It has been found that several systemic and ocular diseases are associated with impaired retinal oxygen extraction. In the present study, retinal oxygen extraction will be measured in different age groups in order to identify age related changes in otherwise healthy subjects. In addition, the study will explore short-term changes in retinal metabolism induced by breathing pure oxygen. Measurements will be performed with dynamic vessel analyzer and laser speckle flowgraphy to evaluate retinal blood flow and retinal oxygen saturation, in order to calculate retinal oxygen extraction.

Inclusion Criteria:

• Men and women aged between 18 and 80 years
• Signed informed consent
• Normal ophthalmic findings, unless the investigator considers an abnormality to be clinically irrelevant for the purpose of the study
• Normal findings in the medical history, unless the investigator considers an abnormality to be clinically irrelevant for the purpose of the study
• Nonsmokers

Exclusion Criteria:

• Abuse of alcoholic beverages or drugs
• Participation in a clinical trial in the 3 weeks preceding the study
• Symptoms of a clinically relevant illness in the 3 weeks before the first study day
• Blood donation during the previous 3 weeks
• Pregnant or breast-feeding women