Systemic blood pressure and intraocular pressure relationship.

The relationship between intraocular pressure (IOP) and arterial blood pressure (BP) was analyzed in response to two pressor agents (norepinephrine and angiotensin II) and two depressor agents (methacholine and isoproterenol) in pentobarbital anesthetized cats. Both IOP and BP were measured manometrically in the same animals. Intravenous norepinephrine and angiotensin II produced dose-dependent increases, whereas intravenous methacholine and isoproterenol produced dose-dependent decreases of both BP and IOP. The IOP response to methacholine was biphasic, with an initial decrease followed by an increase above the pre-drug level. In some experiments a cannula loop was inserted into a carotid artery in order to separate the direct ocular effect of drugs on IOP from that contributed by the changes in systemic BP. Intravenous administration of norepinephrine and angiotensin II produced a larger increase in IOP on the side where drugs were delayed by the loop. Conversely, methacholine produced a larger fall in IOP on the cannulated side while the effect of isoproterenol was essentially unchanged. In other experiments injections were made directly into the ocular arterial blood supply. Norepinephrine and angiotensin II produced a decrease in IOP, methacholine produced a rise of IOP and isoproterenol was not active by this route. The present findings indicate that IOP is largely influenced by arterial BP changes in the acute phase and that the IOP response to drugs is the algebraic sum of effects on systemic BP and their direct ocular effects.