Eye Vessel Compliance as a Function of Intraocular and Arterial Pressure and Eye Compliance

Abstract

The purpose of our study is to develop and validate a methodology to measure the compliance of the vascular network in the eye using biomechanical parameters, namely arterial pressure, intraocular pressure (IOP), and ocular compliance of the eyeball (OC). In vitro experiments were conducted on 6 freshly enucleated rabbit eyes. An inflatable catheter was inserted in the posterior chamber. The balloon was inflated and its volume changed periodically at a rate of 1-2 Hz, yielding variations in the intraocular volume; thus, emulating the volume pulsations of the vascular network in the eye. The IOP was measured continuously with a pressure transducer and the OC was calculated using the outflow facility. The compliance of the balloon, mimicking the compliance of the vascular network, was estimated indirectly from the measurements of IOP, balloon pressure, and OC. The estimated balloon compliance was compared to direct estimates of balloon compliance, based on the balloon pressure-volume curve. In vivo study included 5 white New-Zealand rabbits. The method to estimate the vascular compliance of the eye was tested under normal conditions and after administration of norepinephrine, which induced a vasoconstriction leading to reduction in vascular compliance. In vitro comparison of direct versus indirect estimates of compliance showed a difference that was not significant (0.075 vs. 0.077 μL/mm Hg, P = 0.86). Results from the in vivo study indicated that norepinephrine significantly increased the arterial pulse pressure amplitude, while compliance of vascular network of the eye decreased from 0.18 ± 0.12 to 0.10 ± 0.08 μL/mm Hg (P = 0.001). The eye vascular compliance can be predicted using the IOP, arterial pressure, and OC of the eyeball.