Primary open angle glaucoma (POAG) is associated with inadequate drainage of the aqueous humor via the trabecular meshwork towards the systemic circulation. This may lead to an increase in IOP and may damage the optic nerve. The purpose of glaucoma management is to lower IOP in order to prevent progression of the optic neuropathy and subsequent visual loss. Firstline treatment usually includes IOP-lowering drug therapy. However, if IOP remains uncontrolled and/or the optic nerve damage progresses despite controlled IOP, surgery may be indicated. Deep sclerectomy with a collagen implant (DSCI) is a non-penetrating surgical procedure for the treatment of open angle glaucoma that allows the enhancement of the aqueous outflow. This forms the rationale to conduct this prospective, open label study to assess the 24-hour IOP fluctuation profile recorded with Triggerfish® in patients with POAG before and after DSCI.