Everything About SLT (Selective Laser Trabeculoplasty)

By Dr. Phornrak Sriphon, Ophthalmologist and Glaucoma Specialist

Introduction

In the past, glaucoma treatment typically began with pressure-lowering eye drops, and many patients needed to continue using these medications for years. Today, however, the approach to glaucoma management is evolving. Growing scientific evidence supports the use of Selective Laser Trabeculoplasty (SLT) as an initial treatment option in appropriately selected patients, meaning that treatment does not always have to begin with eye drops.

SLT is a laser treatment applied to the trabecular meshwork, the eye’s natural drainage tissue. It helps improve the outflow of aqueous humor and thereby lowers intraocular pressure without the need for a surgical incision. SLT now plays an increasingly important role in glaucoma management, particularly for appropriately selected patients with open-angle glaucoma and ocular hypertension.

This article explains how SLT works, how effectively it lowers intraocular pressure, who may benefit from the treatment, what to expect during and after the procedure, and the scientific evidence that has established SLT as an important treatment option in modern glaucoma care.

Topic 

1. Why Is SLT Becoming More Widely Used?

2. What Does SLT Stand For?

3. Understanding the Basics Before SLT

4. Which Types of Glaucoma Can Be Treated with SLT?

5. How Does SLT Work?

6. Efficacy and Safety of SLT

7. Key Evidence That Changed Glaucoma Treatment

8. Who Is a Good Candidate for SLT?

9. Preparing for SLT

10. What Happens During an SLT Procedure?

11. Care After SLT

12. Frequently Asked Questions (FAQ)

13. Summary

Topic 1 Why Is SLT Becoming More Widely Used?

Glaucoma is a chronic disease that, once diagnosed, usually requires ongoing treatment and regular monitoring. The primary goal of treatment is to lower intraocular pressure (IOP) to an appropriate level in order to slow further damage to the optic nerve and preserve vision for as long as possible.

Traditionally, glaucoma treatment has often begun with pressure-lowering eye drops, which are effective and have long been a standard treatment. However, successful long-term management of a chronic disease depends not only on how well a medication works, but also on treatment adherence.

In everyday life, some patients may forget to use their eye drops, have difficulty administering them correctly, or experience side effects such as stinging, redness, or ocular surface irritation. When treatment must be continued for many years, these factors can affect how effectively intraocular pressure is controlled.

From Eye Drops to First-Line SLT

Today, a growing body of scientific evidence supports Selective Laser Trabeculoplasty (SLT) as one of the initial treatment options for appropriately selected patients.

Large clinical studies, including the LiGHT Trial, have shown that starting treatment with SLT can provide effective intraocular pressure control and allow many patients to maintain adequate disease control without the need for pressure-lowering eye drops for several years.

This evidence has contributed significantly to changes in modern glaucoma management. International professional organizations, including the European Glaucoma Society (EGS) and the American Academy of Ophthalmology (AAO), recognize SLT as an initial treatment option in appropriately selected patients.

However, SLT is not suitable for every patient with glaucoma. Treatment decisions should take into account the type of glaucoma, the anatomy of the anterior chamber angle, disease severity, the target intraocular pressure, and individual patient factors.

To understand why SLT can lower intraocular pressure, it is helpful to first understand how intraocular pressure is generated and how the eye’s natural drainage system works.

Topic 2 What Does SLT Stand For?

Selective Laser Trabeculoplasty (SLT) is a laser treatment used to lower intraocular pressure (IOP). The laser is applied to the trabecular meshwork, which is the main pathway through which aqueous humor drains from the eye.

The word “selective” refers to an important characteristic of this laser. SLT energy is preferentially absorbed by melanin pigment within the trabecular meshwork. Because the laser delivers relatively low energy in extremely short pulses, it produces less thermal damage to surrounding structures compared with older laser techniques.

SLT does not create a new opening or drainage channel. Instead, it triggers a biological response within the trabecular meshwork involving cellular signaling and tissue remodeling. These changes help reduce resistance to aqueous outflow through the eye’s natural drainage pathway, resulting in lower intraocular pressure.

How Is SLT Different from Other Glaucoma Laser Treatments?

Before SLT became widely used, Argon Laser Trabeculoplasty (ALT) was commonly performed to lower intraocular pressure. ALT relies more heavily on thermal energy and produces structural changes in the treated trabecular meshwork. In comparison, SLT uses substantially less energy and causes less thermal injury to the surrounding tissue.

Laser Peripheral Iridotomy (LPI) is a different type of glaucoma laser procedure. It creates a small opening in the peripheral iris to help equalize pressure and improve aqueous flow between the posterior and anterior chambers of the eye. LPI is commonly used in patients with narrow or closed anterior chamber angles and therefore has a different purpose and mechanism of action from SLT.

Although SLT, ALT, and LPI are all laser procedures used in glaucoma care, they differ in the structures they target, their mechanisms of action, and their clinical indications. The appropriate laser treatment therefore depends on the type of glaucoma and the individual anatomy of the patient’s eye.

Topic 3 Understanding the Basics Before SLT

Before understanding how SLT lowers intraocular pressure, it is important to understand the basic principles of glaucoma and how pressure within the eye is regulated.

Glaucoma is often thought of simply as a disease caused by high eye pressure. In reality, glaucoma is a group of diseases characterized by progressive damage to the optic nerve, known as glaucomatous optic neuropathy. This process involves the progressive loss of retinal ganglion cells and their nerve fibers, leading to characteristic visual field loss and, in advanced stages, potentially irreversible loss of vision.

Elevated intraocular pressure is a major risk factor for glaucoma, but not every patient with glaucoma has high eye pressure. Optic nerve damage can occur even when intraocular pressure remains within the range considered statistically normal for the general population.

At present, optic nerve damage that has already occurred from glaucoma cannot be restored. Treatment therefore focuses on preventing or slowing further damage. Lowering intraocular pressure is currently the only established modifiable treatment with strong clinical evidence for reducing the risk of glaucoma development and slowing disease progression.

The appropriate intraocular pressure is not the same for every patient. Instead, ophthalmologists establish an individualized target intraocular pressure (target IOP) based on factors such as the severity of glaucoma, pretreatment intraocular pressure, rate of disease progression, age, and other relevant risk factors. Since lowering intraocular pressure is central to glaucoma management, the next step is to understand how pressure is generated within the eye and why treating the eye’s drainage system with laser can lower that pressure.

How Is Intraocular Pressure Generated?

Inside the eye is a clear fluid called aqueous humor, which is continuously produced and provides nutrients and oxygen to structures that do not have their own direct blood supply, including the cornea and crystalline lens. Aqueous humor also plays an important role in maintaining the pressure and structural integrity of the eye.

Aqueous humor is produced by the ciliary body, located behind the iris. It then flows through the pupil into the anterior chamber before leaving the eye. The main drainage pathway carries aqueous humor through the trabecular meshwork, into Schlemm’s canal, and subsequently through the downstream drainage channels into the venous circulation around the eye.

Under normal conditions, the production and drainage of aqueous humor remain in balance, helping maintain intraocular pressure within an appropriate range. If resistance to aqueous outflow increases, intraocular pressure can rise even when the amount of fluid being produced remains unchanged.

A useful analogy is a sink with the faucet running at a constant rate. When the drain is functioning properly, the water level remains stable. If resistance within the drain increases while the faucet continues to deliver the same amount of water, the water level begins to rise. A similar principle applies to pressure within the eye.

The Anterior Chamber Angle and the Eye’s Drainage System

The area where the cornea and iris meet is called the anterior chamber angle. This region contains important structures involved in the drainage of aqueous humor.

Within the angle lies the trabecular meshwork, an important part of the conventional aqueous outflow pathway and a major site of resistance to aqueous drainage. After passing through the trabecular meshwork, aqueous humor enters Schlemm’s canal and then flows through smaller downstream drainage channels before reaching the venous circulation around the eye.

The anatomy of the anterior chamber angle is therefore important both for diagnosing glaucoma and for selecting the appropriate treatment. When the angle is open and the trabecular meshwork can be adequately visualized, treatments directed at this structure may be considered. In eyes with narrow or closed angles, the mechanism of disease and the appropriate treatment approach are different.

How Does SLT Lower Intraocular Pressure?

Selective Laser Trabeculoplasty (SLT) is applied directly to the trabecular meshwork with the aim of improving aqueous outflow through the eye’s natural drainage pathway. Unlike some glaucoma medications, SLT does not lower intraocular pressure by reducing aqueous humor production.

SLT uses low-energy laser pulses of very short duration. The laser energy is preferentially absorbed by melanin within the trabecular meshwork, producing minimal thermal damage to surrounding tissue compared with older laser techniques.

The effect of SLT does not result from “creating a hole” or “burning open” the drainage pathway. Instead, the laser triggers a biological response within the trabecular meshwork. Changes in cellular activity and tissue remodeling help reduce resistance to aqueous outflow, allowing fluid to leave the eye more efficiently and thereby lowering intraocular pressure.

Because SLT works through these biological processes, its full pressure-lowering effect does not necessarily occur immediately after treatment. The response is typically assessed over the following weeks, and the degree of intraocular pressure reduction varies among individual patients.

The key principle is that SLT does not create a new drainage pathway; it improves the function of the eye’s existing natural outflow system.

Topic 4 Which Types of Glaucoma Can Be Treated with SLT?

Now that we understand that SLT targets the trabecular meshwork, it becomes clear why this treatment is not suitable for every type of glaucoma.

An important requirement for SLT is that the anterior chamber angle must be sufficiently open for the ophthalmologist to visualize and treat the trabecular meshwork. For this reason, SLT is primarily used in patients with open-angle glaucoma, as well as in patients with ocular hypertension who have an indication for intraocular pressure reduction.

Before considering SLT, the ophthalmologist therefore needs to evaluate the anterior chamber angle using gonioscopy. This examination determines whether the trabecular meshwork is adequately visible and accessible for laser treatment.

Which Patients May Be Considered for SLT?

• Primary Open-Angle Glaucoma

Patients with primary open-angle glaucoma (POAG) represent the main group in whom SLT may be considered. The anterior chamber angle is open, but resistance to aqueous outflow through the trabecular meshwork is increased. This can contribute to elevated intraocular pressure and progressive damage to the optic nerve.

Because SLT directly targets the trabecular meshwork, it may be used as an initial treatment or as an additional treatment in patients who are already using pressure-lowering eye drops.

• Ocular Hypertension

Ocular hypertension refers to elevated intraocular pressure without evidence of glaucomatous optic nerve damage or characteristic visual field loss.

Not every patient with ocular hypertension requires treatment. However, when an individual is considered to be at sufficient risk of developing glaucoma and lowering intraocular pressure is indicated, SLT may be considered as one of the treatment options.

• Normal-Tension Glaucoma

Some patients develop glaucomatous optic nerve damage even though their measured intraocular pressure does not exceed the statistically normal range for the general population. This is known as normal-tension glaucoma (NTG).

Clinical evidence has shown that lowering intraocular pressure from an individual patient’s baseline can reduce the risk of disease progression in appropriately selected patients. Therefore, when further pressure reduction is required and the anterior chamber angle is sufficiently open, SLT may be considered.

However, because patients with normal-tension glaucoma generally have a lower baseline intraocular pressure, the absolute reduction in pressure following SLT may be smaller than in patients with higher pretreatment pressures.

• Pseudoexfoliative Glaucoma

Pseudoexfoliative glaucoma is associated with the accumulation of abnormal extracellular material within the anterior segment of the eye, including the trabecular meshwork. This can increase resistance to aqueous outflow and result in elevated intraocular pressure.

SLT can effectively lower intraocular pressure in appropriately selected patients with pseudoexfoliative glaucoma, and some patients may respond particularly well. However, this form of glaucoma may be associated with higher and more variable intraocular pressure than primary open-angle glaucoma, making continued monitoring of both intraocular pressure and disease progression especially important.

• Pigmentary Glaucoma

Pigmentary glaucoma occurs when pigment released from the iris accumulates within the trabecular meshwork, contributing to increased resistance to aqueous outflow.

SLT can be used to lower intraocular pressure in appropriately selected patients with pigmentary glaucoma. However, because the trabecular meshwork may be heavily pigmented, particular attention must be paid to the risk of a temporary rise in intraocular pressure after laser treatment (post-laser IOP spike). The ophthalmologist may therefore adjust the laser energy and monitor intraocular pressure after treatment according to the individual patient’s risk.

Can SLT Be Performed in Angle-Closure Glaucoma?

A fundamental requirement for SLT is that the ophthalmologist must be able to visualize the trabecular meshwork so that the laser can reach its intended target.

In angle-closure glaucoma, the iris may obstruct part or all of the trabecular meshwork, preventing SLT from being applied to the areas that are closed. SLT is therefore not a primary treatment for the angle-closure mechanism itself. Treatment may instead involve Laser Peripheral Iridotomy (LPI), cataract surgery, or other approaches depending on the underlying mechanism and individual clinical findings.

However, in selected patients who have already received treatment for angle closure and subsequently have a sufficiently open anterior chamber angle with an adequately visible trabecular meshwork, SLT may be considered as an additional option for lowering intraocular pressure.

Therefore, the decision to use SLT is based not only on the diagnostic label, but also on anterior chamber angle anatomy, the extent of visible and accessible trabecular meshwork, the level of intraocular pressure, and the individual treatment target.

Topic 5 How Does SLT Work?

SLT is sometimes misunderstood as a laser that “burns” the trabecular meshwork or creates a new drainage opening. In reality, SLT works in a very different way.

SLT uses a low-energy, 532-nanometer laser delivered in extremely short pulses measured in nanoseconds. The laser energy is preferentially absorbed by melanin pigment within the trabecular meshwork. Because the pulse duration is extremely short, there is minimal transfer of thermal energy to the surrounding tissue. This distinguishes SLT from older laser techniques that produce greater thermal effects and structural changes within the trabecular meshwork.

Selective Photothermolysis

A key principle underlying the development of SLT is selective photothermolysis. This concept relies on differences in the absorption of laser energy by pigment within the target tissue, combined with a very short laser pulse duration to limit the spread of heat to adjacent structures.

As a result, SLT produces substantially less thermal damage and structural alteration to the trabecular meshwork compared with Argon Laser Trabeculoplasty (ALT).

How Does SLT Lower Intraocular Pressure?

Although the mechanisms of SLT have been studied extensively, the cellular processes responsible for its pressure-lowering effect are not yet fully understood. Current evidence suggests that laser treatment of the trabecular meshwork triggers a combination of biological responses.

These responses involve cellular signaling, the release of cytokines and other signaling molecules, immune-cell activity, and extracellular matrix remodeling within the trabecular meshwork.

Together, these biological changes are thought to reduce resistance to aqueous outflow, allowing aqueous humor to pass more efficiently through the trabecular meshwork into Schlemm’s canal and the downstream drainage system. As aqueous outflow improves, intraocular pressure decreases.

In other words, SLT does not create a new drainage pathway; it improves the function of the eye’s existing natural outflow system.

How Is SLT Different from Glaucoma Eye Drops?

SLT lowers intraocular pressure by improving aqueous outflow through the eye’s natural drainage system. In contrast, glaucoma eye drops work through several different mechanisms. Some medications reduce the production of aqueous humor, while others increase aqueous outflow through different drainage pathways.

Therefore, SLT does not lower intraocular pressure by reducing aqueous humor production. Instead, it primarily acts by reducing resistance to aqueous outflow through the trabecular meshwork, allowing fluid to leave the eye more efficiently and thereby lowering intraocular pressure.

Summary

SLT uses low-energy laser treatment directed at the trabecular meshwork. It does not create a new drainage opening and produces minimal thermal damage to the surrounding tissue. Following laser treatment, a series of biological responses occurs within the trabecular meshwork, helping to improve aqueous outflow and lower intraocular pressure.

The minimal thermal structural alteration produced by SLT contributes to its favorable safety profile and is one of the reasons why repeat SLT may be considered in selected patients if its pressure-lowering effect diminishes over time.

Topic 6 Efficacy and Safety of SLT

In general, Selective Laser Trabeculoplasty (SLT) can lower intraocular pressure by approximately 20–30% from pretreatment levels in patients who respond to treatment. Its overall pressure-lowering effect is generally comparable to that achieved with a single topical glaucoma medication.

However, the response to SLT varies among individuals. Some patients experience a substantial reduction in intraocular pressure and may be able to reduce the number of pressure-lowering eye drops they require, whereas others may experience only a modest reduction or may not respond adequately to treatment.

An important factor associated with treatment response is the baseline intraocular pressure. Patients with higher pretreatment intraocular pressure generally tend to achieve a greater pressure reduction. SLT may also be considered in patients with normal-tension glaucoma (NTG); however, because their baseline intraocular pressure is relatively low, the absolute reduction in pressure is often smaller than in patients with higher starting pressures.

The full effect of SLT does not necessarily occur immediately after treatment. Because its pressure-lowering effect depends on biological responses and changes in the function of the eye’s drainage system, treatment response is generally assessed over the following weeks. In patients who respond well, the pressure-lowering effect may persist for several years, although it can gradually diminish over time.

If the initial SLT treatment is effective but its effect later decreases, repeat SLT may be considered in selected patients. This is possible in part because SLT produces minimal thermal structural damage to the trabecular meshwork. However, the response to repeat treatment varies, and the degree of pressure reduction cannot be guaranteed to be the same as after the initial procedure.

In terms of safety, SLT is a non-incisional laser procedure with a generally favorable safety profile. Most adverse effects are mild and temporary, such as eye redness, irritation, mild blurred vision, or anterior chamber inflammation.

An important complication to monitor for is a temporary increase in intraocular pressure after treatment (post-laser IOP spike). This may be particularly important in patients with advanced glaucoma or in eyes with heavily pigmented trabecular meshwork, such as those with pigmentary glaucoma. Depending on the individual risk, the ophthalmologist may administer pressure-lowering medication before or after the procedure and monitor intraocular pressure following treatment.

Importantly, SLT does not cure glaucoma and does not prevent the use of other glaucoma treatments in the future. If intraocular pressure cannot be controlled to the desired level, patients may still require pressure-lowering eye drops, repeat SLT in appropriate cases, or glaucoma surgery.

Overall, SLT is an effective option for lowering intraocular pressure and may reduce the burden of daily eye-drop treatment in some patients. The decision to use SLT should be individualized according to the type and severity of glaucoma, anterior chamber angle anatomy, baseline intraocular pressure, and the patient’s target intraocular pressure (target IOP).

Topic 7 Key Evidence That Changed Glaucoma Treatment

Scientific Evidence Supporting SLT

The role of Selective Laser Trabeculoplasty (SLT) in glaucoma management has changed substantially over the past several years. Traditionally, SLT was often considered after treatment with pressure-lowering eye drops was insufficient. Today, however, SLT may be considered as an initial treatment option in appropriately selected patients.

This shift in clinical practice has been supported by a growing body of scientific evidence, particularly the LiGHT Trial, together with recommendations from major international glaucoma guidelines and professional organizations.

The LiGHT Trial (Laser in Glaucoma and Ocular Hypertension Trial)

The Laser in Glaucoma and Ocular Hypertension Trial (LiGHT) was a large randomized controlled trial conducted in the United Kingdom. It compared an SLT-first treatment strategy with an eye-drop-first strategy in patients newly diagnosed with open-angle glaucoma (OAG) or ocular hypertension (OHT).

Importantly, the LiGHT Trial evaluated more than intraocular pressure alone. It examined outcomes relevant to long-term glaucoma management, including disease control, use of pressure-lowering eye drops, quality of life, the need for additional treatment, and cost-effectiveness.

The initial results showed that many patients who started treatment with SLT were able to maintain adequate intraocular pressure control without requiring pressure-lowering eye drops for several years. At the same time, the SLT-first strategy provided effective intraocular pressure control and overall quality-of-life outcomes comparable to those achieved with an eye-drop-first approach.

Longer-term follow-up has further supported the role of SLT as an initial treatment option, particularly by demonstrating a reduced burden of daily eye-drop treatment and a reduced need for treatment escalation in some patients.

The LiGHT Trial therefore represents an important body of evidence that has contributed to a shift in modern glaucoma management away from the traditional concept of “always starting with eye drops” toward a more individualized choice of initial treatment.

European Glaucoma Society (EGS) Guidelines

Guidelines from the European Glaucoma Society (EGS) recognize SLT as an effective treatment for lowering intraocular pressure and support its use as one of the initial treatment options in appropriately selected patients with open-angle glaucoma or ocular hypertension.

SLT is therefore no longer considered only when eye drops are ineffective or poorly tolerated. In suitable patients, it may be considered from the beginning of the glaucoma treatment plan.

American Academy of Ophthalmology (AAO) Guidelines

The American Academy of Ophthalmology (AAO) guidelines for the management of primary open-angle glaucoma (POAG) recognize SLT as an effective method for lowering intraocular pressure. SLT may be used as an initial treatment or as an adjunct to pressure-lowering medications when additional intraocular pressure reduction is required.

The choice of treatment should therefore be individualized according to factors such as the patient’s intraocular pressure, the severity and rate of glaucoma progression, the target intraocular pressure, medication-related side effects and treatment burden, as well as the individual patient’s preferences and circumstances.

National Institute for Health and Care Excellence (NICE) Guidelines

The National Institute for Health and Care Excellence (NICE) provides more specific recommendations regarding the use of SLT. NICE recommends offering 360° SLT as an initial treatment for patients who are newly diagnosed with non-advanced chronic open-angle glaucoma (COAG).

For patients with ocular hypertension (OHT), NICE recommends offering 360° SLT when intraocular pressure is 24 mmHg or higher and the patient is considered to be at risk of visual impairment within their lifetime. However, individual clinical factors and specific exceptions should also be taken into consideration when selecting treatment.

These recommendations reflect an important change in glaucoma management: SLT is no longer considered only after pressure-lowering eye drops have failed, but may be offered as one of the first treatment options in appropriately selected patients.

Topic 8 Who Is a Good Candidate for SLT?

1. SLT as a First-Line Treatment

SLT may be considered as an initial treatment in patients who are newly diagnosed with primary open-angle glaucoma (POAG) or ocular hypertension (OHT) and have a sufficiently open anterior chamber angle.

Traditionally, treatment often began with pressure-lowering eye drops. However, evidence from the LiGHT Trial and recommendations from major international guidelines now support SLT as an initial treatment option in appropriately selected patients.

One potential advantage is that some patients may achieve adequate intraocular pressure control without having to begin daily eye-drop treatment immediately. This can reduce treatment burden and avoid some of the long-term challenges associated with daily medication adherence.

2. SLT as an Alternative to Eye Drops

SLT may also be considered in patients who are already using pressure-lowering eye drops but experience difficulties with long-term medication use.

These may include frequently forgetting doses, traveling often, difficulty administering eye drops, medication-related stinging or redness, intolerance or allergy to certain medications, or ocular surface disease associated with long-term topical therapy.

In these patients, SLT may help reduce the number of pressure-lowering medications required and, in some cases, may allow eye drops to be discontinued for a period of time. However, the response varies among individuals, and not every patient will be able to stop glaucoma medications completely. Some patients may still require eye drops, but with a reduced medication burden.

3. SLT as an Adjunct to Eye Drops

For many patients, the goal of SLT is not necessarily to discontinue medication, but rather to achieve better intraocular pressure control.

If a patient is already using pressure-lowering eye drops but the intraocular pressure remains above the target IOP, SLT may be added to provide further pressure reduction. In some patients, this may help avoid or delay the need to add multiple additional medications.

Reducing the number of medications required may also decrease treatment complexity, medication-related side effects, and the long-term burden of glaucoma therapy.

4. SLT When Eye Drops Do Not Provide Adequate Control

SLT may also be considered when intraocular pressure remains inadequately controlled despite medical therapy, provided that the anterior chamber angle is open and the trabecular meshwork is accessible to laser treatment.

However, SLT should not necessarily be viewed as a required step before glaucoma surgery. In patients with advanced or rapidly progressing glaucoma, or when a very low target intraocular pressure is required, glaucoma surgery may provide a more appropriate level of pressure reduction and may need to be considered without delaying treatment.

Who May Not Be Suitable for SLT?

SLT may not be appropriate or may have a limited role in certain patients. Examples include eyes in which the anterior chamber angle is closed and the trabecular meshwork cannot be adequately visualized, eyes with active intraocular inflammation, or patients whose disease severity and target intraocular pressure indicate that glaucoma surgery is a more appropriate initial approach.

Therefore, before recommending SLT, the ophthalmologist should evaluate the anterior chamber angle, type and severity of glaucoma, current intraocular pressure, target intraocular pressure, previous treatment, and the individual risk of disease progression.

Topic 9 Preparing for SLT

Before undergoing Selective Laser Trabeculoplasty (SLT), the ophthalmologist will evaluate the condition of the eye, the type and severity of glaucoma, and the level of intraocular pressure that needs to be achieved to determine whether SLT is an appropriate treatment option.

The assessment generally includes measurement of intraocular pressure to establish the pretreatment baseline, together with evaluation of the optic nerve. Visual field testing and Optical Coherence Tomography (OCT) may also be performed as appropriate to assess the severity of glaucoma and establish an individualized target intraocular pressure (target IOP).

Another important examination is gonioscopy, which allows the ophthalmologist to assess the anterior chamber angle. The angle must be sufficiently open and the trabecular meshwork, which is the target of SLT treatment, must be adequately visible and accessible to the laser.

Before SLT, patients generally do not need to stop their pressure-lowering eye drops. Glaucoma medications should usually be continued as prescribed unless the ophthalmologist advises otherwise. Patients should not discontinue or adjust their medications on their own.

SLT is performed using topical anesthesia with anesthetic eye drops and does not require general anesthesia or an injection of anesthetic around the eye. Therefore, patients generally do not need to fast before the procedure and may eat, drink, and take their regular medications as usual unless specifically instructed otherwise.

Patients should inform their ophthalmologist about any medication allergies, current medications and eye drops, previous eye diseases or eye surgery, and any history of intraocular inflammation or infection. This information helps the ophthalmologist assess suitability for SLT and plan the procedure safely.

Topic 10 What Happens During an SLT Procedure?

Selective Laser Trabeculoplasty (SLT) is a relatively quick, non-incisional procedure that can generally be performed on an outpatient basis.

Before the laser treatment begins, the ophthalmologist will apply topical anesthetic eye drops. In some patients, an intraocular pressure-lowering medication may also be given before the procedure to reduce the risk of a temporary increase in intraocular pressure after treatment.

The patient sits at the laser machine in a position similar to a routine eye examination using a slit-lamp biomicroscope. The ophthalmologist then places a special contact lens on the cornea to obtain a clear view of the trabecular meshwork within the anterior chamber angle.

Laser pulses are then applied sequentially along the trabecular meshwork. Approximately 50–100 laser applications may be delivered, depending on the extent of treatment and the technique used. During the procedure, patients may see flashes of light or experience mild ocular discomfort, but significant pain is uncommon.

The laser procedure itself usually takes approximately 5–10 minutes per eye. Patients can generally return home after treatment without the need for hospital admission.

180° vs 360° SLT Treatment

SLT may be applied to part of the trabecular meshwork, such as 180°, or around the full circumference of the anterior chamber angle, 360°, depending on the characteristics of the eye and the treatment plan.

Currently, 360° SLT is widely used and supported by clinical evidence for lowering intraocular pressure. Some clinical guidelines, including those from the National Institute for Health and Care Excellence (NICE) in the United Kingdom, recommend 360° SLT as an initial treatment in certain appropriately selected patient groups.

However, the same treatment approach is not necessarily appropriate for every patient. The extent of treatment and the laser energy used should be individualized according to factors such as anterior chamber angle anatomy, the degree of trabecular meshwork pigmentation, the type of glaucoma, intraocular pressure, and the patient’s individual risk profile.

Topic 11 Care After SLT

After Selective Laser Trabeculoplasty (SLT), most patients can return home on the same day. In some cases, the ophthalmologist may recheck intraocular pressure after the procedure, particularly in patients who are at increased risk of a temporary rise in intraocular pressure (post-laser IOP spike).

Patients who are already using pressure-lowering eye drops should initially continue their medications as prescribed and should not stop them on their own. The full pressure-lowering effect of SLT does not occur immediately. Any reduction or discontinuation of glaucoma medications should therefore be considered only after the ophthalmologist has assessed the patient’s response to SLT and their individual target intraocular pressure.

Most patients can resume normal daily activities after SLT, including reading, using a computer, watching television, and bathing. Patients should avoid rubbing the treated eye vigorously and should follow any specific instructions provided by their ophthalmologist.

Temporary symptoms may include mild blurred vision, eye redness, irritation, or ocular discomfort. These symptoms are usually mild and gradually improve. However, patients should contact their ophthalmologist promptly if they develop severe eye pain, marked redness, a significant decrease in vision, or nausea and vomiting associated with eye pain.

Follow-Up After SLT

The pressure-lowering effect of SLT depends on a biological response within the trabecular meshwork that reduces resistance to aqueous outflow and improves drainage through the eye’s natural outflow system. As a result, the treatment effect may develop gradually over the following weeks. The success of SLT should therefore not be assessed solely on the intraocular pressure measured immediately after the laser procedure.

Follow-up visits are scheduled to assess intraocular pressure and determine whether it has reached the patient’s individualized target intraocular pressure (target IOP). The timing of follow-up may vary depending on the patient’s intraocular pressure, severity of glaucoma, and individual risk profile.

Even when SLT provides good intraocular pressure control, patients still require regular long-term glaucoma monitoring. This may include measurement of intraocular pressure, assessment of the optic nerve, and visual field testing as appropriate.

Importantly, SLT is a treatment for lowering intraocular pressure; it does not cure glaucoma. Glaucoma remains a chronic disease that requires ongoing monitoring to detect progression and preserve vision over the long term.

Topic 12 Frequently Asked Questions (FAQ)

Does SLT Cure Glaucoma?

No. SLT does not cure glaucoma. Glaucoma is a chronic disease characterized by damage to the optic nerve, and damage that has already occurred cannot currently be restored to normal.

The goal of glaucoma treatment—whether with pressure-lowering eye drops, SLT, or surgery—is to lower intraocular pressure to an appropriate level in order to slow further optic nerve damage and preserve the patient’s remaining vision for as long as possible.

SLT is therefore a treatment used to control glaucoma, not to cure the disease.

How Many Times Is SLT Needed, and Can It Be Repeated?

SLT is generally performed initially as a single treatment, followed by monitoring of the intraocular pressure response. In patients who respond well, the pressure-lowering effect may persist for several years.

Over time, the effect of SLT may gradually diminish. In appropriately selected patients, repeat SLT may be considered. This is possible in part because SLT produces minimal thermal structural damage to the trabecular meshwork compared with older laser techniques.

However, the response to repeat SLT may not be identical to that of the initial treatment. The decision to repeat SLT depends on factors such as the patient’s previous response, current intraocular pressure, target intraocular pressure, and the severity of glaucoma.

Can I Have SLT If I Am Already Using Glaucoma Eye Drops?

Yes. SLT is not limited to patients who have never used glaucoma medications. It can also be used as an adjunctive treatment in patients who are already using pressure-lowering eye drops.

In some patients, SLT may provide additional intraocular pressure reduction or reduce the number of eye drops required if the target intraocular pressure can be maintained after treatment.

Patients should therefore not stop or reduce their glaucoma medications on their own, either before or after SLT. Any adjustment to medication should be made only after the ophthalmologist has assessed the patient’s response to treatment.

Does SLT Mean I Will Never Need Glaucoma Surgery?

Not necessarily. If SLT successfully controls intraocular pressure at the desired target, additional treatment may not be required at that time.

However, if intraocular pressure remains above the target intraocular pressure, glaucoma continues to progress, or a lower pressure is required than SLT can achieve, some patients may still need glaucoma surgery in the future.

Importantly, having SLT does not prevent or limit the use of glaucoma surgery or other treatment options later if they become necessary.

What Are the Options If SLT Does Not Lower Intraocular Pressure Enough?

If intraocular pressure remains above the target level after SLT, other treatment options can still be considered. These may include starting, adding, or adjusting pressure-lowering eye drops, performing repeat SLT in appropriately selected patients, or proceeding to glaucoma surgery when indicated.

Several types of glaucoma surgery are available, ranging from Minimally Invasive Glaucoma Surgery (MIGS) to trabeculectomy and implantation of a Glaucoma Drainage Device (GDD). The choice of treatment depends on factors such as the type and severity of glaucoma, the level of intraocular pressure that needs to be achieved, previous treatment, and individual patient characteristics.

SLT is therefore neither a “last resort” nor a mandatory step that every patient must undergo before glaucoma surgery. Rather, it is one of several pressure-lowering treatment options that can be used at different stages of glaucoma management.

Topic 13 Summary

Selective Laser Trabeculoplasty (SLT) is a treatment used to lower intraocular pressure by improving aqueous outflow through the eye’s natural drainage system. It is a non-incisional procedure that can be performed relatively quickly and is supported by clinical evidence regarding both its efficacy and safety.

In appropriately selected patients, SLT may be used as a first-line treatment or in combination with pressure-lowering eye drops. It can provide effective intraocular pressure reduction and may reduce the burden of daily glaucoma medications in some patients. Evidence from the LiGHT Trial and major international clinical guidelines supports the role of SLT in the management of appropriately selected patients with open-angle glaucoma and ocular hypertension.

However, SLT is not suitable for every patient, and the degree and duration of the treatment response vary among individuals. Importantly, SLT does not cure glaucoma. Patients therefore continue to require regular monitoring of intraocular pressure, the optic nerve, visual function, and disease progression.

The choice of glaucoma treatment should not be based simply on which treatment is newer or perceived to be better. Instead, treatment should be individualized according to the type and severity of glaucoma, target intraocular pressure, anterior chamber angle anatomy, current treatment, and other patient-specific factors, with the long-term goal of slowing disease progression and preserving vision.

Reference

LiGHT Trial (3-year)

Gazzard, G., Konstantakopoulou, E., Garway-Heath, D., Barton, K., Wormald, R., Morris, S., ... LiGHT Trial Study Group. (2019). Selective laser trabeculoplasty versus eye drops for first-line treatment of ocular hypertension and glaucoma (LiGHT): A multicentre randomised controlled trial. The Lancet, 393(10180), 1505–1516. https://doi.org/10.1016/S0140-6736(18)32213-X

LiGHT Trial (6-year)

Gazzard, G., Konstantakopoulou, E., Garway-Heath, D., Adeleke, M., Vickerstaff, V., Ambler, G., ... LiGHT Trial Study Group. (2023). Laser in Glaucoma and Ocular Hypertension (LiGHT) Trial: 6-year results of primary selective laser trabeculoplasty versus eye drops for the treatment of glaucoma and ocular hypertension. Ophthalmology, 130(2), 139–151. https://doi.org/10.1016/j.ophtha.2022.09.009

European Glaucoma Society (EGS)

Pazos, M., Traverso, C. E., Viswanathan, A., & European Glaucoma Society. (2025). European Glaucoma Society: Terminology and guidelines for glaucoma (6th ed.). British Journal of Ophthalmology, 109(Suppl. 1), 1–212. https://doi.org/10.1136/bjophthalmol-2025-egsguidelines 

American Academy of Ophthalmology (AAO)

American Academy of Ophthalmology. (2020). Primary Open-Angle Glaucoma Preferred Practice Pattern®. San Francisco, CA: American Academy of Ophthalmology.

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