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More data needed on viability of new minimally invasive glaucoma surgery options
 Elie Dahan |
The development of minimally invasive surgery for glaucoma has been particularly dynamic recently because the classic available techniques — trabeculectomy and silicone tubes — have failed to provide safe surgery in the short and long term.
During the last two decades, blebless surgery has already been attained to a certain degree in the form of nonpenetrating glaucoma surgery (NPGS), which includes deep sclerectomy, viscocanalostomy and the more recent canaloplasty (iScience). NPGS in all its forms has found adept supporters mainly in Europe and South Africa, while in North America and Great Britain, glaucoma surgeons doubted its efficacy mainly because of its long learning curve. Articles on the comparison between penetrating and nonpenetrating techniques have been published mainly by glaucoma surgeons who were proficient with trabeculectomy but did not reach the minimum 200 procedures required to attain an acceptable level of adeptness in NPGS.
The few articles that demonstrate the short-term safety and the long-term efficacy of NPGS have been published by authors who have performed thousands of these dexterity-demanding operations. There is some hope, though, that NPGS will still be popularized with the recent development of CO2 Laser Assisted Filtration Surgery (CLASS) by IOPtima. CLASS has a short learning curve because the creation of the deep sclerectomy under the first scleral flap and the delicate unroofing of Schlemm’s canal is performed with a CO2 laser system adapted to the surgical microscope. The ablation of scleral tissue is gradually and safely performed by the CO2 laser system with low risk of perforation because of its inherent characteristics of blockage by water. The average glaucoma surgeon who is capable of dissecting a 5 mm x 5 mm scleral flap will be able to perform a CO2 laser NPGS after a short wet lab with the IOPtiMate system.
MIGS
The popularization of the Ex-PRESS miniature glaucoma drainage device (Alcon) during the last decade is due to its straightforwardness and its short learning curve when compared to the NPGS techniques. Ex-PRESS implantation is a minimally invasive glaucoma surgery (MIGS) compared with trabeculectomy or silicone tubes, but many consider it a standardized trabeculectomy with safer characteristics. Its innovative traits include its metallic material and its miniature size compared with silicone tubes. Depending on the surgeon’s personal technique, the Ex-PRESS can produce blebs similar to trabeculectomy when the scleral flap is approximately 3 mm x 3 mm or be virtually blebless when the scleral flap is as large as 5 mm x 5 mm, as in the NPGS techniques. A recent article that compared trabeculectomy and the Ex-PRESS procedure in a prospective and randomized manner in the same patient showed higher complete success rates in the latter.
The success of the Ex-PRESS has led to the emergence of other new miniature metallic — i-Stent (Glaukos), Solx Gold Shunt, AquaSys — and non-metallic — CyPass (Transcend Medical), Hydrus (Ivantis) — glaucoma devices whose inventors tried to gain more ground in the search for blebless MIGS. The i-Stent, AquaSys and Hydrus devices try to lower IOP by reducing or bypassing the trabecular meshwork resistance, whereas the Solx and CyPass try to reduce IOP by directing the aqueous to the suprachoroidal space. All of these devices still have to prove their efficiency on a large scale, whereas the Ex-PRESS is already reaching the mark of 100,000 implantations worldwide since receiving the CE mark and being approved by the U.S. Food and Drug Administration in the early 2000s.
The available data for these newer devices are limited, and only time and large-scale studies will determine their future.
Other possibilities
The Trabectome (NeoMedix), which aims to ablate the trabecular meshwork through a small limbal incision, is probably efficient when performed in conjunction with cataract extraction in mild glaucoma cases, but it fails to provide large IOP reduction in more severe forms of glaucoma.
The reason for this limitation is probably due to the fact that resistance to outflow exists not only in the trabecular meshwork but also downstream in the fine plexuses between the external wall of Schlemm’s canal and the aqueous veins.
Canaloplasty does not stand on its own as a new MIGS procedure because it is merely an NPGS technique (viscocanalostomy) “augmented” by a suture that exerts tension on the trabecular meshwork. The fiber optic used during canaloplasty, with its red LED light running through Schlemm’s canal, has probably fascinated glaucoma surgeons who, in the not-distant past, have disregarded NPGS. There are no studies that report on IOP reduction by intracanalicular tension suture alone. In other words, exerting tension on the trabecular meshwork with a suture only, without performing NPGS, will most probably fail to yield significant IOP reduction.
The few available recent articles that compare NPGS alone and canaloplasty show good efficiency in both procedures with some added IOP reduction in the latter. It is time to remember that NPGS has been with us for two decades with tens of thousands of patients often well-controlled by surgery only. NPGS, in all its variants, is still preferred as the procedure of choice by those who have performed it regularly and frequently for years.
It is interesting, though, that a trend opposite to MIGS is on its way in the U.S., with the Tube Versus Trabeculectomy Study aiming to demonstrate that silicone tubes, a highly invasive glaucoma surgery, are superior to trabeculectomy, the less invasive standard.
References:
Arriola-Villalobos P, Martínez-de-la-Casa JM, Díaz-Valle D, Fernández-Pérez C, García-Sánchez J, García-Feijoó J. Combined iStent trabecular micro-bypass stent implantation and phacoemulsification for coexistent open-angle glaucoma and cataract: a long-term study [published online ahead of print Jan. 23, 2012]. Br J Ophthalmol. doi:10.1136/bjophthalmol-2011-300218.
Carassa RG, Bettin P, Fiori M, Brancato R. Viscocanalostomy versus trabeculectomy in white adults affected by open-angle glaucoma: a 2-year randomized, controlled trial. Ophthalmology. 2003;110(5):882-887.
Dahan E, Ben Simon GJ, Lafuma A. Comparison of trabeculectomy and Ex-PRESS implantation in fellow eyes of the same patient: a prospective, randomised study [published online ahead of print Feb. 17, 2012]. Eye (Lond). doi:10.1038/eye.2012.13.
Dahan E, Carmichael TR. Implantation of a miniature glaucoma device under a scleral flap. J Glaucoma. 2005;14(2):98-102.
Dahan E, Drusedau MU. Nonpenetrating filtration surgery for glaucoma: control by surgery only. J Cataract Refract Surg. 2000; 26(5):695-701.
Gilmour DF, Manners TD, Devonport H, Varga Z, Solebo AL, Miles J. Viscocanalostomy versus trabeculectomy for primary open angle glaucoma: 4-year prospective randomized clinical trial. Eye (Lond). 2009;23(9):1802-1807.
Koerber NJ. Canaloplasty in one eye compared with viscocanalostomy in the contralateral eye in patients with bilateral open-angle glaucoma. J Glaucoma. 2012;21(2):129-134.
Maris PJ Jr, Ishida K, Netland PA. Comparison of trabeculectomy with Ex-PRESS miniature glaucoma device implanted under scleral flap. J Glaucoma. 2007;16(1):14-19.
Mermoud A, Schnyder CC, Sickenberg M, Chiou AG, Hédiguer SE, Faggioni R. Comparison of deep sclerectomy with collagen implant and trabeculectomy in open-angle glaucoma. J Cataract Refract Surg. 1999;25(3):323-331.
O’Brart DP, Shiew M, Edmunds B. A randomised, prospective study comparing trabeculectomy with viscocanalostomy with adjunctive antimetabolite usage for the management of open angle glaucoma uncontrolled by medical therapy. Br J Ophthalmol. 2004;88(8):1012-1017.
For more information:
Ton Y, Geffen N, Kidron D, Degani J, Assia EI. CO2 laser-assisted sclerectomy surgery part I: concept and experimental models. J Glaucoma. 2012;21(2):135-140.
Elie Dahan, MD, is an OSN Europe Edition Board Member. He can be reached at Ein Tal Eye Center, 17 Brandeis St., Tel Aviv 62001, Israel; email: elie.dahan@gmail.com.
Disclosure: Dr. Dahan is a consultant for Alcon and IOPtima.