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Predictive Factors for Outcomes of Selective Laser Trabeculoplasty


We sought to  determine predictive factors for selective laser trabeculoplasty (SLT) outcome. 252 eyes from 198 adult patients with open-angle glaucoma who underwent SLT between July 2016 and February 2018 with a minimum 6 month follow up were reviewed. We defined success as ≥20% IOP reduction or ≥1 medication reduction without an IOP lowering procedure. We also evaluated the relationship of these factors to postoperative IOP elevation >5 mmHg (IOP spikes). Our primary outcome measure was association between age, type and severity of glaucoma, pigmentation of the trabecular meshwork (PTM), total energy delivered, and baseline intraocular pressure (IOP) with success. At 2 and 6 months, 33.6% (76/226) and 38.5% (97/252) of eyes met success criteria respectively. Baseline IOP > 18 mmHg was significantly associated with success both at 2 and 6 months, reducing IOP by 5.4 ± 5.3 mmHg (23.7% reduction), whereas those with lower baseline remained at −0.7 ± 4.6 mmHg (4.9% increase) at 6 months (P < 0.001). No other baseline characteristics significantly predicted success or IOP spikes. Patients with higher baseline IOPs had greater success rates and mean IOP reduction at both 2 and 6 months following SLT. Age, type and severity of glaucoma, PTM, or total energy delivery had no association with procedural success or IOP spikes. Patients with higher baseline IOP may experience greater lowering of IOP after SLT. However, SLT may be equally successful for patients with a variety of other characteristics.


Second in frequency only to cataracts, glaucoma causes more cases of blindness worldwide than any other ocular disease and currently affects over 70 million people, 10% of whom eventually lose their sight due to optic nerve damage1. Since it is estimated to continue increasing in incidence, refining treatment approaches become more crucial every year to preserve sight2.

Selective laser trabeculoplasty (SLT) reduces intraocular pressure (IOP) by improving aqueous outflow likely by biological rather than anatomic changes in the trabecular meshwork (TM) with proven efficacy ranging from 15–66% and a better safety profile than its predecessor, Argon Laser Trabeculoplasty (ALT)1,3. Originally indicated only for primary open-angle glaucoma (POAG), it has been shown to be efficacious for many other types of open-angle glaucoma4. Building on the principles of ALT, it uses frequency-doubled short pulse (Q-switched) Nd:YAG laser and selectively targets pigmented cells of the TM without damaging the overall anatomical structure of the meshwork3. The larger spot size of 400 μm for SLT compared to 50 μm for ALT allows for broader coverage of the angle and eliminates the need for as fine a focus while still providing the “champagne bubble” feedback that is generally recommended every two or three burns for appropriate energy delivery5,6,7.

Although efficacy and safety of SLT have been well documented, predictive factors for outcome of SLT tend to vary in the literature and large-scale investigations on this topic are limited. SLT has reportedly worked best for patients with ocular hypertension, POAG, pseudoexfoliation, or pigmentary glaucoma7. Pigmentation of TM (PTM) has not been associated with efficacy of the procedure8, but with higher risk of IOP spikes9. 360° treatment have been reported to be more effective than 180° treatment in one setting10, although many surgeons opt to treat 180° at a time in hopes of decreasing risk of IOP spikes.

With the growing interest in using SLT as first-line treatment and well known issues with medication compliance, determining which patients would have the best response to this therapy is increasingly important11,12,13. In this study, we attempted to determine possible predictive factors for both successful outcomes and common complications, including postoperative IOP spike following SLT treatment.

Patients and Methods

We first obtained University of Missouri Institutional Review Board (IRB) approval who granted us a waiver of informed consent due to the retrospective nature of the study with deidentified data. All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and national research committee and with the 1964 Declaration of Helsinki and its later amendments or comparable ethical standards. We performed a retrospective chart review of 252 eyes of 198 adult open-angle glaucoma patients who underwent SLT at University of Missouri between July 2016 and February 2018 in accordance with the guidelines and regulations of our IRB approval. All patients completed minimum 6 months follow up visit after SLT. We collected pre-op and post-op data at 2 and 6 month follow-up.

Our primary outcome measure was correlation between patient age, type and severity of glaucoma, PTM, or total energy delivery with procedural success. Success was defined as ≥20% IOP reduction or any reduction of medication without increasing IOP, and failure was not meeting these criteria or requiring an additional IOP-lowering surgery before the time point considered. Our secondary outcome measure was association of baseline characteristics to IOP reduction, medication reduction, and postoperative IOP spike (defined as elevation of IOP > 5 mmHg from baseline 1 hour after the procedure).

Laser procedure and protocols

All SLT was performed with the 532 nm frequency doubled Q-switched Nd:YAG laser using 3 ns pulse and spot size of 400 micrometer. Power varied from 0.6 to 1.4 mJ and was titrated until microbubbles were visualized then reduced by 0.1 mJ. The settings for the SLT laser and therefore total energy varied depending on TM pigmentation. At 1 hour post procedure, a Goldmann applanation tonometer was used to check IOP by the treating physician or skilled ophthalmic technician. A drop of Timolol or Brimonidine was given to the operative eye prior to procedure, and no steroid was used postoperatively. No additional ocular hypotensive drops were given after the procedure unless the patient experienced an IOP spike. IOP was checked similarly at 2 weeks, 2 months, and 6 months post-procedure. Full slit lamp examination with gonioscopy and visual acuity testing were done at 2 weeks, 2 months, and 6 months post procedure. Patients remained on their medication regimen until 2 months where medications were adjusted at the physician’s discretion based on disease progression and individual IOP targets.

Statistical analysis

We used paired t-tests to compare preoperative and postoperative IOP. A mixed model (age and preoperative IOP) and logistic regression (type and severity of glaucoma, pigmentation of the trabecular meshwork, total energy, and angle of treatment) with a random patient effect to account for individuals who contributed two eyes to the sample was used for determining predictive factors of success. Independent t-tests and Wilcoxon signed rank test to compare IOP and medication reduction based on preoperative IOP, a Mann-Whitney U test to compare total energy delivery between light and dense PTM groups, and independent t- and chi-square/Fisher’s exact tests to assess associations between factors and IOP spike. We reported all values as mean ± standard deviation for the data with normal distribution, median and interquartile range (IQR) for non-normally distributed data, and percentage (n) for categorical variables unless otherwise noted.


Preoperative characteristics

Baseline characteristics are summarized in Table 1. The mean age of patients was 69.6 ± 11.2 years. Females comprised 49.2% of the sample size. Majority of patients were Caucasian (86.1%) with primary open-angle glaucoma (80.1%). The severity of glaucoma consisted of 43.3% (109/252) mild and 38.1% (96/252) severe according ICD-10 guidelines14,15. Mean preoperative IOP was 17.8 ± 4.4 mmHg and mean preoperative glaucoma medications was 2.0 ± 1.3 [2(2)].

Table 1 Baseline demographic and glaucoma status data (n = 252).

Overall procedural success at 2 and 6 months

By our definition, 33.6% (76/226) of patients had successful SLT outcome at 2 months and 38.5% (97/252) at 6 months. Baseline IOP of 17.8 ± 4.4 (SD) mmHg was reduced to 16.7 ± 4.3 and 15.2 ± 4.9 mmHg at 2 and 6 months respectively, both statistically significant (P < 0.001). Baseline medications were reduced from 2.0 ± 1.3 [2(2)] to 1.6 ± 1.3 [2(2)] at 2 months and 2.0 ± 1.3 [2(2)] at 6 months. This change in medication number was not statistically significant at 2 months (P = 0.709) or 6 months (P = 0.578).

Predictive factors for success

Findings for predictive factors for SLT success are reported in Table 2. The only baseline characteristic that significantly predicted success of SLT was baseline IOP at both 2 and 6 months (P < 0.001). Patients with baseline IOP of>18 mmHg experienced a mean IOP reduction of 3.7 ± 4.2 mmHg (17.3% reduction) at 2 months compared to −0.7 ± 4.1 (4.9% increase) mmHg in patients with baseline IOP ≤ 18 mmHg (P < 0.001). Similarly, at 6 months the patients with higher baseline IOP had mean IOP reduction of 5.4 ± 5.3 mmHg (23.7% reduction) compared to −0.7 ± 4.6 mmHg (4.9% increase) in those with lower baseline IOP (P < 0.001). IOP was not associated with mean medication reduction (P = 0.186).

Table 2 Predictive factors for SLT success at 2 and 6 months.

Predictors for IOP spikes

Our findings for the association between preoperative characteristics and IOP spikes are reported in Table 3. Overall, 5.1% (13/252) eyes experienced IOP spikes (defined as >5 mmHg elevation in IOP after laser surgery). IOP spikes was not associated with procedural success at 2 and 6 months, nor was it with age, type or severity of glaucoma, baseline IOP, PTM, or total energy delivery. None of the patients experienced any other adverse events related to SLT or vision loss ≥ 2 Snellen lines at any point during the follow-up.

Table 3 P-values for IOP Spike vs. patient characteristics or outcome measures.


Many studies have attempted to characterize potential predictive factors of success following SLT and we sought to assess current claims and to contribute currently unexplored predictive factors such as total energy delivery during treatment. Our results agree with the frequently reported finding that baseline IOP is a predictor of SLT success16,17,18,19,20,21,22, while factors such as patient age, PTM, and type of glaucoma are not17,20,21,22,23,24. Some of the literature reports an association between heavily pigmented PTM and IOP spikes but we did not observe this in our population9,24. We found that baseline IOP significantly predicted success at both 2 and 6 months and those with higher IOPs (specifically >18 mmHg) had higher probabilities for a successful outcome and greater lowering of IOP. This result may be the result of flooring effect of any Schlemm’s canal based procedures, where IOP lowering cannot be achieved beyond the level of episcleral venous pressure25,26,27. Age, type and severity of glaucoma, PTM, or total energy delivery did not significantly predict a successful outcome at either 2 or 6 months in our population.

The existing controversy around this topic is likely multifactorial and elements such as varying technique and laser settings, success criteria, study power, and clinical protocols can all influence findings. Predictive factors for SLT success is an increasingly important topic due to growing current interest in using SLT as a first line therapy11. The recent randomized large-scale multi-center trial comparing SLT to eye drops for first-line therapy of glaucoma and ocular hypertension (LiGHT trial) demonstrated 95% of eyes at target IOP at 36 months with only 6 IOP spikes in their 770 patients11,12. These high rates of SLT success compared to ours and other studies may reflect how treatment-naïve eyes may have a favorable response to laser trabeculoplasty improving TM outflow facility, and prior treatment with topical aqueous suppressants may reduce the natural capacity of the patients’ TM and physiologic outflow, thereby limited response to laser trabeculoplasty28. It may also be due to the flexible patient-specific definition of success used in that trial compared to our singular success criteria. Our success rate was consistent with other existing literature that included medically treated glaucoma that generally report rates from 15–66%29,30,31,32.

We also attempted to characterize predictive factors for postoperative IOP spikes. Of the patients in our study 5.1% (13/252) experienced a postoperative IOP spike >5 mmHg over baseline within 1 hours of treatment. None of the predictive factors we evaluated was associated with IOP spikes. Our rate of IOP spikes is also similar to existing literature including medically-controlled glaucoma patients in which spike rates are often 10% or less33,34,35. We found no other complications from the laser procedure and no patients had loss of vision of 2 Snellen lines or more at any point during 6 month follow-up.

While our sample size was greater than many studies on this topic, we are limited by the retrospective nature and the potential for unobserved confounders. Glaucoma patients were not randomly selected and those receiving laser treatment may had certain glaucoma characteristics compared to those managed on medications alone or by incisional surgery. Our sample group may not be generalizable to non-Caucasian ethnicities or types of glaucoma other than primary open-angle. Our conclusions for predictive factors for postoperative IOP spikes must also be interpreted with care given the small incidence number. We also had 54 patients who received bilateral treatment and a “crossover” effect on the contralateral eye is known to potentially result in a significant IOP reduction36,37. While this confounder is not eliminated, it was accounted for in statistical analysis. Additional prospective and randomized studies with a more diversified set of patients will help determine if theses baseline characteristics have the same role in predicting success in patients regardless of ethnicity or type of glaucoma.

We would also like to address the treatment of 180° vs. 360° of the angle. There are multiple existing reports of greater angle treatment resulting in greater response10,38,39. Since our focus was on the factors that result in more favorable SLT outcome we considered degree of treatment to be one of the factors as it represents a variation in the technique. Due to this, considered it as a surrogate for degree of treatment rather than analyzing the groups separately. This also addresses a relevant question for 180° treatment: “Is more better?” since spot number and energy delivery also represent variation in technique. We decided presenting the data this way also can inform clinicians that more power and more spots may not necessarily result in greater response.

Despite these limitations, we have demonstrated that SLT is an effective method to lower IOP and medication burden with a low risk of complication that may have particular benefit for those with higher baseline IOP. Age, type or severity of glaucoma, PTM, and total energy delivery appear to not significantly predict success and patients with a wide variety of these factors will likely benefit equally.


  1. 1.

    Weinreb, R., Aung, T. & Medeiros, F. The Pathophysiology and Treatment of Glaucoma. JAMA. 311(18), 1901–1911, (2014).

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  2. 2.

    Tham, Y. et al. Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis. Ophthalmology. 121(11), 2081–2090, (2014).

    Article  PubMed  Google Scholar 

  3. 3.

    Wong, M., Lee, J., Choy, B., Chan, J. & Lai, J. Systematic review and meta-anaylsis on the efficacy of selective laser trabeculoplasty in open-angle glaucoma. Surv Ophthalmol. 60(1), 36–50, (2015).

    Article  PubMed  Google Scholar 

  4. 4.

    Rieck, J. The pathogenesis of glaucoma in the interplay with the immune system. Invest Ophthalmol Vis Sci. 54(3), 2393–2409, (2013).

    CAS  Article  PubMed  Google Scholar 

  5. 5.

    Noecker R. ALT, MLT, SLT. Glaucoma Today. March 2009.

  6. 6.

    Kramer, T. & Noecker, R. Comparison of the morphologic changes after selective laser trabeculoplasty and argon laser trabeculoplasty in human eye bank eyes. Opthalmology. 108, 773–779 (2000).

    Article  Google Scholar 

  7. 7.

    Saheb, H. 10 Ways to Optimize Treatment with SLT. Rev Ophthalmol. September 2014.

  8. 8.

    Haque M, et al. The Effect of Selective Laser Trabeculoplasty (SLT) With Heavy versus Light Pigmentation of the Trabecular Meshwork (TM). iovs. 2009;50(13).

  9. 9.

    Harasymowycz, P. et al. Selective Laser Trabeculoplasty (SLT) Complicated by Intraocular Pressure Elevation in Eyes with Heavily Pigmented Trabecular Meshworks. Am J Ophthalmol. 139(6), 1110–1113 (2005).

    Article  Google Scholar 

  10. 10.

    Cheema, S. A. et al. Efficacy of 180 vs. 360 Degrees of Selective Laser Trabeculoplasty on Lowering Intraocular Pressure. Invest Ophthalmol Vis Sci. 47(13), 5466 (2006).

    Google Scholar 

  11. 11.

    Gazzard, G. et al. Selective laser trabeculoplasty versus eye drops for first-line treatment of ocular hypertension and glaucoma (LiGHT): a multicentre randomised controlled trial. Lancet. 393(10180), 1505–1516, (2016).

    Article  Google Scholar 

  12. 12.

    Gazzard, G. et al. Laser in Glaucoma and Ocular Hypertension (LiGHT) trial. A multicentre, randomised controlled trial: design and methodology. Br J Ophthalmol. 102(5), 593–598 (2018).

    Article  Google Scholar 

  13. 13.

    Jha, B., Bhartiya, S., Reetika, S., Arora, T. & Dada, T. Selective Laser Trabeculoplasty: An Overview. J Curr Glaucoma Pr. 6(2), 79–90, (2012).

    Article  Google Scholar 

  14. 14.

    Mattox C. Glaucoma Stage Definitions. 2014.

  15. 15.

    Fellman R, Mattox C, Ross K. Know the New Glaucoma Staging Codes. EyeNet Mag, 65-66 (October 2011).

  16. 16.

    Ayala, M. & Enping, C. Predictive factors of success in selective laser trabeculoplasty (SLT) treatment. Clin Ophthalmol. 5, 573–576, (2011).

    Article  PubMed  PubMed Central  Google Scholar 

  17. 17.

    Bruen R, Lesk M, Harasymowycz P. Baseline Factors Predictive of SLT Response: A Prospective Study. J Ophthalmol. 642869 (July 2012).

  18. 18.

    Lee, J., Liu, C., Chan, J. & Lai, J. Predictors of success in selective laser trabeculoplasty for normal tension glaucoma. Medicine (Baltimore). 93(28), e236 (2014).

    Article  Google Scholar 

  19. 19.

    Chun, M. et al. Selective laser trabeculoplasty for early glaucoma: analysis of success predictors and adjusted laser outcomes based on the untreated fellow eye. BMC Ophthalmol. 16, 206 (2016).

    Article  Google Scholar 

  20. 20.

    Mao, A. et al. Development of a prediction rule to estimate the probability of acceptable intraocular pressure reduction after selective laser trabeculoplasty in open-angle glaucoma and ocular hypertension. J Glaucoma. 17(6), 449–454, (2008).

    Article  PubMed  Google Scholar 

  21. 21.

    Martow, E., Hutnik, C. & Mao, A. SLT and adjunctive medical therapy: a prediction rule analysis. J Glaucoma. 20(4), 266–270 (2011).

    Article  Google Scholar 

  22. 22.

    Tzimis, V. et al. Laser trabeculoplasty: an investigation into factors that might influence outcomes. Can J Ophthalmol. 46(4), 305–309, (2011).

    Article  PubMed  Google Scholar 

  23. 23.

    Gracner, T., Naji, M., Hudovernik, M., Gracner, B. & Pahor, D. [Predictive factors of successful selective laser trabeculoplasty in open-angle glaucoma]. Klin Monbl Augenheikd. 224(12), 922–926 (2007).

    CAS  Article  Google Scholar 

  24. 24.

    Koucheki, B. & Hashemi, H. Selective laser trabeculoplasty in the treatment of open-angle glaucoma. J Glaucoma. 21(1), 65–70 (2012).

    Article  Google Scholar 

  25. 25.

    Hirabayashi, M., King, J., Lee, D. & An, J. Outcome of phacoemulsification combined with excisional goniotomy using the Kahook Dual Blade in severe glaucoma patients at 6 months. Clin Ophthlamology. 2018, 715–721 (2019).

    Article  Google Scholar 

  26. 26.

    Hirabayashi, M. T., Lee, D., King, J. T., Thomsen, S. & An, J. A. Comparison Of Surgical Outcomes Of 360° Circumferential Trabeculotomy Versus Sectoral Excisional Goniotomy With The Kahook Dual Blade At 6 Months. Clin Ophthalmol. ume 13, 2017–2024, (2019).

    Article  Google Scholar 

  27. 27.

    Lee, D., King, J., Thomsen, S., Hirabayashi, M. & An, J. Comparison Of Surgical Outcomes Between Excisional Goniotomy Using The Kahook Dual Blade And iStent Trabecular Micro-Bypass Stent In Combination With Phacoemulsification. Clin Ophthalmol. ume 13, 2097–2102, (2019).

    Article  Google Scholar 

  28. 28.

    Carreon T, van der Merwe E, Fellmann R, Murray J, Bhattacharya S. Aqueous outflow - A continuum from trabecular meshwork to episcleral veins. Prog Retin Eye Res. 17AD;57:108-133.

  29. 29.

    De Keyser M, De Belder M, De Belder S, De Groot V. Where does selective laser trabeculoplasty stand now? A review. Eye Vis. 2016;3(10).

  30. 30.

    Yujia, Z. & Ahmad, A. A Review of Selective Laser Trabeculoplasty: Recent Findings and Current Perspectives. Ophthalmol Ther. 6(1), 19–32 (2017).

    Article  Google Scholar 

  31. 31.

    Song, J. Complications of selective laser trabeculoplasty: a review. Clin Ophthalmol. 10, 137–143 (2016).

    CAS  Article  Google Scholar 

  32. 32.

    Atsuya, M., Rumi, K., Shinichi, U., Kenji, M. & Johji, N. Treatment Outcomes and Prognostic Factors of Selective Laser Trabeculoplasty for Open-angle Glaucoma Receiving Maximal-tolerable Medical Therapy. J Glaucoma. 25(10), 785–789 (2016).

    Article  Google Scholar 

  33. 33.

    Abramowitz, B. et al. Selective laser trabeculoplasty vs micropulse laser trabeculoplasty in open-angle glaucoma. Clin Ophthalmol. 12, 1599–1604 (2018).

    CAS  Article  Google Scholar 

  34. 34.

    Barkana, Y. & Belken, M. Selective Laser Trabeculoplasty. Surv Ophthalmol. 52, 634–654 (2007).

    Article  Google Scholar 

  35. 35.

    Hirabayashi, M., Rosenlof, T. & An, J. Comparison of successful outcome predictors for MicroPulse laser trabeculoplasty and selective laser trabeculoplasty at 6 months. Clin Ophthalmol. 13, 1001–1009, (2019).

    CAS  Article  PubMed  PubMed Central  Google Scholar 

  36. 36.

    Rhodes, K. M. et al. Intraocular pressure reduction in the untreated fellow eye after selective laser trabeculoplasty. Curr Med Res Opin. 25(3), 787–796, (2009).

    Article  PubMed  Google Scholar 

  37. 37.

    Kirzhner M, Shildkrot Y, Hughes BA. Cross-over effect of selective laser trabeculoplasty. Poster presented at the: ARVO Annual Meeting, April 2009,

  38. 38.

    Shibata, M. et al. Clinical Results of Selective Laser Trabeculoplasty in Open-angle Glaucoma in Japanese Eyes: Comparison of 180 Degree With 360 Degree SLT. J Glaucoma. 21(1), 17–21, (2012).

    CAS  Article  PubMed  Google Scholar 

  39. 39.

    Nagar, M. A randomised, prospective study comparing selective laser trabeculoplasty with latanoprost for the control of intraocular pressure in ocular hypertension and open angle glaucoma. Br J Ophthalmol. 89(11), 1413–1417, (2005).

    CAS  Article  PubMed  PubMed Central  Google Scholar 

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Author information




V.P. and M.H. collected the data. M.H. and V.P. wrote the text. M.H. performed statistical analysis and M.H. and V.P. prepared the tables. J.A. conceptualized the project and edited the text and tables.

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Correspondence to Jella An.

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Hirabayashi, M., Ponnusamy, V. & An, J. Predictive Factors for Outcomes of Selective Laser Trabeculoplasty. Sci Rep 10, 9428 (2020).

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