SGNT:
Inclusion Criteria:
* Adult participants (\>18 years) with newly-diagnosed and previously untreated POAG or PEXG in one or both eyes. Glaucoma is defined as reproducible visual field (VF) defects that cannot be explained by other disease or damage, and a suspect/abnormal optic nerve head and/or nerve fibre layer defect.
* Participants need to have visual acuity of Snellen ≥ 6/12 (0.5) or better.
* Have performed at least two reliable VFs (SITA-Fast 24-2), with \<33% fixation losses and \<15% false positives
Exclusion Criteria:
* VF damage worse than -10dB in the best eye and -16dB in the worse eye or a paracentral spot with -10dB or less in any eye),
* IOP \>35mmHg in any eye or a mean IOP of 30mmHg or higher (two measurements), •inability to perform VFs,
* pregnancy/breastfeeding,
* those unwilling to abstain from NAM supplements,
* allergic to NAM/niacin,
* diagnosed with cancer in the last 5 years (except treated basal or squamous cell carcinoma),
* a history of liver disease or stomach ulcers,
* disease that prevents long-term follow-up,
* neurologic or other non-glaucomatous conditions apart from cataract that may affect the VF, •inability to understand and speak Swedish or English,
* a history of intraocular surgery (apart from uncomplicated cataract surgery) and
* diseases that are known to affect retinal function (e.g. \> mild age-related macular degeneration, \> stage I diabetic retinopathy).
VBIGS:
Inclusion Criteria:
* Patients aged 18 years or older, with definitive, treated POAG including normal tension glaucoma, PEXG in both eyes
* Best-corrected visual acuity ≥ 6/18
* Severity of visual field loss, MD between -3 and -18 dB. This range includes people with moderate disease which optimises detection of progression.
* Patient must have performed at least two reliable VFs (24-2), with \<33% fixation losses and \<15% false positives.
* Previous selective laser trabeculoplasty is acceptable (IOP-lowering laser treatment) if 3 or more months prior, and normal liver function tests.
* Those taking NAM already will undergo a 1-month washout period before commencing the study.
Exclusion Criteria:
* Patients with a history of hepatic disease, gout, visually significant cataracts, other conditions that can affect VF results, cataract surgery in the last 3 months or glaucoma filtration surgery in last 6 months.
