Rationale: Glaucoma is a group of diseases characterized by progressive neuropathy of the optic nerve associated with visual field loss. Current glaucoma management aims to preserve visual function throughout life by reducing the intraocular pressure. This can be achieved by medical therapy or by surgical procedures such as implantation of a glaucoma drainage device (GDD). Conventionally, the tube of such a device is positioned in the anterior chamber (AC). Unfortunately, the presence of the tube in the AC may have a significant negative impact on the number of endothelial cells of the cornea and may even lead to corneal decompensation. Alternatively, the tube can be positioned in the posterior chamber (i.e. behind the iris). In this study, both procedures will be compared.

Objective: Primary: to determine the loss of corneal endothelial cells after implantation of a Paul GDD with its tube either anterior or posterior of the iris. Secondary: to compare efficacy and safety of both procedures.

Study design: Prospective, randomised, treatment controlled clinical trial. Study population: Pseudophakic patients with glaucoma who need a GDD. Intervention: Implantation of a Paul GDD with its tube anterior/posterior of the iris. Main study parameters/endpoints: Endothelial cell loss of the cornea.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: At present potential benefits and drawbacks of positioning the Paul tube behind the iris are insufficiently known, successful positioning of the tube may require slightly more surgery time and the risk of hyphaema may be higher. It is expected, that in the long run damage to the corneal endothelium is less. Risks of study-related assessments are negligible, burden is low, extra time is about 35+15+35+35 minutes (total 2h).

Inclusion Criteria:

• Age > 18 years
• Informed consent
• Pseudophakic
• Open angle glaucoma, pseudoexfoliation glaucoma, pigment dispersion glaucoma or angle closure glaucoma with sufficiently deep anterior chamber
• Endothelial image at baseline of fair or good quality

Exclusion Criteria:

• Iridocorneal endothelial syndrome or posterior polymorphous dystrophy
• Eyes with a history of penetrating trauma
• Eyes with a history of (intra)ocular surgery other than uncomplicated cataract surgery
• Eyes with corneal disease
• Synechiae posterior
• Pregnant and lactating women