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Arash Kazemi, Arthur J Sit, Sasha A Mansukhani; Effect of Topical Phenylephrine 2.5% on Episcleral Venous Pressure in Normal Human Eyes. Invest. Ophthalmol. Vis. Sci. 2018;59(9):1237.
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Phenylephrine eye drops are commonly used for mydriasis prior to intraocular surgery or fundus examination. They have been shown to elevate intraocular pressure (IOP), but the mechanism of action is poorly understood. As well, as a vasoconstrictor, it may affect episcleral venous tone, but the effect on episcleral venous pressure (EVP) is unknown. In this study we evaluated the effect of topical phenylephrine 2.5% on EVP and IOP in normal subjects.
Twenty eyes from 10 normal subjects (5 males, 5 females; 33 ± 13 years, mean ± SD) were included in the study. Each subject received 3 drops of phenylephrine 2.5% in one eye at 1 minute intervals. The fellow eye served as control. Blood pressure, pulse rate, IOP and EVP of both eyes were measured at baseline, 15 minutes and 60 minutes after instillation of phenylephrine. Systolic and diastolic blood pressures (SBP and DBP), and pulse rate (PR) were determined by a digital monitor. IOP was measured by pneumatonometry. EVP was assessed by using a computer-controlled episcleral venomanometer with video recording and processing to determine the pressure required to initiate collapse of the vein. Changes in IOP, EVP, systolic and diastolic blood pressures, and pulse rate at 15 and 60 minutes were analyzed by two-sample t-tests.
IOP in treated eyes increased 15 minutes after instillation of phenylephrine (P = 0.02, Table) but then decreased close to its baseline level at 60 minutes. There was no significant change in IOP in control eyes at either 15 minutes or 60 minutes. EVP in treated eyes decreased significantly at 60 minutes (P = 0.01) but the change at 15 minutes was not significant (P = 0.3). In control eyes, there was no significant change in EVP at any time point. Also there were no significant changes in systolic and diastolic blood pressures and pulse rate after instillation of phenylephrine compared to baseline (Table).
IOP elevation associated with topical phenylephrine is not due to an increase in EVP in normal subjects. Instead, there is a decrease in EVP, potentially due to vasoconstriction. Future studies are required to identify the mechanism for IOP elevation, and investigate the effect of phenylephrine on IOP and EVP in glaucoma suspects and patients.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
Table. Comparison of IOP, EVP, Blood pressure and pulse rate at 15 and 60 minutes of instillation of phenylephrine 2.5% with baseline in treated and control eyes
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