Circadian Variations in Ocular Blood Flow in Glaucomatous and Normal Eyes

Inclusion Criteria: For the glaucoma patients: * Medical controlled Primary Open Angle Glaucoma with a history of more than 2 years * Topical medication with beta-blockers (timolol, betaxolol, levobunol) * IOP with medication \< 22 mmHg (with a medical history of IOP \> 22 mmHg) * Visual field testing: mild glaucomatous defects (Humphrey 30-2 with MD\>10) * Optic nerve head: C/D-ratio between 0.4 and 0.9 * ametropy \< 3 dpt * Normal findings in the medical history and physical examination unless the investigator considers an abnormality to be clinically irrelevant For the age matched control subjects: * Normal findings in the medical history and physical examination unless the investigator considers an abnormality to be clinically irrelevant * Normal laboratory values unless the investigator considers an abnormality to be clinically irrelevant * Normal ophthalmic findings, ametropy \< 3 dpt. Exclusion Criteria: For the glaucoma patients: * History of trabeculectomy or laser trabeculoplasty * Any other ocular disease with possible vascular involvement such as diabetic retinopathy, age related macular disease, retinal vein or artery occlusion. * Uncontrolled systemic hypertension (defined as systolic blood pressure \> 170 mmHg or diastolic blood pressure \> 100 mmHg) * Diabetes mellitus For the age matched control subjects: * abuse of alcoholic beverages, 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 * History or presence of gastrointestinal, liver or kidney disease * Ametropy \> 3 dpt