In this retrospective study conducted over 12 months, we showed the real-life efficacy and safety of iStent Inject® implantation combined with phacoemulsification in patients with controlled IOP on medical treatment, with a 15% IOP decrease after surgery. A greater reduction in postoperative IOP in eyes with higher IOP at baseline had been previously demonstrated (20), but our population was defined as having medically controlled IOP. With a mean preoperative IOP of 16.29 mmHg, we observed a 15% IOP decrease at one year. Previous studies have established that every 1 mmHg IOP reduction produces a 10% or 19% lower risk of glaucoma progression (21) (22), thus highlighting the clinical relevance of these results. Similarly, 12 months after surgery, we observed a 47% decrease in topical hypotensive medications, or a decrease of approximately 1 medication. The majority of eyes (58%) had a reduction in their medication regimen compared to baseline. Thus, the main result of this combined surgery in most of our patients was to achieve an even lower IOP while reducing the number of medications (23). Furthermore, the mean IOP decreased by more than 2.5 mmHg at 1 year, 1 mmHg more than the reduction expected from phacoemulsification alone, which is on average 1.5 mmHg in both healthy and glaucomatous eyes (24) (25). This result confirms the benefit of stent implantation in addition to cataract surgery in patients with POAG.
These outcomes are consistent with previous studies (16) (20) (26). A large multicenter retrospective Australian study reported a significant decrease in mean IOP and topical medications of 23.2% and 71.5% respectively 1 year after combined surgery with implantation of iStent Inject® in patients with various types of glaucoma. These patients also had a low mean preoperative IOP of 18.27 ± 5.41 mmHg (24). A Brazilian case series (20) with a mean IOP of 16.2 ± 3.1 mmHg at baseline also showed a 19.1% IOP reduction and 94.1% medication reduction 12 months after surgery. On the other hand, in a 3-year prospective case series of patients who underwent iStent Inject® implantation with phacoemulsification, Hengerer et al. (16) demonstrated a 37% reduction in IOP and a 68% reduction in the number of antiglaucoma medications. This greater mean IOP and topical medication reduction compared to our results could be explained by the higher mean preoperative IOP (22.6 ± 3.2 mmHg) and number of medications at baseline. In our study, we noticed a more significant postoperative IOP decrease in the 6 cases having IOP higher than 21 mmHg before surgery. These data suggest that implantation of iStent Inject® may be a viable treatment option even in eyes with higher IOP.
The second generation iStent Inject® device, marketed since 2019, contains 2 stents in the same injector, while the first generation iStent® contains one. The iStent® device has also demonstrated substantial, durable, and safe reductions in IOP and number of medications (27) (28). The greater efficacy of the iStent Inject® device compared to the iStent®, especially since the former contains two stents, has been reported in some previous studies. Manning et al. (17) showed better results with implantation of the iStent Inject® compared to that of iStent® on IOP and topical medication reduction after combined surgery. Indeed, 68.6% vs. 62.7% of cases respectively had an IOP decrease ≥ 20%, and 92.9% vs. 76.1% were no longer on topical medication at 12 months. Likewise, Paletta-Guedes et al. (29) found a significantly greater IOP reduction of 19.1% after combined surgery with iStent Inject® implantation, compared to 4.3% with iStent®. The increased effect of multiple stents was also confirmed by preclinical studies. Bahler et al. (30) (31) have demonstrated further increased outflow facility and IOP decrease after implantation of more than one stent in a human anterior segment model. Similarly, clinical studies have shown that while the first stent is responsible for the majority of IOP decrease, further reduction is achieved after implantation of additional stents (20) (32). At 18 months postoperatively, Katz et al. (32) observed that the mean IOP decrease was significantly greater with the implantation of additional stents as a standalone procedure, with a mean 1.84 mmHg difference in IOP reduction in favor of the 3-stent group compared with the 2-stent group, and a 1.73 mmHg greater IOP decrease in favor of the 2-stent group compared with the 1-stent group. Indeed, three main characteristics differentiate these two devices and promote efficacy of the iStent Inject®, as highlighted in a comparative study by Paletta Guedes et al. (20). First, the iStent Inject® injector contains two preloaded stents rather than one, which are inserted into two distinct regions of the trabecular meshwork, each designed to allow 2.5 µL/min flow of aqueous humor, thus allowing for a more rapid evacuation. Second, each of the two iStent Inject® stents contains four outlet lumens (instead of one for the iStent®), allowing for multidirectional flow and maximizing the number of accessible collector channels. Finally, these stents are smaller and easier to implant, improving procedural efficiency and reducing the risk of complications.
The safety profile of iStent Inject® was very favorable in this study, and we did not report any severe adverse events. Three eyes (6.1%) experienced IOP peaks prior to 7 days postoperatively, which resolved quickly with medical management. These IOP peaks might be due to the fact that patients did not instill their antiglaucoma medications after surgery or to possible transient postoperative inflammation. Moreover, other studies have demonstrated that 13–46% of glaucoma patients experience IOP spikes after phacoemulsification (33). Only one patient (2.0%) underwent incisional surgery after 1.5 months, with placement of a XEN implant, because of persistent high IOP, defined as requiring ≥ 4 topical hypotensive medications, or IOP > 21, or requiring ≥ 1 topical hypotensive medication more than preoperatively. Some possible late complications of MIGS device, not observed in our study, include dislocation or extrusion in the introduction section (34). Mean visual acuity improved after surgery for all patients.
Our study has some limitations. First, our sample is relatively small but rather homogeneous, as the majority of patients had well-controlled preoperative IOP. The absence of a control group introduced the confounding factor of the effects of cataract surgery alone on IOP. As in almost all real-life studies, there was no washout period before or after surgery. Finally, some patients were lost to follow-up because they were returned from our center to their referring ophthalmologists. We did not evaluate postoperatively the progression rate of glaucoma damage based on perimetric data, due to missing data related to patients lost to follow-up. As only the numbers of medications were recorded in the present study, the influence of the type of antiglaucoma medication on postoperative outcomes was not evaluated. Similarly, the influence of prior filtering surgery was not analyzed, as this subgroup of patients was too limited (4 of 49 eyes) to allow a precise evaluation.