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Product Review: iStent Trabecular Bypass Device

Healthcare | May, 2021

According to World Health Organization, glaucoma is one of the leading causes of irreversible blindness and vision loss worldwide. Initial medical interventions for glaucoma mainly consist of topical eye drops or laser trabeculoplasty that intends to reduce intraocular pressure (IOP) greater than 21 mm Hg. If early therapies fail to respond, incisional surgery such as trabeculectomy or glaucoma drainage implantation is undertaken to prevent the advancing of Glaucoma. However, the surgical interventions might lead to labile post-operative IOPs, that require more recovery time, frequent follow-ups, and increase the risk of complications. Even patients undergoing medical therapy for glaucoma can become non-compliant with their treatment due to several reasons such as physical inability to self-administer eye drops, financial burden, intolerance to medication side-effects, etc.

 

Thanks to micro-invasive glaucoma surgery (MIGS), now patients can eliminate their glaucoma and live pain-free with safer procedures compared to incisional surgical methods. The MIGS procedure involves the implantation of surgical devices designed to lower IOP in difficult-to-treat patients via an ab-interno approach, causing as little trauma as possible to produce effective and sustainable results. Over the decade, MIGS space has expanded tremendously and become a significant part of the glaucoma surgical paradigm as it offers many advantages over conventional treatments such as micro-invasive approach, rapid recovery, enhanced safety, minimal trauma, and reduced complications.

 

iStent inject is the latest trabecular bypass device introduced by Glaukos Inc. that can be successfully employed in patients with mild-to-moderate glaucoma. iStent inject is the modified version of the first-generation iStent Model GTS-100, that had the ability to achieve an IOP reduction to less than 15 mm Hg. The second-generation microscale stent, iStent inject is currently the smallest available trabecular device to be implanted in the human body. The device contains two preloaded heparin-coated biocompatible implant-grade titanium stents with

 a central inlet and outlet lumen of diameter 80 microns and the head with four side outlets of 50 microns each. The iStent inject comprises of two multidirectional stents that are implanted in the trabecular meshwork with a single-use injector during the surgical procedures. Creating two bypasses for multidirectional flow through Schlemm’s canal, the iStent inject improves the eye’s natural fluid outflow and maintains normal eye pressure. With an excellent safety profile, the iStent inject not only enhances the efficacy of the treatment but also helps to reduce reliance on glaucoma medication post MIGS surgery. 

 

The iStent inject allows better flow through the trabecular system and episcleral venous system for lower IOP and shows better clinical performance than the first generation iStent. Also, iStent inject is more uniform in design so it helps to allow the procedure to be precise and repeatable. Even clinicians are comfortable in transitioning from the first generation iStent to second generation iStent inject due to its technical advantages. The iStent inject design reduces the number of surgical steps as the clinicians can insert two devices while entering a single eye, and thus raises the efficacy of the surgery and provide positive results. 

 

The iStent inject eliminates the manual approach to surgery, incorporating two preloaded stents in one injector. Visualizing the trabecular mesh, the surgeon inserts the trocar into the TM and presses the injector to deploy the first stent. The procedure is repeated 2 to 3 clock hours apart in the nasal angle with the second stent, which can increase circumferential flow and lower IOP. Several studies have demonstrated that implanting more than one stent can increase the outflow facility up to five-folds. 

 

Cataract surgery solely reduces mean intraocular pressure with open-angle glaucoma, but the results are often unpredictable and insufficient to reduce the dependence on topical medications for controlling IOP. Combining cataract and trabecular micro-bypass stent surgery presents a unique opportunity for select cataract patients with ocular hypertension. For the combined surgery, iStent is highly compatible with established cataract surgery workflow. Some of the key advantages of using Gluakos trabecular micro-bypass device during cataract surgery include optimized outflow with a streamlined injector, enhanced procedural predictability, and increase peace of mind. However, iStent inject should not be used in patients who have 

  • Quick or sudden increase in eye pressure
  • Inflammation of the eye tissue
  • Neovascular glaucoma 
  • Orbital tumor
  • Noticeable birth deformities in the front of the eye 
  • Thyroid eye disease
  • Sturge-Weber Syndrome
  • Any condition that may cause elevated pressure in the eye veins 

 

Comparison 

Microstenting procedures have evolved with advances in medical technology and the introduction of new and improved stenting devices. iStent was the first generation Schlemm’s canal microstent introduced in 2012 in the USA, which showed great safety and efficacy in open-angle glaucoma treatment. To overcome the limitations of iStent, Glaukos develop a second-generation micro stent, iStent inject, which has received FDA approval in 2018 and has been successful in changing the lives of thousands of patients around the world. Another microstent available for treating glaucoma has been introduced by Ivantis, known as Hydrus Microstent.

 

The 8-mm long and slightly shaped Hydrus Microstent is implanted ab-interno with a pre-loaded injector through a clear corneal incision into the Schlemm’s canal. The device is made up of flexible, biocompatible, titanium and nickel alloy and spans 90 degrees of the trabecular meshwork. 

 

All three micro-stents have the capability to bypass the resistance of TM and allow aqueous humor to flow into Schlemm’s canal but there are subtle differences that may be relevant for the glaucoma treatment. The first-generation iStent is a single stent system however, the new generation stent has two stents in one system. Also, the new design of the second stent with some differences in lumen diameter and size holds more value as it provides the ability to access a broader area of the conventional outflow system. The Hydrus Micro-stent follows a completely different strategy to expand the area of coverage. Instead of utilizing multiple stents, Hydrus Micro-stent is in and of itself a longer device, which spans three clock hours of Schlemm’s canal. Through its multimodal mechanism of action, the stent provides both a direct bypass of trabecular meshwork and stretching of TM. After implantation of Hydrus micro-stent, the patient requires fewer medications and is more likely to be medication-free. However, all three micro-stents re-assure safe IOP control.

 

The limitations of optimizing conventional outflow through the Schlemm’s canal with different approaches of all the three micro-stents are inevitable. Wound healing in the operated region can result in scarring, that might require additional interventions. Also, some patients with glaucoma show significant resistance to outflow distal to Schlemm’s canal that may elevate the floor of IOP after surgery. However, the central presence of Schlemm’s canal based MIGS appears to be steadfast in the glaucoma treatment and result in positive outcomes. 

 

Conclusion 

The implantation of iStent inject is considered safe and effective for treating different types of glaucoma either as a stand-alone procedure or when combined with cataract surgery. The iStent inject embodies the five key criteria of minimally invasive glaucoma surgery procedures, including swift recovery, minimal tissue disruption, high safety, modest effectiveness, and ab-interno approach. 

According to TechSci research report on “Global Stent Market By Type of Product (Vascular Stent (Coronary Vascular Stent, Peripheral Vascular Stent, Neurovascular Stent) and Non Vascular Stent), By Material (Metallic Biomaterial, Polymeric Biomaterial and Natural Biomaterials), By Type (Self-Expandable and Balloon-Expandable), By End User (Hospital & Clinics, Ambulatory Care Centers and Others) By Region, Competition, Forecast & Opportunities, 2026”, the global stent market is anticipated to register a significant growth of USD25.8 billion by 2026 owing to rising number of cardiovascular surgeries around the world. The growth can also be contributed to the increasing adoption of sedentary lifestyle and growing consumption of suboptimal diets along with advances in the field of interventional cardiology.

According to another TechSci research report on “Global Ophthalmic Equipment Market By Product (Vision Care Products, Ophthalmology Surgical Devices, Diagnostic and Monitoring Devices, Others) By Application (Glaucoma, Amblyopia, Cataract, Retinal Detachment, Others) By End User (Hospitals & Clinics, Ambulatory Care Centers, Others) By Region, Competition Forecast & Opportunities, 2026”, the global ophthalmic equipment market is expected to show an impressive growth in the coming years owing to factors such as rising incidences of eye diseases and growing demand for surgical and diagnostic medical devices. Moreover, introduction of new technology that provide non-invasive or minimally invasive surgeries are expected to boost the growth of global ophthalmic equipment market. However, the expensive procedures might put a restraint on the market growth, which could be overcome by the government support. 

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