Deep Sclerectomy Versus Trabeculectomy in Normal Tension Glaucoma

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