This will be a prospective, descriptive, mono-center, non-comparative study. A sample of 30 patients who satisfy entry criteria is estimated to be appropriate to provide safety and performance data for this study.

The objectives of the study are to verify the performance and safety of the Glafkos adjustable glaucoma drainage device system. Performance will be measured assessing the possibility to adjust the intra-ocular pressure post-operatively. Safety will be measured by the incidence and severity of adverse events.

The Glafkos device will be implanted in combination with a seton tube. The implant is placed under a scleral flap, in a manner analogous to the ex-Press device (Alcon). The distal end of the draining tube is linked to a seton draining tube, which is linked to a plate placed under the extraocular muscles, creating a filtering space at the orbit (filtering bleb).

Inclusion Criteria:

1. Patient must be 18 years of age or older.
2. Patient shall suffer from primary open angle glaucoma, pseudo-exfoliative glaucoma, or refractory glaucoma after failed previous filtering surgery, in the study eye. Diagnosis is based on glaucomatous optic neuropathy, Shaffer angle greater than 2 as seen on gonioscopy, and visual field defect attributed to glaucoma.
3. Eye to be treated shall be phakic or pseudophakic with no other active ocular disease or disorder except for incipiens cataract. Prior ophthalmic surgery in the study eye shall have been performed more than 3 months before enrollment in this study.
4. Patient condition is indicated for primary and secondary filtration surgery.
5. Presence of ocular hypertension defined as an intraocular corrected pressure (IOP) > 20 mmHg in the study eye, under maximally tolerated medications. The IOP level shall be obtained on 2 consecutive measurements (not taken on the same day) prior to surgery.
6. Distance Snellen best corrected visual acuity (BCVA) better than 0.6 in the fellow eye.
7. For the first three subjects the Snellen BCVA in the study eye should be 0.5 or less. In addition, the visual field defined by the Mean Defect (MD) shall be higher than 10 dB.
8. Optic neuropathy is exclusively attributed to glaucoma.
9. Patient agreed to sign the written inform consent prior to entering into the investigation.
10. Patient is able and willing to complete post-operative follow-up requirements.

Exclusion Criteria:

1. Diagnosis of neovascular glaucoma, congenital glaucoma.
2. History of previous intraocular surgery in the study eye referring to but not limited to extraocular muscles (strabismus), corneal transplant, retinal surgery.
3. Proliferative or severe non-proliferative retinopathy in either eye.
4. Congenital anomaly of the anterior chamber angle in the study eye.
5. Optic neuropathy other than glaucoma in the study eye.
6. Patient with retinal vein occlusion in the study eye.
7. Patient with retinal artery occlusion in the study eye.
8. Patient with corneal opacifications or irregularities that may interfere with the optic nerve evaluation or the IOP measurements in the study eye.
9. Patient with a history of severe eye trauma in the study eye.
10. Patient with ocular malformations such as microphthalmia in the study eye.
11. Patient with concurrent inflammatory/infective eye disorder in the study eye.
12. Patient with any sign of past or present uveitis (anterior/posterior).
13. Patient with severe systemic disease or disabling conditions such as chronic renal failure, post organ transplants.
14. Patient participating in another clinical trial or having participated in another clinical trial less than 3 months prior to entering into the investigation.
15. Patient is pregnant, breast-feeding or unable to make the decision to participate in a clinical investigation (e.g. mentally ill person, mentally handicapped person)