The efficacy of MicroPulse Transscleral Laser Therapy as primary surgical treatment in various types of glaucoma resistant to medical treatment: a retrospective analysis

Abstract

Purpose

To evaluate the results of MicroPulse Transscleral Laser Therapy (TLT) as primary treatment in various types of glaucoma resistant to medical treatment.

Methods

In this retrospective study, the clinical outcomes of 118 eyes from 112 patients treated with MicroPulse TLT were evaluated. Intraocular pressure (IOP) values ​​of patients with primary open-angle glaucoma (POAG), neovascular glaucoma (NVG), pseudoexfoliation glaucoma (PXG), pigmentary glaucoma (PG), angle-closure glaucoma (ACG), aphakic glaucoma (AG), congenital/juvenile glaucoma (PCG/JOAG) and silicone oil-induced glaucoma (SOG) treated with MicroPulse TLT were measured at baseline, 1 day, 1 week and 1, 3, 6 and 12 months (+/- 2 weeks) after application.

Results

79 eyes (66.9%) received single session MicroPulse TLT, 33 eyes (28.0%) received 2 sessions, and 6 eyes (5.1%) received 3 sessions. The initial treatment demonstrated a success rate of 72.8% (n = 86). 39 patients received a subsequent treatment, which elevated the overall success rate to 75.4% (n = 89) at 12 months. Significant reductions in IOP were observed in the POAG (46.5%), NVG (50.4%), PXG (43.7%), PG (52.7%), ACG (50.6%), AG (50.8%), PCG/JOAG (56.2%) and SOG (51%) groups up to 12 months compared to baseline (p < 0.05 for each). At the end of the 12th month, a 75.4% success rate was achieved with a 48.8% decrease in mean IOP in all groups. Consequently, the overall failure rate was 24.6% (n = 29).

Conclusion

As a primary surgical treatment, MicroPulse TLT is an effective and safe, minimally invasive treatment method that reduces IOP and drug burden in various types of glaucoma resistant to medical treatment. Further large-scale, prospective studies are recommended to validate these findings and explore long-term outcomes.

Introduction

The primary objective in glaucoma management is the reduction of intraocular pressure (IOP). Current treatment modalities include pharmacological therapy, laser procedures, and surgical interventions. Although topical medications represent the initial therapeutic approach, they may be insufficient in achieving adequate IOP control in some patients. Trabeculectomy remains the gold standard among surgical options; however, its use is limited by a significant risk of complications [1]. Transscleral continuous wave diode laser cyclophotocoagulation (TSCPC) targets melanin in the pigmented epithelium of the ciliary body. However, TSCPC may also cause collateral damage to adjacent non-pigmented structures such as the ciliary stroma and ciliary muscle [2]. The application of high-energy laser or non-selective tissue targeting in TSCPC has been associated with complications including uveitis, chronic hypotony, phthisis bulbi, and sympathetic ophthalmia [2, 3]. Recent studies suggest that chronic inflammation and fibrovascular remodeling, commonly observed in neovascular glaucoma (NVG), uveitic glaucoma, traumatic glaucoma, and post-vitreoretinal surgery glaucoma, may lead to the development of a hydrophobic layer in the pars plana, thereby compromising the efficacy of laser therapy [4, 5]. Due to these undesirable complications, TSCPC is generally reserved for patients with end-stage, refractory glaucoma and limited visual potential [3].

MicroPulse transscleral laser therapy (TLT) for glaucoma presents a novel approach by delivering laser energy in a segmented fashion, allowing for selective targeting of pigmented cells with lower total energy [6]. The MicroPulse modality reduces the overall thermal load by alternating “on” and “off” cycles, thereby preventing excessive energy delivery to the targeted tissue. Furthermore, the “cool-off” periods between pulses help to preserve surrounding structures and promote tissue recovery [4, 7]. Studies have shown that serious complications such as hypotony and phthisis bulbi are significantly less frequent with MicroPulse TLT compared to continuous wave TSCPC [4]. While some literature emphasizes the importance of total energy delivered in determining both efficacy and complications, other reports highlight the role of glaucoma subtype in treatment outcomes. MicroPulse TLT has demonstrated variable efficacy across different glaucoma subtypes resistant to conventional therapies [4, 6, 8, 9]. However, there is a limited body of evidence supporting the use of MicroPulse TLT as a primary treatment modality [10–12]. This study aimed to evaluate the results of MicroPulse TLT as primary treatment in various types of glaucoma resistant to medical treatment.

Materials and methods

In this retrospective study, the clinical outcomes of 118 eyes from 112 patients treated with MicroPulse TLT at the Harran University Department of Ophthalmology between 2020 and 2024 were evaluated. Patients with IOP above 22 mmHg despite maximal medical treatment and who had not undergone glaucoma surgery or laser surgery before were included in the study. Patients who had been followed in the glaucoma unit for at least 12 months from their initial examination were included in the study. The patients’ IOP values were unresponsive to 12 months (+/- 2 weeks) of medical therapy. The primary objective was to reduce IOP to a range between 6 and 21 mmHg. Treatment success was defined as achieving an IOP below 22 mmHg and a reduction of more than 20% from baseline, with or without the use of IOP-lowering medications. Eyes with primary open-angle glaucoma (POAG), neovascular glaucoma (NVG), pseudoexfoliation glaucoma (PXG), pigmentary glaucoma (PG), angle-closure glaucoma (ACG), aphakic glaucoma (AG), congenital/juvenile glaucoma (PCG/JOAG) and silicone oil-induced glaucoma (SOG) were included. In the SOG group, silicone oil was present in the eye during the MicroPulse TLT procedure. Patients in the NVG group had active NVG. Despite receiving anti-VEGF and photocoagulation therapy in addition to maximal medical treatment, their IOP remained above 22 mmHg. MicroPulse TLT was performed by a single glaucoma specialist (MT) in the operating room after patients signed informed consent. Preoperative IOP-lowering medications included any combination of four topical agent classes (alpha-adrenergic agonists, beta-blockers, carbonic anhydrase inhibitors, and prostaglandin analogs) and one oral agent (acetazolamide). IOP-lowering medications were continued postoperatively and were tapered based on achieving the target IOP of ≤ 21 mmHg, with the goal of reducing the medication burden while maintaining IOP control. A comprehensive eye examination was performed, including visual acuity with Snellen chart (Aurochart, Aurolabs, Madurai). The IOP values of patients treated with MicroPulse TLT were measured using a Goldmann applanation tonometer at baseline, and at postoperative day 1, week 1, and months 1, 3, 6, and 12. The primary outcomes evaluated were IOP reduction and the number of glaucoma medications used. Secondary outcomes included visual acuity and treatment-related complications. Antiglaucoma medications were continued during the early postoperative period and subsequently tapered according to IOP measurements obtained at follow-up visits. Re-treatment was considered if IOP exceeded >/=22 mmHg at any follow-up visit after the first month, despite being on maximal tolerated medical therapy.

MicroPulse diode laser transscleral cyclophotocoagulation application method

A mixture of 0.5% bupivacaine and 2% lignocaine in a 1:1 ratio was applied for peribulbar anesthesia. The Iridex Cyco G6 Glaucoma Laser device (Mountain View, California, United States of America) with a wavelength of 810 nm was used. The laser settings were programmed as follows: power − 2000 mW and 31.33% duty cycle (MicroPulse “on” 0.5 ms, MicroPulse “off” 1.1 ms). The fiber optic tip of the original laser probe (MicroPulse P3 ^®) was lubricated with methyl cellulose eye gel before contact with the eye. The laser probe was applied 1.5 mm behind the limbus by applying light pressure perpendicular to the sclera. To avoid damaging the long posterior ciliary artery, the laser probe was applied to all remaining quadrants except the 3- and 9- hour quadrants with a continuous sliding motion with constant pressure for 160 s (80 s at the top and 80 s at the bottom). Approximately 5 sliding movements were performed in each quadrant for 8 s each. When a “pop” sound occurred, the power was reduced. The mean total laser energy applied in each session was 72.5 ± 21.6 J. All patients underwent 360° for 160 s (80 s at the top and 80 s at the bottom). After the procedure was completed, patients were instructed to discontinue acetazolamide, use 0.3% moxifloxacin and 0.1% dexamethasone eye drops every 2 h for one week, and continue all antiglaucoma drops until follow-up.

Success criteria

Surgical success was defined as IOP between 6- and 21- mmHg and greater than 20% IOP reduction with or without IOP-lowering agents. Surgical failure was defined as failure to meet the aforementioned success criteria or need for incisional glaucoma surgery. Re-treatment with MicroPulse TLT was not considered a failure. Decisions regarding repeat MicroPulse procedure or further surgery in patients with elevated IOP were made on a patient-by-patient basis. In cases where an adequate response was not obtained, at least 1 month was allowed before repeating the procedure. The decision for re-treatment was made at least 1 week after discontinuation of both steroids and oral acetazolamide.

Exclusion criteria

Patients with ocular or systemic infections or inflammatory conditions were excluded from the study. Patients with a history of previous inflammation (history of uveitis) were excluded. Those with a history of prior glaucoma surgery or laser treatment were also excluded. In addition, patients who had undergone non-glaucoma ocular surgeries (such as cataract or eyelid procedures) within the preceding two months were not included.Participants who did not have a regular 3-month follow-up examination were excluded from the study.

Statistical analysis

Statistical analyses were conducted using the Jamovi software package (Version 2.3.28, Jamovi project, 2023, https://www.jamovi.org) and JASP software package (Version 0.18.3, Jeffreys’ Amazing Statistics Program, 2024, https://jasp-stats.org). A p-value of ≤ 0.05 was considered statistically significant. Descriptive statistics were used to summarize the data obtained from the study. Continuous variables were summarized as mean ± standard deviation depending on the distribution, while categorical variables were summarized as number and percentage. For comparisons with small sample sizes (n < 50), the Shapiro-Wilk test was used, while for larger sample sizes (n ≥ 50), the Kolmogorov-Smirnov and Anderson-Darling tests were utilized. Additionally, visual tools such as histograms and Q-Q plots were employed to assess normality. To compare differences in categorical variables between groups, the Fisher-Freeman-Halton test was used in RxC tables where the expected frequencies in cells were less than 5. For statistical comparisons of repeated measurements at baseline IOP, IOP (1. Day), IOP (1. Week), IOP (1. Month), IOP (3. Month), IOP (6. Month), and IOP (12. Month), the Friedman test, a non-parametric alternative to Repeated Measures ANOVA, was used when numerical variables did not show a normal distribution. The normality assumption was checked using the Shapiro-Wilk test and Q-Q plots. Homogeneity of variances was evaluated with Mauchly’s Sphericity test. When significant differences were found in non-parametric test results, the Durbin-Conover test was applied to determine differences over time.

Results

In this study, 79 eyes (66.9%) received single session MicroPulse TLT, 33 eyes (28.0%) received 2 sessions, and 6 eyes (5.1%) received 3 sessions (Table 1). No significant difference was detected in baseline IOP between glaucoma groups (p = 0.143). Post-hoc power analysis revealed an achieved power of 0.68 for a large effect size (f = 0.40). Other pairwise comparisons of baseline IOP values showed no significant differences (p > 0.05 for each). Additionally, no significant differences were found between groups for IOP values at day 1, week 1, month 1, month 3, month 6, and month 12 (p > 0.05 for each) (Table 2). In this study, there were no significant differences in gender, number of laser treatments, or follow-up time between groups (p > 0.05 for each). In terms of age across groups, patients in the PCG/JOAG group were significantly younger compared to those in the other groups (p < 0.05 for each pairwise comparison). Conversely, the ages of participants in the other groups were similar to each other (p > 0.05 for each pairwise comparison).

Table 1.

Demographic and clinical characteristics of patients by group and comparison

	Overall (n = 118)	POAG (n = 37)	NVG (n = 28)	PXG (n = 15)	PG (n = 7)	ACG (n = 8)	AG (n = 11)	PCG/JOAG (n = 8)	SOG (n = 4)	P value
Age †	59.0 ± 15.7	63.0 ± 9.0	62.4 ± 10.0	61.1 ± 7.0	57.4 ± 7.4	62.2 ± 9.6	62.3 ± 21.0	15.1 ± 2.2	65.8 ± 9.7	0.001*
Gender ‡
Female	59 (50.0)	22 (59.5)	13 (46.4)	7 (46.7)	2 (28.6)	4 (50.0)	6 (54.5)	3 (37.5)	2 (50.0)	0.841**
Male	59 (50.0)	15 (40.5)	15 (53.6)	8 (53.3)	5 (71.4)	4 (50.0)	5 (45.5)	5 (62.5)	2 (50.0)
Number Of Laser Treatments ‡
1	79 (66.9)	26 (70.3)	17 (60.7)	10 (66.7)	5 (71.4)	5 (62.5)	7 (63.6)	6 (75.0)	3 (75.0)	0.996**
2	33 (28.0)	9 (24.3)	9 (32.1)	4 (26.7)	2 (28.6)	3 (37.5)	4 (36.3)	1 (12.5)	1 (25.0)
3	6 (5.1)	2 (5.4)	2 (7.1)	1 (6.7)	0 (0.0)	0 (0.0)	0 (0.0)	1 (12.5)	0 (0.0)
Follow-up duration (months) †	16.6 ± 3.0	16.4 ± 3.0	16.9 ± 2.8	16.1 ± 2.9	16.3 ± 3.8	17.1 ± 3.0	17.5 ± 3.0	16.6 ± 3.5	14.2 ± 2.6	0.588*

POAG: Primary Open-Angle Glaucoma, NVG: Neovascular Glaucoma, PXG: Pseudoexfoliative Glaucoma, PG: Pigmentary Glaucoma, ACG: Angle-Closure Glaucoma, AG: Aphakic Glaucoma, PCG/JOAG: Congenital/Juvenile Glaucoma, SOG: Silicone Oil-Induced Glaucoma

‡: n (%), †: Mean ± Standard Deviation

*. Kruskal Wallis-H test

**. Fisher Freeman Halton test

Table 2.

Intraocular pressure and medication use across different time points in patient groups

	Overall	POAG	NVG	PXG	PG	ACG	AG	PCG/JOAG	SOG	P value*
	(n = 118)	(n = 37)	(n = 28)	(n = 15)	(n = 7)	(n = 8)	(n = 11)	(n = 8)	(n = 4)
Baseline IOP †	38.8 ± 5.1	36.5 ± 4.8	39.4 ± 5.5	38.6 ± 4.7	38.3 ± 3.9	41.1 ± 3.2	41.9 ± 6.5	40.8 ± 3.8	40.2 ± 1.5	0.143
IOP (Day 1) †	18.0 ± 4.1	18.5 ± 3.1	16.6 ± 3.6	18.7 ± 4.1	16.3 ± 3.8	19.6 ± 4.2	19.5 ± 4.8	17.4 ± 7.3	19.0 ± 5.0	0.145
IOP (Week 1) †	18.1 ± 4.0	18.6 ± 2.8	17.0 ± 3.5	18.7 ± 3.6	16.9 ± 3.2	19.2 ± 4.9	19.0 ± 5.1	16.5 ± 7.5	18.5 ± 4.5	0.288
IOP (Month 1) †	18.2 ± 3.9	17.9 ± 3.0	17.5 ± 3.4	19.3 ± 3.9	16.9 ± 3.2	18.5 ± 4.1	19.8 ± 5.3	17.5 ± 7.3	19.5 ± 3.7	0.512
IOP (Month 3) †	18.5 ± 3.7	18.4 ± 3.0	17.8 ± 3.3	19.7 ± 3.5	16.7 ± 3.3	19.1 ± 3.7	19.7 ± 5.8	18.2 ± 5.3	19.5 ± 5.0	0.632
IOP (Month 6) †	18.8 ± 3.8	18.5 ± 3.2	18.4 ± 3.4	20.5 ± 3.4	17.9 ± 3.4	18.9 ± 4.3	19.6 ± 5.7	17.6 ± 5.4	18.2 ± 2.6	0.586
IOP (Month 12) †	19.5 ± 3.7	19.1 ± 2.9	19.0 ± 3.6	21.5 ± 3.5	18.0 ± 4.1	20.4 ± 3.8	20.1 ± 5.1	18.2 ± 4.4	19.8 ± 3.9	0.293
P value **	< 0.001	< 0.001	< 0.001	< 0.001	< 0.001	< 0.001	< 0.001	< 0.001	< 0.001
IOP reduction (%) Baseline to 12 Months †	48.8 ± 11.5	46.5 ± 11.2	50.4 ± 12.6	43.7 ± 9.7	52.7 ± 10.6	50.6 ± 7.3	50.8 ± 14.8	55.1 ± 10.6	51.0 ± 8.6	0.203
Meeting the Success Criteria within 12 Months ‡	89 (75.4)	30 (81.0)	20 (71.4)	11 (73.3)	5 (71.4)	6 (75.0)	8 (72.7)	6 (75.0)	3 (75.0)	-
Baseline IOP †	38.8 ± 5.1	36.5 ± 4.8	39.4 ± 5.5	38.6 ± 4.7	38.3 ± 3.9	41.1 ± 3.2	41.9 ± 6.5	40.8 ± 3.8	40.2 ± 1.5	0.143
IOP (Month 12) †	19.5 ± 3.7	19.1 ± 2.9	19.0 ± 3.6	21.5 ± 3.5	18.0 ± 4.1	20.4 ± 3.8	20.1 ± 5.1	18.2 ± 4.4	19.8 ± 3.9	0.293
P value ***	< 0.001	< 0.001	< 0.001	< 0.001	0.022	0.014	0.004	0.014	0.025
Baseline medication †	3.3 ± 0.7	3.3 ± 0.7	3.5 ± 0.6	2.9 ± 0.8	3.4 ± 0.8	3.5 ± 0.8	3.5 ± 0.7	3.1 ± 0.6	3.8 ± 0.5	0.271
Medication (Month 12) †	1.5 ± 1.0	1.6 ± 1.2	1.4 ± 0.8	1.4 ± 1.0	1.9 ± 1.1	1.6 ± 1.1	1.5 ± 0.8	1.6 ± 0.9	1.2 ± 1.3	0.934
P value ***	< 0.001	< 0.001	< 0.001	0.002	0.039	0.013	0.003	0.021	0.029
Follow-up duration (months) †	16.6 ± 3.0	16.4 ± 3.0	16.9 ± 2.8	16.1 ± 2.9	16.3 ± 3.8	17.1 ± 3.0	17.5 ± 3.0	16.6 ± 3.5	14.2 ± 2.6	0.588*

POAG: Primary Open-Angle Glaucoma, NVG: Neovascular Glaucoma, PXG: Pseudoexfoliative Glaucoma, PG: Pigmentary Glaucoma, ACG: Angle-Closure Glaucoma, AG: Aphakic Glaucoma, PCG/JOAG: Congenital/Juvenile Glaucoma, SOG: Silicone Oil-Induced Glaucoma, IOP: Intraocular pressure

‡: n (%), †: Mean ± Standard Deviation

*. Kruskal Wallis-H test

**. Friedman test

***. Wilcoxon test

In the POAG group, significant differences were found between baseline IOP and all other time points and month 12 (46.5%) (p < 0.001 for each). Similar significant reductions in IOP from baseline to month 12 were observed in NVG (50.4%), PXG (43.7%), PG (52.7%), ACG (50.6%), AG (50.8%), PCG/JOAG (56.2%) and SOG (51%) groups (p < 0.05 for each) (Fig. 1). The initial treatment demonstrated a success rate of 72.8% (n = 86). 39 patients received a subsequent treatment, which elevated the overall success rate to 75.4% (n = 89). Consequently, the overall failure rate was 24.6% (n = 29). Of the 29 eyes classified as failures, 18 did not meet the criteria for surgical success ‘defined as an IOP between 6 and 21 mmHg and a reduction of more than 20% in IOP’ while 11 consisted of eyes that underwent incisional glaucoma surgery. As shown in Table 1, the total of the 2nd laser treatment (32.1%) and 3rd laser treatment (7.1%) were the highest in the NVG group. Three patients with NVG, one patient with POAG, one patient with PG, one patient with PXG, and one patient with ACG underwent incisional glaucoma surgery due to failure of MicroPulse TLT. One patient with AG, one patient with pediatric glaucoma, and one patient with SOG underwent glaucoma valve surgery due to failure of MicroPulse TLT. Additionally, another patient with PXG failed due to clinically significant hypotony (Table 2). Although not statistically significant, the most successful results were obtained in POAG patients.

Fig. 1.

Repeated Measures Analysis of Intraocular Pressure Across Different Time Points. This graph shows intraocular pressure (IOP) measurements at various time points (Baseline Initial, Day 1, Week 1, Month 1, Month 3, Month 6, and Month 12) for different patient groups. (POAG: Primary Open-Angle Glaucoma, NVG: Neovascular Glaucoma, PXG: Pseudoexfoliative Glaucoma, PG: Pigmentary Glaucoma, ACG: Angle-Closure Glaucoma, AG: Aphakic Glaucoma, PCG/JOAG: Congenital/Juvenile Glaucoma, SOG: Silicone Oil-Induced Glaucoma)

The number of medications used decreased significantly at 12 months compared to baseline in all groups (p < 0.05 for each group) (Table 2). After the application of MicroPulse TLT, antiglaucomatous treatment was entirely discontinued in 25 eyes (21.1%). Additionally, the number of antiglaucomatous eye drops was reduced in 38 eyes (32.2%). At the beginning of the study, 62% (44) of the patients were using oral Acetazolamide (Diamox) 250 mg tablets. However, at the 12-month/final follow-up post-surgery, none of the patients (0%) required this medication. None of the participants had NLP visual acuity at baseline; however, one participant in the PXG group exhibited NLP visual acuity at the 12-month mark. The number of participants with a visual acuity of 20/200 remained constant at 76 (64.4%). There was no significant difference in visual acuity values between the baseline and the 12-month follow-up (p > 0.05 for each) (Table 3) (Fig. 2). In this study, transient inflammation in the anterior chamber was observed in 3 patients, transient tonic pupil in 2 patients, and low-level hyphema in 1 patient.

Table 3.

Comparison of visual acuity values at baseline and month 12

		Overall	POAG	NVG	PXG	PG	ACG	AG	PCG/JOAG	SOG	P value
		(n = 118)	(n = 37)	(n = 28)	(n = 15)	(n = 7)	(n = 8)	(n = 11)	(n = 8)	(n = 4)
Baseline visual acuity ‡	NLP	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0.797**
	LP– HM	10 (8.5)	2 (5.4)	3 (10.7)	1 (6.7)	0 (0.0)	2 (25.0)	2 (18.2)	0 (0.0)	0 (0.0)
	CF – 20/200	76 (64.4)	25 (67.6)	19 (67.9)	9 (60.0)	3 (42.9)	5 (62.5)	6 (54.5)	6 (75.0)	3 (75.0)
	≥ 20/200	32 (27.1)	10 (27.0)	6 (21.4)	5 (33.3)	4 (57.1)	1 (12.5)	3 (27.3)	2 (25.0)	1 (25.0)
Visual acuity (Month 12) ‡	NLP	1 (0.8)	0 (0.0)	0 (0.0)	1 (6.7)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0 (0.0)	0.383**
	LP – HM	10 (8.5)	2 (5.4)	3 (10.7)	0 (0.0)	0 (0.0)	3 (37.5)	2 (18.2)	0 (0.0)	0 (0.0)
	CF – 20/200	76 (64.4)	26 (70.3)	19 (67.9)	9 (60.0)	3 (42.9)	4 (50.0)	6 (54.5)	6 (75.0)	3 (75.0)
	≥ 20/200	31 (26.3)	9 (24.3)	6 (21.4)	5 (33.3)	4 (57.1)	1 (12.5)	3 (27.3)	2 (25.0)	1 (25.0)

POAG: Primary Open-Angle Glaucoma, NVG: Neovascular Glaucoma, PXG: Pseudoexfoliative Glaucoma, PG: Pigmentary Glaucoma, ACG: Angle-Closure Glaucoma, AG: Aphakic Glaucoma, PCG/JOAG: Congenital/Juvenile Glaucoma, SOG: Silicone Oil-Induced Glaucoma, NLP: No perception of light, LP: Light Perception, HM: Hand Motions, CF: Counting Fingers

‡: n (%)

**. Fisher Freeman Halton test

Footnote: Descriptive statistics are presented as numbers and percentages. The Fisher Freeman Halton test was used to compare categorical variables between groups. This test is suitable for small sample sizes and was employed due to the expected frequencies in some cells being less than 5

Fig. 2.

A and B: Comparison of Visual Acuity Values at Baseline and Month 12 Across Different Patient Groups. (A) Baseline Visual Acuity: This stacked bar chart represents the visual acuity distribution at baseline for various patient groups. The groups are categorized into four visual acuity levels: NLP: No perception of light; LP: Light Perception; HM: Hand motions; CF: Counting Fingers; CF – 20/200: Visual acuity between Counting Fingers and 20/200; ≥ 20/200: Visual acuity of 20/200 or better. (B) Visual Acuity at Month 12: This stacked bar chart shows the visual acuity distribution at the 12-month follow-up for the same patient groups. The categories remain consistent with those at baseline for comparison purposes

Discussion

TSCPC has been used in the literature for severe glaucoma cases, painful eyes with limited visual potential, or after the failure of filtering surgery [2]. In recent years, MicroPulse TLT has begun to be applied in treatment-resistant glaucomas with vision potential, as it causes less damage to the target tissue and results in fewer complications due to the reduction in energy cycles [4, 6, 8]. The effect of MicroPulse TLT may be influenced by various factors. For instance, in NVG, the continuous release of cytokines such as IGF and VEGF can alter its effectiveness. In exfoliative glaucoma, materials on the trabecular meshwork and ciliary body can reduce the laser’s impact on the tissue. In PG, the presence of pigment can enhance the laser’s effect. In PCG/JOAG, the position of the target tissue may change due to buphthalmia. Additionally, in SOG glaucoma, the presence of silicone oil in the environment can affect the outcome.

Success rates ranging from 66% to 90% have been reported in the literature for MicroPulse TLT across different glaucoma subtypes. Al Habash et al., [8] reported a success rate of 97.5% with a 52% reduction in IOP at the end of one year. Williams et al., [13] reported a success rate of 66% with a 51% reduction in IOP; and Zaarour et al., [14] reported a success rate of 66% with a 35.4% reduction. In this study, 75.4% success was found as a result of a 48.8% decrease in IOP at the end of the 12th month, which is consistent with the literature. However, in the study by Magacho et al., [10] 93% success was achieved with a 41% reduction in IOP, and it was reported that this high success was due to the multiple laser (200 J) applied in two sessions. Al Habash et al., [8] reported that NVG had higher success rates in laser treatment, which was due to the baseline high IOP and the high total laser energy delivered (165 J).

In addition to the amount of energy and duration of laser treatment, different success rates have been reported depending on the effect of different glaucoma subtypes, the patient’s age, and previous surgery. Frezzotti et al., [15] reported that the greatest IOP reduction after MicroPulse TLT was in the NVG and AG groups. Tan et al., [16] stated that after 12 months, the success in the NVG group was lower than the other groups and the most successful group was the POAG group. Ariga et al., [17] reported that while there was no significant difference between the groups in all MicroPulse TLT groups at 1 week and 1 month, the success rate was significantly lower in the POAG group at 3 months. Zemba et al., [18] reported that the success rate of MicroPulse TLT in patients with NVG was 70.8% at week 1, which decreased from month 3 onwards to 29.1% at month 12. The laser intensity used in Zemba et al.‘s study was the same as ours. However, the duration and therefore the total amount of energy applied were higher. In this study, statistically significant reductions in antiglaucomatous drops and IOP were observed in all glaucoma subtypes. It was found that the most successful group was the POAG group, but there was no significant difference between the groups. Kramp et al., [11] reported that the success of transscleral diode laser contact cyclophotocoagulation was higher in POAG, in the elderly, and in the patient group without previous surgery, and was worse in the NVG group. Sarrafpour et al., [19] reported that greater reduction in IOP was associated with higher preoperative IOP and higher laser power (62.5–78.125 J) used during surgery. Yelenskiy et al., [9] observed better results in patients who had previous filtering surgery or in patients with POAG. In this study, re-treatments were performed at the same energy levels as the initial session. Unlike other treatments, patients who had previously undergone glaucoma surgery were not included. While some protocols suggest using lower energy for subsequent treatments, our approach was aimed at ensuring a sufficient cyclophotocoagulative effect in these medically refractory cases.

In fact, Chang et al., [12] also stated that different treatment protocols would be more beneficial in glaucoma subtypes. Magacho et al. compared patients who had previously undergone glaucoma surgery with those who underwent MicroPulse TLT as the primary procedure. They reported that fewer laser treatments were sufficient in the group that had not previously undergone glaucoma surgery, that they had a higher success rate, and that visual acuity was preserved. Moreover, they reported that the rates of complications such as hypotony and inflammation were lower in these patients. It is concluded that the eyes of these patients are in better condition for laser treatment and that the laser effect may be more successful as a result [10]. Chang et al. reported that MicroPulse is an effective and reliable treatment for reducing IOP and medication burden as a primary treatment in POAG patients who have not previously undergone glaucoma surgery during the Covid-19 period. They stated that at the end of 12 months in their study, IOP decreased from 27.8 mmHg to 20.2 and they achieved a success rate of 81.7% [12].

Multiple MicroPulse TLT sessions may be required to maintain low IOP levels in the long term. Yelenskiy et al. reported that baseline IOP was the only independent predictor of MicroPulse TLT recurrence [9]. Aquino et al. stated that the low energy amount used in the initial treatment and the glaucoma subtype were influential factors in the need for re-treatment. They noted that re-treatment was applied more frequently, especially in the NVG group [20]. Tekeli et al. found a significantly higher retreatment rate in eyes with secondary glaucoma types compared to eyes with POAG and PXG [21]. It has been reported in the literature that re-treatment was performed at a rate of 26–55%, and when the number of MicroPulse TLT applied in our study was examined; 79 (66.9%) eyes received a single session of treatment, 33 (28.0%) eyes received 2 sessions, and 6 (5.1%) eyes received 3 sessions of treatment. Our re-treatment results were consistent with the literature. In the subgroup analysis, in parallel with the literature (similar to Aquino et al.), we identified the NVG group as the group in which we performed the most repetitions and the group requiring invasive surgery.

MicroPulse TLT reduces the number of antiglaucomatous drops, increasing patient comfort and reducing the side effects that may develop due to medical treatment. Emanuel et al. reported that the mean number of antiglaucomatous drops used decreased from 3.3 to 2.3 at the end of 12-month follow-up [22]. Kuchar et al. reported that the mean number of antiglaucomatous drops decreased from 2.6 to 1.9 after surgery [23]. Chang et al. reported that the mean number of antiglaucomatous drops decreased from 3.3 to 1.9 at 12 months with primary treatment in POAG patients, and Zemba et al. reported that the mean number of antiglaucomatous drops decreased from 2.6 to 2.1 in NVG patients [12, 18]. Al Habash et al. reported that 44 patients initially treated with oral acetazolamide did not require the tablet at 12-month follow-up [8]. In our study, consistent with the literature, the mean number of glaucoma medications decreased from 3.3 ± 0.7 at baseline to 1.5 ± 1.0 at 12 months. In addition, none of the 44 patients who used oral acetazolamide at the beginning needed oral treatment at the end of 1 year.

Patients with refractory glaucoma who underwent TSCPC had poor visual acuity. However, MicroPulse TLT has begun to be applied to patients with better visual acuity. Although most studies have reported that MicroPulse TLT has no direct effect on visual acuity and that visual acuity remains stable in approximately 70–80% of patients. Some publications have reported results showing decreased visual acuity [8, 17]. Chang et al. reported that visual acuity decreased in 1.7% of patients and that this was due to cataracts progressing over time [12]. Varikuti et al. reported that 20.8% of patients had decreased visual acuity after 12 months in their study with patients with a visual acuity level better than > 20/60. They also stated that the most common cause of decreased visual acuity in their study was cataract [24]. Bitirgen et al. also reported that visual acuity decreased in 21.7% of patients, probably due to inadequate IOP control [25]. In this study, visual acuity was found to be largely unchanged from baseline.

In this study, no major complications such as scleral perforation, phthisis bulbi, hypotony, or choroidal detachment were observed in any patient, while transient inflammation in the anterior chamber was observed in 3 patients, transient tonic pupil in 2 patients, and low-level hyphema in 1 patient. In this study, 3 patients with NVG, 1 patient with POAG, 1 patient with PG, 1 patient with PXG, and 1 patient with ACG failed incisional glaucoma surgery. 1 patient with AG, 1 patient with pediatric glaucoma, and 1 patient with SOG failed because of high IOP requiring glaucoma valve surgery. In addition, another patient with PXG failed because of hypotony. In other studies, the rate of application of repeated treatment sessions varies between 26 and 59% [1, 4, 5]. In this study, sufficient IOP reduction was achieved with a single session of TSDLS in 66.9% of the cases, but more than one treatment application (at most 3 sessions) was applied in 33.1% of the cases. In the literature, transient, minor complications such as inflammation, tonic pupil, hyphema, and corneal edema have been reported after MicroPulse TLT application. William et al. reported that prolonged intraocular inflammation was observed with MicroPulse TLT, which may be due to long treatment times (300–319 s) and racial differences [18]. Chang et al. reported that the most common side effect of primary treatment with MicroPulse TLT in POAG patients was transient mydriasis (28%), and no major complications were observed [12]. Zemba et al. stated that NVG is a risk factor for the development of hypotony after MicroPulse TLT treatment. They stated that the outflow resistance of the NVG group was quite high, aqueous humor production was damaged due to ischemia, and even treatments such as MicroPulse TLT may carry a risk of hypotonia [18]. Despite the significant number of NVG patients in our study and the highest number of repeat laser treatments being administered to the NVG group (39.2%), hypotony was not observed. This may be related to the low amount of laser energy applied. The variability in reported efficacy across studies underscores the current lack of consensus on optimal patient selection and laser parameters for different glaucoma subtypes. Our findings, while promising, highlight the need for large-scale, prospective, randomized trials to establish evidence-based protocols for MicroPulse TLT as a primary treatment, defining the roles of total energy, number of sessions, and specific glaucoma etiology in achieving long-term success. Further studies are warranted to provide evidence-based guidance on the efficacy, safety, and optimal laser titration of MicroPulse TLT as a primary treatment modality for various types of glaucoma.

Limitations of the study

The main limitations of our study are its retrospective nature, small sample size of some glaucoma subgroups, lack of a comparative group receiving alternative treatments such as incisional surgery, and failure to determine which factors are responsible for treatment failure with MicroPulse TLT. Post-hoc power analysis revealed an achieved power of 0.68 for a large effect size (f = 0.40). Therefore, the study was underpowered to detect significant differences in outcomes between the various glaucoma subtypes, particularly those with very small sample sizes.

Conclusion

MicroPulse TLT is an effective and safe, minimally invasive treatment method that reduces IOP and drug burden in various types of glaucoma resistant to medical treatment. Additionally, MicroPulse TLT may be used as a temporary treatment session for patients with elevated IOP refractory to maximum tolerated medical therapy before proceeding to incisional glaucoma surgery. Sometimes, repeat laser treatments may be needed to achieve the desired IOP. Long-term prospective studies with larger numbers of cases are needed to evaluate the efficacy of MicroPulse TLT in different glaucoma subtypes.

Abbreviations

AG

Aphakic glaucoma

ACG

Angle-closure glaucoma

CF

Counting Fingers

HM

Hand motions

IOP

Intraocular pressure

LP

Light Perception

NLP

No perception of light

NVG

Neovascular glaucoma

PCG/JOAG

Congenital/juvenile glaucoma

PG

Pigmentary glaucoma

POAG

Primary open-angle glaucoma

PXG

Pseudoexfoliation glaucoma

SOG

Silicone oil-induced glaucoma

TLT

Transscleral laser therapy

TSCPC

Transscleral cyclophotocoagulation

Author contributions

Contributions of authors involved in conception and design of study (MT, OFY); Collection, analysis and interpretation of data (MT); Writing the article (MT, OFY); Critical revision of the article (OFY); All authors have read and approved the manuscript in its current state.

Funding

No funding was received for this research.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Ethical Committee of the Harran University, Turkey approved the present study (Approval number: HRÜ/24.04.21). Informed consent was obtained from all individual participants included in the study. The study adhered to good clinical practice guidelines and the principles of the Declaration of Helsinki.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Competing interests

The authors declare no competing interests.