Part 4

Simplifying MIGS Micro Stent Revision Surgery

In the fourth part of this series, a world-renowned surgeon, Dr. John Berdahl, shares his experience using the latest addition to MicroSurgical Technology’s micro-instrumentation family, the 19g Ahmed Micro Stent cutter. Dr. Berdahl describes the key considerations for the CyPass revision surgery, the surgical steps involved, and summarizes the key learnings with his preferred approach.

19g Ahmed Micro Stent Cutter — pre-insertion into the anterior space (Courtesy of John P Berdahl, MD).

John P Berdahl, MD. Practicing at Vance Thompson Vision in Sioux Falls, USA

Introduction

One of MST’s latest creations in their micro-instrumentation portfolio is the 19-gauge Ahmed Micro Stent Cutter, specifically designed for minimally invasive glaucoma (MIGS) micro stent revision surgery, yielding controlled precision.

Minimally invasive glaucoma micro stent revision surgery

Alcon voluntarily recalled the CyPass device from the market in 2018, based on 5-year data from a post-approval study called the COMPASS XT. The study results indicated a higher rate of endothelial cell loss (ECL) in patients receiving cataract extraction (CE) with CyPass than with CE alone.[1] The results suggest a correlation between CyPass implant depth and ECL. Stents positioned too far forward into the anterior chamber and near the cornea resulted in EC loss.

Following the withdrawal of the device, the American Society of Cataract and Refractive Surgery (ASCRS) committee task force issued a Withdrawal Consensus Statement offering recommendations on monitoring and treatment options for patients implanted with the CyPass.

These recommendations included regular monitoring as well as repositioning, removal, or proximal end trimming in cases of corneal decompensation. The CyPass device can be trimmed to allow shorter anterior chamber exposure, therefore preventing further ECL. While the available intraocular scissors can be used to trim the implant, they can require great force and the use of supporting instruments leaving no free hand for visualization with the gonio prism. To address the need for a cutter with improved precision and control for single-hand technique, MST in collaboration with Iqbal Ike K. Ahmed, MD, FRCSC developed the new 19g Ahmed Micro Stent Cutter.

Key considerations for the CyPass revision surgery

I have had patients come to my practice who have the CyPass device implanted for a long time. While in most cases, my preferred strategy will be observation, in cases where there is evident contact between the stent and the endothelium, with some rubbing of the peripheral endothelium, I intervene with trimming the CyPass tube.

The dark images illustrate the CyPass stent touching the endothelium cells (Courtesy of John P Berdahl, MD).

Attempts at CyPass removal are challenging as scarring has developed around the stent and there is a risk of iridodiaylsis, cyclodialysis, and bleeding.

I recommend regular observation if only one retention ring is visible; trimming is unlikely in these cases. Where two or three rings are visible, but there is good space between the endothelium and the CyPass, then I would elect to observe carefully, but that’s a judgement call. If the stent is long and there is evidence of touching, decreasing endothelial cells, or corneal edema, I trim the stent.

With the new MST Ahmed Micro Stent cutter, I can to trim the stent to the required length in one clean cut. Trimming removes the possibility of the stent making fictious contact with the peripheral endothelium and is my favored approach. The procedure is outlined below.

Surgical Steps Patient Case

1. First, I make a clear corneal incision at 180 away from the CyPass stent.

2. I put in intra-cameral lidocaine.

3. Then I fill up the eye with viscoelastic — all this is carried out under topical anesthesia.

4. Next, I place on the gonio prism and ensure I get good visualization and focus.

5. The MST micro stent cutter comes into play now, I use it with the jaws open over the proximal end of the stent and advance it to just above the iris root.

6. Then, I depress the cutter and here the design of the micro stent cutter creates a mechanical advantage of allowing the cutter to cut through the stent cleanly.

Clean cut with the Micro Stent Cutter (Courtesy of John P Berdahl, MD).

7. The cutter seizes the fragment that’s been cut, and I extract the cutter through my corneal incision.

Retention of the fragment (Courtesy of John P Berdahl, MD).

Cut fragment inside the Micro Stent Cutter jaws (Courtesy of John P Berdahl, MD).

8. I remove the viscoelastic and finish up by hydrating the incision.

9. If more trimming is needed, I repeat these steps.

The features of the micro stent cutter allow me to transform a difficult challenge into a straight-forward procedure.

Specific features

Easing a difficult procedure — Previously, I have trimmed a CyPass stent using heavy- duty intraocular scissors, and while the surgery was a success, it was a challenge because of the force required to trim the stent. I didn’t want the stent under tension as then there is a risk of creating a new cyclodialysis cleft (separation of the ciliary body from the scleral spur, creating a direct connection between the anterior chamber and the suprachoroidal space which can cause chronic hypotony, resulting in hypotony maculopathy, optic disc edema, and decreased visual acuity).

The new MST 19g Ahmed Micro Stent Cutter in action (Courtesy of John P Berdahl, MD).

The 19g Ahmed Micro Stent Cutter is designed to enter the anterior chamber through one corneal incision; single-handedly I was able to cut the implant, affording me the free hand for visualization using the gonio prism. The cutter allows me to trim the CyPass implant to a shorter length in the anterior chamber, preventing ECL. The use of the MST micro stent cutter eases the otherwise challenging procedure using other scissors.

• The coaxial design avoids the need for side incisions, allowing me to use the cutter with one hand and approach the stent directly from 180 away.
• I love that I can approach the stent directly and the device gets locked into position then the guillotine-like cutter comes down for a clean cut, enabling the stent to be trimmed precisely and with good control.
• The eye remains stable throughout with no movement from the stent.
• The cutter captures the trimmed fragment, eliminating the need for additional forceps to go back into the eye and retrieve it, enabling a single surgeon procedure.

Tips for the first time!

• The key is good visualization — being able to see exactly what you are doing; good focus is paramount.
• Make sure not to put torque on the CyPass stent, it’s important to ensure a balance of pressure as you don’t want the stent under tension leading to complications such as cyclodialysis.

Conclusion

The MST Micro Stent Cutter might be used for other eye tube trimming in the future, but for now, it is simply a brilliantly designed micro instrument to simplify the micro stent revision surgery.

Key Learnings

Trimming retains the function of the implant.

Intervention to protect the corneal endothelium may be considered if there is contact between the micro stent and the corneal endothelium resulting in localized endothelial opacification and/or edema or a significant progressive decrease in endothelial cell density that appears related to stent’s positioning or stability.

Some CyPass devices have been removed, however this may be traumatic to surrounding tissue and risk iridodiaylsis, cyclodialysis and bleeding.

Key features of the MST micro stent cutter are control and precision

The key learning tip — ensure you have good visualization.

References

1. ASCRS. Preliminary ASCRS CyPass Withdrawal Consensus Statement. https://ascrs.org/CyPass_Statement. Accessed June 15, 2019.