The goal of this study is to understand if SLT performed at low energy is as effective as SLT performed at standard energy, and also to see if repeating SLT at low energy once a year will prevent or delay the need for daily eye drop medications better than waiting for SLT to wear off before repeating it.

Inclusion Criteria:

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)
   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

Exclusion Criteria:

1. Use of topical IOP-lowering medications for more than 6 cumulative months at any time in the past 5 years (this is a modification implemented during active enrollment)
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

All study data will be de-identified. We will invite other investigators to submit secondary data requests using the data from the study and will work with those investigators to foster additional research studies and manuscripts. The investigators agree to abide by the principles for sharing research resources as described by "Principles and Guidelines for Recipients of NIH Research Grants and Contracts on Obtaining and Disseminating Biomedical Research Resources." All publications based on the study will adhere to the NIH Public Access Policy (Notice NOT-OD-08-033). At the end of the study, all study data will be submitted for permanent archive per the notice of grant award.

At study completion

See above