Externalization of Schlemm's canal (sinusotomy) in glaucoma.

IT is evident that ocular hypertension in glaucoma is usually due to an increased resistance to the outflow of the intra-ocular fluid. In about two-thirds of all patients there is no visible obstacle to the outflow in the anterior chamber angle (so-called wide-angle glaucoma); these pathological changes in the intramural pathways, starting from the trabecular meshwork, are usually held responsible for the circulatory disturbance. Some authors consider the trabecular zone as the site actually affected (Teng, Katzin, and Chi, 1957; Speakman, 1961). Grant (1958) pointed out that this area-accounted for about 75 per cent. of the normal resistance to outflow, but this is not necessarily the site of the pathological process. There are sound arguments in favour of the theory that the outflow is affected in the region of the intrascleral collectors between Schlemm's canal and the anterior ciliary veins (Duke-Elder, 1955; Dvorak-Theobald and Kirk, 1956). Each theory is probably valid in certain cases. The results of histochemical studies carried out in our clinic on fifty scleral specimens obtained during glaucoma surgery confirm the existence of pathological changes in early wide-angle glaucoma. This particularly applies to abnormal mucopolysaccharide distribution. Similar data have already appeared in the literature (Unger, 1963; Larina, 1966). It should be noted, however, that different layers of the sclera are not equally affected. Whatever its nature, the process usually spreads within the sclera "sandwich-wise", affecting some strata and leaving others apparently undamaged, full-thickness involvement being exceptional. The middle layers are most commonly affected, the deep ones less frequently, and the superficial areas very rarely. This supports the hypothesis that the outflow is sometimes obstructed in the trabecular meshwork, and sometimes (more often) in the intrascleral collectors; in other words the obstruction may be either distal or proximal to Schlemm's canal. One may thus speak of an "intrascleral" and a "trabecular" form of glaucoma. These considerations seem to justify a new approach to the surgery of glaucoma, confining the intervention to a very limited region where the outflow is obstructed. Glaucoma may thus be classed into four main types: angular (iris-block), trabecular, intrascleral, and hypersecretional. The methods of surgical management applicable to this pathogenicallyoriented system have been described elsewhere (Krasnov, 1965), and this paper deals with only one of the operations which is in practice the most important.