SLT stands for selective laser trabeculoplasty, a quick in-office laser procedure used to lower eye pressure in people with glaucoma or ocular hypertension. It works by targeting the eye’s natural drainage system to help fluid flow out more efficiently, reducing the pressure that can damage the optic nerve over time. A landmark clinical trial found that SLT kept eye pressure controlled without any eye drops in about three-quarters of patients for at least three years, establishing it as a genuine first-line treatment rather than just a backup when drops fail.
How SLT Lowers Eye Pressure
Inside your eye, fluid called aqueous humor is constantly produced and drained. It exits through a tiny ring of tissue called the trabecular meshwork, which sits at the angle where the iris meets the cornea. In glaucoma, this meshwork becomes less efficient at draining fluid, so pressure builds up.
SLT uses very short pulses of low-energy laser light (lasting just 3 nanoseconds each) to selectively hit pigmented cells within the trabecular meshwork. Because the pulse is shorter than the time it takes for heat to spread to surrounding tissue, only the pigment-containing cells absorb the energy. Lab studies confirm that adjacent cells without pigment show no structural damage at all.
The laser doesn’t simply burn a hole open. Instead, it triggers a biological remodeling process. The treated cells release signaling molecules that recruit immune cells called monocytes, which migrate into the meshwork and begin clearing debris. Genes involved in breaking down the meshwork’s scaffolding get switched on, while genes that build new scaffolding get turned down. The net effect is a looser, more porous drainage tissue. At the same time, the cells lining the drainage canal downstream (called Schlemm’s canal) become more permeable as the junctions between them loosen, in a way that resembles how certain glaucoma eye drops work. All of this adds up to better fluid outflow and lower pressure.
Who Is a Good Candidate
SLT works across a broad range of conditions. It’s appropriate for people newly diagnosed with open-angle glaucoma, those whose pressure isn’t controlled on eye drops, and those who struggle with the cost, side effects, or daily routine of drop therapy. It’s also effective for pseudoexfoliation glaucoma, pigmentary glaucoma, steroid-induced pressure elevation, and high eye pressure after corneal transplant surgery or steroid injections into the eye. Even some patients with primary angle-closure glaucoma can benefit, as long as a prior laser iridotomy has opened the angle enough for the doctor to see the trabecular meshwork.
SLT is not recommended for people with inflammatory or uveitic glaucoma, congenital glaucoma, or any condition that prevents a clear view of the drainage angle during the procedure.
The LiGHT Trial: SLT as First-Line Treatment
The strongest evidence for SLT comes from the LiGHT trial, a large randomized study that compared starting treatment with SLT versus starting with daily eye drops. Over three years, patients in the laser group hit their target pressure at 93% of clinic visits, compared to 91% for the drops group. Zero patients in the laser group needed glaucoma surgery during the study period, while 11 eyes in the drops group did. Quality of life was equivalent between the two groups, and SLT saved roughly £458 (about $580) per patient in healthcare costs.
The trial concluded that SLT is the most cost-effective first-line option for open-angle glaucoma and ocular hypertension, delivering better clinical outcomes while freeing the majority of patients from the daily burden of eye drops.
What the Procedure Feels Like
SLT is performed in a clinic or office, not an operating room. You sit at a slit lamp (the same microscope used during a regular eye exam) while the doctor places a special mirrored contact lens on your eye after numbing it with anesthetic drops. The laser is then applied in a series of brief, low-energy pulses directed at the drainage angle. A typical session involves 50 to 100 spots applied over either half or the full 360 degrees of the meshwork. Most patients feel little more than a mild sensation or occasional slight sting with each pulse. The entire procedure usually takes about 5 to 10 minutes.
Afterward, you can typically go home the same day. Your doctor will likely prescribe a short course of anti-inflammatory drops and schedule a follow-up visit within a few weeks to check your pressure response. Vision may be slightly blurry for the rest of the day, but most people return to normal activities quickly.
How Well It Works and How Long It Lasts
Studies consistently show SLT can reduce eye pressure by around 29% in patients who respond well, an effect that can last up to four years. However, the pressure-lowering benefit does fade over time for many people. Five-year data show that only about 25% of patients maintain a 20% or greater pressure reduction without needing additional drops or surgery. This gradual decline doesn’t mean SLT failed; it means the biological changes it triggers eventually revert, and additional treatment becomes necessary.
One of SLT’s key advantages over the older laser technique it replaced (argon laser trabeculoplasty, or ALT) is that it causes minimal structural scarring to the drainage tissue. This means it can be repeated. Studies on repeat SLT show that a second treatment produces pressure reductions similar to the first: about 43% to 50% of eyes achieve a meaningful pressure drop at six months after retreatment, and roughly 29% to 39% maintain that reduction out to two years. So the realistic long-term plan for many patients is an initial SLT, followed by a repeat session a few years later if pressure creeps back up, with eye drops added as needed along the way.
Side Effects and Risks
SLT is one of the lower-risk procedures in ophthalmology. The most common side effect is mild inflammation inside the eye, which typically resolves within a few days with anti-inflammatory drops. Some patients experience a temporary spike in eye pressure in the hours after treatment, which is why your doctor may check your pressure before you leave the office or at a short-term follow-up. Blurred vision and mild discomfort or redness on the day of the procedure are also common but short-lived.
Serious complications are rare. Because the laser energy is so low and so precisely targeted, it doesn’t cause the kind of permanent tissue damage associated with older laser techniques. This selective approach is what gives the procedure its name and its favorable safety profile.
SLT Compared to Eye Drops
Daily eye drops remain effective for glaucoma, but they come with real drawbacks. Many patients find them difficult to use correctly, forget doses, or experience side effects like eye redness, stinging, darkening of the skin around the eyes, or changes in eyelash growth. Adherence tends to decline over months and years, which silently puts the optic nerve at risk.
SLT sidesteps all of these problems. A single session provides months to years of pressure control with no daily routine required. For patients who do eventually need drops, SLT can reduce the number of medications required. And because it can be repeated, it offers a flexible treatment path that adapts as the disease progresses. The LiGHT trial data showing equivalent quality of life, better pressure control, fewer surgeries, and lower cost has shifted clinical thinking: many ophthalmologists now offer SLT as a first option rather than a fallback.