Open-angle glaucoma damages the optic nerve slowly, often with no symptoms until vision is lost, and the damage can't be reversed. Treatment aims to slow it, mainly by lowering the pressure inside the eye. For most of modern ophthalmology the first step has been a daily eye drop. Many patients, though, find drops hard to keep up for decades: they forget doses, have trouble putting drops in, put up with redness or irritation, and pay for refills that never end.
Selective laser trabeculoplasty (SLT) offers another way to start. This guide covers how SLT works, what the most influential trial found, where it fits next to drops and surgery, and the questions to ask before choosing.
How SLT Works
Fluid inside the front of the eye drains through a spongy tissue at the angle where the iris meets the cornea, called the trabecular meshwork. In open-angle glaucoma that outflow is often slowed. The NIHR Evidence summary of the LiGHT trial (2019) describes SLT as a laser treatment that opens up the eye's drainage channels so more fluid drains out, which lowers pressure.
The word "selective" reflects that the laser is designed to act on specific cells in the drainage tissue rather than cut or burn a new channel. The aim is to help the existing tissue drain better. Ask your specialist how that affects the chance of repeating the treatment later, and whether it changes any future surgical options.
What the appointment usually looks like
- Numbing drops, and often a drop to prevent a short-term pressure spike
- A contact lens placed on the eye so the laser can be aimed at the drainage angle
- A series of short laser pulses while you sit at the machine
- A pressure check before you leave, at many clinics, and a follow-up visit weeks later to see whether pressure has dropped
The effect isn't immediate. Pressure typically falls over the following weeks, which is why the follow-up visit matters.
The LiGHT Trial in Plain Language
The Laser in Glaucoma and Ocular Hypertension (LiGHT) trial was a randomized trial at six UK hospitals, published in The Lancet in 2019 and summarized by NIHR Evidence (2019). It enrolled 718 adults with newly diagnosed open-angle glaucoma or ocular hypertension (high pressure without nerve damage yet). Of these, 356 received SLT first and 362 started on prostaglandin drops, with treatment stepped up in either group as needed. They were followed for 36 months.
| Outcome at three years | SLT first | Drops first |
|---|---|---|
| Needed no drops to keep pressure at target | 74.2% | Not applicable; the summary reports only 3% using no drops |
| Quality of life (EQ-5D score) | 0.89 | 0.90 (difference not meaningful) |
| Vision, pressure and visual field | Similar in both groups | |
| Side effects | More short-lived procedure-related events | More drop-related side effects |
| Cost to the NHS | Laser judged cost-effective, with an estimated saving of £451 per patient in specialist eye care costs | |
Two points in that summary stand out. First, most laser-first patients stayed off drops for three years without doing worse on the outcomes that protect sight. Second, quality-of-life scores were about the same, so the trial didn't find that patients felt dramatically better. The practical gains were fewer drops, fewer drop side effects and lower cost.
What the summary did not say
The NIHR summary notes that the 2017 NICE glaucoma guideline (NG81) recommended a generic prostaglandin drop first, and that the LiGHT findings "may inform" changes to practice. It doesn't itself report a guideline change. If you're in the UK, ask your specialist how current NHS guidance applies to you. Elsewhere, local guidelines and insurance rules shape what you're offered first.
Who SLT Tends to Suit
SLT is used mainly in open-angle glaucoma and ocular hypertension. It's commonly discussed for people who:
- Have trouble using drops reliably, because of memory, arthritis, tremor or a busy routine
- Have side effects from drops, such as redness, irritation or changes around the eyelids
- Find long-term drop costs a real burden
- Prefer one procedure to a daily routine, as long as monitoring continues
- Already use drops but need more pressure lowering and want to avoid adding another bottle
It's less likely to be the answer for some other forms of glaucoma, particularly narrow- or closed-angle disease, where the laser can't reach or treat the drainage tissue in the same way. Advanced glaucoma that needs very low target pressures may need a stronger approach from the start. That's where options like those in our MIGS vs trabeculectomy guide come in.
Where SLT Sits on the Treatment Ladder
| Step | Typical role | Main trade-off |
|---|---|---|
| Eye drops | Traditional first-line treatment; flexible and easy to adjust | Daily routine for life; side effects and cost |
| SLT | First-line alternative or add-on; in-office procedure | Effect may fade; not every eye responds |
| MIGS (minimally invasive surgery) | Mild to moderate disease, often combined with cataract surgery | Operating-room procedure; usually more modest pressure lowering than traditional surgery |
| Trabeculectomy or tube surgery | When lower targets are needed or other steps fail | Bigger operation; longer recovery and closer follow-up |
These steps aren't strictly in sequence. Many patients combine them, for example SLT plus a single drop, or MIGS at the time of cataract surgery. Your stage of disease, target pressure and other eye conditions decide the mix.
Limits and Risks to Understand
- Not everyone responds. Some eyes show little pressure drop. The follow-up visit is how you find out.
- The effect can wear off. Pressure may drift up over time. Repeat treatment or added drops are common next steps.
- Short-term effects. The LiGHT summary reports more transient procedure-related events in the laser group. Ask your clinic what to expect in the first days, such as aching, blurring, redness or a pressure spike, and when to call.
- Monitoring never stops. SLT changes how pressure is lowered, not the need for visual field tests and optic nerve checks.
Thinking About SLT as Part of Care Abroad
People sometimes ask whether glaucoma treatment is worth combining with a trip, especially when they're already traveling for cataract surgery. SLT is short, but it fits poorly with a quick visit:
- The result is judged weeks later, usually by the clinic that did the laser.
- Long-term glaucoma care depends on comparing your test results over years, which works best with one consistent clinic or a well-documented handover.
- If pressure rises after you get home, you need a doctor there who knows what was done.
If you do have glaucoma treatment away from home, bring back your pre- and post-laser pressures, which eye or eyes were treated, how much of the drainage angle was treated, and the clinic's recommendations. Our glaucoma surgery abroad fit test covers the bigger operations, where these issues matter even more.
Questions for Your Glaucoma Specialist
- What type and stage of glaucoma do I have, and what is my target pressure?
- Is my drainage angle open enough for SLT to work?
- Would you suggest SLT first, drops first, or both? Why?
- How will we know whether the laser worked, and when?
- If the effect fades, would you repeat it, add drops or consider surgery?
- How does SLT affect future options if I later need cataract or glaucoma surgery?
- What will my insurance or health system cover for SLT compared with long-term drops?
Living With Either Choice
Whichever first step you and your specialist choose, some habits make glaucoma care work better over the years. Keep a simple record of your pressure readings and visual field dates so you can see trends yourself. Bring a list of every medication you take to each visit, because some general medicines interact with eye pressure or drops. If you use drops, ask the clinic to watch you put one in. Small technique changes, like closing the eye gently afterward and pressing on the inner corner, can reduce how much drug reaches the rest of the body. If you've had SLT, note the date and which eye was treated so any future doctor knows the history. These are small things, but glaucoma is a long game, and good records make each decision clearer.
The Bottom Line
SLT is a well-studied, in-office way to lower eye pressure. In the large LiGHT trial, starting with laser kept most patients off drops for three years, with sight-related outcomes similar to drops and a lower cost to the health system. It isn't a cure, it doesn't suit every type of glaucoma, and its effect can fade. For many people with newly diagnosed open-angle glaucoma or high eye pressure, though, it's a reasonable first option to discuss with an ophthalmologist. The commitment to lifelong monitoring stays the same whichever you choose.