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Twenty-two of 23 eyes with a trans-scleral micro-lumen aqueous drainage tube implanted after failing maximum tolerated medication were evaluable at 3 years.
TAKE HOME MESSAGE: Twenty-two of 23 eyes with a trans-scleral micro-lumen aqueous drainage tube implanted after failing maximum tolerated medication were evaluable at 3 years.
Reviewed by Juan F. Batlle, MD
Santo Domingo, Dominican Republic-Implantation of a trans-scleral micro-lumen aqueous drainage tube (InnFocus MicroShunt, InnFocus)-as a standalone procedure or combined with cataract surgery-is safe and provides sustained lowering of IOP while reducing the need for medication, said Juan F. Batlle, MD.
Results from three years of follow-up in a prospective non-randomized trial were highlighted by Dr. Batlle, director, Centro Laser, and director, Elias Santana Charity Hospital, Santo Domingo.
Dr. Batlle is an investigator in the study enrolling 23 eyes considered eligible for trabeculectomy after failing maximum tolerated glaucoma medication. The trans-scleral aqueous drainage tube was implanted alone in 14 eyes and combined with cataract surgery in 9 eyes. In all cases, mitomycin-C (MMC) 0.4 mg/mL was applied intraoperatively for 3 minutes.
Twenty-two eyes were available for follow-up at 3 years. Mean IOP was 23.8 ± 5.3 mm Hg preoperatively and reduced at last follow-up by 55% to 10.7 ± 3.5 mm Hg. Mean daily medication use was reduced from 2.4 ± 0.9 to 0.5 ± 0.9.
Twenty-one (95%) eyes met the criteria for qualified success (IOP ≤ 21 mm Hg and ≥ 20% reduction in IOP from baseline with or without medication), and complete success, defined by the same IOP criteria without medication, was achieved by 16 (73%) eyes.
The most common complications encountered in the series were immediate postoperative hypotony, which occurred in 3 eyes (13%), and transient choroidal effusion in 2 eyes (8.7%). All of those events were transient and resolved spontaneously without sequelae, and there were no sight-threatening adverse events.
Ins and outs of the procedure
“The trans-scleral drainage tube shunts aqueous humor from the anterior chamber to a bleb formed under the conjunctiva and Tenon’s capsule, bypassing the trabecular meshwork, Schlemm’s canal, the collector channels, and the aqueous veins,” Dr. Batlle said. “Therefore, it has the same mechanism of IOP-lowering as trabeculectomy.
“The results from this study and from other patients I have followed now for over 5 years show that that this procedure also provides IOP reductions that are comparable to those seen with trabeculectomy and exceeding those achievable using canal-based devices that bypass only the trabecular meshwork,” Dr. Batlle said.
However, compared with trabeculectomy, the trans-scleral drainage tube procedure is a faster procedure that eliminates the need for scleral surgery, iridectomy, and suture tension adjustment, he said.
Furthermore, it is minimally invasive surgery that causes little trauma to the eye and allows for faster vision recovery with less pain and a quicker return to work for patients than trabeculectomy, Dr. Batlle added.
“It is the only glaucoma surgery where I can go to bed not worrying about seeing an IOP spike or severe hypotony when the patient returns for follow-up the next day,” he said.
The aqueous drainage tube is implanted ab externo through a 3 mm-long needle tract in the sclera and provides a pathway for aqueous humor to drain from the anterior chamber to beneath the conjunctiva and Tenon’s capsule.
Experiencing the benefits
“During my career, I have probably implanted every kind of glaucoma device, and that experience allows me to really appreciate the benefits of the trans-scleral drainage tube,” Dr. Batlle said.
“As the implantation is an ab externo procedure, I can directly control placement of the device in eyes with narrow or wide angles, and I am able to achieve target IOP through manipulations that include enlarging the sub-conjunctival/Tenon’s flap and/or applying different concentrations of MMC,” he explained.
In addition, Dr. Batlle noted he can stop episcleral bleeding by cauterization-which is important for preventing bleb fibrosis-and that he has the ability to confirm flow and control placement of the distal tip of the device under the Tenon’s flap.
Devices placed in an ab interno approach do not allow for these maneuvers.
Dr. Batlle also highlighted benefit of the novel biomaterial from which the device is constructed-poly(styrene-block-isobutylene-block-styrene) (SIBS).
“SIBS is soft and conforms to the curvature of the eye, and it is particularly remarkable in the fact that it does not encapsulate,” he said. “Therefore, the drainage tube remains patent and a revision procedure can be done if the bleb fails.”
“While the tube device is usually repairable, in a worst-case scenario, I can place another device next to the first or in another quadrant,” Dr. Batlle said. “In contrast, most other devices that have been developed for minimally invasive glaucoma surgery are a one-shot deal-if they don’t work, they can’t be fixed.”
To his knowledge, the trans-scleral aqueous drainage tube is the only new glaucoma device that is being investigated in a randomized, controlled study comparing it against trabeculectomy, Dr. Batlle noted.
“I look forward to this implant becoming commercially available,” he said. “I plan to use it in earlier-stage patients who are developing progressive nerve damage because of poor medication adherence.”
Juan F. Batlle, MD
This article is adapted from Dr. Batlle’s presentation at the 2015 meeting of the American Society of Cataract and Refractive Surgery. Dr. Batlle is a consultant/advisor to InnFocus and to other companies with products for treatment of glaucoma.