The purpose of the investigation is to investigate the relationship between the study device output and tonometric assessments.

60 subjects will be enrolled in total. Enrolled patients will be randomized into one of 8 device groups of 6 subjects each or into the control group containing 12 subjects. Patients in the device arm will receive one session of 3-to 24-hour continuous IOP monitoring with SENSIMED Triggerfish®. SENSIMED Triggerfish® monitoring will begin at 18h ± 2 hours for all patients. SENSIMED Triggerfish® will be installed randomly on right or left eyes. During SENSIMED Triggerfish® monitoring on one eye, GAT and/or Perkins IOP measurements will be taken in the fellow eye every 3 hours. Outside this time they will receive GAT and/or IOP measurements every 3 hours in both eyes until the end of the 24-hours period. Patients in the control group will receive GAT and/or ICare PRO IOP measurements every 3 hours for 24 hours in both eyes.

Inclusion Criteria:

• Signed informed consent for the investigation
• Confirmed diagnosis of primary open angle glaucoma or normal tension glaucoma of similar degree in both eyes
• Age 18-85
• Stable anti-glaucomatous therapy 4 weeks before and throughout the investigation

Exclusion Criteria:

• Patients not able to understand the character and individual consequences of the investigation
• Patients with contraindications for silicone contact lens wear
• Wear of full frame metallic glasses during SENSIMED Triggerfish® monitoring
• Diagnosis of pseudoexfoliation syndrome / pseudoexfoliative glaucoma and of pigment dispersion syndrome / pigmentary glaucoma
• Severe dry eye
• Patients who have had ocular surgery within the last 3 months
• Corneal or conjunctival abnormality or irregularity hindering correct contact lens adaptation
• Allergy to corneal anaesthesia
• Simultaneous participation in other clinical research