Selective Laser Trabeculoplasty (SLT)
What Is Selective Laser Trabeculoplasty (SLT)?
Selective laser trabeculoplasty, commonly known as SLT, is a safe and effective in-office laser procedure used to lower eye pressure in patients with open-angle glaucoma or ocular hypertension (higher-than-normal eye pressure without optic nerve damage). At Greenwich Ophthalmology Associates, our fellowship-trained glaucoma specialists use SLT as both a first-line treatment and a complement to eye drop therapy, helping patients across the greater NY/CT region protect their vision with a gentle, noninvasive approach. If you have been diagnosed with glaucoma or told your eye pressure is elevated, SLT may be an excellent option to consider. Understanding how SLT works, who benefits most, and what to expect during the procedure can help you feel confident about your treatment plan.
SLT is a type of laser treatment specifically designed to improve the natural drainage of fluid inside the eye, which in turn helps reduce intraocular pressure (IOP).
Open-angle glaucoma is the most common form of glaucoma, and it develops when the eye's drainage system gradually becomes less efficient at moving fluid out of the eye. This fluid buildup increases intraocular pressure, which can damage the optic nerve and lead to progressive vision loss. SLT addresses this problem directly by applying low-energy laser pulses to the drainage tissue, helping restore more normal fluid outflow without cutting or altering the structure of the eye.
The term 'selective' refers to how the laser energy interacts with the eye's tissue. SLT targets only the pigmented cells within the trabecular meshwork (the eye's natural drainage channel) while leaving surrounding non-pigmented cells unharmed. Because the treatment does not cause thermal or structural damage to the drainage tissue, SLT preserves the option for future treatments and does not limit other glaucoma therapies down the road.
Major clinical research, including the landmark LiGHT (Laser in Glaucoma and Ocular Hypertension) Trial, has shown that SLT is clinically effective and cost-effective as an initial treatment for open-angle glaucoma. In that study, nearly 70% of eyes treated with SLT first remained at or below their target pressure after six years without needing daily eye drops or surgery. Based on this evidence, both the American Academy of Ophthalmology and the European Glaucoma Society now support SLT as a first-line option alongside or instead of traditional eye drop therapy.
How SLT Lowers Eye Pressure
SLT works by stimulating a natural biological response within the eye's drainage system rather than creating a new drainage pathway or permanently altering tissue.
The trabecular meshwork is a ring of spongy tissue located where the colored part of the eye (iris) meets the clear front surface (cornea). This tissue acts as the primary drain for aqueous humor, the fluid that fills the front of the eye. In open-angle glaucoma, the trabecular meshwork becomes less efficient over time, causing fluid to accumulate and pressure to rise. During SLT, short pulses of low-energy laser light are applied to this tissue in a precise, controlled pattern.
Rather than burning or scarring the tissue, SLT triggers a chemical and biological response within the trabecular meshwork. The laser energy stimulates the body's own cells to remodel and clear debris from the drainage channels, improving their ability to filter fluid out of the eye. This gentle mechanism is what allows SLT to be repeated if the effect diminishes over time, since the underlying tissue structure remains intact.
When used as an initial therapy, SLT typically lowers intraocular pressure by approximately 20% to 30%, which is comparable to the pressure-lowering effect of prostaglandin analog eye drops, the most commonly prescribed class of glaucoma medication. The degree of pressure reduction may vary depending on your starting pressure, the type of glaucoma, and whether you are already using other treatments. Our glaucoma specialists will discuss a realistic target pressure based on your individual condition and risk factors.
Who Is a Candidate for SLT?
SLT is a versatile treatment that works well for a range of patients, from those newly diagnosed to those looking for additional pressure control beyond their current medications.
If you have recently been diagnosed with open-angle glaucoma or ocular hypertension, SLT may be recommended as your first treatment before starting daily eye drops. Research from the LiGHT Trial demonstrated that patients who began with SLT had better long-term disease control, a slower rate of visual field loss, and fewer overall interventions compared with those who started on drops. SLT can be especially appealing for patients who want to avoid the daily routine, cost, and potential side effects of long-term eye drop use.
SLT is also effective for patients who are already on one or more glaucoma medications but need additional pressure lowering. In some cases, a successful SLT treatment can reduce the number of drops you need each day. It is also a helpful option for patients who have difficulty using eye drops consistently due to physical limitations, forgetfulness, or side effects such as redness and irritation.
Because SLT does not cause permanent structural damage to the trabecular meshwork, patients who previously had a successful SLT treatment can often undergo the procedure again when the effect fades. Patients who had an older form of laser treatment called argon laser trabeculoplasty (ALT) may also be candidates for SLT, though the expected pressure reduction may be more modest.
SLT is most effective for open-angle forms of glaucoma. Patients with angle-closure glaucoma, certain inflammatory glaucoma types, or very advanced disease may require different approaches. Our glaucoma specialists will evaluate your eye anatomy, glaucoma type, and treatment history to determine whether SLT is the right choice or whether another option such as glaucoma surgery would be more appropriate.
What Happens During an SLT Procedure
SLT is performed in our office and does not require an operating room, general anesthesia, or any incisions.
On the day of your SLT treatment, you will receive numbing eye drops so you remain comfortable throughout the procedure. A special lens is then placed gently on the surface of your eye to help direct the laser and give your doctor a clear view of the trabecular meshwork. You may also receive an anti-inflammatory or pressure-lowering drop before or after treatment. There is no need to stop eating or change your regular medications beforehand.
The actual laser application takes approximately five to ten minutes per eye. You will sit at a standard slit-lamp microscope, similar to the one used during routine eye exams. Your doctor will deliver a series of brief, low-energy laser pulses to the drainage tissue. Most patients see small flashes of light during the treatment but feel little to no discomfort. The total number of laser applications is typically between 80 and 100, covering either a portion or the full circumference of the trabecular meshwork.
You can return to most normal activities, including reading and watching screens, within the same day. Your doctor will check your eye pressure about 30 to 60 minutes after the treatment before you leave the office. You may be prescribed a short course of anti-inflammatory eye drops to use for several days following the procedure. A follow-up visit is typically scheduled within two to six weeks to assess how well SLT is lowering your pressure. You can learn more about what recovery looks like for various glaucoma procedures on our glaucoma surgery recovery page.
Frequently Asked Questions
Most patients experience little to no pain during SLT. Numbing drops are applied before the procedure, and the low-energy laser pulses feel mild. Some patients notice a brief sensation of warmth or a slight sting with certain laser applications, but this typically passes quickly. After the procedure, mild soreness or light sensitivity may occur for a day or two and usually resolves without treatment.
The pressure-lowering effect of SLT develops gradually over the weeks following treatment. Some patients notice a reduction within the first few days, while for others the full effect may take four to eight weeks to become apparent. Our glaucoma specialists will monitor your pressure during follow-up visits to determine how well the treatment is working and whether any adjustments to your overall care plan are needed.
The effects of a single SLT treatment generally last between one and five years, with many patients experiencing meaningful pressure control for two to three years. The duration varies based on individual factors such as your type of glaucoma, baseline pressure, and overall eye health. As the effect gradually fades, your doctor will discuss next steps, which may include repeating SLT or adding other treatments.
Yes, SLT can be repeated if the initial treatment was successful and the effect has worn off over time. Because SLT does not cause permanent scarring or structural changes to the trabecular meshwork, the tissue can respond to retreatment. Studies show that repeat SLT provides a meaningful and significant reduction in eye pressure, though the magnitude of reduction may be slightly less than the first treatment in some patients. There is no fixed limit on how many times SLT can be performed, but your doctor will weigh the benefits against other available options including alternative laser procedures.
SLT has an excellent safety profile. The most common side effect is mild, temporary inflammation inside the eye, which typically resolves within a few days with or without anti-inflammatory drops. A temporary spike in eye pressure can occur shortly after the procedure, which is why your pressure is checked before you leave the office. Serious complications are rare. SLT does not affect your eligibility for future glaucoma treatments, including eye drops, additional laser procedures, or surgery.
SLT produces a comparable reduction in eye pressure to the most widely used class of glaucoma drops, prostaglandin analogs. A key advantage of SLT is that it eliminates the daily burden of remembering to use drops and avoids common drop-related side effects such as redness, stinging, and changes to the skin around the eyes. The LiGHT Trial also found that patients who started with SLT had a slower rate of visual field progression over time compared with those who began on drops alone. For patients who prefer a treatment that requires fewer daily steps, SLT offers a practical and effective alternative.
Schedule Your Glaucoma Consultation
If you have been diagnosed with glaucoma or ocular hypertension, selective laser trabeculoplasty may help you achieve better pressure control with fewer daily medications. Our glaucoma specialists at Greenwich Ophthalmology Associates are experienced in performing SLT and will work with you to determine whether this treatment fits your needs and goals. We are here to guide you through every step, from your initial evaluation to long-term monitoring, so you can feel confident in your path to preserving your vision.
We encourage you to bring your questions and concerns to your next appointment so we can develop a care plan that addresses your goals and lifestyle.
Learn More About Related Topics
To further your understanding, explore our resources on SLT Laser: A First-Line Alternative to Eye Drops, Glaucoma Treatment Options: Drops, Laser and Surgery, and Laser Peripheral Iridotomy (LPI) for Glaucoma.
You may also find these pages helpful: Angle-Closure Glaucoma: Recognizing the Emergency, Angle-Closure Glaucoma: Symptoms & Emergency Treatment, and Brimonidine Eye Drops for Glaucoma.
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