Selective Laser Trabeculoplasty (SLT)
A quick, in-office laser treatment that improves the eye's natural drainage, backed by the largest randomized trial ever conducted on first-line glaucoma treatment.
What Is SLT?
Selective laser trabeculoplasty (SLT) is a quick, in-office laser treatment that targets the trabecular meshwork — the eye's natural drainage tissue — using pulses of low-energy laser light absorbed selectively by pigmented cells. This triggers a biological response that improves the meshwork's ability to drain fluid, lowering eye pressure over the following weeks.
How It Works & What to Expect
- Performed in the office using only numbing eye drops — no incisions, needles, or sedation
- A special contact lens is used to focus the laser on the drainage angle, visualized with gonioscopy
- The procedure itself takes roughly 5–10 minutes per eye
- Full effect typically develops over 4–8 weeks, so pressure is rechecked at a follow-up visit
- Most patients resume normal activity the same day
Indications
SLT is used across a wide range of open-angle glaucoma and elevated eye pressure situations:
- ✓First-line treatment for open-angle glaucoma or ocular hypertension, as an alternative to starting with eye drops
- ✓Add-on treatment for patients already on drops who aren't at target pressure, or who want to reduce their drop burden
- ✓Pseudoexfoliation glaucoma, where the heavily pigmented drainage angle often responds particularly well
- ✓Pigment dispersion / pigmentary glaucoma, though we use deliberately lower energy settings here given the risk of a post-laser pressure spike in heavily pigmented angles (see our Pigment Dispersion Glaucoma page)
Alternatives
Older argon laser trabeculoplasty (ALT) uses thermal energy that causes more tissue damage and scarring, limiting how many times it can be repeated. SLT was developed specifically to spare the underlying tissue architecture, which is part of why it can generally be repeated when its effect wears off. A newer variant, micropulse laser trabeculoplasty (MLT), delivers energy in very short pulses to further reduce collateral tissue effect, with evidence still evolving relative to SLT's long track record. Eye drops and MIGS surgery are the other main alternatives or complements, discussed on their own pages.
Risks & Side Effects
- ✓A temporary rise in eye pressure in the hours after treatment, which is why pressure is checked shortly after the procedure and a pressure-lowering drop is sometimes given preventively
- ✓Mild, short-lived inflammation inside the eye
- ✓Rarely, a more prolonged pressure elevation requiring additional treatment
- ✓Corneal or other structural complications are rare given SLT's targeted, tissue-sparing mechanism
The LiGHT Trial: The Key Evidence Behind First-Line SLT
The strongest evidence supporting SLT comes from the LiGHT trial, a multicenter randomized controlled trial published in The Lancet in 2019 that compared SLT to eye drops as the very first treatment for open-angle glaucoma and ocular hypertension.1 The trial found that patients started on SLT had better disease control, a better quality of life, and were more cost-effective to treat over 3 years than those started on drops. Notably, about 74% of SLT-treated eyes required no eye drops at all to stay at target pressure three years after treatment, and no patient in the SLT-first group required incisional glaucoma surgery during the trial, compared to a small number in the drops-first group.
A six-year follow-up of the same LiGHT trial cohort, published in 2023, found that the benefits of starting with SLT were sustained over the longer term: SLT-first patients continued to need fewer medications, had better disease control, and had a lower rate of needing incisional glaucoma surgery than those started on drops first.2 Together, these results are why many glaucoma specialists, including our practice, now regularly offer SLT as a genuine first-line option, not just a later add-on.
SLT can be combined with eye drops, and with MIGS or incisional surgery later if needed. It is not an all-or-nothing choice — see our Eye Drops & Oral Medications and MIGS Surgery pages for how these approaches work together.
References
- Gazzard G, Konstantakopoulou E, Garway-Heath D, et al. Selective laser trabeculoplasty versus eye drops for first-line treatment of ocular hypertension and glaucoma (LiGHT): a multicentre randomised controlled trial. Lancet. 2019;393(10180):1505-1516.
- Wright DM, King AJ, Peto T, et al. Six-year outcomes from the multicentre, randomised controlled trial comparing selective laser trabeculoplasty with eye drops as first-line treatment for ocular hypertension and glaucoma (the LiGHT trial). Eye (Lond). 2023.
Frequently Asked Questions
Does SLT hurt?
No. SLT is performed with numbing drops only, takes about 5–10 minutes, and most patients describe it as painless or only mildly uncomfortable.
Can SLT replace my eye drops?
For many patients, yes, at least for a period of years. The LiGHT trial found that about 3 out of 4 SLT-treated eyes needed no eye drops at all three years after treatment. Some patients still need one or more drops in addition to SLT, especially over the longer term.
Can SLT be repeated?
Yes. Unlike older laser trabeculoplasty techniques, SLT is designed to spare the underlying tissue architecture, so it can generally be repeated if its effect wears off over time.
Is SLT covered by insurance?
SLT is a standard, medically recognized glaucoma treatment and is typically covered by Medicare and most vision/medical insurance plans when medically indicated. Our office can help verify your specific coverage.
See a glaucoma specialist. Dr. Robert Gunzenhauser is Harvard-educated and UCLA fellowship-trained in glaucoma, providing expert diagnosis and treatment for Selective Laser Trabeculoplasty (SLT) at Inland Glaucoma Center in Upland, CA.