Relationship Between Intraocular Pressure and Arterial Blood Pressure: An Experimental Study on Pigs

Abstract

Abstract: : Purpose: An experiment was carried out to investigate the relationship between intraocular pressure (IOP) and arterial blood pressure (BP) in an animal model. Methods: Blood pressures were measured with two indwelled catheters inserted in the left carotid artery and jugular vein and IOP were measured with catheter inserted through the cornea into the anterior chamber of both eyes of anesthetized pigs (n=7) under spontaneous ventilation. Plateaus of different levels of BP (about 40, 50<font face="symbol">¼</font> to 140 mm Hg) were achieved by infusion with a syringe–pump of either sodium nitroprusside or angiotensine II at sufficient dosage. After equilibration of both BP and IOP for each plateau, the compliance of the eye ball was estimated by the analysis of the change in IOP induced by direct injection of a known volume (3, 6, 9 and 12 µL) of based saline solution into the anterior chamber with a microdialysis syringe pump. Results: IOP oscillates synchronously to BP with an amplitude of 2.5 ± 1.5 mm Hg in the right eye (intact jugular and carotid vessels) and 1.0 ± 0.8 mm Hg in the left one (occluded vessels). A good linear relationship between IOP and BP is observed instantaneously (r > 0.9; p<0.001) as well as in average (r > 0.85; p<0.001), the dependence of IOP in BP being about 20 % which means that a variation of 20 mmHg in mean BP induced a variation of 4 mmHg in mean IOP. The compliance of the eyeball is very low since an injection of as few as 3 µL induces an increase of IOP as high as 1 mm Hg in average; it slightly varies with BP. Conclusions: In this experimental study, the relationship between IOP and BP is more important than what is usually reported. Three hypotheses are discussed: a variation of aqueous humor secretion, a variation of eyeball compliance and a choroidal pulse.

Keywords: intraocular pressure • blood supply