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OCCLUSION of the anterior chamber outflow pathways by means of a perilimbally placed suction cup leads to an obvious rise in intra-ocular pressure (Rosengren, 1934(Rosengren, , 1956. From this increment in intra-ocular pressure, various investigators (Ericson, 1958; Linner, 1959; Weekers, Prijot, Feron, and Verrier, 1960;Galin, Baras, and Mandell, 1961;Langham, 1962) have estimated the rate of aqueous formation by expressing the observed pressure difference as a volume change (Friedenwald, 1954). It was assumed that in the normal eye the rise in intra-ocular pressure during the application of the cup was proportional to the continued formation and accumulation of aqueous.The normal rate of aqueous formation in man obtained in this manner by Ericson (1958) was 0*8 pl./min., which contrasts sharply with the 1 -9 1./min. measured by Goldmann (1950) using the fluorescein technique, and the 1P3 kl./min. found by Grant (1950) employing tonography. This comparatively low estimate of the rate of aqueous formation was explained by the fact that the pressure of the cup itself causes a rise of 4 mm. Hg in the intra-ocular pressure and that the continuous rise in intraocular pressure during cup application tends to slow down aqueous inflow. Ericson did not correct for these factors since he was concerned with comparisons only. Langham (1962) has shown that aqueous outflow can be largely if not completely prevented by a negative pressure of 50 mm. Hg, provided that the intra-ocular pressure does not exceed 30 mm. Hg. At higher intra-ocular pressures leaks of aqueous do occur and the rate of formation of aqueous may be underestimated. In normal subjects this would seem improbable and the assumption can be made that the low estimate of the rate of aqueous formation is in fact related to the application of the cup, and that suppression of aqueous inflow attends the rise of intra-ocular pressure during the procedure. Langham and Eisenlohr (1963) have demonstrated manometrically in living human eyes that analysis of pressure decay curves indicated an approximately linear relationship between pressure and flow over pressure ranges of 10-25 mm. Hg above the normal, yielding a total mean aqueous formation rate of 2*26 1.l./min. These considerably higher values prompted, therefore, an analysis of the rate of aqueous outflow from the decay curves of intra-ocular pressure to resting levels following the removal of the suction cup. In this report the measurements of aqueous inflow obtained from the increments of intra-ocular pressure during the application of the cup will be contrasted with those which were calculated from the intra-ocular pressure decay curve subsequent to cup removal. The observations *

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WITH the observation by Laqueur (1876) that tension of glaucomatous eyes could be reduced with physostigmine, and the corroboration of Weber (1877) that the same effect attended the use of pilocarpine, both substances have found a permanent place in therapy. Their precise action, however, remains obscure (Sugar, 1957;Becker and Shaffer, 1961).Unlike carbonic anhydrase inhibitors, such as acetazolamide, which lower the intra-ocular pressure in glaucoma by reducing the rate of aqueous formation without alteration of the outflow facility, pilocarpine relieves the obstructed outflow of aqueous in glaucoma. This effect might be explained either by a direct action upon the aqueous outflow episcleral veins or by a direct reduction in the rate of aqueous formation. This technique appears therefore, suitable for the delineation of the site of action of pilocarpine in glaucoma. The details of the suction cup technique and a comparison of the results obtained in a series of normal subjects and glaucomatous patients have been provided in a previous study (Chandler, 1964). The present communication provides similar measurements in a separate series of eleven patients with chronic simple wide-angle glaucoma before and after the use of pilocarpine.I Material Eleven unselected patients (mean age 55 years) with chronic simple glaucoma, who attended the Glaucoma Clinic of the Victoria General Hospital, Halifax, Nova Scotia, for diagnostic purposes before treatment, were studied by the suction cup technique. The relevant clinical details are summarized in Table I (opposite).