SLT stands for selective laser trabeculoplasty, a quick 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. SLT has become one of the most common treatments for open-angle glaucoma and is now frequently used as a first-line option before eye drops.
How SLT Lowers Eye Pressure
Inside your eye, fluid is constantly produced and drained through a tiny mesh-like structure called the trabecular meshwork. In glaucoma, this drainage tissue becomes less efficient, causing fluid to build up and pressure to rise. SLT uses short pulses of low-energy laser light (at a wavelength of 532 nanometers) to target only the pigmented cells within this drainage tissue, leaving surrounding cells unharmed.
The laser doesn’t burn a hole or physically open the drain. Instead, it triggers a biological response. The treated cells release signaling molecules that recruit immune cells to the area. Within days, the number of these immune cells in the drainage tissue increases roughly fivefold compared to untreated tissue. These cells clear debris and break down material clogging the meshwork. At the same time, genes responsible for building up scar-like material in the drain get dialed down, while genes that remove that material get ramped up. The net effect is a remodeled, more permeable drainage system that lets fluid exit the eye more freely.
What the Procedure Feels Like
SLT is done in an eye doctor’s office, not an operating room. You sit at a device similar to the one used during a regular eye exam. Numbing drops are placed in your eye, then a small lens is held gently against it to focus the laser on the drainage tissue. The laser fires a series of brief pulses. Most people feel little to nothing during the procedure, though some notice a mild sensation with each pulse. The entire treatment typically takes about five to ten minutes.
Afterward, your doctor will apply a pressure-lowering drop to help prevent a temporary spike in eye pressure. You can go home the same day, and most people return to normal activities within a day or two. Mild soreness, redness, or blurry vision in the hours after treatment is common and usually resolves quickly.
How Well It Works
The pressure-lowering effect of SLT builds over the first few weeks. Studies show average reductions of about 9% at two weeks, climbing to roughly 12% by three months. The absolute drop varies significantly depending on how high your pressure was to begin with. People starting with pressures above 21 mmHg saw an average 20% reduction at two weeks, while those with lower starting pressures saw closer to a 5% drop. In the broader literature, pressure reductions of 2 to 7 mmHg are typical over the first six months.
A major trial published in The Lancet, known as the LiGHT study, compared SLT head-to-head against daily eye drops as a first treatment for open-angle glaucoma and ocular hypertension. At three years, 74% of patients in the SLT group maintained their target eye pressure without needing any drops at all. The study also found that SLT provided more stable pressure control than drops, at a lower overall cost. These results shifted how many eye doctors approach glaucoma treatment, making SLT a genuine first choice rather than just an alternative when drops fail.
How Long the Effect Lasts
SLT is not permanent. For most people, the pressure-lowering benefit gradually fades over roughly two years. Clinical data shows that repeat treatment is typically performed about 27 months after the initial session, on average. Unlike an older laser procedure called ALT, SLT does not cause significant structural scarring to the drainage tissue, which means it can be repeated.
Repeat treatments do work, though the results tend to be somewhat milder. In one long-term study, 29% to 39% of eyes still had meaningful pressure reduction at 24 months after a second SLT session, compared to 36% to 54% after the first. The pressure reductions were statistically comparable at most follow-up points, but initial treatment generally produced stronger results at the 4, 8, and 12 month marks. Still, repeating SLT remains a valuable option for extending pressure control without adding medications.
Common Side Effects
SLT is considered a low-risk procedure, but mild side effects are the norm rather than the exception. The most common is temporary inflammation inside the eye, which occurs in roughly 83% to 89% of treated eyes. This shows up as mild redness or discomfort in the days following treatment and typically resolves within about five days without lasting consequences.
A temporary spike in eye pressure occurs in about 4% to 7% of patients, usually detected within the first hour after treatment. These spikes are almost always transient. People with pigmentary glaucoma, where extra pigment is present in the drainage tissue, may be at higher risk for more significant pressure spikes. In case reports, pressures in these patients have temporarily reached 30 to 46 mmHg after treatment, which is why doctors monitor pressure closely in the hours following the procedure.
Who Is a Good Candidate
SLT works best for people with open-angle glaucoma, the most common form of the disease. It is also effective for ocular hypertension (elevated eye pressure without nerve damage yet), pigmentary glaucoma, exfoliative glaucoma, steroid-induced glaucoma, and normal-tension glaucoma. It can be used as a standalone first treatment, as an add-on to eye drops, or as a step before considering surgery.
SLT is not appropriate for everyone. It is generally avoided in people with inflammatory glaucoma, because the laser-induced inflammation can worsen pressure spikes. It is also not recommended for advanced glaucoma where the optic nerve is severely damaged and more aggressive intervention is needed. If scar tissue or adhesions block the doctor’s view of the drainage tissue, the procedure cannot be performed effectively. Your eye doctor can determine whether SLT is a suitable option based on the type and severity of your glaucoma and the anatomy of your drainage angle.