One-Year Outcome of PreserFlo MicroShunt Implantation in Patients with Open Angle Glaucoma: Real-World Data from a Tertiary Centre

Abstract

Purpose

To evaluate the one-year clinical outcomes, safety profile, and surgical success of the PreserFlo^® MicroShunt in patients with glaucoma treated at a tertiary referral centre in Malaysia.

Methods

This retrospective study included 40 eyes of 31 patients undergoing PreserFlo MicroShunt implantation performed by two experienced surgeons using a standard ab-externo technique with mitomycin C (0.04% for 3 minutes) and a structured postoperative corticosteroid tapering regimen. Outcomes assessed at 12 months included intraocular pressure (IOP), number of topical glaucoma medications, visual acuity, optic nerve and retinal nerve fibre layer parameters, visual field indices, complications, and surgical success. Complete success was defined as achieving target IOP without medications, while qualified success allowed adjunctive medications.

Results

Mean IOP was reduced from a preoperative median of 19.0 mmHg to 11.5 mmHg at 12 months (p < 0.001). The median number of glaucoma medications decreased from 3.8 to 0.2 drops. At one-year, complete surgical success was achieved in 82.5% of eyes, while qualified success was 95.0%. Surgical failure occurred in 5.0% of eyes. Early postoperative hypotony (IOP ≤5 mmHg) occurred in 17.5%, with persistent hypotony at one year in 2.5%, none of which resulted in vision loss. No cases of sight-threatening complications such as endophthalmitis, corneal decompensation, or loss of light perception were observed. Structural and functional glaucoma parameters remained stable over the follow-up period. Postoperative interventions were required in a proportion of eyes during follow-up.

Conclusion

PreserFlo MicroShunt implantation was associated with reductions in IOP and glaucoma medication burden at one year, with generally acceptable short-term safety outcomes. These findings support its role as an effective bleb-forming minimally invasive glaucoma surgery option for patients requiring lower target IOPs, including those with advanced glaucoma. However, the results should be interpreted in the context of the modest sample size, retrospective design, absence of a comparator group, and need for postoperative interventions. This study provides the first Malaysian real-world data on PreserFlo MicroShunt outcomes and adds to the growing regional evidence base for its use.

Introduction

Elevated intraocular pressure (IOP) is a defining factor in glaucoma, a multifactorial optic neuropathy characterized by progressive retinal ganglion cell (RGC) loss and eventual vision impairment.¹ In industrialized nations, glaucoma remains the leading cause of irreversible blindness, with primary open angle glaucoma (POAG) alone estimated up to 80 million people worldwide which is projected to rise to approximately 111.8 million by 2040.² Clinical evaluation typically centres on three pillars: tonometric IOP measurement, structural assessment of optic nerve head and retinal nerve fibre layer (RNFL) via optical coherence tomography (OCT) or stereoscopic ophthalmoscopy and functional assessment of visual fields via perimetry.³

While glaucoma cannot yet be cured, timely intervention can slow progression. Traditional surgical filtration, such as trabeculectomy, is reserved for patients with insufficient response to laser trabeculoplasty or medical therapy, or those exhibiting rapid glaucoma progression.⁴ For many years, trabeculectomy has been considered the gold standard for surgical glaucoma treatments. Despite its established efficacy in lowering IOP, trabeculectomy carries substantial risk of complications and often requires intensive post-operative management.⁵

The PreserFlo MicroShunt (formerly InnFocus MicroShunt) represents a bleb-forming device using a poly(styrene-block-isobutylene-block-styrene) (SIBS) biomaterial scaffold.⁶ Implanted via an ab-externo route, the device is 8.5 mm in length, has a 350μm outer diameter and a 70μm lumen. The distal tip lies beneath the conjunctiva and Tenon’s capsule, approximately 6 mm posterior to the limbus, creating a posterior subconjunctival bleb, while the proximal tip is positioned in the anterior chamber parallel to the iris.⁷ A fornix-based conjunctival and flap Tenon’s dissection (8 to 10 mm posterior) is followed by intra-operative mitomycin C (MMC) application, typically 0.2–0.4 mg/mL for 2–3 minutes, which has been shown to improve surgical success rate and reduce fibrotic failure.^6,8 The self-regulating lumen design of the MicroShunt reduces the risk of post-operative hypotony, and the SIBS polymer offers excellent biocompatibility with reduced inflammation and fibrosis.^8,9

Early clinical trials and real-world studies suggest that the PreserFlo MicroShunt can achieve IOP reductions similar to trabeculectomy, with an improved safety profile and a more standardized surgical workflow.⁹ Nonetheless, most of the published data derive from European populations, and there is a paucity of Asian-region outcomes. To the best of our knowledge, no peer-reviewed study has yet reported one-year outcomes of PreserFlo MicroShunt in a Malaysian context.

Although early studies suggest that the PreserFlo MicroShunt may achieve substantial intraocular pressure reduction with a potentially more favourable safety profile than traditional trabeculectomy, its precise role within the glaucoma surgical algorithm remains incompletely defined. While some studies have reported lower postoperative intervention burden and more predictable recovery compared with trabeculectomy, others have demonstrated comparatively lower complete success rates when stringent target intraocular pressures are required, particularly in eyes with advanced disease. In addition, most currently available evidence is derived from predominantly European cohorts and controlled study settings, with limited real-world data from Asian populations. This is clinically relevant because ethnic and conjunctival wound-healing differences may influence bleb fibrosis, postoperative management requirements, and long-term surgical outcomes following filtration surgery.

In this study, we report one-year outcomes following PreserFlo MicroShunt implantation at Hospital Canselor Tuanku Muhriz in Malaysia. We examine IOP, best corrected visual acuity (BCVA), vertical cup-to-disc ratio (CDR), peripapillary RNFL thickness, Humphrey visual field indices including mean deviation (MD) and pattern standard deviation (PSD), and number of topical glaucoma medications. To our knowledge, this represents the first study evaluating one-year clinical outcomes of the PreserFlo MicroShunt in a Malaysian population. Our aim is to provide a comprehensive real-world evaluation of this bleb-forming minimal invasive glaucoma surgery (MIGS) device.

Materials and Methods

Study Design and Participants

This retrospective cohort study included patients aged 18 years and above with a diagnosis of open-angle glaucoma who underwent PreserFlo^® MicroShunt (Santen Pharmaceutical Co., Osaka, Japan) implantation at Hospital Canselor Tuanku Muhriz (formerly Universiti Kebangsaan Malaysia Medical Centre) between October 2022 and July 2024. Eyes were required to have a minimum post-operative follow-up of 12 months for inclusion in the outcome analysis.

Exclusion criteria included angle-closure glaucoma and secondary glaucoma such as uveitic, neovascular, or post-traumatic glaucoma which have different pathophysiology and prognosis. The required sample size was estimated using G*Power 3.1.9.7 (Heinrich Heine University, Düsseldorf, Germany) for a paired t-test comparing preoperative and 12-month postoperative IOP. Assuming an expected mean IOP reduction from 39 mmHg to 14mmHg with a standard deviation of 7.4mmHg to 4.4mmHg from Theilig et al,⁷ an alpha of 005, and a power of 0.95, the calculated sample size was 19 eyes. The sample size calculation was based on assumptions derived from previously published studies; however, given differences in baseline characteristics and real-world variability, this may not fully reflect the observed effect size in the present cohort. Therefore, the study should be interpreted as exploratory. All patients meeting the inclusion criteria during the study period were included in the analysis. As both eyes from some patients were included, inter-eye correlation may exist and was not adjusted for; results should be interpreted with caution.

Ethical approval was obtained from the Universiti Kebangsaan Malaysia Medical Research and Ethical Committee (UKMREC; reference JEP-2025-039), and all procedures were conducted in accordance with the tenets of the Declaration of Helsinki.

Surgical Techniques and Post-Operative Management

All PreserFlo MicroShunt procedures were performed by two experienced, certified glaucoma surgeons using a standardized ab-externo technique. Intraoperative MMC (0.04%) was applied for three minutes in all cases. Postoperatively, patients received intensive topical corticosteroid therapy administered two-hourly for approximately four weeks, followed by gradual tapering over three to six months and maintenance at once-daily dosing up to one year, according to clinical response.

Data Collection and Follow-Up

Electronic medical records were reviewed to identify eligible patients and extract relevant data. Demographic variables collected included age, gender, ethnicity and glaucoma subtype. Clinical parameters recorded were BCVA, IOP, vertical CDR, and the number and types of topical anti-glaucoma medications.

Data for these parameters were extracted from medical records at baseline (preoperatively) and at postoperative follow-up visits. Follow-up visits were scheduled at standard postoperative intervals (Week 1, Month 1, Month 3, Month 6, and Month 12), consistent with previous glaucoma surgical studies.^5,10 Predefined acceptable windows were used to account for variability in follow-up: ±3 days for the 1-week visit, ±1 week for the 1-month visit, ±3 weeks for the 3-month visit, and ±1 month for both the 6-month and 12-month visits.

Visual field indices, namely MD and PSD, were obtained using the Humphrey Field Analyzer (Carl Zeiss, Germany), while peripapillary RNFL thickness was measured using spectral-domain OCT Heidelberg Spectralis^TM (Heidelberg Engineering, Germany). They were obtained within 3 months preoperatively and at 12 months postoperatively. Intraoperative and postoperative complications were retrieved from surgical records and follow-up notes. Any postoperative interventions, needling revisions, reoperation, or additional glaucoma procedures were also documented.

Outcome Measures and Definitions

The primary outcome measures were IOP, BCVA, number of antiglaucoma medications, intra- and postoperative complications, and rates of postoperative interventions, revisions and reoperations at 12 months. Secondary outcomes were surgical success rates, classified as complete success (CS), qualified success (QS), or failure (F) according to the standard definitions.⁵ CS was defined as an IOP of 6–21 mmHg (inclusive) with a ≥20% reduction from baseline without anti-glaucoma medications. QS was defined using the same IOP criteria but with the use of medications. F was defined as any of the following: IOP >21 mmHg or <20% reduction from baseline; IOP ≤5 mmHg associated with vision loss on two consecutive visits; reoperation for glaucoma; or loss of light perception. Additional analyses were performed using stricter IOP targets of 6–17 mmHg and 6–14 mmHg to assess success rates among patients requiring lower postoperative IOP. Clinical hypotony with sequelae was defined as IOP ≤5 mmHg associated with clinical findings such as choroidal detachment, shallow anterior chamber, or visual acuity reduction.

Statistical Analyses

Statistical analyses were performed using IBM SPSS Statistics for Windows, Version 29.2 (IBM Corp., Armonk, NY, USA). Statistical significance was set at p<0.05. Data distribution was assessed with the Kolmogorov–Smirnov test. Continuous variables are presented as mean ± standard deviation (SD) for normally distributed data and as median with interquartile range for non-normally distributed data. Comparisons of pre- and postoperative IOP and peripapillary RNFL thickness were conducted using the Wilcoxon signed-rank tests, whereas changes in MD and PSD were analyzed using paired t-tests. To account for multiple comparisons across repeated time points, Bonferroni correction was applied for comparisons of intraocular pressure at each postoperative visit relative to baseline, with an adjusted significance threshold of p < 0.01. Boxplots were generated to illustrate longitudinal trends. Kaplan–Meier survival analysis with Log rank testing was used to estimate CS and QS survival probabilities over 12 months.

Results

A total of 40 eyes from 31 patients who underwent PreserFlo MicroShunt implantation between October 2022 to July 2024 were included in this study. In cases of bilateral surgery, both eyes were analyzed. The demographic and baseline characteristics of the study cohort are summarized in Table 1. The median age was 69.5 years (63.0–76.0) with a predominance of males (61.3%) and Malay ethnicity (58.1%). The most common diagnosis was POAG, accounting for 67.5% (n=27) of treated eyes. The median preoperative BCVA in Logarithm of the Minimum Angle of Resolution (logMAR) was 0.50 (0.18–0.80) and the median baseline IOP was 19 (16–24) mmHg. The median preoperative vertical CDR was 0.90 (0.90–0.90). More than half of the eyes (55%) had a history of previous phacoemulsification.

Table 1.

Baseline Demographic and Clinical Characteristics of Eyes Undergoing PreserFlo MicroShunt Implantation

Variable		Total (n=40 Eyes)
Age, median (IQR)		69.5 (63.0–76.0)
Gender, n (%)	Female	12 (38.7)
	Male	19 (61.3)
Race, n (%)	Malay	18 (58.1)
	Chinese	9 (29.0)
	Indian	4 (12.9)
Pre-Operative Clinical Characteristics	Left eye, n (%)	24 (60.0)
	Preoperative BCVA (logMAR), median (IQR) n=40	0.5 (0.2–0.8)
	IOP, median (IQR) n=40	19 (16.0–24.0) mmHg
	Vertical CDR, median (IQR) n=39	0.9 (0.9–0.9)
	No of medication classes, median (IQR) n=40	4.0 (3–4)
	Mean deviation of Humphrey visual field, mean ± SD n=37	−21.1 ± 6.8 dB
	Moderate (MD=−6.01 to −12 dB), n (%), mean ± SD	4 (10), -10.3±2.0 dB
	Advanced (MD=−12.01 to −20 dB), n (%), mean ± SD	10 (25), -15.6±2.1 dB
	Severe (MD>-20 dB), n (%), mean ± SD	23 (57.5), -25.4±4.4 dB
	Global peripapillary retinal nerve fiber layer thickness, median (IQR)	47 (39.2–62.8)
Previous ocular surgery	Phacoemulsification, n (%)	22 (55.0)
	Trabeculectomy, n (%)	3 (7.5)
	Endoscopic cyclophotocoagulation, n (%)	1 (2.5)
	iStent inject, n (%)	1 (2.5)
	Pars plana vitrectomy, n (%)	1 (2.5)
	No previous surgery, n (%)	16 (40.0)
Glaucoma Subtype	Primary open angle glaucoma, n (%)	27 (67.50)
	Normal tension glaucoma, n (%)	4 (10.0)
	Steroid induced glaucoma, n (%)	4 (10.0)
	Juvenile open angle glaucoma, n (%)	3 (7.5)
	Congenital aphakic glaucoma, n (%)	1 (2.5)
	Pseudoexfoliative glaucoma, n (%)	1 (2.5)

Abbreviations: IQR, interquartile range; SD, standard deviation; BCVA, best corrected visual acuity; logMAR, logarithm of minimum angle of resolution; IOP, intraocular pressure; CDR, cup to disc ratio; MD, mean deviation.

The mean IOP decreased significantly from 22.70 ± 9.21 mmHg at baseline to 8.78 ± 2.90 mmHg at week 1, 10.55 ± 4.02 mmHg at month 1, 11.68 ± 4.90 mmHg at month 3, 10.92 ± 4.66 mmHg at month 6, and 11.18 ± 3.35 mmHg at month 12 (n=38 at final follow-up). To account for multiple postoperative comparisons of intraocular pressure across follow-up visits, Bonferroni correction was applied, with adjusted statistical significance set at p<0.01. IOP reduction from baseline was statistically significant at all postoperative time points and remained consistently lowered by approximately 10mmHg over 12 months as shown in Figure 1. Table 2 demonstrates that the median IOP decreased from 19.00 (16.00–24.00) mmHg at baseline to 11.50 (8.75–14.00) mmHg at 12 months (p<0.001). Significant IOP reduction were observed in eyes with advanced (p=0.005) and severe glaucoma (p <0.001), but not in those with moderate disease. Both POAG and non-POAG groups demonstrated significant post-operative IOP reduction.

Figure 1.

Boxplots illustrating (A) the trend in intraocular pressure (IOP) over 12 months following PreserFlo MicroShunt implantation, and (B) the corresponding changes in IOP from baseline. The central line within each box represents the median, and the lower and upper whickers represent the 5^th and 95^th percentiles. The IOP changes from baseline to Month 1 were statistically significant (p<0.001). Following Bonferroni correction for multiple comparisons (adjusted significance threshold p<0.01), difference from month 6 to month 12 (p=0.019) was not statistically significant. Overall, a sustained reduction in median IOP of approximately 10mmHg from baseline [19.0 (16.0–24.0) mmHg] to Month 12 [11.5 (8.75–14.0) mmHg]. ** Bonferroni-adjusted significance threshold: p<0.01.

Table 2.

Comparison of Intraocular Pressure Reduction at 12 Months Post-Operatively Relative to Baseline for the Entire Cohort, Stratified by Disease Severity and Glaucoma Subtype

Variable		Baseline IOP Median (IQR) (mmHg)	IOP at 12 Months Post-Surgery Median (IQR) (mmHg)	IOP Reduction Median (IQR) (mmHg)	ap-value
Total study eyes		n=40 19.00 (16.00–24.00)	n=38 11.50 (8.75–14.00)	n=38 9.00 (5.00–15.00)	<0.001
Disease severity	Moderate (MD=−6.01 to −12 dB)	n=4 28.00 (18.00–33.50)	n=4 12.00 (10.00–17.00)	n=4 16.00 (8.00–19.50)	0.07
	Advanced (MD=−12.01 to −20 dB)	n=11 18.00 (16.00–19.00)	n=11 10.00 (8.00–17.00)	n=11 5.00 (3.00–11.00)	0.005
	Severe (MD>-20 dB)	n=22 19.50 (16.00–22.50)	n=21 11.00 (8.50–12.00)	n=21 9.00 (6.50–11.50)	<0.001
Glaucoma Subtype	POAG	n=31 18.00 (16.00–20.00)	n=30 10.00 (8.00–12.00)	n=30 8.00 (5.00–10.25)	<0.001
	Non-POAG	n=9 34.00 (22.50–42.00)	n=8 14.50 (10.50–16.50)	n=8 23.00 (13.50–29.50)	0.012

Notes: ^aWilcoxon signed rank test. Significance is marked in bold (p < 0.05).

Abbreviations: IOP, intraocular pressure; IQR, interquartile range; MD, mean deviation; POAG, primary open angle glaucoma.

Figure 2 summarizes longitudinal changes in BCVA, vertical CDR, and the number of topical anti-glaucoma medications. The mean number of antiglaucoma medications decreased significantly as early as one week postoperatively and remained below 0.5 drops at 12 months postoperatively. Neither BCVA nor vertical CDR showed statistically significant changes throughout follow-up. Changes in visual field indices and peripapillary RFNL thickness measured by OCT are presented in Table 3. Both MD and PSD remained stable, from −21.90 ± 6.55 dB and 9.49±2.45 dB at baseline to −19.00 ± 10.76 dB and 9.95 ± 2.62 dB at 12 months, respectively. RNFL thickness also showed no significant change in any sector, suggesting stability of both structural or functional parameters following PreserFlo MicroShunt implantation.

Figure 2.

Line graphs illustrating changes in mean best corrected visual acuity, vertical cup-to-disc ratio and the number of topical anti-glaucoma medications from baseline to 12 months postoperatively. ** Bonferroni-adjusted significance threshold: p<0.01.

Table 3.

Changes in Visual Field Indices (Mean Deviation and Pattern Standard Deviation) and Peripapillary Retinal Nerve Fiber Layer Thickness Following PreserFlo MicroShunt Implantation

Variable	Pre-Surgery	1 Year Post-Surgery	p-value
Humphrey Visual Field indices (dB), mean ± SD (n=34)
Mean Deviation	−21.90 ± 6.55	−19.00 ± 10.76	0.21a
Pattern Standard Deviation	9.49 ± 2.45	9.95 ± 2.62	0.35a
Peripapillary retinal nerve fiber layer thickness (μm), median (IQR) (n=32)
Superotemporal	57.50 (49.00–70.50)	57.50 (49.75–69.00)	0.65b
Superonasal	49.50 (40.00–66.75)	53.50 (42.00–70.25)	0.86b
Nasal	39.00 (23.75–53.75)	39.00 (29.50–55.00)	0.14b
Inferonasal	49.00 (33.25–49.00)	48.00 (39.00–64.00)	0.06b
Inferotemporal	42.00 (36.25–67.00)	44.00 (37.50–61.50)	0.10b
Temporal	49.00 (37.00–58.75)	45.00 (37.50–58.75)	0.23b
Global	47.00 (39.25–62.75)	49.50 (40.00–58.00)	0.77b

Notes: ^aPaired T test; ^bWilcoxon signed rank test. Significant p-value <0.05.

Abbreviations: SD, standard deviation; IQR, interquartile range.

Intra-operative and post-operative events are summarized in Table 4. Intra-operative complications occurred in 8 eyes (20%), including conjunctival buttonhole (3 eyes, 7.5%) and repeated insertion attempts (5 eyes, 12.5%). Early post-operative (<3 months) complications included transient hypotony (IOP ≤5mmHg) in 7 eyes (17.5%) and one eye (2.5%) developed late hypotony (≥3 months). The most frequent post-operative interventions were subconjunctival 5-fluorouracil injections (14 eyes), followed by needling (7 eyes), repeat needling (6 eyes), bleb resuturing (2 eyes), anterior chamber reformation (2 eyes), MicroShunt repositioning (1 eye) and yag and argon laser peripheral iridoplasty (1 eye). Secondary procedures included bleb revision for fibrosis (2 eyes, 5%) and phacoemulsification (3 eyes, 7.5%). Notably, no eye required secondary filtering surgery during the one-year follow-up period.

Table 4.

(A) Intra-Operative Complications; (B) Post-Operative Complications; (C) Post-Operative Interventions; (D) Reoperations and Secondary Procedures During 12-Month Follow-Up Following PreserFlo MicroShunt Implantation

(A) Intra-Operative Complications	No. of Eyes (%)
Conjunctival buttonhole	3 (7.5)
Repeated passes to insert microshunt	5 (12.5)
(B) Post-operative complications	Early (<3 months) n (%)	Late (≥3 months) n (%)
Bleb leak	1 (2.5)	1 (2.5)
Hyphema	2 (5)	0
Hypotony (IOP≤ 5mmHg)	7(17.5)	1 (2.5)
Clinical hypotony with sequelae	5 (12.5)	1 (2.5)
Choroidal detachment	4 (10)	1 (2.5)
Iridocorneal touch	2 (5)	0
Cornea intrastromal bleed	1 (2.5)	0
Microshunt lumen blocked by iris tissue	1 (2.5)	0
Suture abscess	1 (2.5)	0
Bleb fibrosis	3 (7.5)	5 (12.5)
(C) Interventions	No. of eyes (%)
Bleb resuturing	2 (5)
MicroShunt repositioning	1 (2.5)
Needling	7 (17.5)
Repeated needling (>1 needling)	6 (15)
Subconjunctival 5-Fluorouracil (5FU) injection	14 (35)
Yag and argon laser peripheral iridoplasty	1 (2.5)
Anterior chamber reformation	2 (5)
(D) Reoperations/other surgeries	No. of eyes (%)
Bleb revision for bleb fibrosis	2 (2.5)
Trabeculectomy	0
Glaucoma drainage device	0
Phacoemulsification	3 (7.5)

Figure 3 illustrates the Kaplan–Meier survival analysis of surgical success for PreserFlo MicroShunt. For the IOP target of 6–21 mmHg (Figure 3A), the cumulative overall survival probability remained 100% initially, decreasing slightly to 92.5% at 12 months which indicate a low rate of treatment failure. The cumulative CS rate stayed above 85% for the first six months and was 72.5% at one year. This is lower than observed 82.5% CS rate at the final visit because the Kaplan-Meier method records the first loss of CS as an event, even if CS was later regained. With stricter IOP targets of 6–17mmHg (Figure 3B) and 6–14 mmHg (Figure 3C), overall and complete survival probabilities declined earlier and more steeply, consistent with the increased challenge of maintaining lower IOP levels without adjuvant therapy. These trends reflect the target-dependent nature of surgical success with the PreserFlo MicroShunt. With progressively stricter IOP targets (6–17 mmHg and 6–14 mmHg), lower cumulative survival probabilities were descriptively observed over time. These analyses were intended to illustrate how different predefined success criteria may influence the apparent surgical success rate rather than to provide formal statistical comparisons between survival curves. The one-year primary outcomes and causes of treatment failure are summarized in Table 5. CS was achieved in 33 eyes (82.5%), QS in 5 eyes (12.5%) and failure in 2 eyes (5.0%). Both failures had IOP > 21mmHg despite topical anti-glaucoma and underwent bleb revision. Table 6 presents the risk ratios (RR) and odds ratios (OR) for surgical failure across clinical subgroups. The risk of failure was lower in POAG and in patients aged ≥ 60 years (RR < 1), and higher among females (RR=1.22), though all estimates were imprecise due to the small sample size. Both failures occurred in eyes using ≥3 topical medications preoperatively, limiting statistical inference due to the small comparison group. These subgroup analyses should be interpreted with caution due to the limited sample size and low number of failure events.

Figure 3.

Kaplan-Meier survival curves showing the cumulative probability of surgical success following PreserFlo MicroShunt implantation at different intraocular pressure (IOP) target ranges over 12 months: (A) 6–12 mmHg, (B) 6–17 mmHg and (C) 6–14 mmHg. Red lines represent overall success (complete + qualified success), defined as achieving the respective IOP target range with or without anti-glaucoma medications. Blue lines represent complete success, defined as achieving the target IOP without medications. Failure was defined as IOP outside the target range on two consecutive visits, reoperation for glaucoma or loss of light perception vision.

Table 5.

(A) Primary Outcome for Target IOP of 6–21mmHg at 1 Year Post-PreserFlo MicroShunt Implatation; (B) Reasons for Treatment Failure

(A) Primary Outcome	No. of Eyes (%)
Complete success	33 (82.5)
Qualified success	5 (12.5)
Failure	2 (5.0)
(B) Reasons of failure	Total no (%)
IOP >21mmHg	2 (5.0)
<20% IOP reduction	0
IOP ≤5mmHg with vision loss on two consecutive visits	0
Reoperation for glaucoma	2 (5.0)
Loss of light perception vision	0

Abbreviation: IOP; intraocular pressure.

Table 6.

Risk Ratios and Odds Ratios of Surgical Failure by Glaucoma Stage, Glaucoma Subtype, Age, Gender and Number of Pre-Operative Topical Medications

Variable		Total	Failure Cases, n (%)	Success Cases, n (%)	Risk Ratio of Failure (95% CI)	Odd Ratio of Failure (95% CI)
Glaucoma Stage	Moderate	4 (10.81)	0	4 (100)
	Advanced to Severe	33 (89.19)	1 (3.03)	32 (96.97)
Glaucoma Subtype	POAG	27 (67.50)	1 (3.70)	26 (96.30)	0.48 (0.03–7.11)	2.17 (0.13–37.64)
	Non-POAG	13 (32.50)	1 (7.69)	12 (92.31)
Age	≥60 years old	31 (77.5)	1 (3.23)	30 (1)	0.29 (0.02–4.20)	3.75 (0.21–66.77)
	<60 years old	9 (22.5)	1 (11.11)	8 (88.89)
Gender	Female	18 (45)	1 (5.56)	17 (94.44)	1.22 (0.08–18.20)	0.81 (0.05–13.92)
	Male	22 (55)	1 (4.55)	21 (95.45)
Number of Pre-operative Topical Medications	≥3	36 (90)	2 (5.56)	34 (94.44)
	<3	4 (10)	0 (0)	4 (100)

Abbreviations: POAG, primary open angle glaucoma; CI, confidence interval.

Discussion

Unlike trabecular or suprachoroidal MIGS, which primarily enhance physiological outflow, the PreserFlo MicroShunt functions as an ab-externo subconjunctival device that forms a bleb and achieves lower postoperative IOP. It is now classified as minimally invasive bleb surgery (MIBS).

In our cohort of 40 eyes treated with the PreserFlo MicroShunt, we observed a sustained and clinically meaningful IOP reduction, approximately 10 mmHg from baseline 22.7 ± 9.2 mmHg to 11.2 ± 3.4 mmHg at 12 months. This was accompanied by a substantial drop in topical medication burden (mean < 0.5 drops). These results echo recent real-world data showing IOP reductions in the 30–55% range after MicroShunt implantation.^10–13 We observed a lower postoperative IOP in this cohort compared to studies such as Panarelli et al This may reflect differences in baseline IOP, disease severity, MMC protocol, and postoperative management. Importantly, structural and functional parameters including the BCVA, CDR, RNFL thickness and visual field indices remained stable, indicating effective pressure control without collateral damage to the optic nerve or RNFL. Nevertheless, given the advanced disease stage, RNFL measurements may be subject to a floor effect.

The Kaplan–Meier analysis applying three target IOP thresholds (6–21, 6–17 and 6–14 mmHg) revealed that survival probabilities declined progressively with stricter targets: overall success at ~95% for the broadest range, but lower for tighter criteria. This pattern underscores that surgical success depends not only on device performance, but also on the target pressure chosen and postoperative bleb management. Similar trends have been described in larger cohorts of MicroShunt patients.^14,15 In particular, the divergence between overall (complete + qualified) and CS curves in our dataset highlights the clinical reality that adjunctive medications often bridge the gap when bleb alone is insufficient.

When compared with established filtering surgery such as trabeculectomy, the role of the PreserFlo MicroShunt in eyes requiring lower target IOP, particularly in more advanced glaucoma, remains an area of active debate. The InnFocus MicroShunt Versus Trabeculectomy Study (IMS) is the only randomized, multicentre trial directly comparing these two procedures in patients with uncontrolled primary open-angle glaucoma and no prior incisional glaucoma surgery.¹⁶ In this study, 527 patients were randomized to undergo either trabeculectomy or PreserFlo MicroShunt implantation, with surgical success defined as an IOP reduction of ≥20% from baseline and an IOP ≤21 mmHg, with or without topical medication. At one year, success rates were high and comparable between groups, achieved in 80.3% of eyes in the trabeculectomy arm and 77.0% of the PreserFlo arm. While trabeculectomy demonstrated slightly greater absolute IOP reduction, this was accompanied by a higher frequency of postoperative interventions, whereas the PreserFlo MicroShunt showed a more predictable postoperative course with fewer reinterventions and no meaningful difference in overall safety outcomes. These findings highlight a clinically relevant balance between efficacy and surgical burden, supporting the PreserFlo MicroShunt as a viable alternative to trabeculectomy in selected patients, particularly when safety, reproducibility, and postoperative management are key considerations. Our real-world Asian cohort which applied MMC 0.4 mg/mL and a standardised postoperative regimen showed even higher complete success rate (82.5%) at the 6–21 mmHg target, which may reflect selection, surgical technique or early learning-curve optimization.

Short-term safety outcomes in our series were also favourable: early-postoperative hypotony occurred in 17.5% of eyes (versus ~24.3% in historical trabeculectomy series), and only 2.5% had bleb leak.¹⁷ In our study, no eye required a secondary filtering surgical procedure within the first year. Additionally, our method circumvented tube-related issues that are frequently observed in glaucoma drainage devices, such as corneal decompensation and tube erosion.¹⁸ These findings support the notion that the MicroShunt offers a better safety profile compared to traditional filtration surgery.^19,20 Moreover, the consistent medication reduction and fewer post-operative interventions align with data suggesting fewer reinterventions and bleb-related complications with this device.²¹ Schlenker et al stated that despite higher initial device costs, the reduction in postoperative care and complications makes the PreserFlo MicroShunt a cost-effective surgical option in the medium to long term.²² While outcomes appear broadly consistent with previously reported results of trabeculectomy and other glaucoma surgeries, direct comparisons cannot be made due to differences in study design, patient populations, and the absence of a control group.

Unlike trabecular or suprachoroidal MIGS, which primarily enhance physiological outflow, the PreserFlo MicroShunt functions as an ab-externo subconjunctival device that forms a bleb and achieves lower postoperative IOP. This positions it within the emerging category of MIBS, marrying the less invasive nature of MIGS with the deeper IOP-lowering potential of traditional trabeculectomy-level surgery.^20,23 Comparative studies indicate that, compared to the XEN Gel Stent, the MicroShunt may achieve a more posterior bleb with fewer cystic changes or needlings—likely reflecting its larger lumen and ab-externo implantation route.²⁴ This difference in bleb morphodynamics may underpin our favourable outcomes, especially in a cohort where many eyes underwent prior phacoemulsification and had advanced glaucoma. More than half of the eyes in this cohort had undergone prior phacoemulsification, which may potentially influence conjunctival integrity, wound healing response, bleb morphology, and subsequent filtration surgery outcomes. Previous intraocular surgery has been associated with altered subconjunctival fibrosis and variable bleb function in glaucoma filtration procedures. However, the present study was not adequately powered to evaluate the independent effect of prior phacoemulsification on surgical success or postoperative outcomes. Future larger studies are warranted to further investigate this potential confounding factor. From a practical standpoint, the MicroShunt emerges as a compelling option between non-bleb MIGS (which often cannot achieve very low target IOPs) and standard trabeculectomy (which carries higher risk and demands intense follow-up).

In exploring potential risk factors for surgical failure, although statistical significance was not achieved (likely due to sample size and low failure event count), our data showed a trend towards higher failure risk in patients under 60 years, females, non-POAG types and those on ≥3 preoperative medications. This aligns with literature identifying younger age, more prior medications and robust wound-healing responses as negative prognostic factors after filtering surgery.^25–27 Clinically, this emphasizes the importance of patient selection, intraoperative MMC dosage, and close postoperative bleb surveillance in achieving optimum outcomes.

The use of a relatively higher MMC concentration (0.04% for 3 minutes) in all cases likely contributed to the favourable surgical success observed in our cohort. This approach was intentionally standardized because many eyes demonstrated features associated with higher risk of filtration failure, including advanced glaucoma, multiple preoperative medications, and previous ocular surgery. However, the present study did not evaluate individualized MMC titration according to specific patient risk profiles, and future studies may further clarify the optimal balance between antifibrotic efficacy and hypotony-related complications.

A critical component of filtration surgery success relates to the modulation of wound healing and conjunctival inflammation. In glaucoma filtration procedures, excessive conjunctival and Tenon’s fibrosis is a key driver of bleb failure. Topical corticosteroids are a mainstay in postoperative management precisely because they suppress inflammatory mediators and reduce fibroblast proliferation, contributing to more favourable bleb morphology and reduced need for bleb-related interventions.^28,29 Although most studies focus on the early postoperative period, confocal microscopy studies demonstrate that topical steroid use leads to lower conjunctival stromal reflectivity and reduced inflammatory cell density, which correlates with less intensive postoperative management and potentially improved surgical success.²⁹ In the context of our cohort, the prolonged and structured corticosteroid protocol with intensive dosing in the first month followed by a taper over 3–6 months and daily maintenance through one year may have contributed to sustained bleb function and a lower rate of failure. This approach likely attenuated the chronic inflammatory component of wound healing and minimized subconjunctival fibrosis, which are known impediments to filtration success.³⁰ While definitive prospective trials delineating optimal steroid dose and duration are lacking, this practice aligns with broader surgical principles of inflammation control after filtering procedures and may represent an important practical strategy to enhance long-term bleb performance.

Limitations of our study include its retrospective design, single-centre setting, modest sample size and absence of a trabeculectomy or XEN comparator arm. Its relatively short follow-up duration of 12 months precludes assessment of long-term bleb survival, late-onset complications, and device durability. As PreserFlo MicroShunt implantation was introduced at our centre in 2023, this analysis represents early outcomes from an ongoing cohort. Continued follow-up is underway, and future analyses at 3 and 5 years will be important to better define long-term efficacy and safety. Inclusion of both eyes from some patients introduces potential inter-eye correlation, which was not adjusted for in the statistical analysis and may affect the validity of p-values. On the other hand, the absence of multivariable analysis limits the ability to account for confounding factors, particularly given the heterogeneous glaucoma subtypes included. In addition, as a single-centre retrospective study, the findings may not be generalizable to other populations or practice settings.

Despite these limitations, this study has several important strengths. To our knowledge, this represents the first real-world Malaysian study evaluating one-year outcomes following PreserFlo MicroShunt implantation. All procedures were performed using a standardized surgical technique, consistent MMC protocol, and structured postoperative corticosteroid regimen, thereby reducing procedural variability. In addition, the study provides comprehensive evaluation of both structural and functional glaucoma outcomes, including visual field indices and retinal nerve fibre layer measurements, alongside Kaplan–Meier survival analyses using multiple predefined intraocular pressure targets. The inclusion of a predominantly advanced glaucoma cohort also reflects a clinically relevant population requiring lower target intraocular pressures in routine tertiary-centre practice.

Future large-scale, prospective, multicentre trials with extended follow-up (≥3–5 years), stratified by glaucoma subtype and diving into bleb morphology (via anterior-segment OCT), will help refine long-term effectiveness, cost-effectiveness and optimal patient selection.

Conclusion

This study represents the first Malaysian real-world analysis of PreserFlo MicroShunt outcomes, demonstrating robust IOP reduction, marked medication-burden reduction, and a favourable short-term safety profile at one year. Success rates were highest when target IOP thresholds were moderate while stricter targets revealed earlier and more frequent failures which highlight the importance of realistic goal setting in surgical glaucoma. Positioned as a true MIBS device, the MicroShunt bridges the gap between less potent MIGS and high-risk trabeculectomy, offering a reproducible surgical option with strong clinical utility. Longer-term data and head-to-head comparisons will further delineate its place in the glaucoma surgery algorithm. Future prospective multicentre studies with larger cohorts and longer follow-up are needed to better define long-term bleb survival, optimal antifibrotic strategies, patient selection criteria, and comparative effectiveness against trabeculectomy and other bleb-forming glaucoma procedures. Further evaluation in Asian populations may also help clarify ethnic and wound-healing factors influencing surgical outcomes.

Funding Statement

This research received no external funding.

Informed Consent Statement

The requirement for informed consent was waived by the Universiti Kebangsaan Malaysia Medical Research and Ethics Committee (UKMREC; reference JEP-2025-039) due to the retrospective nature of the study and the use of anonymized data.

Author Contributions

All authors made a significant contribution to the work reported, whether that is in the conception, study design, execution, acquisition of data, analysis and interpretation, or in all these areas; took part in drafting, revising or critically reviewing the article; gave final approval of the version to be published; have agreed on the journal to which the article has been submitted; and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.