Clinical tonography has added greatly to our understanding of the pathogenesis of chronic simple (open angle) glaucoma. There has been adequate confirmation of the initial conclusion of Grant1 that "increase in intraocular pressure in glaucoma is practically always, possibly exclusively, caused by increased resistance to outflow of aqueous humor from the eye (i.e., subnormal facility of outflow), and not by hyperformation of the aqueous humor." However, with the increased use of repeated tonography the rare exceptions to this thesis appeared. Thus, Becker and Friedenwald,2 in reviewing 1500 tonograms on 250 consecutive patients, noted 5 subjects who had repeated tracings demonstrating elevated tensions without impaired facility of outflow. These eyes were demonstrated to have normal values for corneal curvature and scleral rigidity. Ballintine3 also noted a few patients with chronic simple glaucoma and elevated intraocular pressure but with normal facilities and normal scleral rigidities. With use of the