1. Age 18 or older and in good health 2. Each eye with one of the following qualifying diagnoses (diagnoses may differ between eyes): 1. High-risk ocular hypertension (OHT): IOP > 21 mmHg without glaucomatous optic neuropathy (excavation, diffuse or focal thinning or notching of the neuroretinal rim, visible nerve fiber layer defects, or asymmetry of the vertical cup-to-disc ratio of >0.2 between eyes) [enrollment of trial participants with High-risk OHT will be capped at 25% of total enrollment] 2. Mild primary open-angle glaucoma: glaucomatous optic neuropathy, visual field mean deviation better than -6.0 dB with no points in the central 5° <15 dB (see figure on next page) 3. Moderate primary open-angle glaucoma: glaucomatous optic neuropathy, visual field mean deviation equal to or worse than -6.0 dB but no worse than -12.0 dB and no central 5° points <15 dB or mean deviation -12.0 dB or better with 1 central 5° points <15 dB (see figure on next page). 3. Each eye with BCVA 20/200 (UK 6/60) or better 1. Use of topical IOP-lowering medications for more than 6 cumulative months at any time in the past 5 years 2. Any history of IOP-lowering laser (prophylactic iridotomy not included) or surgical procedure 3. Advanced POAG in either eye (worse than moderate POAG as defined above) 4. Glaucoma other than POAG (including pigmentary and pseudoexfoliation glaucoma) in either eye 5. Mean IOP > 35 mmHg at either the screening or baseline visit in either eye 6. Narrow or closed angle (Shaffer Grade 0, 1, or 2) in either eye 7. Contraindications to SLT or any other study intervention 8. Any corneal pathology that would preclude accurate assessment of IOP by Goldmann tonometry in either eye 9. Any intraocular surgical procedure within the past 6 months in either eye 10. Inability to attend all scheduled study visits 11. Pregnant or planning to become pregnant in the next 4 years