Surgical procedures aimed to lower IOP with little tissue trauma

By Cheryl Guttman Krader

New generation of surgical procedures for glaucoma are being performed with good facility and encouraging safety and efficacy results. Now, time will tell whether these techniques maintain their initial promise and how they impact the treatment algorithm for glaucoma, reported Steven D. Vold, MD.

Steven D. Vold, MD, demonstrates the proper OR microscope position for inserting the Hydrus Microstent.

“Our standard surgical procedures for glaucoma are effective in lowering IOP, but their benefit occurs with costs that include loss of best-corrected vision,” said Dr. Vold, who is in private practice, Fayetteville, AR. “The premise for developing new surgeries was to create minimally invasive techniques that would be associated with good efficacy, but better safety and more rapid patient recovery so that they might be used to intervene earlier than we do now with trabeculectomy or tube shunt surgery.”

Dr. Vold pointed out “these new procedures are also allowing comprehensive cataract surgeons to expand their practice into surgical glaucoma.”

He reviewed the two newer glaucoma surgeries that have FDA approval–the ab interno trabeculotomy (Trabectome, NeoMedix) and the microbypass trabecular stent (iStent, Glaukos)–and the array of procedures that are still investigational.

The ab interno trabeculotomy procedure uses a proprietary device to remove tissue at the level of the juxtacanalicular trabecular meshwork and inner wall of Schlemm’s canal. The procedure can be done as stand-alone surgery, although Dr. Vold said he generally combines it with cataract surgery.

Results from clinical trials demonstrate that the combination approach results in greater IOP-lowering compared with cataract surgery alone, as well as a more persistent treatment benefit. In a Kaplan-Meier survival analysis of clinical trial data, estimated success rates at over 24 months were 80% for eyes undergoing the combined procedure compared with just 45% for those having only cataract surgery.

Little more skill

The microbypass stent procedure, which also involves an ab interno approach, is designed to restore continuous physiologic outflow by creating a patent bypass through the trabecular meshwork to Schlemm’s canal. Performing the implantation involves a short learning curve that requires understanding of the local anatomy.

Proper placement of Glaukos iStent SupraResults of the U.S. IDE trial showed that a significantly higher proportion of patients undergoing stent placement with cataract surgery achieved the primary endpoint at 1 year (IOP ≤21 mm Hg without medication) compared with controls having cataract surgery alone, 72% vs. 50%, respectively.  The procedure also had a good safety profile, although it has been criticized for its somewhat modest IOP-lowering effect.

“There is evidence that greater IOP lowering, potentially to levels in the low teens, can be achieved with implantation of two or three stents,” said Dr. Vold. “Ongoing studies are evaluating whether image-guided positioning of the stent could lead to better outcomes.”

Glaukos has two other products in development: one designed for precise and predictable automated insertion of multiple microbypass trabecular stents into the eye (iStent Inject) and the other being an ab interno suprachoroidal stent (iStent Supra) for improving uveoscleral outflow.

Two well-placed iStents

Ivantis has developed and is evaluating a flexible “scaffold” (Hydrus) to permanently dilate and support Schlemm’s canal. Made of nitinol, the device measures about 3 clock-hours in length and is designed to re-establish flow to multiple collector channels. 

Early clinical data from a cohort of patients showed mean IOP was reduced from 20.3 mm Hg while on two medication at baseline to about 15 mm Hg at 6 months with the use of only 0.2 medications on average.

Fully enrolled

Transcend Medical is developing a polyimide suprachoroidal micro-stent (CyPass Micro-Stent) for implantation in an ab interno approach. The pivotal U.S. trial is now fully enrolled with more than 500 patients and is investigating the procedure done in combination with cataract surgery. However, the device is currently available in Europe where it is being used as a stand-alone procedure as well.

Transcend CyPass Micro-Stent is placed in a precise location just below the surface of the eye to create a new pathway for the drainage of fluid, thereby reducing IOP. (Photos courtesy of Steven Vold, MD)

“Early trial results are encouraging, indicating the combined procedure results in about 35% IOP-lowering with a reduction in medication use,” said Dr. Vold. “There are positive data from follow-up that is available over 4 years for the earliest patients who received this device from both inside and outside the United States.”

AqueSys is conducting a clinical trial in the United States investigating its soft stent (XEN gel stent) that is designed to provide controlled aqueous outflow through the subconjunctival pathway. The surgery is done through a corneal incision, and the U.S. trial is enrolling patients with refractory glaucoma. The device is available in Europe and, when used as a primary surgical procedure, was shown to reduce IOP to the mid-teens and to have durable efficacy.

“This is potentially a much safer and faster procedure than traditional trabeculectomy, and it has a much shorter recovery period,” Dr. Vold added.

A similar microshunt device being developed by InnFocus (previously known as the MIDI Arrow) is currently being investigated for placement in an ab externo approach, although ab interno surgery seems feasible, according to Dr. Vold. Early results from a small study outside the United States show that it consistently lowers IOP to the low teens whether performed as a stand-alone procedure or combined with cataract surgery.