We glaucoma surgeons have a plethora of options for managing IOP in glaucoma patients—we can approach the canal, we can enter the suprachoroidal space, or we can create blebs or use lasers. For me, a paper published by Saheb and Ahmed in 2012 set the benchmark for our goals with MIGS: an ab interno microincision, minimally traumatic, with at least modest efficacy, a favorable safety profile, and rapid recovery.1 I believe there are important considerations of safety and efficacy when we choose a device to achieve these goals.
IOP Reduction
Recent studies have shown a similar performance in terms of IOP control between the iStent inject® (Glaukos Corp.) and the Hydrus Microstent (Alcon). In its 2-year pivotal trial versus cataract surgery, the iStent inject® met its primary outcome measure (a reduction in unmedicated diurnal IOP from baseline of ≥20% and change in unmedicated diurnal IOP from baseline in month 24) in 75.8% of patients.2 In the 2020 COMPARE study between the iStent and the Hydrus Microstent, 80% of the participants who received the Hydrus achieved the primary outcome of an IOP of ≤18 mmHg and no topical glaucoma medications at 12 months.3
Safety
Yet, the abovementioned were in vitro studies. Although supporting data are not available, in my practice, I have not seen the clinical benefit of implanting such a large device (the 8-mm Hydrus). In a contralateral eye study between either the iStent inject® or the iStent inject® W (both from Glaukos Corp.) versus Hydrus, Schultz et al found no difference in efficacy, but the Hydrus device had two postoperative adverse events (one device dislocation and one malposition).4
Safety is very important with all the MIGS procedures. If I am operating on patients with mild disease and my aim is to reduce their glaucoma medication therapy, then I prefer a procedure with a low rate of complications. Rates of secondary surgical interventions in recent MIGS studies are as follows: 10.4% in the ROMEO study5 with the OMNI Surgical System (Sight Sciences); 7.5% for the Hydrus device and 5.4% for iStent inject® in Holmes et al6; and 25.5% in an 8-year follow-up study7 of combined phacoemulsification and excimer laser trabeculotomy.
Ahmed et al performed a post-hoc analysis to compare the corneal endothelial safety over 5 years of three MIGS devices: the iStent inject®, the Hydrus Microstent, and the CyPass Micro-Stent (Alcon).8 Although the CyPass has since been withdrawn from the market, in this study, the Hydrus impacted endothelial cell count significantly compared to the iStent inject® (Figure).
Figure. Evidence from pivotal trials of 3 MIGS devices showing the proportion of patients experiencing ≥20% endothelial cell loss at 5 years (Data adapted from Ahmed IIK et al, JCRS 2024).8
In all their trials, the iStent devices have shown an overall safety profile fairly similar to that of cataract surgery alone.2 In my experience evaluating patients' outcomes, iStent devices target the site of pathology and promote a rapid recovery of vision.
SUMMARY
Glaucoma surgery is a highly complex, decision-orientated discipline that requires an intimate understanding of the disease process—it is very important to identify where the patient is in their individual disease journey. Then, we have to select the right procedure at the right time. All of these canal-based procedures have their own indications, but in terms of safety, I don't think any device outperforms the iStent inject® W.
To hear more from Dr. Masood, visit https://eyetube.net/spotlight/glaukos-international/glaukos-egs-symposium-2024-video-4
1. Saheb H, Ahmed IIK. Micro-invasive glaucoma surgery: current perspectives and future directions. Curr Opin Ophthalmol. 2012;23(2):96-104.
2. Samuelson TW, Sarkisian SR, Lubeck DM, et al. Prospective, randomized, controlled pivotal trial of an ab interno implanted trabecular micro-bypass in primary open-angle glaucoma and cataract: two-year results. Ophthalmology. 2019;126(6):811-821.
3. Ahmed IIK, Fea A, Au L, et al. A prospective randomized trial comparing hydrus and istent microinvasive glaucoma surgery implants for standalone treatment of open-angle glaucoma: the COMPARE study. Ophthalmology. 2020;127(1):52-61.
4. Shultz M, Chorbajian A, Zohouralen A. Comparative effectiveness and safety of two different trabecular MIGS devices with and without ab interno canaloplasty in patients with primary open-angle glaucoma. Ophthalmol Ther. 2023;12(6):3307-3322.
5. Vold SD, Williamson BK, Hirsch L, et al. Canaloplasty and trabeculotomy with the OMNI system in pseudophakic patients with open-angle glaucoma: the ROMEO study. Ophthalmol Glaucoma. 2021;4(2):173-181.
6. Holmes DP, Clement CI, Nguyen V, et al. Comparative study of 2‐year outcomes for Hydrus or iStent inject microinvasive glaucoma surgery implants with cataract surgery. Clin Exp Ophthalmol. 2022;50(3):303-311.
7. Riesen M, Funk J, Töteberg-Harms M. Long-term treatment success and safety of combined phacoemulsification plus excimer laser trabeculostomy: an 8-year follow-up study." Graefe's Arch Clin Exper Ophthalmol. 2022; 260(21):1-12.
8. Ahmed IIK, Sheybani A, De Francesco T, Samuelson TW. Corneal endothelial safety profile in minimally invasive glaucoma surgery. J Cataract Refract Surg. 2024;50(4):369-377.
INDICATIONS FOR USE: The iStent inject® is intended to reduce intraocular pressure safely and effectively in patients diagnosed with primary open-angle glaucoma, pseudo-exfoliative glaucoma or pigmentary glaucoma. The iStent inject® can deliver two (2) stents on a single pass, through a single incision. The implant is designed to stent open a passage through the trabecular meshwork to allow for an increase in the facility of outflow and a subsequent reduction in intraocular pressure. The device is safe and effective when implanted in combination with cataract surgery in those subjects who require intraocular pressure reduction and/or would benefit from glaucoma medication reduction. The device may also be implanted in patients who continue to have elevated intraocular pressure despite prior treatment with glaucoma medications and conventional glaucoma surgery. CONTRAINDICATIONS: The iStent inject® System is contraindicated under the following circumstances or conditions: • In eyes with primary angle closure glaucoma, or secondary angle-closure glaucoma, including neovascular glaucoma, because the device would not be expected to work in such situations • In patients with retrobulbar tumor, thyroid eye disease, Sturge-Weber Syndrome or any other type of condition that may cause elevated episcleral venous pressure. WARNINGS/PRECAUTIONS: • For prescription use only. • This device has not been studied in patients with uveitic glaucoma. • Do not use the devices if the Tyvek® lid has been opened or the packaging appears damaged. In such cases, the sterility of the device may be compromised. • Due to the sharpness of certain injector components (i.e. the insertion sleeve and trocar), care should be exercised to grasp the injector body. Dispose of device in a sharps container. • iStent inject® is MR-Conditional; see MRI Information below. • Physician training is required prior to use of the iStent inject® System. • Do not re-use the stent(s) or inserter, as this may result in infection and/or intraocular inflammation, as well as occurrence of potential postoperative adverse events as shown below under “Potential Complications.” • There are no known compatibility issues with the iStent inject® and other intraoperative devices (e.g., viscoelastics) or glaucoma medications. • Unused product & packaging may be disposed of in accordance with facility procedures. Implanted medical devices and contaminated products must be disposed of as medical waste. • Due to the sharpness of certain injector components (i.e. the insertion sleeve and trocar), care should be exercised to grasp the injector body • The surgeon should monitor the patient postoperatively for proper maintenance of intraocular pressure. If intraocular pressure is not adequately maintained after surgery, the surgeon should consider an appropriate treatment regimen to reduce intraocular pressure.
INDICATION FOR USE: The iStent inject® W, is intended to reduce intraocular pressure safely and effectively in patients diagnosed with primary open-angle glaucoma, pseudo-exfoliative glaucoma or pigmentary glaucoma. The iStent inject® W, can deliver two (2) stents on a single pass, through a single incision. The implant is designed to stent open a passage through the trabecular meshwork to allow for an increase in the facility of outflow and a subsequent reduction in intraocular pressure. The device is safe and effective when implanted in combination with cataract surgery in those subjects who require intraocular pressure reduction and/or would benefit from glaucoma medication reduction. The device may also be implanted in patients who continue to have elevated intraocular pressure despite prior treatment with glaucoma medications and conventional glaucoma surgery. CONTRAINDICATIONS: The iStent inject® W System is contraindicated under the following circumstances or conditions: • In eyes with primary angle closure glaucoma, or secondary angle-closure glaucoma, including neovascular glaucoma, because the device would not be expected to work in such situations. • In patients with retrobulbar tumor, thyroid eye disease, Sturge-Weber Syndrome or any other type of condition that may cause elevated episcleral venous pressure. WARNINGS/PRECAUTIONS: • For prescription use only. • This device has not been studied in patients with uveitic glaucoma. • Do not use the device if the Tyvek® lid has been opened or the packaging appears damaged. In such cases, the sterility of the device may be compromised. • Due to the sharpness of certain injector components (i.e. the insertion sleeve and trocar), care should be exercised to grasp the injector body. Dispose of device in a sharps container. • iStent inject® W is MR-Conditional; see MRI Information below. • Physician training is required prior to use of the iStent inject® W System. • Do not re-use the stent(s) or injector, as this may result in infection and/or intraocular inflammation, as well as occurrence of potential postoperative adverse events as shown below under “Potential Complications.” • There are no known compatibility issues with the iStent inject® W and other intraoperative devices. (e.g., viscoelastics) or glaucoma medications. • Unused product & packaging may be disposed of in accordance with facility procedures. Implanted medical devices and contaminated products must be disposed of as medical waste. • The surgeon should monitor the patient postoperatively for proper maintenance of intraocular pressure. If intraocular pressure is not adequately maintained after surgery, the surgeon should consider an appropriate treatment regimen to reduce intraocular pressure. • Patients should be informed that placement of the stents, without concomitant cataract surgery in phakic patients, can enhance the formation or progression of cataract. ADVERSE EVENTS: Please refer to Directions For Use for additional adverse event information. CAUTION: Please reference the Directions For Use labelling for a complete list of contraindications, warnings and adverse events.
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