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Arash Kazemi, Jay W McLaren, Arthur J Sit; Repeatability of Episcleral Venous Pressure Measurement. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2911.
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© ARVO (1962-2015); The Authors (2016-present)
Episcleral venous pressure (EVP) is an important determinant of intraocular pressure (IOP) and can be measured by estimating the pressure required to compress an episcleral vein to a predetermined endpoint. This study evaluates the repeatability of EVP measurement in proximal and distal segments of an episcleral vein, two adjacent veins in the same field of view, and two separate measurements in different sessions.
Episcleral venous pressure (EVP) was measured in 17 eyes of 17 patients by using a computer-controlled automated episcleral venomanometer that recorded a video sequence of the vessel as it was compressed. The measured applied pressure was synchronized with the video stream and image analysis software was used to determine the pressure that collapsed a selected segment of an episcleral vein to a predetermined endpoint. In high-quality video recordings, we compared EVP in a proximal segment to EVP in a distal segment of the same vein and EVP between two adjacent veins in the same field of view. We also compared EVP from two measurement sessions in the same eye that were 2 - 4 hours apart. Significances of differences were determined by using paired t-tests and relationships between measurements were illustrated by Pearson correlation. Limits of agreement between measurements were calculated and defined as the mean difference ± 2 standard deviation (SD) of the difference.
Mean EVP in proximal segments (7.9 ± 3 mmHg; ± SD) was not different from mean EVP in distal segments (8.0 ± 2.8 mmHg; p= 0.72). EVP in the two segments were correlated (r=0.98, p<0.001, n=10) and limits of agreement were -1.4 to 1.2 mmHg. Mean EVP in the two adjacent vessels of the same field (6.9 ± 2.4 mmHg and 6.6 ± 2.2 mmHg) were not different from each other (p=0.16). EVP in the two vessels were correlated (r=0.98, p<0.001, n=10) and limits of agreement were -0.7 to 1.2 mmHg. Mean EVP was 6.0 ± 2.3 mmHg and 6.1 ± 2.3 mmHg in the first and second measurement sessions respectively (p=0.79) and were correlated (r=0.96, p<0.001, n=17), and limits of agreement between these measurements were -1.4 to 1.3 mmHg.
EVP measurements are consistent between different segments along the same vein and between different veins in the same field. Repeated measurements of EVP within the same eye separated by 2-4 hours are also consistent to within less than 1.5 mmHg.
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