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Adan Villamarin, Sylvain Roy, Nikolaos Stergiopulos; Estimation of the Vascular Compliance of the Eye using an Intraocular Pressure-Ocular Compliance Relation. Invest. Ophthalmol. Vis. Sci. 2011;52(14):6045.
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To develop and validate a methodology to measure the compliance of the vascular network in the eye using biomechanical parameters, which were the arterial pressure, the intraocular pressure (IOP) and the ocular compliance (OC).
in vitro experiment included 6 freshly enucleated eyes. An inflatable catheter (Fogarty type) was inserted in the posterior chamber. Ocular compliance was initially calculated and the volume of the balloon when inflated was then changed periodically at a rate of 1-2 Hz yielding variations in the intraocular volume in the range of ±10 to 20 µl. The intraocular pressure was continuously measured with a strain gauge manometer. The compliance of the catheter (mimicking the compliance of the vascular network) was directly estimated based on the pressure-volume measurements (C=ΔV/ΔP) and was then compared to the method using the measurements of the OC, the IOP and the pressure in the catheter. 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 measurements versus estimates of compliance showed a difference that was not significant (p = 0.86). The compliance of the balloon calculated experimentally and theoretically was 0.075 µl/mmHg and 0.077 µl/mmHg, respectively. Results from in vivo study indicated that norepinephrine significantly increased the arterial pulse pressure amplitude while arterial compliance decreased notably from 0.19 µl/mmHg (± 0.11) to 0.13 µl/mmHg (± 0.08) (p = 0.001).
The study showed the accuracy of our model to estimate the arterial compliance of the eye in comparison with the classic method quantifying the pressure-volume measurement. The results depicting a decrease in arterial compliance were plausible, as we expected that contraction of vascular smooth muscles and increase in pressure would lead to a decrease in vascular compliance.
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