The number of glaucoma sufferers rises every year,1 as has the advent of new technology with which to treat this disease. Microinvasive glaucoma surgeries (MIGS) are proving especially advantageous with their high efficacy and safety profiles, and ability to treat earlier cases of mild to moderate glaucoma.
Of the most recent developments in MIGS, the iStent inject (Glaukos), provides several significant advantages, including a greater ease of insertion and the potential for greater intraocular pressure (IOP) lowering due to its dual stent design.
Potential for lower IOP
The gold standard of glaucoma treatment is in lowering the patient’s IOP. Traditionally, this is accomplished through pharmacotherapy. While generally effective, the often complicated and burdensome regimen of drops leads to well-documented compliance issues and a significantly reduced quality of life for patients.
Cataract surgery has long been shown as an effective means of initially reducing IOP, however these effects can be extended with the implantation of a stent. While one stent will lower IOP, adding an additional stent increases the potential for even greater IOP lowering as well as for a reduction in medication.
The iStent inject comes pre-loaded with two heparin coated, titanium stents which provides the ability to implant more than one stent without leaving the eye, making the procedure easier on the surgeon and reducing possible trauma risk. Studies have repeatedly demonstrated the favorably high safety profiles of the iStent inject.2-9
Increased efficacy and responder rates of multiple stents have also been shown with studies demonstrating 80% to 100% of eyes achieving ≥20% IOP reduction with one to no medications.6-9 Katz et al reported that after ~3.5 years of postoperative follow-up, 91% of patients who had pre-operatively been on one to three medications experienced a stable IOP reduction of ≥20% without medication in comparison to the still significant 61% of one stent eyes.6
Placement of these stents can also affect the effectiveness of the treatment. While stents will still work if not near a collector channel, efficacy is greatly increased the closer stents are to these channels. Therefore, the ability to cover more clock hours of the trabecular meshwork with the iStent inject’s unique dual-stent design increases the potential of reaching collector channels, thereby allowing for better results.
Additionally, while the stents will decrease pressure, the natural episcleral back pressure prevents hypotony and the accompanying visual problems. For patients with mild glaucoma, these risks cannot readily be justified. However, the safety profile of the iStent inject is excellent, with many studies showing no complications such as hypotony and hyphema nor other device-related adverse events.2-9
An added benefit is the increased possibility of medication reduction as studies have shown ≥80% eyes with multiple stents require fewer medications, with many reduced to only one medication or eliminating medications entirely.4,6,8-9 This is of particular advantage to mild patients who are typically only on one or two medications as the pressure lowering potential of the stents often allows for the opportunity to eliminate medications entirely.
While some physicians may prefer to keep patients on medications regardless of the pressure drop achieved through combined cataract surgery and the iStent inject, it is prudent to reset the patient’s baseline and test the pressure without medication. It is very possible the medications that were once needed are no longer necessary as a result of the pressure drop provided by these procedures.Ease of insertion
In addition to the benefits of two pre-loaded stents, the elegance with which these stents are implanted is another significant advantage. Though there may be a slight learning curve for some surgeons, the actual procedure is elegant and straightforward with less probability of tissue trauma and possible adverse events. Instead, the injector is inserted perpendicular into the trabecular meshwork until an indent is visible, which will aid in ensuring the stents are placed at the correct depth. The stents are then injected with the push of a button, and the injector is retracted.
The key, as with most MIGS devices, is visibility, which is aided through the use of gonioprisms. Rotating the patient’s head away will also aid in visualization. Some surgeons prefer to implant the stents prior to performing the cataract surgery due to concerns of corneal edema and visibility once the cataract is removed.
However, this should not be an issue as cataract surgery is much less traumatic than it may have once been. Injecting the stents post-cataract surgery allows for optimum visualization as the angle once the cataract is removed opens up and enhances visibility and there is more space in the anterior chamber to maneuver.
Cataract surgery alone will effectively lower eye pressure, however, it is not always consistent, and the pressure may not stay controlled. With the iStent inject’s unique design which allows for a bi-directional flow of aqueous, the pressure reducing effects of cataract surgery are enhanced. With this better pressure control often comes a reduction in medication which leads to a much better quality of life for patients.
Joseph Gira, MD
Dr. Gira is a board-certified ophthalmologist with Ophthalmology Consultants in St. Louis, MO. He did not report any relevant financial disclosures.
1. Tham YC, Li X., Wong TY, Quigley HA, Aung T, Cheng CY. Global prevalence of glaucoma and projections of glaucoma burden through 2040: a systematic review and meta-analysis. Ophthalmology. 2014;121(11):2081–2090. doi: 10.1016/j.ophtha.2014.05.013.
2. Samuelson TW. Prospective, randomized, multicenter clinical investigation of the Glaukos iStent inject. Presented at: American Society of Cataract and Refractive Surgery annual meeting; April 13-17, 2018; Washington.
3. Fea A. M., Belda J. I., Rekas M., et al. Prospective unmasked randomized evaluation of the iStent inject® versus two ocular hypotensive agents in patients with primary open-angle glaucoma. Clinical Ophthalmology. 2014;8:875–882. doi: 10.2147/opth.s59932.
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