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N. S. Ekdawi, A. Sit; Computerized Measurement of Episcleral Venous Pressure. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2844.
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Episcleral venous pressure (EVP) is an important determinant of intraocular pressure (IOP). Understanding how it is regulated is critical in understanding IOP regulation and the mechanisms of action of glaucoma medications. Existing methods to measure EVP compress an episcleral vein and estimate the pressure when an arbitrary amount of blanching has occurred. However, this method is unreliable due to lack of a definitive endpoint. The purpose of this project was to develop a more precise, reproducible method for EVP measurement using a modified venomanometer.
A commercially available Episcleral Venomanometer (EyeTech Ltd, Morton Grove, IL) was modified to include video capture to allow post-hoc assessment of the exact time that the vessel diameter was compressed to 10% and 50% of baseline diameter. This was referenced to a time-stamped simultaneous pressure recorded by a transducer. Healthy volunteers aged 18-90 years were recruited from employees and students at the Mayo Clinic (Rochester, MN) and the local area. Mean EVP measured in 4 quadrants (supertemporal, infratemporal, supranasal, and inferonasal) in each eye was calculated. IOP was measured using Goldmann tonometry.
Ten eyes from 5 subjects (2 females, 3 males) were included in the study. Average age of the subjects was 28 years (range 21 to 35 years). The mean IOP was 12 ± 2.6 mmHg (mean ± SD), and no subject had the diagnosis of glaucoma. The average EVP was found to be 5.2 ± 0.32 mmHg (mean ± SD) at 10% and 9.3 ± 1.08 mmHg (mean ± SD) at 50% compression.
Our modified EVP measurement system allowed us to precisely measure the EVP in a small sample of normal subjects, with standard deviation was less than published values for a similar age group. This system will be useful for the assessment of changes in EVP resulting from disease states and glaucoma therapies.
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