Effect of Topical Phenylephrine 2.5% on EVP in Normal Human Eyes

Study Overview
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Brief Summary
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Phenylephrine hydrochloride ophthalmic solution is an alpha-1 adrenergic receptor agonist commonly used topically for dilation prior to ocular fundus examination. In the eye, phenylephrine acts locally as a potent vasoconstrictor and mydriatic by constricting ophthalmic blood vessels and the radial dilator muscle of the iris. Episcleral venous pressure (EVP) is a determinant of intraocular pressure (IOP) and can be measured non-invasively by venomanometry. Since phenylephrine is a vasoconstrictor, it may affect episcleral venous tone, but the effect on EVP is unknown. Understanding the physiology of episcleral veins helps us in better understanding of pathophysiology of glaucoma.

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

Conditions
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Assess Phenylephrine on EVP and IOP

Intervention / Treatment
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* Drug: Phenylephrine 2.5%


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Any self-declared ethno-racial category. Medically healthy subjects. Subjects with two healthy eyes. Intraocular pressure (IOP) less than 22 mmHg in each eye. Best-corrected visual acuity (BCVA) in each eye 20/50 or better. Open angles in both eyes. Contact lens wear stopped at least 3 days prior to study, and during the study. Ability to cooperate for examinations required for study. Exclusion Criteria: Chronic or acute ophthalmic diseases including glaucoma, wet type macular degeneration, uveitis and clinically significant cataract. Evidence of ocular infection, inflammation, clinically significant blepharitis or conjunctivitis. Cornea pathologic changes preventing reliable measurement. Narrow anterior chamber angle. Previous intraocular surgeries, laser procedures, and intravitreal injections. Previous corneal refractive surgeries. Myopia greater than -6.00 D spherical equivalent. Hyperopia greater than +2.00 D spherical equivalent. Lack of suitable episcleral vein for measurement. Ocular trauma within the past 6 months. Ocular infection or ocular inflammation in the past 3 months. Ocular medication of any kind within 30 days of study visit. Known hypersensitivity to Phenylephrine or topical anesthetic medication. Severe hypertension: Systolic blood pressure greater than 180 mmHg and/or diastolic blood pressure greater than 105 mmHg. A known history of ischemic heart disease (angina or myocardial infarction), cerebrovascular accidents, cardiac arrhythmias, cerebral or aortic aneurysms. Uncontrolled diabetes mellitus. Uncontrolled hyperthyroidism. Use of some systemic medications within 30 days prior to study including: β-adrenergic antagonists, α-adrenergic agonists and antagonists, calcium channel blockers, diuretics, vasodilators, monoamine oxidase inhibitors, and systemic steroids. Participation in any interventional study within the past 30 days prior to study visit. Women who are pregnant.

Ages Eligible for Study
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Minimum Age: 18 Years

Sexes Eligible for Study
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All

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Intervention Model: Single Group Assignment
Masking: None (Open Label)


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: Phenylephrine<br>Subjects will receive topical phenylephrine 2.5% eye drop instilled in one eye after all baseline measurements. | Drug: Phenylephrine 2.5%<br>* Instilling phenylephrine 2.5% eye drop<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in Episcleral Venous Pressure (EVP) | EVP will be measured non-invasively using a custom-modified slit-lamp mounted venomanometer. This device utilizes the pressure chamber technique, in which a clear flexible balloon is placed against the conjunctival surface of the eye, and the pressure is increased until an episcleral vein is noted to blanch. The system for pressure-chamber based venomanometry includes a computer-controlled motor drive to increase pressure automatically, a transducer to record pressure, and a high-definition video camera to record vein collapse. Pressure measurements are synchronized with the video stream and image analysis software is used to determine the pressure required to collapse the vein to a specific pre-determined degree as measured in mmHg. | baseline, 60 minutes | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in Intraocular Pressure (IOP) | Intraocular pressure will be measured in mmHg after topical anesthesia by using the pneumatonometer. There will be a minimum of three IOP measurements and a mean will be accepted as IOP. | baseline, 60 minutes |