Ocular Physiology, Regional Blood Flow
Conditions
Keywords
vitamin C, retinal blood flow, intraocular pressure, retinal vessel diameter
Brief summary
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.
Interventions
DIETARY_SUPPLEMENTvitamin C (Mayrhofer) 24mg/min i.v. for 64 min
Substance: Ascorbic acid (Mayrhofer) Manufacturer: Mayrhofer, Linz, Austria Dosage form: i.v. Dosage: 24mg/min over 64 min Dosage reference: Ting HH 1996
DIETARY_SUPPLEMENTPlacebo
Substance: Physiologic saline solution 0.9% (placebo) Dosage form: i.v. Dosage: 24ml/min over 64 min
OTHER100% O2 (AGA) two times for 12 min
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
Sponsors
Medical University of Vienna
Study design
Allocation
RANDOMIZED
Intervention model
CROSSOVER
Primary purpose
DIAGNOSTIC
Masking
DOUBLE (Subject, Investigator)
Eligibility
Sex/Gender
MALE
Age
19 Years to 35 Years
Healthy volunteers
Yes
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
Design outcomes
Primary
| Measure | 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 |
Countries
Austria
Outcome results
None listed