An expanding armamentarium of minimally invasive and micro-invasive glaucoma surgery (MIGS) procedures is transforming glaucoma management.
“About one-half of patients with glaucoma are using two medications,” said Steven D. Vold, MD, founder and CEO, Vold Vision, Fayetteville, AR. “We know that adding a third or fourth agent often does not provide much additional intraocular pressure (IOP)-lowering benefit. However, traditional surgery with trabeculectomy and tube shunts is accompanied by significant problems.”
Dr. Vold said it is an exciting time in glaucoma surgery with several approaches available and others on the horizon. Dr. Vold shared his perspective on glaucoma devices at the Glaucoma Symposium during the 2017 Glaucoma 360 meeting.
In the past, cyclophotocoagulation performed via a transscleral approach was reserved as a last-resort procedure for end-stage glaucoma. Today, cyclophotocoagulation using micropulse laser technology (MicroPulse P3, Iridex) is a sutureless procedure that effectively reduces IOP and medication use with greater safety, said Dr. Vold.
“We are still learning how to titrate the treatment effect with diode laser cyclophotocoagulation, but the availability of a new illuminated probe is expected to enable titration of the treatment effect with enhanced precision,” he added.
Trabecular bypass procedures
Gonioscopy-assisted transluminal trabeculotomy (GATT) is an ab interno, sutureless, conjunctival-sparing procedure developed by Ronald Fellman, MD, and Davinder Grover, MD. It can be performed under topical anesthesia through a small incision, 1.8 mm to 2.4 mm, and creates a 360º trabeculotomy.
The iStent trabecular micro-bypass stent (Glaukos) was the first FDA-approved MIGS device. Two next-generation trabecular micro-bypass stents, the iStent Inject (Glaukos) and Hydrus Microstent (Ivantis), are being investigated in U.S. IDE studies.
The idea for the iStent Inject, which received the CE Mark in 2009, comes from evidence that IOP lowering is enhanced by placement of multiple iStents. Using two stents, iStent Inject allows for two access points through the trabecular meshwork (TM), expanding potential outflow through Schlemms canal, said Dr. Vold.
“The device is easily inserted, and that can make it an attractive procedure for cataract surgeons who do not do a lot of angle surgery,” Dr. Vold added.
The Hydrus Microstent received the CE Mark in 2011. It is a nitinol device that creates an entry point through the TM and stents open several clock hours to enhance aqueous outflow through Schlemms canal.
“This procedure has worked well in our patients thus far,” Dr. Vold said. “We now have encouraging results with 5 years of follow-up.”
He added that in the future, the procedure may be modified with a YAG laser to create additional access to the collector channels thus enhancing outflow if there is need to augment the IOP-lowering effect long-term.
Enhancing uveoscleral outflow
The CyPass Micro-Stent (Alcon Laboratories), approved by the FDA in 2016, and the iStent Supra (Glaukos), which is still investigational, lower IOP by increasing uveoscleral outflow. Discussing this mechanism, Dr. Vold referred to the benefit of prostaglandin analogues.
“Prostaglandin analogues have a substantial IOP-lowering effect,” Dr. Vold explained. “We know they act by increasing uveoscleral outflow. In fact, uveoscleral outflow is considered to be IOP-independent and contributes up to 57% of natural aqueous outflow.”
Dr. Vold pointed out that by tapping into the uveoscleral outflow pathway bypasses Schlemms canal and collector channels, which may be atrophic in glaucoma patients. The hope for these devices is to provide significant IOP lowering with the safety profile similar to cataract surgery alone.
The CyPass Micro-Stent is a supraciliary device that had impressive efficacy in clinical trials, reducing IOP in patients with mild-to-moderate glaucoma by up to 35% while reducing medication use. Recently published results from the U.S. pivotal trial, COMPASS, reported 93% of patients achieved an IOP <18 mm Hg without medications.
“We now have 7.5 years of experience with this device, and the long-term data are also impressive,” Dr. Vold said.
There also is potential to increase the IOP-lowering effect achieved with the CyPass Micro-Stent by delivering viscoelastic to the supraciliary and suprachoroidal spaces to create and maintain a space for enhanced aqueous outflow. If that approach proves effective, this device may be considered in eyes with more moderate or advanced glaucoma, Dr. Vold said.
The platform also may be used as a sustained-release drug delivery system and for treating retinal neovascular disease.
Subconjunctival filtration procedures
The XEN Gel stent (Allergan), also approved by the FDA in 2016, and the investigational InnFocus Microshunt Glaucoma Drainage System (InnFocus), lower IOP by creating a pathway for aqueous humor outflow to the subconjunctival space. The XEN Gel stent represents the third generation of the device. Featuring a 45-µm lumen, its design provides good IOP lowering while protecting against hypotony.
With follow-up to 1 year after implantation of the current XEN Gel stent, IOP was reduced by 40% and medication burden by 85%. Data from 3 years of follow-up with earlier iterations of the device show sustained efficacy.
The procedure for implanting the XEN Gel stent is a sutureless procedure that involves a needle stick. Mitomycin-C is used, and a bleb is created, but it is an ab interno procedure, where the filtration bleb is lower lying and less avascular than the blebs created with ab externo procedures, such as trabeculectomy or the ExPress Glaucoma Filtration Device (Alcon Laboratories), Dr. Vold said.
“Up to 25% of the blebs following the XEN implant procedure require needling, but my sense is that as we gain experience, we can potentially reduce the needling rate to 5% to 10%,” he added.
Which device for which patient
Dr. Vold said that in the future, patient-specific imaging and diagnostics will enable individualized surgical decision-making.
“It would be nice if we could optimize the results for each patient by determining if he or she would benefit most from a trabecular bypass procedure versus a supraciliary approach or subconjunctival surgery,” Dr. Vold said.
Until such guidance is available, Dr. Vold suggested that trabecular bypass procedures may be considered for patients with mild disease or who have not been on medications long-term, based on the expectation that they still have a functioning collector system.
Implantation of a supraciliary device could be considered an excellent option for patients with mild-to-moderate glaucoma. Considering the favorable safety profile of these surgeries, both trabecular bypass and supraciliary procedures are being considered for early glaucomatous disease.
Dr. Vold said the subconjunctival microshunts are a promise option for treating moderate-to-advanced glaucoma. Compared with the trabecular micro-stents and supraciliary implants, subconjunctival microshunt surgery may be less likely to be adopted by comprehensive ophthalmologists and cataract surgeons.
“My sense is that surgeons interested in implanting the subconjunctival devices will have previous experience dealing with filtration blebs,” he said.
Finally, the future may combine aqueous outflow implants with drug delivery to achieve the best long-term results.
“We need to think of glaucoma as not just a medical disease or just a surgical disease, but rather as an interventional disease, where even laser trabeculoplasty and micropulse cyclophotocoagulation will have roles for management earlier in the disease process than they have in the past,” Dr. Vold said.