by the direct measurement of pressures within the canal of Schlemm in the eyes of normal monkeys (Perkins, 1955). The altered blood flow in laminated aqueous veins following compression of episcleral vessels in glaucomatous eyes (Goldmann, 1949), and the direct measurement of resistance to outflow in normal eyes after removal of the trabecular meshwork (Grant, 1958), support the former view. Morphological studies which have attempted to establish the site of obstruction have been handicapped by the difficulty in obtaining rapidly-fixed glaucomatous material at an early stage in the disease, and by the variations in normal structure which have made observations of pathological change difficult to assess. Various authors have reported abnormalities within the trabecular meshwork, the canal, or the scleral plexus. In the meshwork, obstruction has been -attributed to spongy or foamy degeneration of the cytoplasm (Flocks, 1959; Becker, 1959), to granular degeneration of collagen, and to proliferation of endothelial cells (Teng, Paton, and Katzin, 1955). Trabecular sclerosis has been described (Theobald and Kirk, 1956; Kornzweig, Feldstein, and Schneider, 1958), although it is not clear which portion of the fibres becomes sclerotic, nor has a distinction been made between thickening due to swelling and that due to fibre proliferation. A uniform thickening of the clear zone has been described in trephine biopsies among other changes in the meshwork (Unger and Rohen, 1960), and proliferation of the so-called curly collagen in the clear zone has been found in one case of glaucoma (Garron, 1959a). Adhesions