Over the last decade, there has been a renaissance in glaucoma surgical treatment options when it comes to angle surgery as well as devices that can help encourage outflow through the trabecular meshwork. An early development in the field of minimally invasive glaucoma surgery (MIGS) was the introduction of the iStent (Glaukos) in 2012.¹ Since then, multiple versions of these trabecular microbypass stents have been released, including the second-generation iStent, iStent inject, iStent inject W, and now the iStent infinite. Each iteration includes a nuanced change in design — and with each device, there are strategies that can help surgeons to place them most successfully. 

The iStent infinite is the latest iteration of the trabecular bypass stents and offers a way to deliver treatment to patients who have failed prior medical surgical intervention, either as a standalone procedure or combined with cataract surgery. This is the first of the iStents that have obtained a standalone indication in the United States. The prospective, multicenter 12-month pivotal trial of iStent infinite,² implanted as a standalone procedure in primary open-angle glaucoma patients who had failed prior surgical intervention, found that 73.4% of patients had a greater than 20% reduction in intraocular pressure (IOP). The trial also found 91.7% of subjects reduced or maintained their medication burden and had a mean diurnal IOP of 16.9 mmHg. This represented a mean IOP reduction of 6.5 mmHg, down from 23.5 mmHg at baseline.³

New Device Features

In addition to the standalone indication, the iStent infinite offers a new injector system that allows implantation of 3 wide flange stents across 180° of Schlemm’s canal (Figure 1). There are several notably different aspects of this injector system. First, the injector has a silicone sleeve that auto-retracts once placed into the main wound. This protects against the egress of viscoelastic by creating a barrier at the main wound and helping to ensure a firm chamber.

Another notable difference is the addition of a singulator button. This positions the stents to the top of the injector for deployment. 

The reason this device is called “infinite” is because in the new design, there is no limit to the number of times a stent can be deployed. In previous iStent injectors, when a surgeon needed to reload the stent and try to inject again, they were limited to 4 clicks. With the iStent infinite, surgeons can rethread and inject as many times as is necessary for appropriate placement.

Instruction of Procedure

Here is a step-by-step protocol to place the iStent infinite, along with surgical tips: 

1. Create or use a corneal main wound made with a keratome. Use viscoelastic to inflate the anterior chamber to a firm pressure that won’t allow for striae once the gonioprism is placed. 
2. Turn the head of the patient away, while also tilting the microscope to an approximately 35° angle. The view should be magnified to the point where the surgeon can only see the gonioprism and the angle under the microscope. Elimination of the white of the sclera is ideal. The best approach is an en face view of the trabecular meshwork (Figure 2).
3. Using a gonioprism, visualize the angle such that you can see the dark band of the trabecular meshwork clearly with the white band of the scleral spur underneath it and the ciliary body band underneath that. Surgeons should be aiming to place stents into the trabecular meshwork, so visualization of each layer of the angle is essential. 
4. Insert the handpiece so that the auto-retracting introducer goes into the main wound and retracts back to expose the trocar. This will protect against viscoelastic egress during implantation. 
5. The first stent is already primed and ready to be injected. Because there are 3 stents, they should be placed approximately 2 to 3 clock hours apart. The placement of the first stent typically relies on surgeon preference. I find that placing the center stent first allows me to have the best view and helps me to gauge proper spacing to place the others. 
6. Gently aim for the pigmented trabecular meshwork and insert the stent without excessive pressure into the meshwork. This will create a small dimple in the space. Press the stent delivery button (black button) for deployment. Hold the button while moving the injector back, confirming stent placement, then release the button once the trocar is completely disengaged from the stent. 
7. Next, press the singulator (purple tab) to deploy the next stent to the front of the injector. Then aim for the second position (which for me tends to be to the left of the middle stent) and press the deployment button. 
8. Remember, because the deployment button can be pushed infinite times, if the stent is not in the perfect location, it can be rethreaded and deployed again. 
9. Press the singulator button to prime the third stent to the front. For the last stent, the surgeon can pivot the injector all the way to the edge of the main wound. However, some surgeons prefer to exit the eye to allow for maximum pivot. This allows reinflation with viscoelastic and the opportunity to move the microscope in the direction of the last stent so that there is better visualization of the outer edge of the angle. 
10. As a final step, take a moment to visualize every stent and make sure they are positioned correctly and not dislodged in any way before removing all the viscoelastic from the eye. 

Conclusion

Overall, I find the changes in the injector system for iStent infinite conducive to a more streamlined surgery that helps eliminate the viscoelastic egress and allows for unlimited attempts for repositioning, if needed. Moreover, the data behind the multiple stents have also showed beneficial IOP control in patients undergoing implantation either as a standalone procedure or with cataract surgery.⁴ A meta-analysis of 248 subjects implanted with 3 iStents found a 22% weighted mean reduction in IOP compared to implantation of 1 iStent at 18 months 30% and 41% decrease in IOP with 2 implants and 3 implants, respectively.⁵ The use of iStent infinite is yet another effective way to help manage glaucoma patients in a safe manner. GP

Sahar Bedrood, MD, PhD, is a cataract and glaucoma surgeon at Advanced Vision Care in Los Angeles. She reports consultancy to and speaker’s fees from AbbVie, Glaukos, Théa Laboratories, BVI, Elios Vision, and Nova Eye. Reach her at saharbedrood@gmail.com.

References

1. Craven ER, Katz LJ, Wells JM, Giamporcaro JE; iStent Study Group. Cataract surgery with trabecular micro-bypass stent implantation in patients with mild-to-moderate open-angle glaucoma and cataract: two-year follow-up. J Cataract Refract Surg. 2012;38(8):1339-1345. doi:10.1016/j.jcrs.2012.03.025

2. Investigation of the Glaukos trabecular micro-bypass system, model iS3, in subjects with refractory glaucoma. ClinicalTrials.gov Identifier: NCT03639870. Updated April 23, 2021. Accessed September 26, 2024.

3. Sarkisian SR Jr, Grover DS, Gallardo MJ, et al. Effectiveness and safety of iStent infinite trabecular micro-bypass for uncontrolled glaucoma. J Glaucoma. 2023;32(1):9-18. doi:10.1097/IJG.0000000000002141

4. Malvankar-Mehta MS, Iordanous Y, Chen YN, et al. iStent with phacoemulsification vs phacoemulsification alone for patients with glaucoma and cataract: a meta-analysis. PLoS One. 2015;10(7):e0131770. doi:10.1371/journal.pone.0131770

5. Malvankar-Mehta MS, Chen YN, Iordanous Y, Wang WW, Costella J, Hutnik CM. iStent as a solo procedure for glaucoma patients: a systematic review and meta-analysis. PLoS One. 2015;10(5):e0128146. doi:10.1371/journal.pone.0128146