The PAUL Glaucoma Implant in the management of uveitic glaucoma—3-year follow-up

Abstract

Background/objectives

Evaluate the mid-term outcomes of the PAUL Glaucoma Implant (PGI) in the management of uveitic glaucoma.

Subjects/methods

This was a single-centre, multi-surgeon, retrospective analysis of 50 consecutive cases of PGI for uveitic glaucoma performed between April 2019 and August 2021. Primary outcomes include: complete and qualified success (IOP ≥5 mmHg to ≤21 mmHg with ≥20% IOP reduction) or failure (IOP exceeding the success criteria, additional glaucoma procedures, no perception of light vision). Secondary outcomes included: visual acuity, IOP, medications, complications and intraluminal stent removal.

Results

We included 50 eyes of 41 patients. Mean age was 45.8 ± 19.8 years (range 6–81 years) in this heterogenous and complex cohort. Mean pre-op IOP was 30.6 ± 9.8 mmHg on 3.9 ± 0.9 medications. In total, 62% of patients were on acetazolamide, and 64% required systemic immunosuppression. At final follow-up (mean: 35.8 ± 9.8 months, range 5–58 months), IOP and medications were significantly reduced (12.2 ± 4.4 mmHg, requiring 1.1 ± 1.3 medications, p < 0.0001). Resulting in 48% complete and 92% qualified success rates. Failure occurred in 8% of cases, 6% due to hypertension but only one case of prolonged hypotony (2%).

Conclusions

To date, this study represents the first publication looking specifically at the efficacy and safety of the PGI in the management of complex uveitic glaucoma. With an average follow-up of 3 years, it shows high levels of complete and qualified success with few complications.

Introduction

Glaucoma is a common complication of uveitis, affecting ~10–20% of all cases [1, 2]. Amongst the population at our tertiary referral centre the prevalence is 19.5% [3, 4]. Furthermore, those diagnosed with chronic uveitis have a significantly greater prevalence, estimated at 46% of cases [2].

The aetiology of the raised intraocular pressure (IOP) in uveitis can be due to either closed or open angle mechanisms. In the former, synaechial closure of the angle and lens occurs due to progressive inflammation leading to increases in IOP. Conversely, the open angle mechanism is suspected to be due increased resistance acting within the trabecular meshwork (TM) outflow either due to protein deposition or destruction due to recurrent or chronic inflammation in the absence of the above [5]. This can then be exacerbated by corticosteroid use which causes further trabecular resistance, likely due to the upregulation or deposition of various proteins and materials within the TM [6].

Given that the primary pathology in either mechanism affects the TM outflow pathway, it has been shown that bypassing this drainage route can be highly effective in lowering the IOP of uveitic patients. Traditionally, this been achieved by either trabeculectomy or tube shunt surgery [7–11]. Whilst both methods, as well as newer minimally invasive bleb surgeries (MIBS – Preserflo Microshunt or XEN Gel stent), have been shown to be successful in managing these conditions, tube surgery is often a preferred option given its overall reliability and utility in primary or refractory cases [12, 13]. In our unit, we have previously demonstrated this success using the Baerveldt-250 tube [11].

Whilst the valveless Baerveldt tube has proven more effective than other valved tubes at lowering IOP and controlling glaucoma, large studies demonstrate a higher rate of post-operative hypotony, resulting in complications such as choroidal effusion, suprachoroidal haemorrhage, shallow anterior chamber and hypotonous maculopathy [14, 15]. As a result, Baerveldt tubes require aqueous outflow restriction at the time of surgery to prevent early hypotony which commonly prevents early aqueous drainage and IOP control.

The PAUL® Glaucoma Implant (PGI; Advanced Ophthalmic Innovations, Singapore, Republic of Singapore) is a novel glaucoma drainage device with similar specifications to the Baerveldt-350 mm² tube plate (342 mm²) but a much smaller internal tube lumen (127 µm vs 300 µm) which, when unstented, offers no limitation to aqueous flow but when internally stented with a 6/0 prolene, offers instant drainage of aqueous from day 1 post-operatively with very little risk of post-operative hypotony. It has shown very promising published early results in the management of adult and paediatric glaucomas [16–19]. This paper looks at the medium-term results of the PGI in the management of uveitic glaucoma.

Methods

This retrospective, consecutive case series analysed the results of the PGI in uveitic glaucoma undertaken in a single centre by multiple surgeons. We evaluated the medium-term (35.8 ± 9.8 months, range 5–58 months) post-operative outcomes with all cases undertaken between April 2019 and August 2021. Cases were conducted under the supervision of six consultants at the Manchester Royal Eye Hospital. All patients required a diagnosis of uveitis to be included. There were no exclusion criteria based upon age with the cohort including 6 patients aged 17 or below.

In our unit, it is standard practice for cases of uveitic glaucoma to be managed collaboratively between the uveitis and glaucoma teams. Patients typically receive a pre-operative enhanced steroid regime tailored to their condition the week prior to surgery. This can range from more frequent drop therapy to recommendations for oral prednisolone.

The surgical technique is as described in a prior publication from our unit [19].

Primary outcome measures

Primary outcome measures comply with the World Glaucoma Association (WGA) recommendations for complete (unmedicated) or qualified (medicated) success and failure [20]. Failure criteria were as follows:

1. IOP outside of the target range (6–21 mmHg) or <20% reduction from baseline on two consecutive visits after 3 months—first visit used as the time of failure.

2. Increase in ocular anti-hypertensive medications compared to pre-operatively.

3. Further glaucoma procedures (e.g. additional tube shunt/cyclodiode laser).

4. Removal of the implant.

5. Severe visual loss related to the glaucoma surgery (endophthalmitis, suprachoroidal haemorrhage with visual loss, enucleation, evisceration, phthisis bulbi) or progression to no perception of light vision for any reason.

Time to failure and rates of complete or qualified success were analysed at six monthly intervals from the date of operation to the final follow-up.

Secondary outcome measures

Secondary outcome measures were analysed at each visit, including: visual acuity (logMAR), IOP, number of medications, complications and further procedures performed.

Complications were classified as early, before 3 months, or late, occurring after 3 months follow-up. A serious complication was defined as any complication that required major surgery (reoperation in the operating room) to manage the complication. Any clinic-based procedures undertaken at the slit lamp were not considered a reoperation but were evaluated. Particular attention was paid to the rates of Prolene® intraluminal stent removal, collating time to removal with the effect on IOPs and number of medications.

Visual acuity was assessed using LogMAR testing and numerical equivalents of low vision categories were used (counting fingers: 2.1 logMAR, hand movement: 2.4 logMAR, perception of light: 2.7 logMAR and no perception of light: 3.0 logMAR) as per Moussa et al. [21].

Statistical testing

GraphPad Prism 10 was used for all statistical analyses. All data were demonstrated to be non-parametric. As such, two-tailed non-parametric testing was undertaken using the Wilcoxon matched-pairs signed rank test. Kaplan–Meier survival analyses were performed to analyse the time to failure following surgery. A p value of <0.05 was considered significant. Variables were reported as mean ± standard deviation (SD) unless stated otherwise.

Results

Baseline demographics

Between April 2019 and August 2021, 50 eyes of 41 patients with a pre-existing diagnosis of uveitis had a PGI inserted at the Manchester Royal Eye Hospital, UK. Mean follow-up was 35.8 ± 9.8 months (range 5–58 months). Baseline patient demographics are summarised in Table 1 and show near equal proportions of males (52%) and females (48%), right (56%) and left (44%) eyes and with an average age of 44.8 ± 19.8 years. The large SD is accounted for by the choice to include 43 adult (>18 years old) and 7 paediatric (≤18 years old) cases giving an age range of 6–81 years. Sadly, one patient died 6 months after surgery, however, at final follow-up (5 months) their tube remained functioning well (VA 0.2 logMAR and IOP 9 mmHg on 0 medications). Otherwise, the next shortest follow-up was at 20 months in a patient whose tube failed and data were censored.

Table 1.

Patient demographics at PGI insertion.

Demographic/characteristic	Data
Mean age (years) ± SD	45.8 ± 19.8
Range	6–81 years
Gender n (%)
Male	26 (52%)
Female	24 (48%)
Ethnicity n (%)
White	30 (60%)
Asian	9 (18%)
Afro Caribbean	8 (16%)
Other/mixed	3 (6%)
Lens status
Phakic	31 (62%)
Pseudophakic	18 (36%)
Aphakic	1 (2%)
Uveitis diagnosis
Idiopathic	20 (40%)
Anterior	12 (24%)
Panuveitis	5 (10%)
Intermediate	3 (6%)
Posterior occlusive	1 (2%)
Infectious uveitis	7 (14%)
HSV keratouvieits	3 (6%)
VZV (with ARN)	2 (4%)
CMV	1 (2%)
Syphilis	1 (2%)
Sarcoid	4 (8%)
HLA B27 related	4 (8%)
Fuch’s heterochromic cyclitis	3 (6%)
Juvenile idiopathic arthritis (JIA)	3 (6%)
TINU	2 (4%)
Tuberculosis	1 (2%)
Sympathetic ophthalmia	1 (2%)
Anterior scleritis	1 (2%)
Secondary outcome baseline demographics
Visual acuity (logMAR)	0.50 ± 0.61
Intraocular pressure (mmHg)	30.56 ± 9.80
Number of medications	3.88 ± 0.90
Diamox required (%)	62%
Systemic immunosuppression (%)	64%
Previous Glaucoma Surgery n (%)	16 (32%)
Trabeculectomy	6 (12%)
Preserflo Microshunt (PMS)	3 (6%)
Tube surgery	1 (2%)
Deep sclerectomy	1 (2%)
Cyclodiode laser (incl. micropulse)	2 (4%)
Ab-interno canaloplasty	1 (2%)
Trabecular micro-bypass iStent	1 (2%)

Pre-operative VA, IOP and number of medications are also described in Table 1 and in the “Secondary outcomes” section. Prior surgical interventions are also collated with the most common surgery performed prior to tube surgery being trabeculectomy (12%), followed by Preserflo Microshunt (6%), cyclophotoablative procedures (4%) and then single cases of the following: deep sclerectomy, Ahmed tube, ab-interno canaloplasty and iStent (2% each).

Whilst cases typically received an enhanced pre-operative steroid regime on the week of surgery, prior to this, 88% of cases required topical steroids to control inflammation. In total, 64% of eyes were on systemic immunosuppression, with some eyes requiring multiple agents: 24 eyes (48%) required disease-modifying antirheumatic drugs (9 methotrexate, 6 azathioprine, 4 tacrolimus, 4 mycophenolate mofetil, 1 ciclosporin and 1 hydroxychloroquine), 20 eyes (40%) required oral prednisolone and 10 eyes (20%) required biological agents (8 adalimumab, 2 golimumab, 1 infliximab).

Of the 50 eyes, 40 (80%) were stable on treatment, with 34 (68%) quiescent and 6 (12%) with stable chronic background inflammation. A further 10 eyes (20%) exhibited evidence of active inflammation <12 weeks prior to surgery.

Our standard intraoperative surgical technique included the use of Mitomycin C (MMC), typically 0.5 mg/ml, however, due to a short-term supply issue between December 2019 and January 2020 only 82% of cases received MMC [19]. This meant MMC was not applied in five cases (10%) and 5-fluorouracil (5-FU) was utilised instead in four (8%).

Primary outcome

By final follow-up (mean: 35.8 ± 9.8 months) complete success occurred in 48% of cases; with the addition of medications this increased to 92% (see Fig. 1). This means there was only an 8% failure rate. The four cases of failure occurred at 20, 35, 43 and 50 months with an average time to failure of 37.0 ± 12.9 months. Two of these failures occurred in each eye of the same patient, diagnosed with idiopathic hypertensive uveitis. The reasons for failure included:

• Two with an IOP above 21 mmHg on two consecutive visits.

• One with an IOP below 21 mmHg but a <20% IOP reduction on two consecutive visits.

• One with an IOP below 6 mmHg on two consecutive visits.

Fig. 1. A Kaplan–Meier survival curve for eyes implanted with PAUL Glaucoma Implant over the duration of follow-up.

Success: IOP 6–21 mmHg and >20% IOP reduction from baseline on two consecutive visits after 3 months without an increase in medications and no severe complications or visual loss (complete success: without medications, qualified success: with medications).

Regarding the ongoing management of the three hypertensive failures: one maintained an IOP of 18 mmHg on four medications at final follow-up and is being closely monitored; the second was listed for tube revision surgery; and the final one was also noted to have corneal endothelial decompensation with raised pressures so was listed for a second PGI with simultaneous Descemet’s Stripping Automated Endothelial Keratoplasty (DSAEK).

For the one case (2%) of hypotony, occurring at 46 months, the patient had a flare of uveitis which resulted in a single episode of hypotony with an IOP of 2 mmHg, symptomatic hypotony and macular folds following stopping their regular immunosuppressants. Upon restarting these, temporary symptomatic resolution and increase in the IOP occurred, however, by 50 months IOP fell back to 5 mmHg at two subsequent visits, fulfilling the failure criteria.

Complications and additional surgical interventions are detailed in the “Secondary outcomes” section.

Further sub-analyses were performed to evaluate success rates at different final IOP targets (IOP ≤18, ≤15 or ≤12 mmHg) as per WGA guidance [20]—these are graphically represented in Fig. 2 on the scatter plot. Using these targets, complete success rates were 46%, 40% and 32% respectively; increasing to 90%, 80% and 58% for qualified success when medications were introduced. It is, however, important to state that most cases (58%) did not have their prolene intraluminal stent removed as the IOP target was achieved without this. Further details regarding prolene removal can be found in the “Secondary outcomes” section.

Fig. 2. Scatter plot comparing pre-operative and final visit Intraocular pressure.

Horizontal lines denote IOP thresholds (21, 18, 12 and 6 mmHg). The higher diagonal line represents “no effect” and the lower one, a 20% IOP reduction.

Secondary outcomes—VA, IOP and medications

Post-operative outcomes were analysed at regular time intervals (1 week, 1 month, 3 months and then every 6 months until final follow-up). The mean pre-operative BCVA was 0.50 ± 0.61 logMAR. Despite a short-term reduction in visual acuity of two lines (0.71 ± 0.71 logMAR) at 1 week post-operatively, this had almost fully recovered by 1 month (0.53 ± 0.62 logMAR) and by final follow-up there was no significant change with a VA of 0.49 ± 0.71 logMAR (p > 0.05). There was no significant difference at final follow-up (p = 0.14).

Mean pre-operative IOP was 30.6 ± 9.8 mmHg using 3.9 ± 0.9 medications, including 62% requiring oral acetazolamide. IOP initially falls significantly in the 1st week post-operatively (11.0 ± 5.1 mmHg without medications) before climbing to ~15.0 ± 5.0 mmHg at 3 months as the capsule forms around the plate (Fig. 3a). As medications were gradually re-introduced, IOP fell back within the range of 11.3 ± 3.4 mmHg to 13.7 ± 4.8 mmHg over the remainder of the attendances until final follow-up. Comparing to pre-operative IOP, at final follow-up this had significantly reduced to 12.2 ± 4.4 mmHg, using 1.1 ± 1.3 medications (p < 0.0001 for each) with no patients requiring acetazolamide (Fig. 3b, c). Mean percentage IOP reduction was 60.1%.

Fig. 3. A series of graphs comparing the pre- and post-operative means (±95% confidence interval) for IOP and number of medications.

A Compares IOP at all data collection timepoints until 48 months post-operatively. The second two graphs compare B IOP and C number of medications between pre-operative levels (n = 50), at 36 months (n = 27) and at final follow-up (n = 50). Two-way Wilcoxon testing demonstrates a significant reduction, in IOP and medications, at both 36 months and final follow-up (p < 0.0001).

Secondary outcomes—complications and further surgeries

Complications were divided into early (<3 months) and late (>3 months) onset—detailed in Table 2A.

Table 2.

Tables detailing the (A) early and late complications following PGI insertion and (B) any further interventions.

A—Post-operative complications
Early (within 3 months of surgery)		Late (over 3 months after surgery)
Hypotony	4	Cataract	6
Self-limiting (<8 weeks)	3
Leaking incision	1
Cataract	3	Cystoid macular oedema (CMO)	3
Long tube in anterior chamber	3	Symptomatic diplopia	2
Fibrinous uveitis	2	Microbial keratitis	2
With tube blockage	1
Without blockage	1
Cystoid macular oedema (CMO)	2	VR Macular pathology (ERM and VMT)	2
Hyphaema (self-resolving)	1	Hyphaema and vitreous haemorrhage	1
Self-resolving corneal decompensation	4	Hypotony	1
Retracted tube requiring surgical extension	1	Corneal decompensation requiring surgery	1

B—Additional surgical procedures following PGI surgery
Cataract extraction	10 (20%)
Tube trimming	3 (6%)
At the time of cataract surgery	2 (4%)
Standalone	1 (2%)
Extension of tube into anterior chamber	1 (2%)
XEN® Gel stent to tube plate extension	1 (2%)
Second PAUL Glaucoma Implant and DSAEK	1 (2%)

Overall, there were five cases (10%) of hypotony with four (8%) occurring in the early post-operative category and only one (2%) occurring after 3 months. Early hypotony was due to one (2%) leaking paracentesis which was successfully re-sutured and three cases (6%) of numerical hypotony, all of which self-resolved by 8 weeks without further intervention. The only late hypotony initially occurred at 46 months and reached the failure criteria by 50 months—further detailed description can be found in the “Primary outcome” section.

Fibrinous uveitis occurred in two eyes (4%). One was associated with a neovascular complex, the other had prior episodes of fibrinous uveitis with nanophthalmos diagnosed pre-operatively. The case with the neovascularisation required intracameral Avastin within 2 weeks of the initial operation causing regression of the vessels and complete success at final follow-up (48 months). Hyphaema occurred in only one early and one late case. In the latter, this was associated with vitreous haemorrhage, however, was due to rubeosis secondary to Sickle cell and diabetes rather than the tube or uveitis. Cystoid macular oedema (CMO) occurred in two early and three late cases, however, given the case cohort it is hard to attribute causality.

Cataract progressed and required surgery in 10 cases (20%). Pre-existing symptomatic cataract of variable severity was present in four cases (8%) with one of those graded as intumescent with no fundal view (2%). As an early complication, progression of cataract was noted in 6% of cases, however, was most common as a late complication (14%). Average interval to cataract surgery was 12.5 ± 8.3 months. All cases were successfully managed with cataract extraction, however, as one was aged 10 they did not have an IOL inserted. As expected, visual acuity initially deteriorated following the tube surgery from a mean VA of 0.37 ± 0.23 logMAR to 0.95 ± 0.79 logMAR prior to cataract extraction, however, following cataract extraction this improved to 0.17 ± 0.18 logMAR at final follow-up for this sub-group (32.38 months). Regarding IOP, prior to cataract surgery this measured 13.0 ± 1.6 mmHg using 0.7 ± 0.9 medications. By final follow-up, there was a trend to a lower IOP of 11.3 ± 2.8 mmHg (p = 0.059) and no significant change in medication requirements (0.9 ± 1.1, p = 0.813).

One tube which was intraoperatively deemed to have been cut short, retracted out of the anterior chamber at 4 weeks leading to raised IOP. Initially, the prolene was removed at 3 weeks post-operatively to try and allow drainage, without effect, however, the tube was then revised using a 24-gauge cannular sheath extension technique back into the correct position.

Self-limiting corneal oedema occurred in four cases (8%) in the early post-operative period with one late case (2%) of corneal decompensation which was listed for DSAEK with simultaneous second PGI due to ineffectual IOP control also.

Finally, only two late cases (4%) experienced symptoms of diplopia which were successfully managed by the orthoptic department with conservative measures.

No cases of endophthalmitis or tube or shunt erosion were recorded, and two late cases of microbial keratitis were deemed unrelated to the glaucoma or PGI surgery.

Additional procedures following tube insertion (listed in Table 2B) include: 10 cataract extractions, 3 tube trimmings (2 occurred at the time of cataract surgery), 1 tube extension into AC, 1 XEN bleb-extending procedure and 1 subsequent PGI with simultaneous DSAEK.

Secondary outcomes—prolene removal

Prolene intraluminal stent was removed in 21 cases (42%) by a mean of 6.9 ± 5.6 months (range 0.75–23 months). This led to a significant reduction in IOP from 24.7 ±7.0 mmHg to 14.3 ± 2.7 mmHg (p < 0.0001). Whilst there was a trend to a reduction of medications, from 2.0 ± 1.4 reducing to 1.4 ± 1.2, this was not significant p = 0.096. There were no associated cases of hypotony at the time of removal.

Discussion

We report our medium-term results with the PGI in the management of complex uveitic glaucoma. To our knowledge, this is the first paper of its kind looking specifically at this device in the management of uveitic glaucoma.

The results of this study are comparable to a cohort of uveitic patients managed with Baerveldt-250 mm² tubes at our centre [11]. In that study of 42 patients, complete and qualified success rates were 30.6% and 72.2%, respectively at 3 years. For our cohort, with an average follow-up of 3 years, success rates were 48% and 92%, respectively. Failures in the Baerveldt cohort were due to IOP above target in 8.3% and hypotony in 5.6% of cases. Comparatively, most of the 8% of failures in our PGI cohort were due to raised IOP (6%) with only one case (2%) due to hypotony. Regarding IOP, Baerveldt tube reduced IOP by 58% to an average of 12.3 mmHg using 1.1 medications at 3 years with almost identical reductions in our PGI cohort which reduced IOP by 56.7% to an average of 12.2 ± 4.4 mmHg, using 1.1 ± 1.3 medications. Finally, the rate of hypotony in our cohort was 10%, with only one patient requiring re-suturing of a leaking paracentesis and only one meeting failure criteria. Conversely, in the Baerveldt cohort, hypotony rates were much higher, with 26% requiring anterior chamber reformation. As such, our results indicate that the PGI offers similar efficacy but greater safety and perhaps a greater success rates when compared to this previously published Baerveldt data. Similar success rates, IOP and complications can be found in other publications with one quoting hypotony rates of 10% when the larger Baerveldt-350 plate was used [22, 23].

Multiple short-term studies have been published looking at the efficacy of the PGI. Typically, these found 1–2 year qualified success rates (IOP ≤ 21 mmHg) between 84%, in a paediatric cohort, to 97% in adult pseudoexfoliative glaucoma [16–19, 24]. If the IOP target is reduced to ≤18 mmHg then this falls to 71.8%–84.4% [17, 25, 26]. Finally, the only other cohort with 3-year follow-up found a 85.4% qualified success rate (IOP ≤ 18 mmHg), however, rates of complications, including hypotony (35%) were significantly higher, likely due to variations in technique [27]. These figures are in-keeping with our results, with 92% achieving IOP ≤ 21 mmHg and 90% ≤18 mmHg.

Regarding the one case of late-onset hypotony, this occurred at 46 months due to a flare of ocular inflammation. They met the failure criteria 4 months later, after a temporary recovery, following recommencing immunosuppressants. We note that this patient had their prolene removed at 15 months with an IOP of 17 mmHg using only one medication. Following removal, the IOP was 15 mmHg on no medications. For our cohort, average IOPs before prolene removal was 24.7 ± 7.0 mmHg using 2.0 ± 1.4 medications. As such, this patient had comparatively lower pressures and medication requirements which may have contributed to the potential for hypotony and caution should be applied in removing the stent-suture in these cases. Our typical practice in uveitic patients is to maintain a small number of medications, if IOP is controlled, rather than removing the stent to minimise this risk. We appreciate this may, however, reduce the overall IOP reduction and potentially reduce the complete success rate.

Interestingly, in patients who underwent cataract extraction (n = 10), when comparing IOP pre-cataract and at final follow-up, there was a near-significant trend to IOP reduction (−1.70 mmHg, p = 0.059) with no significant change in medications (+0.2 drops, p = 0.813). As such, it seems that cataract extraction following PGI surgery does not increase IOP. This is in-keeping with the literature, which found similar with other types of glaucoma drainage devices [28, 29]. Conversely, another study suggested that cataract extraction following tube surgery increases IOP and recommended techniques to mitigate against it [30].

It has previously been found that in PGI cases with or without MMC, success parameters were not affected [19]. In our study, there were five cases where no antimetabolite was used and four where 5-FU was used instead of MMC due to a temporary shortage. In 41 cases the standard MMC protocol was followed. Mean IOP for these sub-groups was 15.0 ± 7.6 mmHg using 1 ± 1.2 medications without MMC, 8.75 ± 3.8 mmHg using 1.25 ± 1.5 medications with 5-FU and 12.2 ± 3.9 mmHg using 1.04 ± 1.4 medications when MMC was applied. Additionally, there was one (20%) failure in the no antimetabolite group, none in the 5-FU group and two (4.9%) in the MMC group. Whilst the small number in each sub-group prohibits accurate statistical analysis and caution should be taken with interpreting these results, there does seem to be a lower IOP in each of the groups where antimetabolite was used.

The retrospective nature of our study does limit the data we can collect, especially with less regular follow-up over the COVID-19 Pandemic. One patient died early in the review process due to an unrelated cause. The decision was made to keep them in the analysis to maintain the continuous, consecutive nature of the case series. One patient was lost to follow-up at 20 months as they transferred hospital. We are mindful that the 2½-year data collection window (April 2019–August 2021), as well as the open-ended study design, increases the risk of introducing attrition bias. Sample numbers reduce significantly after the 36-month data collection point (n = 27) compared to at the 42 (n = 12) or 48 (n = 9) month timepoints, however, IOP and medication results remained stable despite this (Figs. 1 and 3). Our study does not include any visual field data, instead concentrating on IOP and medication outcomes. Our study does not include any visual field data, instead concentrating on IOP and medication outcomes. This would however be interesting to analyse in future projects.

In summary, the PGI offers excellent surgical success rates at an average of 3 years post-operative follow-up. We have demonstrated the effective use and safety of the device in the management of uveitic glaucoma. We feel this represents a promising change in practice and as such, in our unit, the PGI is now the preferred tube of choice in cases of uveitic glaucoma.

Summary

What was known before

• Glaucoma drainage devices are effective in lowering IOP in uveitic glaucoma, however, traditional devices (e.g. Baerveldt tube) have significant rates of hypotony which can lead to poor visual outcomes.

• The PAUL Glaucoma Implant has been proven to be an effective device in lowering IOP in multiple different types of glaucoma, but there are no research articles looking at uveitic glaucoma described in the literature.

What this study adds

• This 3-year average follow-up cohort (n = 50) is the only paper to date which looks specifically at a cohort of complex uveitic glaucoma managed with the PAUL Glaucoma Implant.

• It shows IOP reduction and surgical success rates comparable to Baerveldt tube but with lower rates of post-operative hypotony.

• This paper suggests that the PAUL Glaucoma Implant is a safe and effective tool in the management of uveitic glaucoma.

Author contributions

JR—project design and planning, case finding, data collection, wrote and referenced all sections of the paper, statistical analysis, created figures and tables, interpreted results, submission to journal and responded to reviewers. FT—project design and planning, case finding, data collection, interpreted results, involved in writing and reviewing of the paper. KY, JY, CF—undertook surgical cases and reviewed paper prior to submission. LA—undertook surgical cases, initial project planning and reviewed paper prior to submission. All authors approved of the manuscript prior to submission.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Competing interests

The authors declare no competing interests.

Ethics approval

As per the recommendations of the Health Research Authority (HRA) Research Ethics Committee (REC) guidance tool, no ethical review from an institutional review board or REC was required for this retrospective, observational study and the research was conducted in accordance with the principles of the Declaration of Helsinki.