This study investigated the efficacy of a single PGI in managing refractory PCG. The results indicate the cumulative probability of a successful outcome reaching 86.6% within the 12-month follow-up. Within the first three months post-implantation, only four eyes (13.4%) experienced complications; choroidal detachment and tube exposure. Importantly, no further complications were reported in any of the patients during the remainder of the 12-month observation period. These findings underscore the potential of PGI in effectively managing refractory PCG with a low incidence of complications.

In cases where IOP remains uncontrolled following initial surgery, several surgical options are considered. These include filtration surgery with anti-fibrosis drugs, GDDs, or cyclodestructive procedures. GDDs are categorized into open-tube (non-restrictive) and valved (flow-restrictive) devices. Open-tube devices, exemplified by the Molteno and Baerveldt implants, provide non-restricted drainage. In contrast, valved devices, such as the Krupin implant or AGV, regulate flow to minimize complications associated with hypotony during the immediate postoperative period. The Baerveldt and AGV implants are widely used, with smaller sizes available, making them suitable for pediatric cases. Children, in particular, may be prone to implant extrusion and exposure. Non-valved GDDs have been noted to offer sustained and reduced IOP control over an extended period in pediatric patients compared to valved GDDs [14]. In a separate recent study, it was noted that there was no discernible variance in the success rates at 12 and 24 months between eyes implanted with AGV and those with Baerveldt implants within the pediatric population [15]. The AGV, equipped with a flow-restrictive device, has a smaller surface area than the Baerveldt, potentially affecting the extent of IOP reduction and predisposing the patient to a more pronounced hypertensive phase. In a study reported by Ou et al., the cumulative success probability of AGV in patients with PCG was 63% within one year [16]. Razeghinejad et al. report the cumulative success probability of AGV implantation in patients with PCG as 96% ± 4.4% within the first year [10]. In another study comparing AGV and Baerveldt implantation in patients with PCG, the success rates were 53.4% and 78.8%, respectively [17]. There is no study in the literature regarding the success rates of PGI in patients with primary congenital glaucoma. Our study demonstrates that within a one-year follow-up period, the cumulative success probability of PGI reached 86.6%. Complications associated with GDDs include hypotony leading to a shallow anterior chamber and choroidal detachments, tube-cornea touch, tube obstruction, exposed tube or plate, endophthalmitis, and retinal detachment. Careful consideration of implant characteristics and patient factors is crucial in selecting the most appropriate device for optimal outcomes.

In recent times, there has been a notable surge in interest regarding surgical interventions for childhood glaucoma. This is attributed to the adoption of novel surgical techniques used to treat adult glaucoma procedures for congenital glaucoma surgery. Among these innovations, the PGI has emerged as a novel GDD designed to mitigate postoperative complications commonly associated with existing GDDs. Successful applications of the PGI in shunt surgery for glaucoma are reported [13]. The PGI is characterized as a valveless aqueous shunt with specific dimensions, including an endplate surface area of 342.1 mm², a width (leading to trailing edge) of 16.1 mm, and an endplate width (wingspan) of 21.9 mm. Encapsulation around the endplate stands out as one of the predominant causes of failure following GDD surgery. Notably, the endplate surface area of the PGI surpasses that of the AGV, a comparable device. This is believed to contribute to a reduced incidence of encapsulated blebs in the PGI [13]. In our study, the need for bleb revision was not observed in any patient. group. The PGI tube exhibits specific dimensions, with an internal diameter of 0.127 mm, less than half the inner diameter of the AGV. Additionally, the external diameter of the PGI tube is 0.467 mm, representing a significant reduction compared to the AGV. This specific design feature has demonstrated advantageous outcomes for the PGI, as studies consistently show not only adequate reduction in IOP but also a diminished occurrence of hypotony [12, 13]. These attributes underscore the potential clinical benefits of the PGI in the context of glaucoma management, particularly in comparison to the AGV. All subjects included in the study demonstrated buphthalmic eyes. The PGI, known for its pliable, soft silicone construction, was utilized without encountering any size-related complications among the participants. This suggests that the implant adequately conformed to the ocular dimensions of the patients’ eyes. The reduced caliber of the PGI tube represents a significant advantage in mitigating the risk of corneal endothelial damage and lowers the likelihood of conjunctival erosion [12, 18]. Despite its smaller tube diameter and reduced reserve flow capacity, the PGI remains sufficiently sized to offer minimal resistance to aqueous outflow. In our study, IOP was maintained at or below 21 mmHg at the end of the 12-month follow-up period in 26 of 30 eyes (86.6%) which underwent PGI surgery. In addition, the mean number of medications at 12 months was 0.9 ± 1.2.

Postoperative hypotony stands as a significant and potentially vision-threatening complication following GDD surgery in pediatric patients [19]. To address this concern, the PGI tube, being a non-flow restricting implant, incorporates intraluminal stent placement as a preventive measure against hypotony. Instances of hypotonia are reported in patients undergoing PGI surgery with mitomycin C, especially after the removal of Prolene stents [19]. The exact cause of hypotony remains unclear, but it is hypothesized that the use of mitomycin C may lead to excessive filtration, and reduced scarring could contribute to a sudden drop in IOP upon Prolene stent removal. In the present study, mitomycin C was intentionally omitted from the surgical protocol for all PGI procedures. Furthermore, Prolene suture removal occurred uniformly at the one-month mark for all patients, and no instances of hypotonia were observed in this cohort. This approach, abstaining from mitomycin C and timely removal of Prolene stents, was effective in preventing postoperative hypotony in the studied patients. The use of antimetabolites, such as mitomycin C, aims to inhibit fibroblast proliferation and subsequently reduce collagen production, thereby enhancing surgical outcomes. However, this strategy may inadvertently tip the balance toward hyperfiltration, potentially leading to complications like hypotony [7]. The literature on the use of mitomycin C specifically for GDDs in the pediatric cohort is limited and presents conflicting results [20,21,22].

The occurrence of erosion or extrusion of GDD represents a significant complication uniquely associated with this type of surgery. This complication elevates the risk of endophthalmitis, primarily due to the shunt’s exposure connecting to the anterior chamber. A study notes the incidence of endophthalmitis post-GDD implantation as 9 cases in a sample of 542 eyes [23]. Notably, 6 out of these 9 instances involved tube erosion. In certain situations, even after attempts at repair, the necessity to remove the device arises due to this complication. In contrast, the incidence of extrusion concerning the implant body in patients undergoing PGI surgery is notably lower. A specific surgical series reports only one case of implant body extrusion [24]. Furthermore, in the PGI Study Group series, tube exposure was documented in 4.1% of the patients [12]. This rate of occurrence is higher than that of body extrusion in GDD surgery in general. However, resolving tube exposure is comparatively simpler, typically involving re-covering with tissue such as donor sclera or pericardium [25]. In our study, tube extrusion was observed in a single patient. We hypothesize that the inadequacy of tube stabilization through suturing contributed to this occurrence. To address this, we reinforced the stabilization of the tube in the affected patient and subsequently re-covered it using pericardium, sealing it finally with a conjunctival autograft.

The present study is constrained by its small sample size, retrospective nature, short follow-up period and lack of a control group. Preoperative and postoperative corneal endothelial density assessments were not conducted in our study. Future investigations should involve larger cohorts and extend follow-up durations to comprehensively assess the efficacy and safety of PGI in refractory PCG patients.

To the best of our knowledge, this study is the first to describe the safety and efficacy of PGI in the treatment of patients with refractory PCG. The findings of this investigation reveal that PGI possesses a notably high rate of both complete and qualified success. Additionally, there was a significant reduction in IOP and a decrease in the number of medications post-implantation. Moreover, the PGI is characterized by an advantageous safety profile, complemented by minimal post-operative care requirements. The outcomes of this study are promising, highlighting the potential of PGI as a viable therapeutic option in the realm of glaucoma treatment. There is a need for comparative studies that evaluate PGI against other glaucoma surgical procedures and different types of GDD.