Purchase this article with an account.
William J. Lavery, Jeffrey W. Kiel; A Rabbit Model To Study The Effects Of Posture On Ocular Hydrodynamics. Invest. Ophthalmol. Vis. Sci. 2011;52(14):1523.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
In humans, moving from an upright to a supine position causes gravity-dependent increases in cranial arterial and venous pressure (i.e., the "hydrostatic column effect"). Curiously, the IOP increase to this posture change is smaller than expected for the change in height of the eye above the heart, which suggests a venous regulatory mechanism, since the Goldmann equation predicts that IOP and EVP should change equally. This regulatory mechanism is poorly understood, and so the purpose of this study was to develop an animal model to explore the effects of postural change on ocular hydrodynamics.
In anesthetized rabbits (n=35), we measured mean arterial pressure (MAP), IOP, and orbital venous pressure (OVP) by direct cannulation; carotid blood flow (BFcar) by transit time ultrasound, heart rate (HR) by a digital cardiotachometer, and aqueous flow (Flow) by fluorophotometry. The protocol entailed 60 min of baseline measurements in a head up position, followed by 90 min of downward tilt (i.e., hindquarters level with head). Data were analyzed by paired t-tests.
Tilt caused immediate, significant increases in MAP, IOP, and OVP. MAP increased by 4.85 ± 0.44 mmHg (from 70.90 ± 0.88 to 75.76 ± 1.06, p<0.01), IOP increased by 1.05 ± 0.28 mmHg (from 15.54 ± 0.54 to 16.39 ± 0.55, p<0.01), and OVP by 1.64 ± 0.10 mmHg (from 2.93 ± 0.13 to 4.57 ± 0.15, p<0.01). HR decreased by 11 ± 3 bpm (296 ± 4 Vs 284 ±4, p<0.01). Flow was unchanged (3.21 ± 0.16 Vs 2.99 ± 0.22 µL/min, p>0.05) as was BFcar (33 ± 1.5 Vs 34 ± 1.6 mL/min, p>0.05).
The increase in MAP was significantly greater than the increases in IOP or OVP (p<0.001). In addition, the increase in OVP was greater than the increase in IOP (p<0.01). There was a slight, non-significant decrease in Flow during tilt, which may have contributed to the IOP increase being smaller than OVP; alternatively, episcleral venous pressure may be better regulated than OVP. Nonetheless, the pattern of responses to posture change in the rabbit model is qualitatively similar to those reported for humans, despite the much smaller size of the rabbit. We conclude that tilt in the rabbit is a useful model for studying ocular hydrodynamic responses to changing posture.
This PDF is available to Subscribers Only