The effect of arterial pressure on the ocular pressure-volume relationship in the rabbit

• Published in: Experimental eye research Vol. 60; no. 3; pp. 267 - 278
• Main Author: Kiel, J.W.
• Format: Journal Article
• Language: English
• Published: London Elsevier Ltd 01-03-1995; Elsevier
• Subjects: Animals; arterial pressure; Biological and medical sciences; Blood Pressure - physiology; Choroid - blood supply; eye; Eye - anatomy & histology; Eye and associated structures. Visual pathways and centers. Vision; Female; Fundamental and applied biological sciences. Psychology; intraocular pressure; Intraocular Pressure - physiology; intraocular volume; Laser-Doppler Flowmetry; Male; ocular rigidity; peripheral circulation; rabbit; Rabbits; Regional Blood Flow; Regression Analysis; Sodium Chloride; Vertebrates: nervous system and sense organs; eye; arterial pressure; intraocular volume; intraocular pressure; ocular rigidity; rabbit; peripheral circulation; Eye; Visual system; Vertebrata; Mammalia; Volume; Rabbit; Arterial pressure; Hemodynamics; Lagomorpha; Intraocular pressure
• ISSN: 0014-4835; 1096-0007
• DOI: 10.1016/S0014-4835(05)80109-5

The purpose of this study was to quantify the effect of mean arterial pressure (MAP) on the ocular pressure-volume relationship. The experiments were performed in pentobarbital anesthetized rabbits instrumented with occluders on the thoracic aorta and inferior vena cava to control MAP which was measured via a cannula in the centra ear artery. To vary the ocular volume and measure the intraocular pressure (IOP), two 23 gauge needles were inserted through the pars plana into the vitreous: one needle was connected to a saline-filled syringe and the other needle was connected to a pressure transducer. In one group of animals (
n = 5), pressure-volume curves were determined at MAPs of 100, 80, 60, 40 and 20 mmHg and post mortem by cumulative saline injections (2
μl) every 1–5 sec. In a second group (
n = 7), pressure-volume curves were obtained at MAPs of 80, 60 and 40 mmHg and post mortem by saline infusion at 0.5
μl sec
−1 until the IOP reached 100 mmHg. The infusion protocol was repeated in a third group (
n = 11) where the choroidal flux and the concentration of moving blood cells (CMBC) were measured by a laser Doppler flowmeter as indices of choroidal blood flow and the blood volume, respectively. MAP had three primary effects on the ocular pressure-volume relationship: (1) the baseline IOP varied exponentially with MAP, (2) the steepness of the initial portion of the pressure-volume curves was MAP-dependent and (3) the curves exhibited a ‘plateau’ as the IOP approached the prevailing MAP at MAPs ≧ 40 mmHg. All of the curves in the living eye intersected and became indistinguishable from the post mortem curve when the IOP exceeded the prevailing MAP. The flux and CMBC measurements indicated that the MAP-dependence of the initial portion of the curves was due to failure of choroidal autoregulation and diminished increases in choroidal blood volume at the lower MAPs, and that the plateau portion of the curves was due to expulsion of blood from the eye. It is concluded that MAP has a significant effect on the ocular pressure-volume relationship.