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Year : 2020  |  Volume : 2  |  Issue : 1  |  Page : 29

Pattern scanning laser trabeculoplasty versus selective laser trabeculoplasty in patients with primary open angle glaucoma

Department of Ophthalmology, Fundación Oftalmológica Nacional, Bogotá, Colombia

Date of Submission07-Apr-2020
Date of Decision16-Apr-2020
Date of Acceptance24-May-2020
Date of Web Publication20-Oct-2020

Correspondence Address:
Dr. Sandra Belalcázar Rey
Calle 50 # 13-50, Bogotá 110231
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/PAJO.PAJO_16_20

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Purpose: The aim of this study is to compare the reduction percent of intraocular pressure (IOP) after selective laser trabeculoplasty (SLT) or pattern laser scanning trabeculoplasty (PSLT) in a group of patients with hypertensive glaucoma.
Materials and Methods: A quasi-experimental prospective study of the patients with baseline IOP of 20 mmHg or more (with at least 1 IOP lowering medication) underwent either PSLT or SLT at 360°. IOP was measured in the following time points: Hour 1, Day 1 and 7, months 1, 3, 6, and 12 after the laser procedure.
Results: The mean age was 68.1 ± 10.1 in the PSLT group and 71.8 ± 4.0 in the SLT group. Eleven eyes (8 patients) underwent PSLT and 9 eyes (6 patients) underwent SLT. Baseline IOP was 22.45 ± 2.4 mmHg, PSLT; 25.0 ± 2.2 mmHg, SLT; (P > 0.05) on an average of 2.4 medications. In the PSLT group, the mean IOP at 1 h, 1, 3, 6 and 12 months was 19.0 ± 5.0, 14.7 ± 2.4, 15.3 ± 3.0, 14.5 ± 2.7, and 13.0 ± 3.1, respectively. In the SLT group, the mean IOP at 1 h, 1, 3, 6 and 12 months was 25.6 ± 6.4, 15.9 ± 4.4, 15.3 ± 2.6, 16.7 ± 4.8, and 21.2 ± 4.3, respectively. IOP was significantly lower in the PSLT group compared to the SLT group at 1 h (P < 0.01) and 12 months (P < 0.01). No serious adverse events were recorded.
Conclusions: PSLT was similar in effect compared to SLT at 1, 3, 6 months, and more effective than SLT at 12 months.

Keywords: Ocular hypertension, open-angle glaucoma, pattern laser scanning trabeculoplasty, selective laser trabeculoplasty

How to cite this article:
Rey SB, Perez MC, Aguilar MC, Ríos Calixto HA, Colón SR, Forero HD. Pattern scanning laser trabeculoplasty versus selective laser trabeculoplasty in patients with primary open angle glaucoma. Pan Am J Ophthalmol 2020;2:29

How to cite this URL:
Rey SB, Perez MC, Aguilar MC, Ríos Calixto HA, Colón SR, Forero HD. Pattern scanning laser trabeculoplasty versus selective laser trabeculoplasty in patients with primary open angle glaucoma. Pan Am J Ophthalmol [serial online] 2020 [cited 2021 Aug 1];2:29. Available from: https://www.thepajo.org/text.asp?2020/2/1/29/298634

  Introduction Top

Four decades ago, laser trabeculoplasty was introduced to lower intraocular pressure (IOP) in patients with open-angle glaucoma.[1] Krasnov first reported the use of a laser on the trabecular meshwork to increase drainage of aqueous humor[2],[3] Argon Laser Trabeculoplasty (ALT) was described in the 1970s[4] which aimed to improve the outflow of aqueous humor through photocoagulation of the trabecular meshwork. Two decades later, selective laser trabeculoplasty (SLT) was introduced to selectively target pigmented TM cells without the coagulative damage to the TM architecture or non-pigmented cells that occurred in ALT. SLT is equally effective and produces less post-laser anterior chamber inflammation and leaves the trabecular meshwork intact with minimal damage to the endothelial cells.[5] This is in contrast to ALT, which may result in scarring of the trabecular meshwork and peripheral anterior synechiae formation.[6] At present, SLT has mostly replaced ALT due to its similar effectiveness, safety and possibility of repeat treatments.[3]

Recently, a computer-guided Pattern Scanning Laser Trabeculoplasty (PSLT) has been described[6] which applies a sequence of pattern laser spots onto the trabecular meshwork using a 577 nm yellow laser. Automatic rotation with calculated alignment of each pattern allows consecutive treatment of the entire trabecular meshwork without overlapping or excessive gaps in between.[7] The pulse duration is much shorter compared to ALT (5–10 ms vs. 0.1 s) which produces less tissue scarring and coagulative damage. Lee et al. reported a study whereby the use of sub-threshold power PSLT compared to ALT caused less coagulative damage to the trabecular meshwork and therefore less subsequent formation of a scar tissue (Morphological Changes in Trabecular Meshwork after Patterned and ALT in Cats).

The efficacy is maintained by applying approximately ten times more spots for the same area of treated trabecular meshwork.[7]

There are five previous studies that have evaluated the safety and efficacy of PSLT in glaucoma eyes.[7],[8],[9],[10],[11] Three studies have shown that PSLT is similar to SLT in reducing IOP at 6 months.[7],[8],[11] The purpose of this study is to compare the IOP after SLT and PSLT in a group of patients with hypertensive glaucoma. It is the first study to include 1 year data for PSLT.

  Materials and Methods Top

This study was conducted in an ophthalmological center in Bogotá, Colombia from January 2015 to September 2016 and was approved by the institutional review board. All patients provided written informed consent.

This was a nonrandomized prospective interventional study with patients recruited from June 2015 to June 2016. Eligible patients were 40 years of age or older, had ocular hypertension with an open angle or primary open angle glaucoma and had an IOP of 20 or more at two separate readings (using one or more IOP lowering medication). Patients who had had any type of ocular surgery (except iridotomy) within the previous 3 months were excluded.

Patients who were selected for laser trabeculoplasty from the glaucoma clinic were invited to participate in the study. The type of laser to be used was determined by the patient´s insurance which authorized one or the other. One or both eyes could be included in the study, if eligible. If both eyes were included, the same type of laser was used and the procedure was done simultaneously. All laser procedures were performed by two surgeons from the glaucoma department (SB and HDF).

Laser procedure

Pattern scanning laser trabeculoplasty

All eyes received a single session of 360° laser treatment. PSLT was performed using the PAtterned SCAnning Laser (PASCAL, Streamline 577; Topcon Inc., Tokyo, Japan). A starting power level of 500 mW for 10-ms was chosen and power was reduced or increased until light blanching of the trabecular meshwork was achieved. After titration, power was maintained but the pulse duration was automatically reduced to 5 ms to produce sub visible lesions. The treatment was administered in 32 steps, where each pattern is composed of three rows of 13 spots each (1152 in total), with zero spacing between the adjacent spots.

Selective laser trabeculoplasty

SLT treatment was performed using the OPTOSLT M laser (OPTOTEK medical, Ljubljana, Slovenia). Starting power was set at 0.6 mJ and titrated to produce cavitation bubbles, after which it was reduced in 0.1 mJ increments until only occasional bubbles were observed. In all cases, a total of 90-100 non-overlapping spots were applied on 360° at energy levels ranging from 0.4 to 0.8 mJ per pulse.

Intraocular pressure measurements

A drop of brimonidine 0.2% was instilled in all treated eyes 5 min before starting the laser. Patients were prescribed either topical diclofenac 0.1% or topical nepafenac 0.1%, one drop four times daily for 4 days. All IOP measurements consisted of three readings using Goldmann applanation tonometry, and the average was used in data analysis. The IOP was measured by an ophthalmologist uninvolved with the study masked to treatment. IOP was measured 1 h after the laser was finished, then 1, 7 days, 1, 3, 6 and 12 months after the laser procedure. All readings were performed approximately at the same time of day to avoid errors related to diurnal IOP variation. Adverse events were recorded at each visit.

Statistical analysis

Data are expressed as mean ± standard deviation where appropriate. Categorical variables are described in terms of frequencies and percentages. Data were analyzed using a two tailed unpaired t-test, Mann–Whitney U-test, and repeated measures analysis of variance.

All analyses were conducted using Graphpad Prism Version 5 (GraphPad Software, Inc., La jolla, CA, USA). Primary outcomes were IOP and percentage change in IOP from baseline. Treatment success was defined as an IOP reduction ≥25% from baseline.

  Results Top

A total of 20 eyes from 14 patients were included (8 women, 6 men). Demographic an clinics characteristics are shown in [Table 1]. All patients had ocular hypertension with an open angle or primary open angle glaucoma and had an IOP ≥20 mmHg. One patient in the PSLT group and 2 patients (3 eyes) in the SLT group were lost to follow-up at 12 months.
Table 1: Demographic and clinical characteristics

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The groups were comparable in all characteristics, including the number of medications used. Baseline IOP was slightly higher in the SLT group, but this was not statistically significant. There were no serious adverse events in both groups. [Table 2] shows the IOP values and percent reduction from baseline for all time points. IOP was significantly lower in the PSLT group in the 1st h and especially at month 12 compared to SLT [Figure 1]. There was a significantly higher percentage IOP reduction at Day 7 in the SLT group compared to the PSLT group. All other time points were not significantly different.
Table 2: Intraocular pressure (mmHg) and percent reduction of intraocular pressure from baseline for both groups

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Figure 1: Intraocular pressure measurements (mean ± standard error of the mean). A significantly lower intraocular pressure was observed in the pattern laser scanning trabeculoplasty group at 1 h and 12 months compared to selective laser trabeculoplasty (P < 0.05)

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Success (IOP decrease of ≥25%) was achieved with the PSLT in 64% at 3 months, 82% at 6 months and 80% at 12 months. In the SLT group success was achieved in 100% at 3 months, 63% at 6 months and 17% at 12 months (P values were: 0.1, 0.6, and 0.04, respectively).

  Discussion Top

The results of this study showed that at 1, 3, 6, and 12 months follow-up the IOP and IOP percentage reduction was similar between PSLT compared to SLT. This study presents the first 1 year results of PSLT. Interestingly, at 12 months, PSLT produced a significantly lower IOP (13 mmHg) compared to SLT (21.2 mmHg). However, it must be taken into account for the interpretation of the results that 1/3 of the patients in the SLT group had lost follow-up at 12 months which can influence the validity of this result. IOP percentage reduction was not significantly different probably due to a large variation in the values. Treatment success (percentage decrease >25%) was similar for both groups at 3 and 6 months, but significantly higher in the PSLT group at 12 months (80% vs. 17%, P = 0.04). There were no significant side effects or complications.

There are few publications on PSLT as it is not a widely available technology. The first report was a pilot study by Turati et al. in 2010[9] which included 47 eyes of 25 patients with open angle glaucoma. They reported a mean percentage IOP decrease of 23.6% at 3 months and 24.2% at 6 months. Their final analysis included 30 eyes. Barbu et al.[10] demonstrated a reduction of mean IOP from 20.2 to 15.6 mmHg (23%) in 20 eyes of 20 patients at 2 months after PSLT treatment.

Three studies have compared PSLT to SLT with a 6 month follow-up. A poster presented by Nosaki[7] reviewed in a retrospective study 12 eyes that underwent PSLT treatment and compared them with 13 eyes that underwent SLT. PSLT produced an IOP decrease of 33% versus 21% with SLT at 6 months and the study concluded that the effect was similar between both lasers. Mansouri and Shaarawy[8] in 2016 published the only randomized prospective study comparing PSLT to SLT (58 eyes of 29 patients). They found that at 6 months the percentage IOP reduction was 19.1% for PSLT and 18.5% for SLT with P = 0.52.

A comparative study of PSLT versus SLT in a hypertensive group (similar to ours) was published by Kim et al. in 2014.[11] They included 18 eyes in the SLT group (baseline IOP 25.27 mmHg) and 17 eyes in the PSLT group (baseline IOP 24.11 mmHg). They found a 37% IOP decrease in the SLT group compared to a 27.1% decrease in the PSLT group at 6 months with no statistical difference at any of the time points. The values of this study are quite similar to ours (40.6% SLT and 34.4% PSLT at 6 months). This suggests that the larger percentage decrease seen in our study compared to previous publications may be due to a higher baseline IOP just like in the publication by Kim et al. A higher baseline IOP has been shown to be the strongest predictor of treatment effect in SLT.[12],[13],[14]

A retrospective study with 41 eyes of 25 patients with open angle glaucoma or ocular hypertension assessing the efficacy and safety of PLT was published in 2018. They demonstrated a mean IOP reduction of 16.1%, 17.1%, and 18.3% at 1, 3, and 6 months respectively; with a success rate at 6 months of follow-up on 48.78% (Clinical Outcomes of patterned laser trabeculoplasty as adjuvant therapy in open-angle glaucoma and ocular hypertension).

This study showed a lower IOP in PSLT after 1 year. It is known that the effect of SLT decreases with time. The average reduction of SLT after 6 months is 21.8%–29.4%, at one year 16.9%–30% and 7.7%–27.8% at 2 years.[12] Percentage reduction in our SLT group at one year was 16.0 ± 14.5 which is in the range reported previously, although on the lower side. Surprisingly, percentage reduction in our PSLT group was 41.7% ± 15.1% at one year. Although this is a very small sample size of 10 eyes in the PSLT group and 6 eyes in SLT, it is possible that the IOP lowering effect of PSLT lasts longer than SLT. Further studies with larger sample sizes are needed to investigate this point.

This study also included measurement of IOP 1 hour after performing both lasers. IOP was significantly lower in the PSLT group compared to SLT (19.0 vs. 25.6 mmHg, P < 0.01). One patient developed an IOP spike (increase of 5 mmHg) in the SLT group (11%) compared to zero IOP spikes in the PSLT group. The study supports the publication by Tutati et al.[9] who reported no IOP spikes after PSLT in their series of 47 eyes. IOP spikes in SLT occur in 0%–28% of eyes[15],[16] (average 4.5%–10% in prophylactically treated eyes) and although the mechanism is unknown it is thought to be due to trabeculitis from the laser. The total energy delivered per eye after PSLT is about 3.5J versus 0.1J on an average in SLT,[9] so one would expect a larger percentage of IOP spikes with PSLT which does not appear to be the case. In a series of 12 eyes treated with PSLT one patient developed an IOP spike,[7] and hence, it is still a possibility with this kind of laser.

The mechanism of action of either type of trabeculoplasty is not entirely clear. In SLT, minimal structural damage is produced so there are several theories as to why it lowers IOP. It seems to induce liberation of free oxygen radicals which induces peroxidation of the meshwork, it alters the intercellular junction altering flow across Schlemm´s canal and increases the release of cytokines that lead to remodeling of the juxtacanalicular extracellular matrix.[17] In PSLT, the smaller size of the laser spots (100 vs. 400 μm in SLT) means a much larger number of shots (100 vs. 1056), and because of the smaller spot size, it covers 30% less of the trabecular meshwork compared to the 100 shot treatment with SLT. There is also a lack of visible tissue scarring and damage[18] in PSLT which suggests a similar mechanism to SLT.

Alternatives to SLT are being investigated with a number of different lasers. Micropulse laser trabeculoplasty (MLT) delivers energy in repetitive microsecond pulses followed by an intermittent rest period, reducing the build-up of thermal energy with no observable coagulative damage. In a series of 48 eyes, MLT decreased IOP by 19.5% with a 21.4% reduction in medication use.[17] Titanium-sapphire laser trabeculoplasty (TSLT) uses a 790 nm wavelength laser which emits near-infrared energy in pulses ranging from 5 to 10 ms. This is thought to allow deeper penetration into the juxtacanalicular meshwork so it is absorbed by pigmented phagocytic cells, preserving the trabecular meshwork tissue.[19] A study of 37 eyes showed an IOP decrease of 32% at a mean follow-up of 15 months, compared to 25% with ALT.[19] There was no statistical difference between the two groups. IOP spikes occurred in one patient who underwent TSLT.

Using the PSLT laser for trabeculoplasty has the advantage of using an equipment that could be more versatile than the average SLT laser. The PSLT laser can be used for retinal photocoagulation, iridoplasty, and trabeculoplasty. From a developing nation's perspective, this could be an incentive to switch to PSLT trabeculoplasty, especially in institutions with a limited budget.

This study has several limitations. The type of laser was not assigned randomly and it is a small sample size, especially at the 12-month follow-up. The reason for this is likely due to the inclusion criteria, as hypertensive patients despite medical therapy are rare in Colombia, where truly hypertensive primary open-angle glaucoma is not very frequent.[20] We are concerned about the statistical independence of fellow eyes that were treated and included in the statistical analysis. Three out of six SLT subjects were treated in both eyes. The fact that the treatment response in one eye potentially correlates the one in the fellow eye can not be ignored. SLT appears to have a crossover effect in the fellow eyes of treated patients with a pressure lowering effect. A statistically significant IOP reduction in the fellow untreated eyes of patients with OAG was demonstrated by the retrospective review of Onakoya et al., in which the mean IOP reduction was 26% in the treates eyes and 25.9% in the untreated eyes at 3 months (IOP Changes Post SLT in the contralateral Untreated Eyes of Nigerian Patients with Primary Open Angle Glaucoma). This same effect was seen in a study by Rhodes et al., which showed a mean reduction in IOP of 18.8% and 11.2% at 6-month post-treatment in the treated eye and untreated eye, respectively (IOP reduction in the untreated fellow eye after SLT). Another study by Latina and associates reported a decreased in IOP of 3.7%, 5.0%, and 9.7% at 1 day, 1 week, and 6 months after laser therapy in the untreated eye compared to a decreased of 30.2%, 16.3%, and 18.7% in the treated eye (Q-seithed 532-nm Nd:YAG Laser Trabeculoplasty (SLT).

This cross over effect is thought to result from the systemic biologic effects of selective trabeculoplasty through systemic dissemination of pro-inflammatory chemical substances inciting a similar effect in the contralateral eye (IOP Changes Post SLT in the contralateral Untreated Eyes of Nigerian Patients with Primary Open Angle Glaucoma).

Caution should be taken when interpreting our results as no data on the long term effect of PSLT exists. All patients were on an average of two drops and medication was not altered during the study. This means that the multiple medications may have had some effect on the final percentage reduction of both lasers. However, it is an interesting finding that although trabeculoplasty is thought to be more effective when less medications are used, our patients had an excellent response to both lasers even when on multiple glaucoma medications.

  Conclusions Top

PSLT trabeculoplasty appears to be an effective and safe treatment for ocular hypertension. According to our study PSLT trabeculoplasty was similar in effect compared to SLT at 6 months and more effective than SLT at 12 months. Both lasers had a larger percentage IOP reduction compared to previous studies, even though patients were on an average of 2.4 types of glaucoma drops (probably related to a higher baseline IOP). Larger studies and longer follow-up are required to evaluate the effect of PSLT compared to the current standard of care in trabeculoplasty, SLT.

Financial support and sponsorship


Conflicts of interest

Sandra Belalcazar Rey MD, speaker Topcon 2018. The preliminary results of this study were shown during 2018 American Academy of Ophthalmology (AAO) Annual Meeting. The study was registered at Clinicaltrials.gov (NCT02679482).

  References Top

Pham H, Mansberger S, Brandt JD. Argon laser trabeculoplasty. The gold standard: Argon laser trabeculoplasty versus selective laser trabeculoplasty. Surv Ophthalmol 2008;53:641-5.  Back to cited text no. 1
Krasnov MM. Laser puncture of the anterior chamber angle in glaucoma (a preliminary report). Vestn Oftalmol 1972;3:27-31.  Back to cited text no. 2
Samples JR, Singh K, Lin SC, Francis BA, Hodapp E, Jampel HD, et al. Laser trabeculoplasty for open-angle glaucoma: A report by the American academy of ophthalmology. Ophthalmology 2011;118:2296-302.  Back to cited text no. 3
Worthen D, Wickham M. Laser trabeculotomy in monkeys. Invest Ophthalmol Vis Sci 1973;12:707-11.  Back to cited text no. 4
Lee JW, Chan JC, Chang RT, Singh K, Liu CC, Gangwani R, et al. Corneal changes after a single session of selective laser trabeculoplasty for open-angle glaucoma. Eye (Lond) 2014;28:47-52.  Back to cited text no. 5
Kramer T, Noecker R. Comparison of the morphologic changes after selective laser trabeculoplasty and argon laser trabeculoplasty in human eye bank eyes. Ophthalmology 2001;108:773-9.  Back to cited text no. 6
Nosaki M. Outcomes of Patterned Laser Trabeculoplasty Versus Selective Laser Trabeculoplasty in Open Angle Glaucoma. Poster Presented at. Boston, MA: ASCRS/ASOA Symposium & Congress; 2014.  Back to cited text no. 7
Mansouri K, Shaarawy T. Comparing pattern scanning laser trabeculoplasty to selective laser trabeculoplasty: A randomized controlled trial. 2017;95:e361-5.  Back to cited text no. 8
Turati M, Gil-Carrasco F, Morales A, Quiroz-Mercado H, Andersen D, Marcellino G, et al. Patterned laser trabeculoplasty. Ophthalmic Surg Lasers Imaging 2010;41:538-45.  Back to cited text no. 9
Barbu CE, Rasche W, Wiedemann P, Dawczynski J, Unterlauft JD. Pattern laser trabeculoplasty and argon laser trabeculoplasty for treatment of glaucoma. Ophthalmologe. 2014;111:948-53. doi: 10.1007/s00347-014-3036-x.  Back to cited text no. 10
Kim JM, Cho KJ, Kyung SE, Chang MH. J Korean Ophthalmol Soc. 2014;55:563-9. Korean. Published online April 15, 2014. https://doi.org/10.3341/jkos.2014.55.4.563.  Back to cited text no. 11
Leahy KE, White AJ. Selective laser trabeculoplasty: Current perspectives. Clin Ophthalmol 2015;9:833-41.  Back to cited text no. 12
Hodge WG, Damji KF, Rock W, Buhrmann R, Bovell AM, Pan Y. Baseline IOP predicts selective laser trabeculoplasty success at 1 year post-treatment: Results from a randomised clinical trial. Br J Ophthalmol 2005;89:1157-60.  Back to cited text no. 13
Martow E, Hutnik CML, Mao A. SLT and adjunctive medical therapy: A prediction rule analysis. J Glaucoma 2011;20:266-70.  Back to cited text no. 14
Damji KF, Bovell AM, Hodge WG, Rock W, Shah K, Buhrmann R, et al. Selective laser trabeculoplasty versus argon laser trabeculoplasty: Results from a 1-year randomised clinical trial. Br J Ophthalmol 2006;90:1490-4.  Back to cited text no. 15
Barkana Y, Belkin M. Selective laser trabeculoplasty. Surv Ophthalmol 2007;52:634-54.  Back to cited text no. 16
Lee JW, Yau GS, Yick DW, Yuen CY. Micro pulse laser trabeculoplasty for the Treatment of Open-Angle Glaucoma. Medicine (Baltimore) 2015;94:e2075.  Back to cited text no. 17
Lee JY, Ha SY, Paik HJ, Kwon KY, Kim YY. Morphologic changes in trabecular meshwork after patterned and argon laser trabeculoplasty in cats. Curr Eye Res 2014;39:908-16.  Back to cited text no. 18
Goldenfeld M, Melamed S, Simon G, Ben Simon GJ. Titanium: Sapphire laser trabeculoplasty versus argon laser trabeculoplasty in patients with open-angle glaucoma. Ophthalmic Surg Lasers Imaging 2009;40:264-9.  Back to cited text no. 19
Rueda JC, Lesmes DP, Parra JC, Urrea R, Rey JJ, Rodríguez LA, et al. Valores de paquimetría en personas sanas y con glaucoma en una poblacion colombiana. MedUNAB 2007;10:81-85.  Back to cited text no. 20


  [Figure 1]

  [Table 1], [Table 2]


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