MICS & MIGS: combined surgery with microstent devices

Take-home: MIGS is a viable option in patients with mild–moderate glaucoma with an IOP that has been unable to be controlled by medications or who have poor medication compliance. The combination of MICS and MIGS can offer an effective surgical treatment for POAG when the IOP reduction following cataract surgery alone is not sufficient to reduce the need for glaucoma therapies. 

Reviewed by Christophe Baudouin, MD, PhD, FARVO

More than 60.5 million people worldwide were affected by glaucoma by the year 2010; this is expected to increase to nearly 80 million by 2020.¹ Of these patients, 74% will have primary open-angle glaucoma (POAG), the number two cause of blindness worldwide. Cataract is the leading cause of blindness. It has been shown that the volumetric growth of cataract can be a risk for high ocular pressure and POAG.

Increasing life expectancy and the high visual requirements of patients have inspired physicians to find new therapeutic strategies to fight these two important causes of blindness. For this reason, new minimally invasive surgery techniques to remove cataract and reduce IOP– microincision cataract surgery (MICS) and micro-invasive glaucoma surgery (MIGS) – have been developed. The two procedures can be performed together.

MICS is an approach to cataract surgery that uses an incision of less than 2.0 mm to reduce surgical invasiveness and at the same time improve surgical outcomes. This technique is the best to perform in eyes with other diseases, such as POAG, because of the low rate of surgical manipulation and induced inflammations.

While there had previously been limited surgical options for patients with mild–moderate glaucoma, MIGS procedures are creating new options for patients who do not meet the criteria for trabeculectomy. These procedures have a better safety profile than other invasive techniques, with fewer complications and a more rapid recovery time. They have been shown to be effective in decreasing IOP as well as a patient’s need for medications, which is important given a typically low compliance rate for medication adherence.²

The main indications for MIGS are POAG with mild–moderate optic nerve damage, pseudoexfoliation glaucoma or pigmentary dispersion glaucoma, POAG uncontrolled with maximum pharmacologic treatment or with barriers preventing adequate medication dosing.

The main contraindications are angle-closure glaucoma, secondary glaucoma, moderate–advanced POAG, previous unsuccessful glaucoma surgery or severely uncontrolled IOP.³

There are several definitions of MIGS, but the American Glaucoma Society, which is the largest society of glaucoma specialists in the United States, provides the following working definition:

·      IOP lowered by improving the outflow of eye fluid. This is the same mechanism that is used in traditional glaucoma surgery.

·      Approach from inside the eye.

·      Limited surgical manipulation of the sclera.

·      Little manipulation of the conjunctiva.

In meeting these criteria, MIGS procedures do not preclude the possibility of future, more traditional surgical approaches such as trabeculectomy or tube shunt surgery.

Overall, MIGS procedures have been touted as safer than traditional trabeculectomy or tube shunt surgeries. This is because they do not have some of the associated complications of the traditional procedures, such as low eye pressure (hypotony) and bleb infection.

Many MIGS procedures involve the implantation of small devices. MIGS procedures are generally faster than trabeculectomy and tube shunt surgeries, and shortened surgical time can be very important for the safety of the patient. Many MIGS procedures are combined with cataract surgery, adding a short amount of time to the total surgical procedure.

Lastly, an important point is that while most MIGS procedures are safe, they are less effective than other traditional surgical procedures in lowering eye pressure, for example in patients affected by severe glaucoma with IOP greater than 30 mmHg.

MIGS with microstents can provide an effective way to treat glaucoma in a less invasive manner and earlier in the disease process. Although good surgical skills and experience are required, recovery is faster and there are fewer complications compared with traditional procedures, as tissue dissection is not required.

MIGS with microstents

Over recent years, new microstent devices for ab interno MIGS have been developed.

Aimed at the subconjunctival space is the XEN Gel Stent (AqueSys). Other implants – including the Hydrus Microstent (Ivantis) and the first- and second-generation iStent Trabecular Micro-Bypass Stents (Glaukos) – target the Schlemm canal, while the third-generation iStent and the CyPass microstent (Transcend Medical) are aimed at the suprachoroidal space.

Personal experience

Figure 1Of the devices listed above, the microstents with which we have the most experience are the iStent Trabecular Micro-Bypass Stent (Glaukos, Laguna Hills, CA) (Figure 1) and the XEN Gel Stent (Aquesys Inc.) (Figure 2).

Figure 2

The iStent Trabecular Micro-Bypass Stent received FDA approval in 2012. This is the smallest FDA-approved device, measuring 0.3 mm in height and 1 mm in length, and is a heparin-coated non-ferromagnetic titanium stent with a snorkel shape to facilitate implantation. The device is placed using a sterile single-use inserter through a 1.5 mm corneal incision. The applicator is inserted into the anterior chamber and across the nasal angle, while the angle is carefully visualised with a goniolens. The pointed tip allows penetration of the trabecular meshwork and insertion into Schlemm’s canal, and three retention arches ensure that the device will be held in place. In our department, 23 eyes were implanted with this device. iStent implantation with phacoemulsification resulted in a significantly lower long-term decrease in IOP and the number of medications used compared with phacoemulsification alone. No major complications were found in our series.

The XEN Gel Stent has a CE mark and is an investigational device that is currently undergoing clinical trials. The implant is made of a soft collagen-derived gelatin that is known to be non-inflammatory. The XEN Gel Stent is 6 mm long and about the width of a human hair. The goal of implantation is to create an outflow path of aqueous humour from the anterior chamber into the non-dissected tissue of the subconjunctival space. A little bleb is obtained by injecting mitomycin-C in the superotemporal sub-conjunctival space, which is then massaged with a sponge towards the superonasal quadrant. The implant is injected through a small corneal incision into the superonasal quadrant, passing through the Schlemm canal with an inserter similar to those used for IOLs. The device is easily seen through the conjunctiva.

Figure 3

Like other implants, it can be inserted in conjunction with MICS. We have good experience (21 implants) of this combined surgery with 1 year of follow up. IOP was reduced from 25.8 mmHg ± 5.26 mmHg (mean ± standard deviation) at baseline before surgery to 13.8 ± 1.09 mmHg at 1 year for the combined surgery with XEN Gel stent. Furthermore, the mean number of glaucoma medications was reduced from 2.6 at baseline before surgery to 0 at 1 year. The reduction of IOP has persisted and we have experienced no major complications. There was just one patient, who had not interrupted antiplatelet therapy although preoperative discontinuation was required, in whom we did not succeed in implanting the device because of a diffuse sub-conjunctival haemorrhage soon after mitomycin-C injection.

Figure 4

After implanting this device, one of the most interesting features of follow-up is the possibility of verifying the correct position of the stent by using an anterior optical coherence tomography (OCT). Recently, we tested a combined anterior and posterior swept source OCT, the DRI OCT Triton plus (Topcon Medical Japan Co., Ltd.), which provides deep images of the anterior chamber and a better penetration of the deeper layers of the eye such as the sclera. As shown in Figures 3–5, the bleb and the XEN Gel stent conforming to tissue in a human eye are easily detected with this new OCT. These follow-up images allow measurements and detection of any postoperative complications such as tiny dislocations of the

Figure 5device.

Conclusions

In patients with mild–moderate glaucoma with an IOP that has been unable to be controlled by medications or who have poor medication compliance, MIGS appears to be a viable option. Clinical trials have shown there to be a significant decrease in IOP over periods of up to 24 months, along with a significant decrease in medication usage. The procedure has maintained a high safety profile with minimal adverse effects. There are a few FDA-approved devices, such as iStent, and multiple new devices pending, such as XEN Gel Stent. MIGS can provide a method of treatment for glaucoma patients that decreases reliance on medications without the safety risks of more invasive procedures.

The combination of MICS and MIGS by implanting a microstent can offer an effective surgical treatment of POAG because the reduction of IOP caused by cataract surgery alone may not be sufficient to reduce a patient’s need for glaucoma therapies.  

References

1. Quigley HA, Broman AT. Br. J. Ophthalmol. 2006; 90(3): 262-267.

2. Randy Craven E, et al., J. Cataract. Refract. Surg. 2012; 38(8): 1339-1345.

3. Francis BA, et al., Ophthalmology 2011; 118: 1466-1480.

Dr. Antonio Toso

E: antonio.toso@gmail.com

Dr. Simonetta Morselli

E: simonetta.morselli@gmail.com

Dr. Alessandra De Gregorio

E: adegregorio@email.it

Dr. Alberto Amisano

E: amisano.alberto@gmail.com

Dr. Toso is head of the Vitreoretinal Surgery Unit, Department of Ophthalmology, S. Bassiano Hospital, Bassano del Grappa, Italy.

Dr. Morselli is head of the Department of Ophthalmology at S. Bassiano Hospital, where Dr. De Gregorio is a consultant and Dr. Amisano practices.

None of the authors have financial interests in the products mentioned.