SLT stands for selective laser trabeculoplasty, a 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, and it can be used as a first-line treatment instead of daily eye drops or alongside them. (In some contexts, SLT also stands for speech and language therapist, but the medical eye procedure is the more common search.)
How SLT Works
Inside your eye, fluid is constantly being produced and drained. It drains through a tiny ring of tissue called the trabecular meshwork. In glaucoma, this meshwork becomes less efficient, fluid backs up, and pressure inside the eye rises. Over time, that elevated pressure damages the optic nerve and can lead to vision loss.
SLT uses a precisely tuned laser to target only the pigmented cells within the meshwork, leaving surrounding tissue unharmed. A short burst of energy heats these pigmented cells before neighboring cells absorb enough energy to be affected. This selective approach triggers a biological healing response: the body sends in new cells that repopulate the meshwork, produce fresh structural material, and clean out debris that was clogging the drainage pathway. The result is improved fluid outflow and lower eye pressure.
Who Is a Candidate
SLT is used for people with primary open-angle glaucoma (the most common type), ocular hypertension, and several secondary forms of glaucoma including pseudoexfoliative glaucoma, pigmentary glaucoma, and steroid-induced glaucoma. It can also help in normal-tension glaucoma, though the pressure reductions tend to be more modest.
It is not recommended for neovascular glaucoma, congenital glaucoma, or uveitic glaucoma with active inflammation. If the drainage angle of the eye is extensively closed or can’t be clearly seen during the procedure, SLT isn’t an option. People with a history of uveitis who have been free of inflammation for a significant period may still benefit.
What the Procedure Feels Like
SLT is performed in a clinic or office, not an operating room. Numbing drops are placed in the eye, and a special lens is held against it so the doctor can visualize the drainage tissue. The laser pulses are delivered over a few minutes. Most people feel little to no discomfort during the procedure itself.
Mild inflammation is common afterward. In the original FDA study of 120 patients, about 83 to 89 percent had some degree of inflammation inside the eye in the days following treatment. This typically resolves on its own or with a short course of anti-inflammatory drops. Pain or discomfort was reported in about 5 percent of patients, redness in another 5 percent, and a temporary pressure spike in roughly 5 to 6 percent. Corneal swelling is rare, occurring in less than 1 percent of cases.
Most people return to normal activities like reading, using screens, and light work within a few days. Follow-up visits are typically scheduled the day after the procedure and then every one to three weeks for two to three months to monitor pressure.
How Well It Works
The landmark LiGHT trial, one of the largest studies comparing SLT to eye drops as a first treatment for glaucoma, found that nearly 70 percent of eyes treated with SLT stayed at or below their target pressure after six years without needing drops or surgery. That’s a significant finding because it means many patients can avoid the daily burden, cost, and side effects of eye drop medications for years.
That said, SLT is not permanent. In longer-term follow-up studies, the success rate was about 62 percent at one year, 34 percent at two years, and 24 percent at four years, with an average time to needing additional treatment of about 18 months. These numbers vary depending on how strictly “success” is defined and the severity of someone’s glaucoma. Many patients eventually need a repeat procedure or the addition of drops.
Why SLT Can Be Repeated
An older version of this procedure, called argon laser trabeculoplasty (ALT), used higher energy that caused permanent structural scarring of the drainage tissue. That scarring limited ALT to essentially one or two treatments in a lifetime. SLT, by contrast, uses a different laser type that selectively targets pigmented cells without causing the same mechanical and thermal injury to the surrounding tissue structure. Because the meshwork isn’t scarred, SLT can be repeated when its effects wear off. This repeatability is one of the main reasons SLT has largely replaced ALT in clinical practice.
SLT as a First Treatment vs. Add-On
Traditionally, eye drops were the default first step for managing glaucoma, with laser reserved for patients who didn’t respond well or couldn’t tolerate their medications. That approach has shifted. Growing evidence supports SLT as a first-line treatment, meaning it can be offered before eye drops are ever started. For many patients, this eliminates the need for daily drops entirely, at least for several years.
SLT also works as an add-on for people already using drops who need additional pressure lowering, and as a replacement strategy for patients who want to reduce the number of medications they use. Some people struggle with the cost, side effects, or simple inconvenience of remembering daily drops, and SLT offers an alternative path to pressure control.