SLT as First-Line Glaucoma Treatment: The LiGHT Trial Explained
Last updated: October 2026
For most of our careers, newly diagnosed glaucoma meant a prostaglandin drop. The LiGHT trial changed that. Selective laser trabeculoplasty (SLT) given first kept most eyes drop-free, controlled the disease at least as well, and prevented more surgery. In the UK, NICE now recommends offering SLT first.
The LiGHT trial
- Design: 718 treatment-naive patients with open-angle glaucoma or ocular hypertension were randomised to SLT first or eye drops first, then treated to an individual target IOP with escalation as needed.
- Primary outcome: health-related quality of life (EQ-5D) at 3 years. Clinical outcomes, cost-effectiveness and safety were secondary.
| Outcome | 3 years (Lancet 2019) | 6 years (Ophthalmology, published 2022) |
|---|---|---|
| Quality of life | No difference between arms | No significant difference |
| Drop-free at target, SLT arm | About 74% | 69.8% |
| Disease progression | — | 19.6% SLT vs 26.8% drops |
| Trabeculectomy | None in SLT arm vs 11 in drops arm | 13 SLT vs 32 drops |
| Cataract surgery | — | 57 SLT vs 95 drops |
| Cost | SLT about 90% likely to be more cost-effective | — |
What guidelines say now
- NICE (NG81, updated 2022): offer SLT as first-line treatment for newly diagnosed ocular hypertension and open-angle glaucoma.
- AAO Preferred Practice Pattern and European Glaucoma Society: list laser trabeculoplasty as an acceptable initial therapy alongside medication.
- Drops remain appropriate when SLT is unavailable, unaffordable, contraindicated, or not the patient's preference.
How SLT works and how it is done
| Parameter | SLT | ALT (for contrast) |
|---|---|---|
| Laser | Q-switched, frequency-doubled Nd:YAG, 532 nm | Argon, 488/514 nm |
| Spot size | 400 µm (covers the whole trabecular meshwork) | 50 µm |
| Pulse duration | 3 nanoseconds | 0.1 seconds |
| Energy | Typically 0.4–1.2 mJ, titrated to just below or at "champagne bubble" formation | Titrated to blanching |
| Tissue effect | Selective photothermolysis of pigmented TM cells. Biological (cytokine and macrophage) response, no coagulative scarring. | Coagulative burns and scarring |
| Repeatable | Yes | Limited |
- LiGHT used 360° treatment with about 100 non-overlapping spots.
- Give an alpha-agonist (apraclonidine or brimonidine) to blunt the post-laser IOP spike, and check IOP about an hour later in advanced disease.
- Full effect takes 6–8 weeks; review then before judging success.
- Low-energy annual repeat SLT is being tested (the COAST trial).
When to be careful
- Heavily pigmented angles (pigment dispersion, pseudoexfoliation): use lower energy, as IOP spikes are more likely.
- Angle closure: the trabecular meshwork must be visible. SLT is not a treatment for closed angles.
- Uveitic glaucoma: generally avoid.
- Very high IOP or advanced field loss: SLT alone may not reach target, so plan escalation early.
- Rare complications: transient iritis, hyphema, and corneal oedema or haze (reported mainly in high myopes).
Viva pearls
- SLT: 532 nm, 3 ns, 400 µm. ALT: 50 µm, 0.1 s.
- LiGHT's primary outcome was quality of life, not IOP. A common viva trap.
- SLT works in pseudophakic eyes and can be repeated.
- Best responders tend to have higher pre-treatment IOP.
Related: setting a target IOP, new glaucoma drugs, implants and MIGS and landmark trials.
Key sources
- AOP: LiGHT six-year results
- College of Optometrists: SLT as first line of defence
- Gazzard G et al. LiGHT 6-year outcomes (UCL Discovery)
- Gazzard G et al. Lancet 2019;393:1505–16 (3-year results)
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