The aim of the study is to investigate pressure lowering effect of two surgical methods canaloplasty and trabeculectomy in patients with open angle glaucoma, in which under local pressure lowering therapy the progression of the disease could not be stopped, and thus a pressure lowering surgical intervention is necessary. The risks in the postoperative course in Canaloplasty in the literature as lower than for the trabeculectomy with mitomycin-C. Conversely, large glaucoma centers questioning the effectiveness of permanent pressure lowering of canaloplasty. Precisely this question is investigated in the study.

Inclusion Criteria:

• patients with open angle glaucoma and excavation of 0.4 - 0.8
• 60 eyes of 60 patients (30 patients for trabeculectomy, 30 patients for Canaloplasty) The ratio of female / male is not involved.
• Eye pressure under local therapy: 20mmHg and above (corrected with pachymetry table).
• Local drug therapy: at least 2 eye pressure lowering ingredients or absolute intolerance to preservatives or eye drops.
• general anesthesia possible.
• The operation must be signed by the surgeon as a state-of-the-art performed without complication to be evaluated. If the operation does not meet this criterion, the patient is excluded from the study.

Exclusion Criteria:

• all patients are not included in the group of inclusion criteria, or:
• Phenprocoumon therapy.
• operation is not done state-of-the-art.
• after the surgery: additional eye pressure lowering surgery, cataract surgery, keratoplasty, laser surgery in the anterior eye segment (except suture lysis after trabeculectomy)
• Uveitis, or possible inflammation of the eye
• Previous eye pressure lowering operations or laser interventions
• Corneal Refractive Surgery (pseudophakia allowed)