Novel procedures bring glaucoma surgery into realm of cataract, corneal subspecialists
Microinvasive glaucoma surgery can achieve a modest IOP target with a good safety profile for appropriately selected patients with open-angle glaucoma.
By Cheryl Guttman Krader; Reviewed by Leon W. Herndon, MD
Durham, NC-Microinvasive glaucoma surgery (MIGS) is an emerging category that can be readily learned by cataract surgeons and corneal subspecialists.
“However, the need for close surveillance of the [patient with] glaucoma must still be kept in mind,” said Leon W. Herndon, MD, associate professor of ophthalmology, Duke University Eye Center, Durham, NC. “Randomized trials are needed to determine the efficacy of the MIGS procedures compared with trabeculectomy, which remains the gold standard for incisional glaucoma surgery.”
The reason why non-glaucoma specialists would be interested in learning MIGS procedures relates to data on the prevalence of comorbid cataract and glaucoma combined with the benefits of MIGS procedures.
“In the United States alone, more than 3 million cataract procedures are performed each year, and more than 650,000 [patients with] cataracts have co-existing glaucoma or ocular hypertension,” Dr. Herndon said.
“Cataract surgery by itself can lower IOP, but most patients still need medication for IOP control,” he said. “MIGS procedures performed with an ab interno surgical approach cause minimal tissue trauma, are associated with a better safety profile and faster recovery than traditional filtering surgery, and do not preclude the success of more aggressive surgical intervention if it is needed in the future.”
The MIGS procedures seek to avoid bleb formation and rely on augmentation of the physiologic outflow pathways. These techniques, which include the microbypass trabecular stent (iStent, Glaukos) and ab interno trabeculectomy (Trabectome, NeoMedix), are appropriate for patients with mild-to-moderate glaucoma because they achieve a modest IOP target (~15 to 16 mm Hg). Eligible patients also are limited to those with an open angle and must be able to tolerate topical medications, which will probably still be needed to some degree after surgery, Dr. Herndon said.
Describing some published results from the MIGS procedures, Dr. Herndon said that in a study of 304 patients who had concurrent cataract surgery with ab interno trabeculectomy, mean IOP decreased from 20 mm Hg at baseline to 15 mm Hg at 1 year. The medication requirement was also significantly reduced.
“There were very few complications, but 78% of eyes developed some hyphema,” he said.
In the U.S. IDE study of the microbypass trabecular stent, 240 eyes were randomly assigned to undergo cataract surgery alone or with the stent. After 1 year, the proportion of eyes achieving IOP of 21 mm Hg or less without medication was significantly higher in the combined group compared with the controls having cataract surgery alone (73% versus 50%). A significant difference in this endpoint favoring the combined group was maintained at 2 years (61% versus 50%).
Studies have also been undertaken evaluating outcomes after implantation of multiple stent devices. In a study where patients underwent cataract surgery and received two or three stents, there was a trend for IOP to be lower in the group with two stents compared with those with three stents implanted. However, the average daily medication use was significantly lower for eyes with three stents implanted.
The Schlemm’s canal scaffold (Hydrus, Ivantis [not FDA approved]), is still being evaluated in a U.S. IDE study. The device has the CE mark, and early European data show that its use results in IOPs in the mid-teens at 1 year.
Dr. Herndon also noted that compared with the above procedures, a lower IOP target (<13 mm Hg) can be achieved with a trabeculectomy-type procedure (Ex-PRESS shunt, Alcon Laboratories). This “kinder and gentler trabeculectomy” can be performed in eyes with open or narrow angles. Based on its IOP-lowering efficacy, it might be considered appropriate to manage eyes with moderate-to-advanced glaucoma, those with progressive normal-pressure glaucoma, and for patients with intolerance to most medications, Dr. Herndon said.
Cornea surgeons who might be interested in performing MIGS should familiarize themselves with intraoperative gonioscopy, Dr. Herndon suggested.
“After implanting the IOL, deepen the anterior chamber, tilt the patient’s head about 35º away from yourself, and angle the microscope about 35º toward yourself,” Dr. Herndon said. “Then place a surgical gonioprism on the cornea with the non-dominant hand and use a Sinskey hook or similar instrument in the dominant hand to approach the angle and mimic the subtle wrist pronation needed for implantation.”
Leon W. Herndon, MD
Dr. Herndon is a consultant and lecturer for Alcon Laboratories and Glaukos. This article is adapted from Dr. Herndon’s presentation during Cornea 2012 at the annual meeting of the American Academy of Ophthalmology.