In 1953 Friedenwald and Becker1 published a detailed analysis of the assumptions made by Grant2,3 when he formulated his theoretical basis for tonography. Among those assumptions was the following: "There is no change in the rate of secretion and diffusion of aqueous during tonography, i. e., flow is constant and the same as in the undisturbed eye."1
It was pointed out by the above-mentioned authors that small changes in flow would cause large errors in the estimation of the volume changes in the eye during tonography. For instance, a reduction in flow would result in an overestimation of the change of volume and in the coefficient of the facility of outflow.
It would therefore be of considerable theoretical interest to test the above-cited hypothesis experimentally in such a manner as to ascertain whether or not the rate of inflow and/or diffusion change during the four minutes of