Adequate perfusion and oxygenation is essential for the function of the inner retina. Although it is known that oxygen tension is very well autoregulated in the retina, the physiological mechanisms behind this regulation process are not fully explored. The development of new instruments for the non-invasive measurement of oxygen tension in retinal vessels now allows for the more precise investigation of these physiological processes. The current study seeks to evaluate the retinal oxygen saturation in healthy subjects while breathing different oxygen mixtures to achieve a hypoxic and a hyperoxic state.

Inclusion Criteria:

• Men and women aged between 18 and 35 years
• Nonsmokers
• 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, ametropy < 3 Dpt.

Exclusion Criteria:

• Regular use of medication, abuse of alcoholic beverages, participation in a clinical trial in the 3 weeks preceding the study (except oral contraceptive)
• Symptoms of a clinically relevant illness in the 3 weeks before the first study day
• Presence of any form of anemia
• Blood donation during the previous 3 weeks
• Pregnancy