In short: Selective laser trabeculoplasty is safe and effective for reducing IOP in patients with glaucoma. However, not all patients respond to treatment and its effects are not permanent even in those who respond well.
By Dr Jacky W.Y. Lee, FRCSEd
IOP is one of the important modifiable risk factors for glaucoma progression. Laser trabeculoplasty is a minimally invasive laser therapy that helps regulate aqueous outflow. Selective laser trabeculoplasty (SLT) was approved by the United States Food and Drug Administration in 2001 and is currently the most commonly performed laser trabeculoplasty procedure because of its good safety profile. SLT is a simple office procedure that requires no external wounds or scarring and minimal downtime, and has almost no permanent side effects. The biggest advantage of SLT is that it is repeatable.
Who are the best patients to treat?
Laser trabeculoplasty is most suitable for primary open angle glaucoma (POAG), ocular hypertension (OHT) or normal tension glaucoma (NTG). NTG is particularly common in Asia, and laser trabeculoplasty may be a safer option than filtration surgery in patients who have progressive retinal nerve fibre layer damage despite a normal to low IOP.
SLT is equally useful for phakic or pseudophakic patients.1 Even in those with primary angle closure, SLT is effective if at least 90 degrees of the trabecular meshwork is visible for treatment.2,3 The effect of laser in pseudoexfolation or pigmentary glaucoma is similar to that in POAG.4,5
For those with previously failed trabeculectomy, laser trabeculoplasty may be performed as an alternative to needling or bleb revision. SLT may have a role in various secondary glaucomas, such as steroid-induced glaucoma, but there is not enough evidence at present to draw any solid conclusions.6,7
When to offer laser trabeculoplasty?
Laser trabeculoplasty may be offered as primary treatment for IOP lowering to reduce the potential limiting effects that various antiglaucoma medications may have on SLT efficacy, although studies on the influence of antiglaucoma medication on SLT outcome have pointed in both directions. For patients who are already on medication but who have inadequate pressure control, laser trabeculoplasty may be offered as adjuvant treatment to further reduce the IOP or to reduce the number of medications required; it may also be of use in patients with intolerances to medication, whether side effects or allergic reactions.
For patients considering undergoing glaucoma filtration surgery procedures, laser trabeculoplasty may be used as a bridging therapy to delay the need for more invasive procedures.
Why laser trabeculoplasty?
In my local population (Chinese patients with pigmented trabecular meshwork), SLT is effective in around 50–60% of patients, lowering the IOP by ≥20% from baseline.8-10 The overall mean IOP reduction, including responders and non-responders, is around 20–30%. However, the IOP may climb back up over the course of months to years, necessitating the resumption of antiglaucoma medications, a repeated laser trabeculoplasty or other filtration procedures.11-15
Despite these seemingly mediocre results, we have to consider that laser trabeculoplasty is probably the safest glaucoma intervention to date. Meta-analysis has shown that SLT is essentially a very safe laser treatment, with only a few transient side effects that include anterior chamber reaction, IOP spikes during the first few hours, eye pain, conjunctivitis, corneal oedema and blurred vision. Rarer complications can include corneal haze, scarring, choroidal effusion and macular oedema.16 There does not seem to be any permanent damage to the corneal structures in open-angle eyes, although in those with anatomically narrow angles, a 5% loss of endothelial cell count has been reported and is most likely attributed to the closer space between the trabecular meshwork and the cornea.3,17
SLT also has the potential advantage of dampening 24-hour and inter-visit IOP fluctuations, which have been associated with disease progression.18-20
What do patients need to know before treatment?
Prior to SLT, apart from understanding the aim, risks and benefits of laser trabeculoplasty, patients should be made aware that not everyone responds to the treatment. At present, there is no effective way to predict who will and who will not respond, although those who have a higher pre-treatment IOP are more likely to benefit from a more substantial IOP reduction; this is by far the most consistent predictor of success.8-10
In addition, patients with very high IOPs are unlikely to have adequate control with laser trabeculoplasty alone and; they should be prepared to undergo further procedures. In those who respond, medications can be gradually reduced after a plateau is reached, anywhere from 1 to 3 months after laser. The laser is not permanent and the rate of efficacy loss depends on the individual. The sustainability of the second, third or fourth laser trabeculoplasty is yet to be determined.
How to perform a successful laser trabeculoplasty
Nagar et al.’s study on POAG patients revealed that treating 360° of the trabecular meshwork resulted in a higher success rate than 90° or 180°.21 SLT should be performed with confluent laser spots to 360° of the pigmented trabecular meshwork with an initial energy of 0.8 mJ that is titrated until bubble formation is just visible on every shot. Recent studies have shown that delivering a higher total energy is associated with a greater amount of IOP reduction but that overlapping shots do not give additional benefit.22-24
After laser, there is probably little difference whether we prescribe no postoperative eye drops, a topical non-steroid anti-inflammatory eye drop or a topical steroid.25 The key is not to excessively suppress the inflammatory process as the inflammatory cytokines help to reduce the outflow resistance at the trabecular meshwork.
Patients may choose to initially undergo treatment for one eye to determine whether they are responders: nearly 80% of the time, the response is coherent in both eyes.26 For non-responders, repeated treatment is unlikely to produce different results; for initial responders whose laser effect wears off with time, re-treatment can offer a response similar to the initial treatment, although it has not yet been confirmed whether a detrimental pattern exists after multiple repeated treatments.27
In addition to SLT, newer laser trabeculoplasty technologies such as micropulse laser trabeculoplasty, titanium-sapphire laser trabeculoplasty and pattern scanning trabeculoplasty have an even more favourable safety profile with less post-laser inflammation and fewer IOP spikes.
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Dr Jacky W.Y. Lee, FRCSEd
Dr Jacky Lee is Associate Consultant in Ophthalmology at the Hospital Authority of Hong Kong, Honorary Clinical Assistant Professor at the University of Hong Kong and Honorary Clinical Assistant Professor at the Chinese University of Hong Kong.