The Hydrus on a quarter
The Trabectome handpiece tip
The SOLX Gold Shunt after
Source: Ike K. Ahmed, M.D.
The CyPass MIGS device
Source: Transcend Medical
remain the standard
surgical choice, but
others may be safer
Editors' note: This column discusses
devices not commercially available in the U.S.
The pros and cons of
trabeculectomy have not radically changed over the decades—the technique
involves moving the aqueous away from the anterior chamber to the subconjunctival space.
"No other procedure will get a patient out of [intraocular pressure (IOP)] trouble as quickly as a trab," said Thomas W. Samuelson, M.D., Minnesota Eye Consultants, Minneapolis. "This rapid and often dramatic IOP reduction is worth the risk in far advanced patients but less so in early disease. There's always been a void for the early-to-moderate visual field loss patients."
The influx of several different types of devices (most of which are not commercially available in the U.S.) has allowed surgeons to start tailoring surgical treatment options at earlier phases in the disease. With almost 60 million people worldwide affected by glaucoma, these kinds of individualized treatments will become more commonplace, experts said. With patient non-compliance a significant factor in treatment, the newer surgical devices may allow glaucoma specialists to bypass that issue altogether. The latest devices can be categorized into ab interno, ab externo, or bleb forming, said Iqbal "Ike" K. Ahmed, M.D., assistant professor of ophthalmology, University of Toronto, and most are micro-incisional glaucoma surgery (MIGS).
Dr. Samuelson said he prefers "micro-incisional" to describe procedures that utilize enhanced microsurgical techniques and "minimally invasive" to describe procedures that are both micro-invasive and have lower risk. Very few procedures are both micro-incisional and minimally invasive. For example, procedures such as canaloplasty (iScience Interventional, Menlo Park, Calif.) might be considered lower risk, but certainly are not micro-incisional. Conversely, the EX-PRESS Glaucoma Filtration Device (Alcon, Fort Worth, Texas), which uses a short tube under the scleral flap to help make trab more successful, is micro-incisional, but "anything that might subject the eye to hypotony carries risk, so I would not qualify it as
Dr. Ahmed added BAGS—or blebless ab externo glaucoma surgery—to the growing list of acronyms to better incorporate the SOLX Gold Shunt (SOLX, Waltham, Mass.) and canaloplasty. The benefit of either BAGS or MIGS is an improved safety profile compared with trabeculectomy, he said.
"To me, as soon as we do a
scleral dissection, we're no longer discussing MIGS," he said. To quickly differentiate, he said MIGS IOP targets are typically a little higher, with more mild-to-moderate patients; BAGS are reserved for a bit more aggressive surgery where IOP reduction is greater but the risks are higher as well; and finally, traditional bleb-forming surgery is "the ultimate in efficacy" but exposes
patients to higher risks.
"All these new procedures must be trying to challenge the standard of trabeculectomy," said Norbert Pfeiffer, M.D., professor of ophthalmology, University Medical Center, Mainz, Germany. "Trabeculectomy is far from ideal; we are looking for options that should at least be similar if not superior [to] the outcomes we've achieved with trabeculectomies in the past."
Whether any of these devices can eventually replace trabeculectomy will depend on the outcomes of clinical studies currently underway or those that have yet to be undertaken.
"It requires favorable results
before we can declare MIGS the new standard," Dr. Pfeiffer said.
With "over $500 million invested in the space," an increased interest from industry, and improved instrumentation, innovation will continue, Dr. Ahmed said.
new surgical technique
Patient selection is a major factor in how successful the newer devices might be.
"Not every device will work well for every patient, and understanding that is incredibly important," Dr. Ahmed said. The technical side of performing these newer procedures differs from trab, and surgeons need to plan for a slight learning curve, Dr. Samuelson said.
"You're performing anterior chamber angle surgery," Dr. Pfeiffer said, referring to the Hydrus Intracanalicular Implant (Ivantis, Irvine, Calif.), a canalicular scaffold that increases outflow facility by bypassing the trabecular meshwork and dilating Schlemm's canal to increase circumferential flow. "We're working in a part of the eye that's not easily visible. Surgeons need to be comfortable with the anatomy and know where Schlemm's canal is before using these devices." Additionally, he noted the newer devices mandate a bimanual surgical approach with a gonioscope in one hand that is more technically challenging.
Ab interno procedures
Fortunately, MIGS procedures "are very forgiving," Dr. Ahmed said. "There's not a lot of downside to these procedures."
With MIGS, there are a lot of options. Subtle differences exist between the devices, and experts agree additional studies will vet out long-term risks associated with the devices.
The iStent (Glaukos, Laguna Hills, Calif.) works by placing the
device directly into Schlemm's canal; second- and third-generation devices are also being developed for implantation into Schlemm's via the trabecular meshwork (iStent inject) or into the suprachoroidal space
"The iStent is a bit more minimalist than other devices," Dr. Samuelson said. "At 1 mm long, the potential for disrupting the anatomy is small, and it can be titrated if necessary." At 8 mm, "the Hydrus is
recruiting more collector channels, and there's a better chance of increased IOP reduction, when compared to a single iStent," he said. Studies by Dr. Ahmed and others have shown that mean IOPs of 15 mm Hg or less can also be attained by implanting two iStent devices.
At 6 months, Dr. Pfeiffer's group reported "the majority of patients were medication free in the [Hydrus Intracanalicular Implant] eye," he said, with a mean IOP drop of about seven points from baseline in one study and almost nine points in another study. Both Drs. Ahmed and Samuelson were part of a study that showed the Hydrus induced a 92% increase in outflow facility.
The Trabectome (NeoMedix, Tustin, Calif.) is used for ab interno trabeculectomy to decrease outflow resistance, employs high-frequency electrocautery, and is typically part of a phacotrabeculectomy procedure.
"An ongoing debate is whether it's better to cauterize or to stent," Dr. Ahmed said.
The CyPass (Transcend Medical, Menlo Park, Calif.) is a MIGS device inserted into the suprachoroidal space during routine cataract surgery, immediately after IOL implantation. The SOLX Gold Shunt is an ab externo approach that requires more dissection than other devices involving this space, Dr. Samuelson said.
"There's no head-to-head comparisons between the CyPass, the Glaukos suprachoroidal device (G-3), or the SOLX, but it is clear that the SOLX is going to have to work much better than the others to justify the additional dissection necessary for implantation," Dr. Samuelson said.
Looking down the road, once the investigational devices are approved for use in the U.S., Dr. Samuelson said trab will still be an important procedure, "but we'll match the appropriate disease risk to the inherent risk of each surgery. There's no need to subject someone with mild-to-moderate glaucoma and minimal field loss to a filtration bleb."
Dr. Ahmed agreed, noting patients on one medication with controlled IOP don't necessarily need glaucoma surgery, but those who are on two or three medications and/or not well controlled could benefit from the newer MIGS procedures.
"Schlemm's canal is arguably the safest place to work, but it's technically the most difficult," he said, "while the suprachoroidal space is the easiest place to work." The key will be perfecting the tradeoff between acceptable risk and desired outcomes, he said.
Editors' note: Dr. Ahmed has financial interests with Alcon, AqueSys (Irvine, Calif.), Glaukos, Ivantis, NeoMedix, and Transcend Medical. Dr. Pfeiffer has financial interests with Ivantis. Dr. Samuelson has financial interests with Abbott Medical Optics (Santa Ana, Calif.), Alcon, AqueSys, Glaukos, and Ivantis.
Ahmed: 416-625-3937, firstname.lastname@example.org
Pfeiffer: 49 6131 17 7085, email@example.com