The present study aims to investigate whether FLIO can also detect shorttime changes in retinal metabolism induced by hyperoxia and hypoxia. For this purpose, 48 healthy subjects will be included in the present study and changes in FLIO will be assessed during breathing of 100% oxygen to induce hyperoxia as well as during breathing of 12% oxygen in nitrogen to induce hypoxia. Since stimulation with flickering light also induces a higher metabolic demand in the retina (functional hyperemia), thisprovocation test will also applied during breathing of the different gas mixtures and compared to baseline. To gain information about retinal blood flow, optical coherence tomography angiography (OCT-A) will be performed. The results of the present study can help to gain more insight into the physiology of the retinal metabolism and might give grounds to establish new biomarkers in future studies.

Inclusion Criteria:

• Men and women aged between 18 and 35 years

  • Normal ophthalmic findings
  • Ametropia ≤ 6 diopters
  • Normal findings in the medical history and physical examination including ECG unless the investigator considers an abnormality to be clinically irrelevant
  • Nonsmokers

Exclusion Criteria:

Regular use of medication, abuse of alcoholic beverages or drugs

• Participation in a clinical trial in the 3 weeks preceding the study
• Treatment in the previous 3 weeks with any drug (except contraceptives)
• Symptoms of a clinically relevant illness in the 3 weeks before the first study day
• Blood donation during the previous 3 weeks
• History or family history of epilepsy
• Pregnant or breast-feeding women
• Women of childbearing potential (neither menopausal, nor hysterectomized, nor sterilized) not using effective contraception