The purpose of this study is to assess whether deep sclerectomy is as effective in lowering intraocular pressure (IOP) as trabeculectomy in patients with normal tension glaucoma.

Subjects with normal tension glaucoma that is unstable with current medication needing filtration surgery are recruited in the study. All patients meeting the inclusion criteria and giving informed consent will be randomized to whether having deep sclerectomy or trabeculectomy.

Inclusion Criteria:

• Signed Informed Consent
• Normal Tension Glaucoma with typical nerve fiber layer defects in red-free photographs and/or optical coherence tomography (OCT) and possible equivalent visual field defects, IOP never more than 21 mmHg, and open anterior chamber angle
• Glaucoma unstable with current medication assessed by a glaucoma specialist

Exclusion Criteria:

• Secondary Glaucoma e.g. due to previous injury or uveitis
• Exfoliation syndrome
• Pigment dispersion syndrome
• Previous transscleral or endoscopic cyclophotocoagulation
• Previous other glaucoma surgery
• Previous retinal detachment
• Previous intraocular surgery like vitrectomy and other retinal surgery
• Wet age-related macular degeneration
• Diabetic retonopathy
• Previous corneal transplant or previous refractive surgery
• Fuchs' dystrophy and other abnormalities compromising corneal clarity like scars
• The patient does not want to participate in the study
• The patient does not speak Finnish, Swedish or English
• Dementia
• Only eye with vision worse than 20/200 or loss of central visual field