IN SHORT: A low-energy form of the procedure, selective laser trabeculoplasty, has helped to address safety concerns associated with the argon form
Prostaglandin-based topical therapy has been the ‘go-to treatment’ for open-angle glaucoma for decades. In contrast, laser trabeculoplasty has conventionally remained reserved for patients unresponsive or unable to adhere to medication-based therapy.
Recent years, however, have brought the level of technologic advancement needed to move laser trabeculoplasty into the limelight as an effective open-angle glaucoma treatment.
However, with argon laser trabeculoplasty (ALT)—the original laser therapy for glaucoma—requiring a hot, high-energy laser that carries a noteable risk of collateral damage to surrounding tissue, safety concerns are a key disadvantage of this treatment modality.
Fortunately, the subsequent development of a cool, low-energy form of the procedure, called selective laser trabeculoplasty (SLT), has helped to ameliorate safety concerns.
By using a low-energy, Q-switched, frequency-doubled Nd:YAG laser with a short exposure time of up to 5 ns, the SLT laser is primed to specifically target pigmented trabecular meshwork cells without damaging surrounding tissue.1 And studies show that SLT is just as effective as ALT at lowering IOP in glaucoma patients.1, 2
Spurred by encouraging reports about the efficacy of SLT laser systems, I have spent recent months using the OptoYAG and SLT laser system (Optotek d.o.o, Slovenia) in my clinic in Ivano-Frankovsk, Ukraine. While doing so, I have been pleasantly surprised at how easy it has been to integrate an advanced piece on technology within my practice, and I have also become more aware of the realities of using laser technology to treat a condition that is classically managed with eye drops.
Seeing the advantage
The system is a combined unit that consists of two lasers—a ND:YAG and SLT laser—used for different applications. As the ND:YAG laser has penetrative properties, it is best utilised in the treatment of diseases in which there is a need to create a hole or incision in tissue.
For example, the laser is used during iridotomy and in the treatment of secondary cataract or limited regional haemorrhages. For the latter, the creation of a small hole allows blood to move into the vitreous humor, where it can be absorbed without detriment to ocular health.
In contrast, the SLT laser stimulates tissue rather than cutting through it. As such, when applied to an eye with open-angle glaucoma, the laser stimulates the pigmented trabecular cells and macrophages responsible for filtering and draining the aqueous humor, thus triggering a clearance process in the trabecular meshwork,3 which, in turn, lowers the elevated IOP seen in open-angle glaucoma.
Importance of patient selection
An important observation I have made while working with the SLT laser is that the results achievable are strongly influenced by disease. Patients at stages 1 and 2 of the disease seem to achieve better outcomes than those at later stages. Specifically, mean IOP reductions of 5.9 and 5.7 mm Hg were achieved among my patients with stage 1 and 2 glaucoma, respectively.
Of note, these levels of reduction were seen in more than 80% of patients. In comparison, SLT therapy was effective in no more than 50% of my stage 3 patients, resulting in a mean IOP reduction of only 4.7 mm Hg among this group at 1 to 3 months post-SLT.
Published literature, including a 2016 study by Schlote et al., support my observation that SLT outcomes are worse with advanced open angle glaucoma.4 This suggests that while such technology is exciting and offers favourable outcomes for glaucoma patients, it is important to recognise that such outcomes are not universal for all patients. Thus, it is vital that the treating physician selects patients for treatment appropriately.
In addition to disease stage, other factors, such as angle width and pigmentation level, influence both the outcomes obtainable with SLT and the technical settings that must be used when treating patients with the laser.
For example, in eyes with a higher degree of pigmentation, it is better to use a relatively low energy beam or apply treatment in several stages to minimise the risk of burns. In eyes with low levels of pigmentation, SLT is not really worthwhile as its ability to lower IOP in such eyes is minimal. Similarly, this treatment is typically ineffective in patients with pseudoexfoliation glaucoma.
As with any therapeutic intervention, while SLT laser offers great benefits and outcomes, it does carry a risk, albeit a low one, of side effects. My experience with the laser revealed just one case of IOP increase among a treatment group with more than 100 patients.
In this case, IOP rose to 35 mm Hg after SLT treatment. However, it dropped back to normal levels within 2 weeks (during which hypotensive eye drops were used to maintain IOP at acceptable levels). But as transient IOP rise has been widely reported after laser procedures, this is an observation that is not too unexpected.5
It is often believed by physicians and patients that laser therapy is a very expensive treatment that the average person simply cannot afford. In reality, however, the cost of laser-based glaucoma treatment is comparable with the cost of a 5-month supply of eye drops.
Given the longer lasting outcomes achieved with SLT and the one-time investment, it is actually more cost effective to have laser therapy than continue on long-term topical therapy. This misconception highlights a need for improved education on this treatment modality among physicians and patients, to ensure that patients who stand to benefit both financially and phsyically from opting for laser therapy over medication are presented with all their options at an early-disease stage, when good outcomes are still achievable.6
Some physicians may also hold the belief that a combined system will be more complicated to use than a conventional YAG laser or traditional ALT. However, this is not the case. With features such as fine-energy setting buttons located next to the joystick included in the device for ease of use, there is no significant learning curve with this device compared with standard YAG lasers.
Physicians used to using ALT in open-angle glaucoma will notice increased treatment precision on making the switch to SLT. This is because the SLT’s 400 µm laser beam diameter covers the full size of the trabeculae, thus eliminating a need for extremely accurate aiming.
In contrast, the laser beam used in ALT has a diameter of 50 µm, which will always require greater aiming precision to deliver the best treatment outcome possible—no matter how skilled the surgeon. Furthermore, when the ALT laser is used, there is a risk of rebound increase in IOP 6 months after treatment that is not seen with SLT.7
SLT therapy provides a safe treatment option for open-angle glaucoma patients who have had little success after taking conventional topical therapy for several years. With the added benefit of proven efficacy and safety as a first-line treatment in these patients, it seems the adoption of SLT in glaucoma treatment is likely to grow in coming years.
As a procedure that produces similar outcomes to those achieved with eyedrops, SLT offers the added advantage of eliminating the compliance problem that is often seen with patients on long-term eyedrop therapy (that is, with their eye drops and follow-up appointments).
Cost savings from a single laser treatment versus years of multiple eye drop regimes are also worth noting. This further adds to my confidence in the future of SLT in open-angle glaucoma treatment.
However, a key factor that is likely to make or break the uptake of this procedure by eye care practices worldwide is proper education of both patients and ophthalmologists. This will be vital in ensuring that only the most appropriate patients (early-stage glaucoma patients) are selected for treatment. By doing so, this promising technology can consistently be used to its full advantage and deliver the exemplary results for which it is capable.
Dr Andrij Savich
Dr Andrij Savich has no financial interest.
1. KF Damji, et al. Br J Ophthalmol. 1999;83:718–722.
2. AM Bovell, et al. Canadian Journal of Ophthalmology. 2011;doi:10.1016/j.jcjo.2011.07.016.
3. TR Kramer and RJ Noecker. Ophthalmol. 2001;108:773-79.
5. Y Barkana and M Belkin. Surv Ophthalmol. 2007;52:634-654.
6. JD Stein et al. Arch Ophthalmol. 2012;130:497-505.
7. Sihota R. Lasers in primary open angle glaucoma. Indian J Ophthalmol. 2011 Jan; 59(Suppl1):S114–S117.