Eye Drops vs. SLT: Which Is Better for Early Glaucoma?
When someone is first told they have early glaucoma or are at risk of developing it, one of the first big decisions is how to start treatment. Traditionally, the answer has been simple: eye drops. They lower pressure inside the eye and have been the backbone of glaucoma care for decades.
But in the last 10–15 years, selective laser trabeculoplasty (SLT) has stepped forward as a serious contender for first-line treatment. In fact, several large trials now suggest that for many people, SLT may be the better starting point.
So which approach makes more sense in early disease? Let’s walk through what the evidence shows — not just about eye pressure, but also about visual field protection, side effects, compliance, and long-term consequences.
Why lowering eye pressure matters
Glaucoma slowly damages the optic nerve, and once that damage is done, it’s permanent. The single proven way we can slow or prevent this is by lowering intraocular pressure (IOP).
The Early Manifest Glaucoma Trial (EMGT) made this crystal clear: patients whose IOP was lowered had slower rates of visual field loss than those who weren’t treated. The lesson is simple — the lower the pressure, the slower the disease.
That’s why both drops and SLT aim for the same target: bring the pressure down and keep it steady over time.
The case for eye drops
Eye drops are the classic starting point, and for good reason.
They work. The UK Glaucoma Treatment Study (UKGTS) showed that latanoprost, a common prostaglandin analogue (PGA), cut the risk of visual field deterioration by about half compared with placebo.
They’re adjustable. If one drop doesn’t bring pressure low enough, doctors can add a second or third medication, tailoring treatment to the eye’s response.
They’re accessible. Most patients can walk into a pharmacy and leave with their treatment the same day they’re diagnosed.
But drops come with challenges that build up over the long term.
Compliance: the elephant in the room
Eye drops only work if they’re taken consistently — every day, at the right time, and with good technique. In real life, this doesn’t always happen.
Studies using electronic monitoring devices show that only about 30–60% of patients take their drops as prescribed. Sometimes bottles are forgotten, sometimes people struggle with technique, and sometimes side effects make them quit altogether. Since glaucoma is usually symptomless in early stages, it’s easy for patients to deprioritize drops.
That inconsistency matters. Research has shown that patients with higher day-to-day IOP fluctuation are more likely to lose vision fields faster. A missed drop here and there adds up.
Side effects: not always trivial
Each drug class has its own set of issues:
Prostaglandin analogues (PGAs): the most effective single-agent drops, but long-term they can cause prostaglandin-associated periorbitopathy (PAP). This includes sunken eyelids, droopy lids, and fat atrophy around the eye — changes that can sometimes be reversed if the drug is stopped. They can also darken the iris permanently and make eyelashes grow.
Beta-blockers: can lower blood pressure and heart rate, worsen asthma, and sometimes cause fatigue or depression.
Alpha-agonists (like brimonidine): often cause allergy, with red, itchy eyes after months or years.
Carbonic anhydrase inhibitors: can sting and leave a bitter taste, and in some patients worsen corneal health.
Then there’s the hidden culprit: preservatives, especially benzalkonium chloride (BAK). Over years, BAK exposure damages the ocular surface, leading to dry eye, irritation, and inflammation. Patients often don’t realize their “glaucoma symptoms” are actually side effects of the treatment itself.
The case for SLT
Selective laser trabeculoplasty (SLT) is a quick, office-based laser procedure that targets the drainage tissue of the eye, making it easier for fluid to flow out and lowering pressure.
The treatment takes about 5 minutes, is painless for most patients, and can be repeated when the effect wears off (typically after a few years).
What the evidence says
The landmark LiGHT trial directly compared SLT-first to drops-first in patients with ocular hypertension or early glaucoma.
After 6 years, patients who started with SLT had less disease progression than those who started with drops.
About 70% of SLT-first patients remained drop-free at 6 years, meaning their pressure was controlled without daily medication.
Fewer patients in the SLT group needed glaucoma surgery or cataract surgery.
Quality of life was at least as good, and SLT was more cost-effective for the healthcare system.
In other words, SLT doesn’t just match drops — it may outperform them in the long run.
Side effects of SLT
SLT is generally very safe. Some patients get a bit of redness or inflammation for a few days, or a short-lived pressure spike. Rarely, the laser effect may not work, but in that case patients can still start drops as usual.
Compared to a lifetime of potential drop toxicity, the side effect profile of SLT is remarkably light.
Visual field progression: drops vs SLT
Both drops and SLT lower IOP, and both slow down visual field loss. The real question is: which approach does it more reliably?
With drops: When patients are highly adherent, PGAs in particular are very effective at protecting visual fields. UKGTS proved that. The problem is that many patients simply don’t take them as prescribed, and that inconsistency leads to progression.
With SLT: The effect doesn’t depend on daily patient behavior. Once the laser is done, pressure reduction is “built in.” That reliability seems to translate into less progression at the population level, as shown in the LiGHT trial.
So while both strategies work under ideal conditions, SLT tends to win in the real world, where adherence is imperfect.
Long-term perspective
Think about glaucoma care not just in months, but over decades.
Drops: Effective but burdened by adherence issues, systemic and ocular side effects, and cumulative preservative toxicity. Many patients end up on multiple bottles, each adding cost and complexity.
SLT: Repeatable, drop-sparing, and doesn’t compromise the ocular surface. Even if patients eventually need drops, delaying that exposure by 5–10 years can make a big difference in quality of life.
So, which should come first?
There isn’t a one-size-fits-all answer, but here’s a practical way to frame it:
SLT is often the better starting point if:
You want to minimize or avoid long-term drops.
You’re worried about forgetting or struggling with adherence.
You already have dry eye or ocular surface problems.
You like the idea of a “do it once and forget about it” treatment.
Drops are still a good option if:
You’re comfortable with daily treatment and likely to be consistent.
You prefer to avoid procedures.
You want something that can be started immediately while waiting for a laser appointment.
For many doctors today, SLT is becoming the default first-line option, with drops reserved for those who prefer them or when laser isn’t available.
Final thoughts
Both eye drops and SLT share the same ultimate goal: protecting vision by keeping pressure low and steady. The key difference is in how reliably and comfortably that’s achieved over years.
Drops work — but only if taken consistently, and they carry a real burden of side effects.
SLT works — without daily effort, and with fewer long-term downsides.
For most people with early glaucoma, SLT is no longer “alternative therapy.” It’s often the smarter first choice.