Two-Stent Injection Lowers IOP in Various Glaucoma Types

Prospective, Nonrandomized, 36-Month Study of Second-Generation Trabecular Microbypass Stents With Phacoemulsification in Eyes With Various Types of Glaucoma

Hengerer FH, Auffarth GU, Riffel C, Conrad-Hengerer I
Ophthalmol Ther. 2018;7:405-415

Study Summary

This prospective, nonrandomized, consecutive cohort study aimed to assess 36-month outcomes after cataract surgery and implantation of two second-generation trabecular microbypass stents (iStent inject) into eyes with various types of glaucoma.

Of the 81 eyes included, 60 had primary open-angle glaucoma (POAG), 15 pseudoexfoliative glaucoma (PEX), four appositional narrow-angle glaucoma, and one each pigmentary or neovascular (secondary) glaucoma. Data were reported as the proportion of eyes that achieved ≥ 20% intraocular pressure (IOP) reduction, IOP ≤ 18 mmHg, and IOP ≤ 15 mmHg, as well as the proportion of eyes achieving a reduction in the number of medications at month 36 vs the preoperative regimen. All subjects were Caucasian and had surgery with a single surgeon in Germany.

At baseline, 32.1% of eyes had undergone previous glaucoma surgery, 56% were receiving three to four preoperative medications, and one eye (1%) was medication-free. Mean preoperative IOP was 22.6 ± 6.2 mm Hg, and mean medication burden was 2.5 ± 1.1 medications. In a subgroup analysis of the preoperative data, patients with POAG were similar to the overall cohort, whereas those with PEX had about a 1 mm Hg higher IOP and a higher mean medication burden, at 2.8 medications. Of the original cohort, not all eyes were followed for the full 36 months. Therefore, some of the postoperative subgroup analyses were performed at 12 months' follow-up.

Among the 41 eyes followed for 36 months, mean IOP decreased to 14.3 ± 1.7 (37% reduction), and mean medication burden to 0.8 ± 0.9 (68% reduction), compared with baseline. In addition, 78% of eyes achieved an IOP reduction of ≥20% from baseline, with 100% of eyes having IOP ≤ 18 mm Hg and 71% having ≤ 15 mmHg.

All patients had uncomplicated implantation of two stents after cataract extraction. No adverse events resulting from the stent were observed. Three patients underwent additional glaucoma surgery during the follow-up period because of increased IOP or progression of glaucoma unrelated to stent implantation.

In conclusion, these results are consistent with previously reported studies on both the first- and second-generation trabecular microbypass stent. Stents can lower IOP more so than cataract extraction alone, and have a lower adverse event profile when compared with gold-standard glaucoma surgeries.

Viewpoint

The second-generation trabecular microbypass stent, iStent inject, gained premarket approval by the US Food and Drug Administration in June 2018, and has been available to implant since September 2018.

It comes preloaded on a 23G trocar, with two stents per injector. Compared with the first-generation iStent, which was required to be loaded by the surgeon, the second-generation stent is meant to simplify the procedure. In addition, the latest version of this stent can be directly inserted into the trabecular meshwork. Once released from the trocar, the stent's head will sit in Schlemm's canal, and its midsection in the trabecular meshwork, whereas the flange will remain in the anterior chamber. The technical difficulty is significantly less than that of the first-generation iStent, which requires the surgeon to manually thread the L-shaped stent into the trabecular meshwork.

Data from the first-generation iStent studies showed that there is a significantly greater benefit in the reduction of IOP with the implantation of two stents, as opposed to just one.^[1,2] Thus, the recommendation for iStent inject is to implant two stents 2 to 3 clock hours apart.

This study supports previous data suggesting significant IOP reduction with iStent inject.^[3] However, it should be noted that this study assessed a homogenous population of Caucasian patients in Germany, although it is known that there is a higher rate of glaucoma in the African-American population.^[4] Further studies including such populations, who also often have more severe types of glaucoma, need to be performed to better understand for which patients iStent inject will be most efficacious.

This study also did not perform any direct comparison of IOP lowering with the stent vs cataract extraction alone, but did compare the results with data from studies that report average IOP lowering with cataract surgery alone.^[5,6,7] From this, it was extrapolated that cataract extraction with insertion of two second-generation stents lowers IOP more than if cataract surgery alone were performed. A head-to-head study by the same group of surgeons comparing populations with similar preoperative pressures and types of glaucoma would better validate this conclusion.

Given the recent recall of the CyPass stent, the options for angle-based minimally invasive glaucoma surgery have decreased. Therefore, the promising data of significant IOP reduction with the second-generation iStent presents a good option for patients. Given that the iStent inject is less difficult to implant, it may be more widely adopted by not only glaucoma surgeons but also general ophthalmologists.

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