Age-related macular degeneration (AMD) and glaucoma are among the leading causes of blindness in the western world. Elevated intraocular pressure (IOP) is a well known major risk factor for glaucoma. In addition, there is growing evidence that vascular factors, including arterial hypertension and hypotension, may play a role in the pathogenesis of AMD and glaucoma. To gain more insight into these mechanisms in humans is the primary goal of the present study.

Optical coherence tomography (OCT) delivers three dimensional, volumetric reflectivity information through transparent media in vivo. Moreover, the images show a high choroidal penetration and a resolution comparable to an histologic examination when infrared light sources are used. Because of its non-invasive character, OCT provides an ideal method for diagnosis and monitoring of retinal and choroidal abnormalities.

The present study aims to investigate whether choroidal thickness is temporarily altered by changes in IOP or systemic hemodynamic parameters. IOP will be increased by the use of a suction cup technique, mean arterial blood pressure will be altered by intravenously administered Phenylephrine or Sodium-Nitroprusside.

Inclusion Criteria:

• Men and women aged between 18 and 35 years, nonsmokers
• Men and women will be included in equal parts
• Normal findings in the medical history and physical examination unless the investigator considers an abnormality to be clinically irrelevant
• Normal findings in the laboratory testings unless the investigator considers an abnormality to be clinically irrelevant
• Normal ophthalmic findings, ametropia less than 1 diopter

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 (except oral contraceptives)
• Symptoms of a clinically relevant illness in the 3 weeks before the first study day
• Blood donation during the previous 3 weeks History of hypersensitivity to the trial drugs 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
• History of migraine
• Pregnancy