Effects of Vitamin C on Hyperoxia-Induced Reduction of Retinal Blood Flow

Study Overview
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Brief Summary
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High arterial blood oxygen tension leads to vasoconstriction of retinal vessels, possibly related to an interaction between reactive oxygen species and endothelium-derived vasoactive factors. Vitamin C is a potent antioxidant capable of reversing endothelial dysfunction due to increased oxidant stress. Vitamin C appears to have vasodilatory properties, but the underlying mechanisms are not well understood. In the present study we hypothesized that hyperoxic vasoconstriction of retinal vessels could be diminished by vitamin C. Ocular blood flow will be determined by non-invasive methods, including laser Doppler velocimetry and the Zeiss retinal vessel analyser.

Official Title
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Effects of Vitamin C on Hyperoxia-Induced Reduction of Retinal Blood Flow

Conditions
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Ocular Physiology, Regional Blood Flow

Intervention / Treatment
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* Dietary Supplement: vitamin C (Mayrhofer) 24mg/min i.v. for 64 min
* Dietary Supplement: Placebo
* Other: 100% O2 (AGA) two times for 12 min


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Men aged between 19 and 35 years, nonsmokers Body mass index between 15th and 85th percentile (Must A 1991) Normal findings in the medical history and physical examination unless the investigator considers an abnormality to be clinically irrelevant Normal laboratory values unless the investigator considers an abnormality to be clinically irrelevant Normal ophthalmic findings, ametropia < 3 Dpt. Exclusion Criteria: Regular use of medication, abuse of alcoholic beverages, participation in a clinical trial in the 3 weeks preceding the study Treatment in the previous 3 weeks with any drug Symptoms of a clinically relevant illness in the 3 weeks before the first study day History of hypersensitivity to the trial drug or to drugs with a similar chemical structure History or presence of gastrointestinal, liver or kidney disease, or other conditions known to interfere with, distribution, metabolism or excretion of study drugs Blood donation during the previous 3 weeks

Ages Eligible for Study
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Minimum Age: 19 Years
Maximum Age: 35 Years

Sexes Eligible for Study
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Male

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: Diagnostic
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Double


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: 1<br>vitamin C (Mayrhofer) | Dietary Supplement: vitamin C (Mayrhofer) 24mg/min i.v. for 64 min<br>* Substance: Ascorbic acid (Mayrhofer) Manufacturer: Mayrhofer, Linz, Austria Dosage form: i.v. Dosage: 24mg/min over 64 min Dosage reference: Ting HH 1996<br>Other: 100% O2 (AGA) two times for 12 min<br>* Substance: 100% oxygen (AGA, Vienna, Austria, gases for human use) Manufacturer: AGA, Vienna, Austria, gases for human use Dosage form: Inhalation through an oxygenmask over a period of 12 minutes two times per study day. Dosage reference: Strenn K 1997<br>|
| Placebo Comparator: 2<br>Placebo | Dietary Supplement: Placebo<br>* Substance: Physiologic saline solution 0.9% (placebo) Dosage form: i.v. Dosage: 24ml/min over 64 min<br>Other: 100% O2 (AGA) two times for 12 min<br>* Substance: 100% oxygen (AGA, Vienna, Austria, gases for human use) Manufacturer: AGA, Vienna, Austria, gases for human use Dosage form: Inhalation through an oxygenmask over a period of 12 minutes two times per study day. Dosage reference: Strenn K 1997<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Retinal arterial and venous diameter (Zeiss retinal vessel analyzer) |  | in total 6 hours | 
| Retinal blood flow velocity (laser Doppler velocimetry) |  | in total 6 hours | 
| Intraocular pressure (applanation tonometry) |  | in total 10 minutes | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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vitamin C, retinal blood flow, intraocular pressure, retinal vessel diameter