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The iStent devices: iStent, iStent inject, and iStent Supra

Author(s):

Antonio M. Fea

Simona Scalabrin

Carlo Lavia


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Abstract:

The goal of current glaucoma treatment is to stop or slow disease progression, characterized by optic disc cupping and a distinctive pattern of permanent visual field loss. Current glaucoma interventions (medications, surgery, laser, etc.) achieve this goal almost exclusively by reducing the intraocular pressure (IOP), which is the only modifiable risk factor. Nevertheless, with medical therapy, IOP control relies on patients’ adherence and persistence, and poor patient compliance remains a major factor of disease progression, leading to the need for invasive surgery. Minimally invasive glaucoma surgery (MIGS) aims to provide a less invasive and safer means of reducing IOP than traditional incisional glaucoma surgery, with a reduction in dependency on topical medications and minimal undesired effects. This is an essential shift in glaucoma surgical philosophy.

The current MIGS approaches include techniques with different mechanisms of action: increasing trabecular or suprachoroidal outflow, reducing aqueous production, or increasing subconjunctival filtration. Nevertheless, the original MIGS paradigm was to provide a restoration of the natural outflow pathway, and Glaukos (San Clemente, CA, USA) was one of the first companies to address both the conventional (trabecular/Schlemm’s canal) and the alternative (uveoscleral/suprachoroidal) pathways.

The opportunity to produce miniaturized, drug-releasing devices, together with the observation that a minimal percentage of medication is delivered into the eye by traditional means (eye drops), recently paved the way for the development of slow-releasing devices to be implanted into the anterior chamber. In this chapter we will present and discuss the devices produced by a single company, Glaukos. The chapter is divided into an introductory part, which outlines the pathways and the potential advantages of these devices, a second part, which mainly deals with the implantation procedures, and a final part, in which personal opinions and some potential developments are presented. Some of the points are highlighted in boxes for ease of reading.

New Concepts in Glaucoma Surgery Series: Volume 1, pp. 119-136 #9
Edited by: John R. Samples and Iqbal Ike K. Ahmed
© Kugler Publications, Amsterdam, The Netherlands

Video:

Video 1. Suboptimal visualization of the TM

Video Description: Suboptimal visualization of the TM: the pressure on the goniolens determines the occurrence of wrinkles on the cornea and the presence of bubbles under the goniolens, which hamper correct visualization of the angle structures. Furthermore, the relative angle between the goniolens and the cornea is incorrect.

Video 2. Correct visualization of the angle through the goniolens

Video Description: Correct visualization of the angle through the goniolens: some blood is visible in SC of the first patient, whereas some areas of pigmentation are evident in the second patient. By applying gentle pressure, it is possible to move the lens on the cornea to explore different areas.

Video 3. Differences between two goniolenses

Video Description: Differences between two goniolenses. The first goniolens (Glaukos) allows a wider view but has a lower magnification than the Ocular Instrument (Bellevue, WA, USA) lens.

Video 6. (a) Checking the correct positioning of the iStent

Video 6. (b) The stent, sitting in SC, is seen through the TM

Video 7. (a) The iStent is superficially placed but can be inserted into the right position by pushing on it

Video 7. (b) The same maneuver is used in this case, but the stent is too superficial. It is regrasped and pushed into position

Video 9. (a) The iStent Inject inserter is introduced into the anterior chamber. The insertion sleeve is retracted when close to the TM, revealing the trocar. The trocar is placed perpendicular to the TM before firing the iStent

Video 9. (b) The iStent Inject inserter is introduced into the anterior chamber. The insertion sleeve is retracted when close to the TM, revealing the trocar. The trocar is placed perpendicular to the TM before firing the iStent.

Video 10. (a) Correct firing of two iStent Injects

Video Description: Correct firing of two iStent Injects. Please note that the stents are placed more than two hours away from each other.

Video 12. (a) After implantation, balanced saline solution is used to clear the blood from the angle

Video Description: After implantation, balanced saline solution is used to clear the blood from the angle. Then, by pressing on the incision, the pressure in the anterior chamber is reduced to visualize the reflux of blood from the bore of the stent. At the slit lamp, the reflux of blood is visualized through the bore of the stent because of the pressure changes induced during gonioscopy at the one-week follow-up examination.

Video 12. (d) After implantation, balanced saline solution is used to clear the blood from the angle

Video Description: After implantation, balanced saline solution is used to clear the blood from the angle. Then, by pressing on the incision, the pressure in the anterior chamber is reduced to visualize the reflux of blood from the bore of the stent. At the slit lamp, the reflux of blood is visualized through the bore of the stent because of the pressure changes induced during gonioscopy at the one-week follow-up examination.

Video Caption: Video 13. The iStent Inject is too superficial; the insertion sleeve is used to insert it deeper into the TM


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