Selective laser trabeculoplasty (SLT) uses short pulses of low-energy laser light to target pigmented cells in your eye’s drainage tissue, triggering a biological response that helps fluid flow out more freely and lowers eye pressure. The procedure typically reduces intraocular pressure (IOP) by 20% to 35%, and it’s now recommended as a first-line treatment for open-angle glaucoma in many countries.
What Happens Inside the Eye
Your eye constantly produces a clear fluid called aqueous humor, which drains through a spongy ring of tissue called the trabecular meshwork. In glaucoma, this meshwork becomes less efficient at draining fluid, causing pressure to build up and gradually damage the optic nerve. SLT works by restoring drainage through this tissue.
The laser selectively targets pigmented (melanin-containing) cells in the trabecular meshwork. These darker cells absorb the laser energy much more readily than the surrounding unpigmented cells, which is where the “selective” in the name comes from. The energy delivered is extremely brief, just 3 nanoseconds per pulse, and low-power (typically 0.4 to 1.2 millijoules). This is enough to trigger a biological reaction without burning or scarring the tissue.
That biological reaction is the real engine of SLT. The laser energy sets off a controlled inflammatory and immune response within the meshwork. The body sends immune cells called monocytes to the treated area, and the meshwork cells begin releasing signaling molecules that kick off a remodeling process. Over the following weeks, the extracellular matrix (the structural scaffolding between cells) is reorganized, cell junctions loosen, and the tissue becomes more permeable. The canal that collects drained fluid also becomes more conductive. The net effect: fluid flows out more easily, and eye pressure drops.
How SLT Differs From Older Laser Treatments
The predecessor to SLT, argon laser trabeculoplasty (ALT), used a continuous-wave laser that delivered significantly more energy and created thermal burns in the trabecular meshwork. Those burns caused permanent scarring, which meant ALT could generally only be performed once on each eye. If the effect wore off, there was limited tissue left to treat again.
SLT’s 532-nanometer wavelength laser and ultrashort pulse duration avoid this problem. Because the energy targets only pigmented cells and doesn’t generate enough heat to scar surrounding tissue, the meshwork’s overall structure stays intact. This is what makes the procedure repeatable.
How Effective Is SLT?
For primary open-angle glaucoma, reported IOP reductions range from about 7% to 36%, depending on disease severity and baseline pressure. One prospective study of patients with a specific type of glaucoma found an average IOP reduction of 31% at one year, with 85% of eyes achieving at least a 20% pressure drop. Generally, patients with higher starting eye pressure and more pigment in their drainage angle tend to see larger reductions.
When used as a first-line treatment (before eye drops), SLT achieves drop-free disease control in roughly 75% of eyes at three years. Success rates are also higher when SLT is used as a first treatment rather than added after drops have already been started.
How Long the Effect Lasts
SLT is not a permanent fix. Its pressure-lowering effect gradually fades for many patients. One large retrospective study found that about 80% of treated eyes still had a meaningful effect at 3 years, but that dropped to around 61% by 5 years. Within that same 5-year window, nearly half of eyes required an additional procedure, whether a repeat SLT or a different type of surgery. Over 10 years, about 60% of patients need retreatment.
The good news is that repeat SLT works. A study tracking patients for two years after a second treatment found that 29% to 39% of eyes maintained clinically significant pressure reductions, numbers that were statistically comparable to initial treatment results. No concerning pressure spikes were recorded after either the first or second procedure in that study.
What the Procedure Feels Like
SLT is done in the office, not an operating room. You sit at a slit lamp (the same type of microscope used during a routine eye exam), and your doctor places a special lens on your eye after numbing it with drops. The laser is applied through this lens in a series of brief pulses around the drainage angle. The entire treatment takes roughly 5 to 10 minutes. Most people feel little to nothing during the procedure, though some notice a mild sensation with each pulse.
Afterward, your vision may be slightly blurry and your eye may feel irritated or look red. Mild inflammation inside the eye is extremely common, occurring in more than 80% of treated eyes, but this is actually part of how SLT works. It typically resolves within about 5 days. Your doctor will likely prescribe anti-inflammatory drops for a short period. About 5% of patients experience mild pain or discomfort, and roughly 5% to 6% have a temporary pressure spike in the hours after treatment. These spikes are transient and monitored at a follow-up visit, usually the next day or within a week.
Recovery is fast. There’s no patch or shield required, and most people return to normal activities within a day. The full pressure-lowering effect develops gradually over weeks as the biological remodeling process takes place, so your doctor will check your pressure at follow-up visits over the next one to three months to gauge the response.
Who Gets the Best Results
Two factors consistently predict how well SLT will work: your starting eye pressure and how much pigment is in your drainage angle. Higher baseline IOP gives the laser more room to produce a noticeable drop. Eyes with more pigment in the trabecular meshwork absorb the laser energy more efficiently, so treatment tends to be more effective in those cases. Eyes with very little angle pigmentation are more likely to have a limited response.
SLT is effective across several types of glaucoma, including primary open-angle glaucoma, pseudoexfoliative glaucoma, and normal-tension glaucoma. It is not appropriate for closed-angle glaucoma, where the drainage angle is physically blocked rather than dysfunctional. Your eye doctor can assess your angle pigmentation and anatomy during a gonioscopy exam to determine whether you’re a good candidate.