The hypothesis is that the pressure in the retinal veins increases from chronic lack of oxygen and leads to decreased blood flow. On the basis of high altitude mountaineering this hypothesis should be verified. At the same time the adaptation capacity of the blood circulation should be analyzed, and a relationship to mountain sickness should be found.

Conduct a field study to describe and quantify the retinal venous pressure (RVP) in healthy volunteers under conditions of controlled chronically reduced ambient pressure and oxygen partial pressure in the mountains. Obtaining indications regarding the adaptation of the retinal vascular system behavior to controlled, long-term hypoxic changes. Comparisons with blood pressure, pulse, oxygen saturation level and the appearance of symptoms of acute mountain sickness are made in order to obtain a better understanding of the development of high altitude illness.

Inclusion Criteria:

• healthy

Exclusion Criteria:

• eye diseases
• systemic diseases
• term medication (except contraceptives)
• pregnancy
• allergies to the ingredients Alcain, Tropicamide and Phenylephrine

healthy volunteers