SLT valuable tool in individualized approach for glaucoma management

By Inder Paul Singh, MD; Special to Ophthalmology Times

Glaucoma is the most common cause of irreversible blindness worldwide, with management options targeted at reducing IOP.¹ Reduction is achievable through myriad treatments-including topical and oral medications, incisional surgeries, and laser-based modalities-but the surge of minimally invasive glaucoma surgeries (MIGS) raises new questions regarding the reliance of the traditional gold standards.

With so many options at their disposal, ophthalmologists must continually evaluate the role of each procedure to determine the safest and most effective path forward for patients.

Pinpointing the obstruction

One of the most important challenges that glaucoma surgeons face is determining the best procedure for each patient. The outflow system is multifaceted, with potential blockages occurring in the trabecular meshwork, Schlemm’s canal, or the collecting ducts.

With so many customized treatment options, one thought is whether ophthalmologists could better deduce the location of outflow blockage through selective laser trabeculoplasty (SLT). SLT works through selective photothermolysis of the pigmented trabecular meshwork cells.

A study analyzing the microarchitecture of Schlemm’s canal before and after SLT showed that the degree of canal expansion positively correlates to the degree of IOP reduction in glaucoma patients. The authors postulated this correlation provided direct evidence for the structural effect of SLT on the trabecular meshwork, in addition to the ability of SLT to increase trabecular aqueous outflow.²

Since SLT effectively and selectively treats blockages localized to the trabecular meshwork, its outcome provides invaluable information regarding the patient’s pathology.

A successful SLT can determine that the primary obstruction is most likely within the targeted trabecular meshwork. Alternatively, a minimally effective SLT procedure would find that the main obstruction most likely lies outside the meshwork.

The benefits of this diagnostic information are manifold. However, the greatest benefit tailors to individualized treatment. The information provided by SLT may help select future procedures based on the ability to selectively target the problem areas.

A patient with a fairly unsuccessful SLT most likely has a predominant blockage outside of the trabecular meshwork, and should therefore undergo a MIGS procedure that can effectively treat Schlemm’s canal and the collecting ducts. Ab-interno canaloplasty (ABiC) may be the next best step in such a patient.

The comprehensive approach of ABiC removes a lot of the guesswork from the planning of a customized treatment plan for each patient, with the potential to decrease the number of procedures and increase the effectiveness of their management overall.

Viable first-line therapy?

The aforementioned approach puts SLT at the front line of management. Though it offers the significant benefit of acting as a diagnostic aid, its effectiveness as a stand-alone treatment must also be closely scrutinized.

One study showed SLT provides at least a 20% reduction in IOP in 75% of primary-open angle glaucoma (POAG) eyes.

This was in line with a control group treated with latanoprost, which demonstrated a similar reduction in 73% of eyes.³

Another study comparing SLT and prostaglandin eye drops reported a drop in IOP of 29.9% and 25.4%, respectively.⁴

Overall, the data to this point have shown that SLT is equally capable of reducing IOP compared with first-line topical medications. 

Given the similar efficacies of these approaches, other intangibles should be considered so that management decisions can be made on a patient-to-patient basis. While effective at lowering IOP, ocular hypotensive medications are not without downsides.

Prolonged use of such medications has been shown to negatively affect quality of life. In addition, some formulations contain inactive ingredients that have been associated with ocular surface disease. The patient’s tolerance to local side effects-such as hyperemia changes in periocular pigmentation, tearing, and foreign body sensation-should be assessed, as these are all common occurrences with first-line medication use.

Final thoughts

SLT, with its ability to reduce IOP in glaucoma patients, its usefulness as a potential diagnostic aid, and its synergy with MIGS is a valuable and underutilized tool in the surgeon’s vast arsenal.

Inder Paul Singh, MD

E: ipsingh@amazingeye.com

Dr. Singh is an ophthalmologic surgeon from The Eye Center of Racine and Kenosha, WI. Dr. Singh is a consultant of Ellex.

References

1. Friedman DS, Wolfs RC, O'Colmain BJ, et al., and The Eye Disease Research Group. Prevalence of open-angle glaucoma among adults in the United States. Arch Ophthalmol. 2004;122:532-538.

2. Skaat A, Rosman MS, Chien JL, et al. Microarchitecture of Schlemm canal before and after selective Laser trabeculoplasty in enhanced depth imaging optical coherence tomography. J Glaucoma. 2017;26:361-366.

3. Nagar M, Ogunyomade A, O'Brart DP, Howes F, Marshall J. A randomised, prospective study comparing SLT with latanoprost for the control of intraocular pressure in ocular hypertension and open angle glaucoma. Br J Ophthalmol. 2005;89:1413-1417.

4. Alvarado JA, Iguchi R, Martinez J, Trivedi S, Shifera AS. Similar effects of SLT and prostaglandin analogs on the permeability of cultured Schlemm canal cells. Am J Ophthalmol. 2010;150:254-264.