The Response of Intraocular Pressure to Systemic Hypercapnia and Hyperoxia

Study Overview
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Brief Summary
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The purpose of this study is to determine how intraocular pressure responds to changes in the levels of carbon dioxide or oxygen that a healthy individual inspires.

Detailed Description
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In response to changes in the composition of inhaled gases, blood vessels will dilate or constrict. As a result, hypercapnia or hyperoxia may affect the production and drainage of aqueous humour in the anterior chamber of the eye. The balance between the production and drainage of the aqueous humour determines the intraocular pressure. As this system is hydrodynamic, it is expected that any increase or decrease in the production of aqueous humour due to dilation or constriction of the capillaries within the ciliary body will be compensated by increased or decreased drainage at the trabecular meshwork. Therefore intraocular pressure is not expected to show a response to hypercapnia or hyperoxia, but this supposition needs to be tested in a stably controlled manner of inducing inhaled gas provocations. This study will measure the intraocular pressure at varying levels of hypercapnia and hyperoxia using a sequential rebreathing circuit and automated gas blender. This will allow the precise targeting and stable control of end-tidal partial pressure values of carbon dioxide and oxygen. In this study, intraocular pressure will be measured at seven different inhaled gas stages. The seven stages are as follows: Baseline, measured in eye A (PETCO2=38mmHg and PETO2=100mmHg) 10% hypercapnic increase, measured in eye A (PETCO2=42mmHg and PETO2=100mmHg) 20% hypercapnic increase, measured in eye A (PETCO2=46mmHg and PETO2=100mmHg) Baseline, measured in both eyes (PETCO2=38mmHg and PETO2=100mmHg) 250% hyperoxic increase, measured in eye B (PETCO2=38mmHg and PETO2=250mmHg) 500% hyperoxic increase, measured in eye B (PETCO2=38mmHg and PETO2=500mmHg) Baseline, measured in eye B (PETCO2=38mmHg and PETO2=100mmHg)

Official Title
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The Response of Intraocular Pressure to Systemic Hypercapnia and Hyperoxia

Conditions
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Intraocular Pressure

Intervention / Treatment
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* Device: RespirAct


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Age range 18-30 years old Visual acuity of 20/20 or better Exclusion Criteria: Refractive error >±6.00 DS and/or ± 2.00 DC History or presence of ocular disease Family history of diabetes or glaucoma History of intraocular or refractive surgery Nursing or pregnant women History of clinically diagnosed endocrine disease History of vascular disease, cardiovascular disease, or any treated respiratory disorders (seasonal asthma excluded from this so long as subject not taking Rx at the time) History of systemic hypertension Habitual smoking Use of medications that affect blood flow

Ages Eligible for Study
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Minimum Age: 18 Years
Maximum Age: 30 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

| Intervention/Treatment |
| --- |
|Device: RespirAct|Participants will breathe through a mask connected to a sequential rebreathing circuit and gas blender. The following seven gas stages will be targeted for about 10 minutes each: Baseline, measured in eye A (PETCO2=38mmHg and PETO2=100mmHg) 10% hypercapnic increase, measured in eye A (PETCO2=42mmHg and PETO2=100mmHg) 20% hypercapnic increase, measured in eye A (PETCO2=46mmHg and PETO2=100mmHg) Baseline, measured in both eyes (PETCO2=38mmHg and PETO2=100mmHg) 250% hyperoxic increase, measured in eye B (PETCO2=38mmHg and PETO2=250mmHg) 500% hyperoxic increase, measured in eye B (PETCO2=38mmHg and PETO2=500mmHg) Baseline, measured in eye B (PETCO2=38mmHg and PETO2=100mmHg)|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Intraocular pressure | Intraocular pressure will be measured using Goldmann applanation tonometry. | Intraocular pressure will be measured during the study visit, ten minutes into each of the seven inhaled gas provocation stages | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Retinal blood flow | Retinal blood flow will be measured using the Canon Laser Blood Flowmeter in a subset of participants asked to return for a second visit. This will demonstrate that retinal blood flow behaves as the study claims that it does. | Retinal blood flow will be measured during the second (optional) study visit, ten minutes into each of the seven inhaled gas provocation stages | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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Intraocular pressure, Hypercapnia, Hyperoxia, Rebreathing circuit