Significant IOP Reduction after Combined Phacoemulsification and Micro-Invasive Glaucoma Surgery (MIGS)

Abstract

In a controlled clinical trial, we investigated long-term results after trabecular micro-bypass stent implantation in routine cataract surgery in eyes with chronic open angle glaucoma. Combined phacoemulsification and trabecular microbypass implantation proved to be an effective and safe treatment method to reduce intraocular pressure, reducing the burden on local drug treatment. Implantation offers a good option for additional pressure reduction. Microsurgical procedures to reduce intraocular pressure, which are minimally traumatic and are performed ab interno and characterized by efficiency, a high safety profile and a rapid healing process, should be used more frequently.

Since decades, trabeculectomy is the gold standard in glaucoma surgery. Recently trabecular stents bypass the compromised trabecular meshwork, creating a direct route from the anterior chamber into Schlemm’s canal and improving aqueous outflow. In a prospective randomized clinical study, we investigated the long-term results, safety and efficacy of trabecular microbypass stent implantations as part of a routine cataract surgery in eyes with mild to moderate chronic open-angle glaucoma. In combined surgeries, phaco PCIOL plus trabecular micro bypass implantation, has shown reasonable efficacy in lowering IOP and the necessary IOP reducing medications. Our results showed a favorable benefit-to-risk profile.

Keywords: Micro-Invasive Glaucoma Surgery; Trabeculectomy; Glaucoma

Introduction

There are currently three different modes of operation for Micro- Invasive Glaucoma Surgery (MIGS): trabecular stents, suprachoroidal stents and subconjunctival stents. Trabecular stents improve the outflow of aqueous humor into the Schlemm’s canal. Examples are the iStent and the iStent inject. Both stents are implanted while being guided by gonioscopy into Schlemm’s canal. This is located at the level of the pigmented trabecular meshwork at the border to the non-pigmented trabecular meshwork. Suprachoroidal stents, such as the CyPass Micro-Stent (currently removed from the market), conduct the aqueous humor into the suprachoroidal space. The CyPass Micro-Stent is implanted more deeply, far below Schlemm’s canal, into the supraciliary space. Stents for use in the subconjunctival space are, for example, the XEN gel implants, which are implanted far above Schlemm’s canal, directly below the Schwalbe line, into the non-pigmented trabecular meshwork. The operating principle of subconjunctival outflow is similar to a small trabeculectomy.

iStent inject is a trabecular micro-bypass system with two preloaded implants made of heparin-coated, non-ferromagnetic titanium. The implants are very small. At 360 μm x 230 μm, they are the smallest medical devices used in humans. They have two ends; at one end, the inlet opening protrudes into the anterior chamber, while the other end opens out into the Schlemm’s canal in a pointed conical shape wifth four lateral outlet openings. The middle part of the stent is fixed in the trabecular meshwork. The implants thus connect the anterior chamber with Schlemm’s canal. They bridge the point of highest outflow resistance, the juxta-canalicular trabecular meshwork, the Fontana spaces, facilitating the outflow of aqueous humor there. The juxta-canalicular trabecular meshwork contains 50-70% of the total discharge resistance. Increased flow resistance in the trabecular meshwork is the primary cause of increased eye pressure in open angle glaucoma. The aqueous humor then flows from the anterior chamber into the stent, from the stent into Schlemm’s canal, from Schlemm’s canal into the collector channels, and from the collector channels into the episcleral veins. Two stents are always implanted, at a distance of 30 degrees, in the nasal lower quadrant, because the density of the discharging collector channels is highest there. The iStent inject received a CE mark in the EU and an Investigational Device Exemption (IDE) for clinical studies from the US FDA.

Implantation is possible under topical anesthesia, and there is no need to stop anticoagulants and platelet aggregation inhibitors beforehand. In the combined procedure, following phacoemulsification and IOL implantation, the pupil can optionally be narrowed intracamerally with 1% acetylcholine chloride solution. To prepare for intraoperative gonioscopy, viscoelastic is injected into the anterior chamber, the operating microscope is tilted by 35 degrees and the patient’s head is turned slightly to the contralateral side. The gonioscope, according to Jacobson, is placed on the cornea. To identify Schlemm’s canal, we induce flow reversal from the episcleral vessels towards the collector channels and Schlemm’s canal prior to implantation. Flow reversal is achieved by gently pressing and massaging the sclera with hummingbird tweezers, for example. Schlemm’s canal then turns slightly reddish for a few minutes as a result of the blood reflux. The injector has a trocar with a 23-gauge protective cover. This is inserted into the anterior chamber via a 1.4 mm wide clear corneal incision. The stent is then implanted ab interno into Schlemm’s canal. Immediately after implantation, a small reflux hemorrhage occurs through the central opening of the implanted iStents inject, from the Schlemm’s canal into the anterior chamber. This is a desired criterion of success for good positioning in the canal. Finally, it is possible to optionally introduce Trypan blue into the anterior chamber and document the blue coloration of the collector channels and episcleral veins.

In a controlled, randomized, single-blind study, we investigated the long-term results after trabecular micro-bypass stent implantation in routine cataract surgery in eyes with chronic open-angle glaucoma. The results are summarized in Table 1. The average reduction in eye pressure with the combined procedure was 6.4 mmHg (25.4%). In the comparison group of standard cataract surgery alone without stent, eye pressure decreased by an average of 2.2 mmHg (10.0%) [1-26].

  

    
Intraocular pressure [mmHg]
    
0 months
    
3 months
    
6 months
    
9 months
    
12 months
  
  

    
preoperative [0 months]
  
  

    
postoperative [3-12 months]
  
  

    
Phaco + HKL (n=35)
    
22
    
19.5
    
19.9
    
19.7
    
20
  
  

    
Phaco +    HKL + iStent® inject (n=36) 
    
25.1
    
18.2
    
18.6
    
18.5
    
19.4
  

Table 1: Phaco + HKL: IOP after standard cataract surgery in 35 eyes: the
average intraocular pressure reduction was 2.5 mmHg (11.4%) after three
months, 2.1 mmHg (9.5%) after six months, and 2.0 mmHg (9.1%) after twelve
months.