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Nitika Arora, Jay McLaren, Arthur J Sit; Repeatability of Episcleral Venous Pressure Measured at Different Speeds. Invest. Ophthalmol. Vis. Sci. 2016;57(12):4600. doi: https://doi.org/.
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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 estimated by using automated venomanometry. A clear flexible membrane is placed over an episcleral vein, the pressure behind the membrane is increased linearly, and the pressure required to initiate collapse of the vein is recorded. Accurate assessment of venous pressure requires that the method not affect EVP. In this study, we assessed the effect of the rate of pressure increase on the measured EVP.
EVP was measured in 16 normal eyes of 9 participants by using a computer controlled venomanometer. A clear flexible membrane was placed against the surface of an episcleral vein and images of the vein were recorded at 30 frames/sec as the pressure behind the membrane was increased linearly from 0 to 22 mmHg. The pressure associated with the initiation of venous collapse was determined from the images and assumed to be equal to EVP. Each vein was measured twice, as the pressure was increased at 6.1 mmHg/sec (fast), 4.6 mmHg/sec (medium) and 3.1 mmHg/sec (slow). Differences in the estimate of EVP at each speed were examined by using paired t-tests and relationships between EVP measured at different speeds were examined 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 was 8.5 ± 2.8 mmHg (mean ± SD), 8.0 ± 1.9 mmHg and 7.6 ± 2.0 mmHg at fast, medium, and slow speeds respectively. EVP calculated at each speed was not significantly different from those calculated at other speeds (p≥0.17).Limits of agreement and minimum detectable differences (α=0.05, 1-β=0.8) for each comparison are listed in Table 1.
EVP measurements in the same vein are consistent between different speeds of measurement. This suggests that rate of pressure increase in venomanometry does not affect EVP. If venomanometry does affect EVP, it does so on a timescale longer than the time required for our measurements.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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