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N. Karyotakis, H. Ginis, A. Dastiridou, M. Tsilimbaris, I. Pallikaris; Temporal characteristics of the Ocular Pulse Amplitude and their dependence on average intraocular pressure. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6407.
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© ARVO (1962-2015); The Authors (2016-present)
The purpose of this study was to analyze the temporal characteristics of the Ocular Pulse by using manometric data from living human eyes.
An intraoperative invasive manometric device was used to measure the intraocular pressure (IOP). The measurements were performed at 10 patients (4 men and 6 women, aged 61 years, sd 15) before cataract surgery. The study was approved by the Institutional Review Board. The IOP was artificially increased to 40 mmHg by infusion steps of known volume of saline in the anterior chamber of the eye. At 40 mmHg the infusion stopped and the sensor recorded the IOP decay curve over time for 3 minutes. From this continuous signal the Ocular Pulse (OP) amplitude and systolic-diastolic slopes were analyzed at different average IOP levels. To reduce noise, several (10-15) pulses were registered and averaged using a purposely-developed MATLAB (The Mathworks, Inc, MA, USA) script. The OP was approximated using an asymmetric triangular pulse characterized by different slopes at the systolic and diastolic phase of the cardiac function. The amplitude of the measured pulses and the corresponding slopes of the triangle pulses were calculated at three different average IOP levels (25, 30 and 40mmHg) for all subjects. The triangular pulse approximation mathematically led to a predicted linear relationship between the ocular pulse amplitude (OPA) and the period (T) of the cardiac cycle.
Average slopes during the systolic and diastolic phase were 23.54 (sd 7.4) and -9.22 (sd 2.4) υL/sec respectively. Both slopes increased linearly with IOP (R2=0.86). There was a linear relationship (R2=0.98) between the amplitude corresponding to the triangular pulse approximation and the actual (peak to peak) OPA. Based on this observation, a simple linear formula that can be used to convert the measured OPA at the equivalent OPA at different heart rates was constructed: OPAo=OPAm *HRo/HRm , where OPAo corresponds to OPA at a reference heart rate (HRo) and OPAm the measured OPA at a heart rate of HRm.
The shape of the ocular pulse depends on the average IOP. OPA is directly proportional to the period of the cardiac cycle. It is suggested that when OPA values are reported the associated heart rate should also be noted.
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