Volume responses of the eye to pressure loadings imitating tonography

Abstract

By means of an instrument for manometric measurement of intraocular pressure in experimental animals (rabbits) the changes in volume of the eye were measured immediately after pressure loadings corresponding to changes in intraocular pressure during tonography by means of various weights. The aqueous humour excreted under these conditions was analysed. In the course of each increase in the intraocular pressure the facility of the outflow was recorded. The effect of the duration of the raised intraocular pressure on subsequent volume-changes was also studied. Increases of 10, 20 and 30 mm Hg in the intraocular pressure for a period of 5 min have detectable effects on the eye. After returning to the initial pressure, the flow of aqueous through the eye increases in all the measured groups. In the first group, which roughly corresponds to tonography with a weight of 5.5 g, this increase is statistically insignificant, while in the two other groups, corresponding to tonography with weights of 10 and 15 g respectively, this increase is statistically significant. The increase in the flow of the aqueous through the eye following irritation is associated with a breakdown of the blood-aqueous barrier; whilst the facility of outflow does not change significantly in the course of repeated loadings of the eye. Direct dependence was found between the duration of the load and the changes in the flow of the aqueous humour after return to the initial pressure. Conditions of flow through the eye were not essentially changed by ligation of the homolateral common carotid artery in spite of the fact that the basic intraocular pressure fell considerably after the ligation.