Effect of Topical Phenylephrine 2.5% on Episcleral Venous Pressure in Normal Human Eyes

Abstract

Purpose Phenylephrine has been shown to affect intraocular pressure (IOP) but the mechanism of action is poorly understood. However, its action as a vasoconstrictor suggests possible effects on episcleral venous pressure (EVP). In this study, we evaluated the effect of phenylephrine on EVP and IOP in healthy subjects. Methods Forty eyes of 20 subjects were included. Each subject received 3 drops of phenylephrine 2.5% in one eye at 1-minute intervals. The fellow eye served as control. Blood pressure, heart rate, and IOP and EVP of both eyes were measured at baseline, 15 minutes, and 60 minutes after instillation of phenylephrine. IOP was measured by pneumatonometry. EVP was assessed by using a computer-controlled episcleral venomanometer. Changes in IOP, EVP, blood pressure, and heart rate at 15 and 60 minutes were analyzed by paired t -tests. Results IOP increased 15 minutes after instillation of phenylephrine in both treated ( P = 0.001) and control eyes ( P = 0.01) and returned to baseline at 60 minutes. The change in IOP at 15 minutes was not significantly different between the 2 groups. EVP in treated eyes was unchanged at 15 minutes ( P = 0.8) but decreased significantly at 60 minutes ( P < 0.001). In control eyes, there was no change in EVP at any time ( P > 0.6). There were no significant changes from baseline in systolic and diastolic blood pressure and heart rate after instillation of phenylephrine. Conclusions IOP elevation associated with topical phenylephrine is not caused by an increase in EVP in healthy subjects. Instead, EVP decreases with phenylephrine, but the mechanism remains to be determined.

Time‐course characterization of intraocular pressure in murine steroid‐induced ocular hypertension: Effects of route, schedule, and concentration

“…In addition to examining the magnitude and timing of IOP elevations, we evaluated diurnal variation in IOP. Under normal physiological conditions, IOP exhibits diurnal fluctuations, which have been linked not only to endogenous cortisol rhythms but also to changes in aqueous humor production, conventional outflow facility, episcleral venous pressure, autonomic tone, and behavioral factors such as activity and posture 31–34 . Consistent with this, saline‐treated control mice showed a small but significant increase in afternoon IOP compared to morning measurements.…”

Time‐course characterization of intraocular pressure in murine steroid‐induced ocular hypertension: Effects of route, schedule, and concentration

“…In addition to examining the magnitude and timing of IOP elevations, we evaluated diurnal variation in IOP. Under normal physiological conditions, IOP exhibits diurnal fluctuations, which have been linked not only to endogenous cortisol rhythms but also to changes in aqueous humor production, conventional outflow facility, episcleral venous pressure, autonomic tone, and behavioral factors such as activity and posture 31–34 . Consistent with this, saline‐treated control mice showed a small but significant increase in afternoon IOP compared to morning measurements.…”

Delayed Onset Spontaneous Hyphema After an OMNI Surgical Procedure

“…Interestingly, the left eye of our patient had a similar IOP in the mid to high single digits after trabeculectomy but did not develop hyphema. This indicates that IOP in this range is not sufficient for blood reflux, as it is likely near or slightly above the typical EVP level of 6–9 mm Hg 11–13 . Instead, there needs to be an inciting event affecting only one eye, such as compression from a pillow while sleeping in the lateral decubitus position which drops IOP below EVP when the pillow is removed.…”

“…This indicates that IOP in this range is not sufficient for blood reflux, as it is likely near or slightly above the typical EVP level of 6-9 mm Hg. [11][12][13] Instead, there needs to be an inciting event affecting only one eye, such as compression from a pillow while sleeping in the lateral decubitus position which drops IOP below EVP when the pillow is removed. It is also possible that a functioning trabeculectomy bleb allows for rapid clearance of any blood in the anterior chamber, minimizing the chance of symptomatic visual acuity changes.…”

Relationship Between Diurnal Variations of Episcleral Venous Pressure and Intraocular Pressure

“… 67 Topical phenylephrine 2.5% also reduces EVP by approximately 1 mm Hg in normal subjects but does not have a significant effect on IOP. 22 Given the small effect or limited duration of action, current medications do not appear to be suitable options for therapeutic modulation of EVP as a primary mechanism of action. However, novel compounds currently in development may provide options.…”

“…This technique has been used to identify changes in EVP for both investigational and approved drugs. 22 , 23 , 35 In brief, subjects' eyes were anesthetized with one to two drops of proparacaine. A clear flexible bulb was placed against an episcleral vein (same vessel utilized for all measurements), visualized through a slit-lamp biomicroscope as vessels with a straighter profile and located deeper than conjunctival vessels ( Fig.…”

Time‐course characterization of intraocular pressure in murine steroid‐induced ocular hypertension: Effects of route, schedule, and concentration

“…In addition to examining the magnitude and timing of IOP elevations, we evaluated diurnal variation in IOP. Under normal physiological conditions, IOP exhibits diurnal fluctuations, which have been linked not only to endogenous cortisol rhythms but also to changes in aqueous humor production, conventional outflow facility, episcleral venous pressure, autonomic tone, and behavioral factors such as activity and posture 31–34 . Consistent with this, saline‐treated control mice showed a small but significant increase in afternoon IOP compared to morning measurements.…”

Delayed Onset Spontaneous Hyphema After an OMNI Surgical Procedure

“…Interestingly, the left eye of our patient had a similar IOP in the mid to high single digits after trabeculectomy but did not develop hyphema. This indicates that IOP in this range is not sufficient for blood reflux, as it is likely near or slightly above the typical EVP level of 6–9 mm Hg 11–13 . Instead, there needs to be an inciting event affecting only one eye, such as compression from a pillow while sleeping in the lateral decubitus position which drops IOP below EVP when the pillow is removed.…”

“…This indicates that IOP in this range is not sufficient for blood reflux, as it is likely near or slightly above the typical EVP level of 6-9 mm Hg. [11][12][13] Instead, there needs to be an inciting event affecting only one eye, such as compression from a pillow while sleeping in the lateral decubitus position which drops IOP below EVP when the pillow is removed. It is also possible that a functioning trabeculectomy bleb allows for rapid clearance of any blood in the anterior chamber, minimizing the chance of symptomatic visual acuity changes.…”

Relationship Between Diurnal Variations of Episcleral Venous Pressure and Intraocular Pressure

“… 67 Topical phenylephrine 2.5% also reduces EVP by approximately 1 mm Hg in normal subjects but does not have a significant effect on IOP. 22 Given the small effect or limited duration of action, current medications do not appear to be suitable options for therapeutic modulation of EVP as a primary mechanism of action. However, novel compounds currently in development may provide options.…”

“…This technique has been used to identify changes in EVP for both investigational and approved drugs. 22 , 23 , 35 In brief, subjects' eyes were anesthetized with one to two drops of proparacaine. A clear flexible bulb was placed against an episcleral vein (same vessel utilized for all measurements), visualized through a slit-lamp biomicroscope as vessels with a straighter profile and located deeper than conjunctival vessels ( Fig.…”

Time‐course characterization of intraocular pressure in murine steroid‐induced ocular hypertension: Effects of route, schedule, and concentration

“…In addition to examining the magnitude and timing of IOP elevations, we evaluated diurnal variation in IOP. Under normal physiological conditions, IOP exhibits diurnal fluctuations, which have been linked not only to endogenous cortisol rhythms but also to changes in aqueous humor production, conventional outflow facility, episcleral venous pressure, autonomic tone, and behavioral factors such as activity and posture 31–34 . Consistent with this, saline‐treated control mice showed a small but significant increase in afternoon IOP compared to morning measurements.…”

Delayed Onset Spontaneous Hyphema After an OMNI Surgical Procedure

“…Interestingly, the left eye of our patient had a similar IOP in the mid to high single digits after trabeculectomy but did not develop hyphema. This indicates that IOP in this range is not sufficient for blood reflux, as it is likely near or slightly above the typical EVP level of 6–9 mm Hg 11–13 . Instead, there needs to be an inciting event affecting only one eye, such as compression from a pillow while sleeping in the lateral decubitus position which drops IOP below EVP when the pillow is removed.…”

“…This indicates that IOP in this range is not sufficient for blood reflux, as it is likely near or slightly above the typical EVP level of 6-9 mm Hg. [11][12][13] Instead, there needs to be an inciting event affecting only one eye, such as compression from a pillow while sleeping in the lateral decubitus position which drops IOP below EVP when the pillow is removed. It is also possible that a functioning trabeculectomy bleb allows for rapid clearance of any blood in the anterior chamber, minimizing the chance of symptomatic visual acuity changes.…”

Relationship Between Diurnal Variations of Episcleral Venous Pressure and Intraocular Pressure

“… 67 Topical phenylephrine 2.5% also reduces EVP by approximately 1 mm Hg in normal subjects but does not have a significant effect on IOP. 22 Given the small effect or limited duration of action, current medications do not appear to be suitable options for therapeutic modulation of EVP as a primary mechanism of action. However, novel compounds currently in development may provide options.…”

“…This technique has been used to identify changes in EVP for both investigational and approved drugs. 22 , 23 , 35 In brief, subjects' eyes were anesthetized with one to two drops of proparacaine. A clear flexible bulb was placed against an episcleral vein (same vessel utilized for all measurements), visualized through a slit-lamp biomicroscope as vessels with a straighter profile and located deeper than conjunctival vessels ( Fig.…”