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A. Dastiridou, D. De Brouwere, H. Ginis, G. Kymionis, M. Tsilimbaris, I. Pallikaris; Invasive Measurement of the Change in Ocular Pulse Amplitude and Pulsatile Ocular Blood Flow in Relation to the Intraocular Pressure. Invest. Ophthalmol. Vis. Sci. 2008;49(13):4128.
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Ocular pulse amplitude (OPA) is the variation of the intraocular pressure (IOP) with the heart rate and is associated with the pulsatile component of ocular blood flow. The pulsatile blood volume that flows through the eye is directly related to the OPA through the derivative of the eye's pressure -volume relationship. The purpose of this study was to measure OPA in a wide range of clinically relevant IOP levels and to calculate the corresponding pulsatile component of the ocular blood flow in cataract patients.
Fifty four patients (60 eyes) undergoing cataract surgery were enrolled in the study. Mean age was 67 (SD=17) years. This study was approved by the Institutional Board and performed under the patient’s informed consent. A previously described computer-controlled device for the intraoperative measurement and control of IOP was used. The device, comprising a pressure transducer and a dosimetric pump is connected to the anterior chamber of the eye through a 21 gauge catheter needle. This device was used to artificially increase the IOP from 15 to 45 mmHg by infusing a saline solution in steps of 4 µl. The IOP was continuously recorded for 2 seconds in each step in order to measure the pulsatile change in IOP during this interval. OPA was derived as the peak-to-peak IOP variation in each of the 2sec time intervals. Pulsatile Ocular Blood Flow (POBF) was obtained converting the OPA to the corresponding change of ocular volume derived from the rigidity diagram. Systemic blood pressure and pulse rate were monitored during the measurement and remained stable in all patients.
The average OPA was 2.28mmHg (SD=1.05) for measurements conducted at 15 mmHg increasing to 3.29 mmHg (SD=1.65) at 45 mmHg. Except from one eye, in all measurements an increase of the OPA was observed for increasing IOP. In average, OPA increased by 44% when increasing the IOP from 15 to 45 mmHg. The average Friedenwald’s Coefficient for rigidity was 0.0137 mmHg/µL (SD=0.0054). The corresponding POBF was 814µL/min (SD=439) at 15mmHg decreasing to 390µL/min (SD=215) at 45mmHg. The decrease of POBF with increasing IOP, despite the increase of OPA, is explained by the exponential character of the pressure-volume relationship of the eye.
A model was developed to calculate the pulsatile component of ocular blood flow based on precise values of heart rate, rigidity and OPA. POBF was estimated for a wide range of the IOP in a large number of human eyes.
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