Determine the Effect of Intraocular Pressure (IOP), Optic Nerve Imaging, Venous Congestion in Volunteers Prone Position 5 Hours

Study Overview
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Brief Summary
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The purpose of this study is to provide data that would give the investigators a better understanding of the physiologic changes that occur and may contribute to post operative blindness. An improved understanding may lead to the development of protocols or devices that reduce the chance of catastrophic visual loss.

Detailed Description
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Post operative vision loss resulting from nonocular surgery is a devastating, poorly understood and potentially preventable complication. Ischemic optic neuropathy, affecting both the anterior or posterioir portions of the optic nerve, is the most common cause of postoperative vision loss(POVL). Other, less common causes include retinal artery occlusion, retinal vein occlusion, retinal embolism, and cortical blindness. The estimated incidence of POVL in patients undergoing general anesthesia is 1/60,000. The incidence dramatically increases in cardiopulmonary bypass and prone spine surgery with estimates at 1/1600 and 1/1100, respectively. The etiology is unknown but it is thought to be multifactorial, and several potential risk factors have been identified, including degree of hypotension, preoperative hematocrit, external compression of the eye, blood loss and prone position. The investigators are proposing eight volunteers in two different sessions of 5.5 hours each. The first session the volunteer will lie prone of the flat Jackson table and the second session the volunteer will spend 5 hours prone on the Jackson table with a table elevation of 6 inches. The following measurements will be done: Intraocular Pressure (IOP) with a device called the Tonopen-XL, the Nidex NM 200 to visualize the retinal optic nerve imaging, refractometry, ultrasound, corneal thickness pachymetry, measurement of proptosis, measurement of pupillary reflex, The volunteers do not receive anesthetic medications or intravenous fluids and will provide a baseline for comparision with patients enrolled in the prospective study.

Official Title
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A Pilot Study to Determine the Effect on Intraocular Pressure, Optic Nerve Imaging and Other Markers of Venous Congestion of Volunteer Subjects in the Prone Position for a Period of Five Hours

Conditions
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Blindness

Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: subjects willing to consent Exclusion Criteria: individuals unable to tolerate prone position for 5 hours individuals unable to tolerate contact lens placement females who are pregnant individuals with a sensitivity to proparacaine hcl 0.5% or tropicamide 1% individuals who are unable to have repeated mesaurements of intaocular pressure

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 65 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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Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| 1. flat Jackson table<br>All measurements previously described will be done with the patient in the prone postion and Jackson table flat. | |
| 2. Elevated Jackson tablet<br>All measurements previously described will be performed with subjects placed prone on the elevated Jackson table. | |

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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ischemic optic neuropathy, cortical blindness