Influence of the intra-ocular pressure on the formation of the aqueous humour and the outflow resistance in the living eye.

THIS study deals with the problem of the regulation of the intra-ocular pressure and the influence of pressure on the formation and the resistance to outflow of the aqueous humour. The main experimental approach has been to analyse the relationship between the steady state intra-ocular pressure and varied rates of flow of fluid through the anterior chamber of living and dead eyes. In the experiments on living animals, the normal rate of flow of aqueous humour was augmented by infusions of fluid directly into the anterior chamber. Provided that the factors determining the normal intraocular pressure remain constant, it is evident that the equilibrium pressure in the eye will increase proportionately with the rate at which fluid is infused into the eye. In the experiments to be described. a linear relationship was found in dead eyes over a wide range of pressures but not in eyes of living animals. The results of these studies were consistent with a Qoncept of homeostatic reflex activity in the eye which acted to minimize changes in the intra-ocular pressure, by altering either aqueous humour formation or the outflow resistance. This possibility was examined in further experiments in which the normal intra-ocular pressure and dynamics were modified experimentally. These included procedures for decreasing the rate of aqueous humour formation and the outflow resistance, and experiments in which either the nervous or the vascular supply to the eye was altered. Recently, the problem of the influence of pressure on aqueous humour dynamics has taken on additional significance following the introduction oftonography (Grant, 1950, 1951) for the measurement of the outflow facility and aqueous humour formation. This technique has been widely used in experimental and clinical studies, and its validity rests on the assumption that a moderate increase in intra-ocular pressure (10 to 15 mm. Hg) does not