The study protocol was approved by the Ethics Committee of the Medical University of Vienna and followed the guidelines set forth in the Declaration of Helsinki. A total of 43 healthy male subjects between 18 and 35 years, who signed written informed consent, was included. Before entering the study all subjects had to pass a screening examination that included physical examination, 12-lead electrocardiogram, hematological status (hemoglobin, hematocrit, red blood cell [RBC], mean cell hemoglobin [MCH], white blood cell [WBC], platelet count, activated partial thromboplastin time [APTT], and thrombin time), clinical chemistry (sodium, potassium, creatinine, glutamate pyruvate transferase [GPT], alanine aminotransferase [ALAT], γ-glytamyl transferase [γ-GT], total bilirubin, total protein), hepatitis B and C, and human immunodeficiency virus [HIV] serology, urinalysis (WBC, nitrite, pH, protein, glucose, ketones, urobilinogen, bilirubin, blood/hemoglobin), and a urine drug screening. Subjects were excluded if any abnormal value was found as part of the prestudy screening unless the investigators considered an abnormality to be clinically irrelevant. Other exclusion criteria were clinically relevant illness, blood donation, or intake of any medication, vitamin, or mineral supplement in the 3 weeks before the study. In addition, an eye exam was performed, which consisted of visual acuity, slit-lamp biomicroscopy, funduscopy, and measurement of IOP. Exclusion criteria were ametropia ≥ 3 diopters (D), anisometropia ≥ 3 D, or any signs of eye diseases. All subjects had to abstain from beverages containing alcohol or caffeine for 12 hours before each study day.