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A. Dastiridou, H. Ginis, D. De Brouwere, N. Karyotakis, M. Tsilimbaris, I. Pallikaris; Axial Length, Ocular Rigidity and Pulsatile Ocular Blood Flow. Invest. Ophthalmol. Vis. Sci. 2009;50(13):414.
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© ARVO (1962-2015); The Authors (2016-present)
A negative correlation between axial length (AL) and pulsatile ocular blood flow (POBF) has been suggested by means of pneumotonometry, but has been questioned because of the possible confounding effect of ocular volume on ocular rigidity. In this study the effect of AL on ocular rigidity, ocular pulse amplitude (OPA) and pulsatile ocular blood flow is investigated.
Sixty three patients (63 eyes) undergoing cataract surgery, with different refractive errors and no other ocular pathology were enrolled in this study. Mean AL was 24.82 (range 21.15-32.49) mm. The study was approved by the Institutional Board and performed under the patient’s informed consent. An invasive, computer controlled device, comprising a microdosimetric pump and a pressure sensor, is connected to the anterior chamber under topical anaesthesia with drops. The system is used to raise the intraocular pressure (IOP) from 15 to 40 mmHg, by infusing the eye with a saline solution. After each 4 ul infusion step, the IOP is continuously recorded for 2 seconds. Starting from an initial level of 40 mmHg an IOP decay curve for a time interval of 1 minute is obtained. Blood pressure and pulse rate were measured and remained stable during the procedure. The rigidity coefficient is calculated by an exponential fit to the pressure volume data after correction for outflow. OPA is measured as the maximum IOP flunctuation during the cardiac cycle. Pulse volume (PV) is assessed transforming the OPA to the corresponding volume change. The real time pressure signal is filtered and POBF is estimated based on a theoretical model.
Ocular rigidity coefficient was 0.021 (sd 0.005)ul -1. A negative correlation between the rigidity coefficient and AL (r=-0.64,p<0.01) is documented. Increasing AL is associated with decreased OPA (r=-0.70, p<0.01, r=-0.75, p<0.01), PV (r=-0.38, p<0.01, r=-0.52, p<0.01) and POBF (r=-0.29, p=0.02, r=-0.26, p=0.04) at baseline and elevated IOP respectively. The relation with POBF is significant after adjusting for age, mean blood pressure, and heart rate.
Ocular volume is a determinant of ocular rigidity. POBF is shown to be reduced in high myopia after incorporating each eye’s ocular rigidity coefficient in the calculation algorithms. These results may have implications on ocular pulse studies and the pathophysiology and clinical ramifications of myopia.
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