Elsevier

Survey of Ophthalmology

Volume 57, Issue 1, 2 January 2012, Pages 1-25
Survey of Ophthalmology

Major Review
The Changing Conceptual Basis of Trabeculectomy: A Review of Past and Current Surgical Techniques

https://doi.org/10.1016/j.survophthal.2011.07.005Get rights and content

Abstract

The original intent of glaucoma surgery was to allow aqueous humor to exit more easily either through the sclera or into the suprachoroidal space. The former came to be called, generically, a glaucoma filtering procedure. As this surgery evolved, some explored the concept of lowering pressure without producing a hole in the sclera, with its resultant “filtering bleb.” For example, Cairns hoped that cutting open the edges of Schlemm’s canal would allow aqueous to leave without producing a filtering bleb; however, it became apparent that Cairns’s “trabeculectomy” only worked when a filtering bleb developed. The goal of today’s trabeculectomy is the creation of a longlasting transscleral fistula. In fact, trabeculectomy is a misnomer as excision of trabecular meshwork is unimportant. Frequently, the tissue excised to create a trans-scleral fistula is sclera, cornea, or both. The current trabeculectomy is really a guarded sclerokeratectomy. Newer techniques hope to increase aqueous outflow through Schlemm’s canal to avoid complications associated with subconjunctival filtering blebs. Non-penetrating glaucoma surgeries (deep sclerectomy, viscocanalostomy) and ab interno trabecular surgery attempt to lower intraocular pressure with bleb-less procedures. We describe the recent evolution of glaucoma surgery, particularly the idea that intraocular pressure may be lowered satisfactorily without creating a filtering bleb.

Introduction

When introduced almost a half-century ago, trabeculectomy gained widespread acceptance in surgical management of glaucoma because low intraocular pressure (IOP) was achieved with fewer complications than those associated with competing procedures. The search for better results continues today as trabeculectomy itself has been modified to improve success rates and reduce complications. Interestingly, the original intention of pioneers in trabeculectomy was to lower IOP without transscleral filtration and the development of a filtering subconjunctival bleb. However, their efforts yielded the guarded filtration procedure that remains the mainstay of modern glaucoma surgery. Today, surgical innovation has returned to the concept of bleb-less glaucoma surgery, with procedures such as deep sclerectomy and viscocanalostomy.

In his seminal paper, Cairns described the goal of trabeculectomy as excising a short length of the Canal of Schlemm, with its trabecular adnexae, thus leaving two cut ends opening directly into aqueous humor, with no trabecular tissue remaining as a barrier at that point, and restoring the integrity of the corneoscleral coat over the area of the excision.34 Although naming this procedure trabeculectomy was appropriate (because trabeculum was removed to open Schlemm’s canal), the procedure might also have been accurately called canalostomy. Importantly, the objective of trabeculectomy was to lower IOP without inducing external filtration, but in Cairns’s initial cases, inadvertent blebs occurred in one-third of patients. Given the complication rates of full-thickness filtering procedures used at that time, Cairns viewed this result as undesirable. Pathology later showed fibrotic closure of the cut ends of Schlemm’s canal. Additionally, the presence of Schlemm’s canal in the trabeculectomy specimen did not correlate with outcomes.226 A filtering bleb was present in the majority of successful cases, and the amount of fluorescein-stained aqueous in the bleb correlated with success rates.226 Therefore, the procedure that started as a “trabeculectomy” actually worked as a guarded filtration procedure, but the nomenclature remained unchanged.

We will not use the word trabeculectomy in the rest of this review unless the procedure being discussed is, in fact, a trabeculectomy. When commenting on the operation typically performed today and commonly called “trabeculectomy” we will use more accurate terminology, such as “sclerokeratectomy,” or whatever actually describes the operative technique.

The aqueous humor leaves the eye through two pathways. The conventional pathway consists of aqueous humor passing through the trabecular meshwork (TM), across the inner wall of Schlemm’s canal into its lumen, and then into draining collector channels, aqueous veins, and finally the episcleral venous system, rejoining the bloodstream from whence it came.10, 89 The nonconventional or uveoscleral pathway may be traced through the uveal meshwork and anterior face of the ciliary muscle, the suprachoroidal space, and out through the sclera. The uveoscleral pathway carries less than 10% of total aqueous outflow.24 Studies on non-glaucomatous eyes have shown that total outflow facility decreases with age. Although Becker19 showed that in primary open-angle glaucoma patients the magnitude of decrease in outflow facility was similar to that reported for non-glaucomatous patients, Larsson et al142a concluded that the absolute value of outflow facility in open-angle glaucoma patients was significantly less than in age-matched controls.

The major site of resistance within the TM has not yet been well characterized; in normal eyes, however, the majority of outflow resistance occurs in the juxtacanalicular trabecular meshwork.5, 71, 116, 155, 183 In normal human eyes 75% of the resistance to the aqueous humor outflow is localized in the TM and 25% occurs beyond Schlemm’s canal.70, 92, 268 Importantly, this is not the case with well-developed glaucoma.66, 98, 99

To this point in this review we have considered the thinking that led those who developed trabeculectomy and the many modifications of trabeculectomy that followed. The goal was to develop a procedure for glaucoma that would be both most effective and least likely to cause complications. Because glaucoma was a condition that was defined by intraocular pressure above a certain level (usually 21 mm Hg), it seemed reasonable to set as a goal for surgery lowering the pressure below that.250 What has since become apparent is that the level of pressure tolerated by different eyes varies widely, some not having progressive optic nerve damage with high intraocular pressures and others rapidly losing vision with low pressures.

Additionally, there are suggestions that fluctuation, as well as the absolute level, of intraocular pressure may play a role in progressive damage to neural tissue.235, 251 It is entirely possible that there are some eyes in which such fluctuation is of importance, and others in which the absolute level is more important.

A changed understanding of glaucoma has led to a changed conceptual framework for glaucoma surgery. With a better knowledge of the precise level of intraocular pressure tolerated by a particular eye, whether or not fluctuation of intraocular pressure is important, and where the site of resistance to aqueous outflow lies for that particular eye, it should become possible to select which of a variety of glaucoma surgical procedures is most appropriate for that particular eye. We detail differences in concept and technique of transscleral or transcanal filtration techniques.

Section snippets

Aqueous Filtration Through Schlemm’s Canal (No Bleb)

The idea of performing trabeculectomy was based on the concept that outflow resistance resides mainly in the TM and inner portion of Schlemm’s canal.92 Sugar248 was the first to perform experimental trabeculectomy with a lamellar scleral flap on eye-bank eyes and then in a living human eye. When performed on a woman with pigmentary glaucoma, the procedure was not satisfactory in controlling IOP, though gonioscopy showed that a portion of the trabeculum had been excised. Sugar248 coined the term

Guarded Filtering Surgery

After it became apparent that the Cairns’s trabeculectomy functioned best in the presence of a subconjunctival filtering bleb, efforts were made to embrace the formation of blebs while minimizing complications. Fronimopoulos et al were the first to introduce the concept of “guarded filtration” by a scleral flap.82 This important modification of full-thickness fistulizing operations, which were the dominant procedures before the introduction of trabeculectomy, significantly reduced the risk and

Summary and Conclusion

Sugar248, 249 and Cairns34 devised a procedure to facilitate egress of aqueous through Schlemm’s canal by excising a fragment of the TM, determined experimentally to be the site of greatest outflow resistance. We now known that, in open-angle glaucoma, pathology may also exist more distal to the trabecular meshwork, especially in chronic forms.98, 99 The major reason for successful IOP reduction in Sugar’s and Cairns’s series was actually aqueous draining to the subconjunctival space. Modern

Method of Literature Search

In order to prepare this review we conducted a Medline and PubMed search of the literature for the period between 1960 and 2010 using the following key words as well as various combinations of them: trabeculectomy, guarded filtering surgery, mitomycin-C, 5-fluorouracil, amniotic membrane, anti-VEGF, beta radiation, non-penetrating glaucoma surgery, viscocanalostomy, deep sclerectomy, Trabectome, iStent, ab interno trabeculectomy, ab externo trabeculectomy, and canaloplasty. Reference lists from

VI. Disclosure

The authors reported no proprietary or commercial interest in any product mentioned or concept discussed in this article.

References (290)

  • T.M. Aaberg et al.

    Nosocomial acute-onset postoperative endophthalmitis survey. A 10-year review of incidence and outcomes

    Ophthalmology

    (1998)
  • A.M. Agbeja et al.

    Conjunctival incisions for trabeculectomy and their relationship to the type of bleb formation—a preliminary study

    Eye (Lond)

    (1987)
  • A. al-Hazmi et al.

    Effectiveness and complications of mitomycin C use during pediatric glaucoma surgery

    Ophthalmology

    (1998)
  • M.N. Alp et al.

    Nd:YAG laser goniopuncture in viscocanalostomy: penetration in non-penetrating glaucoma surgery

    Int Ophthalmol

    (2010)
  • J.A. Alvarado et al.

    Juxtacanalicular tissue in primary open angle glaucoma and in nonglaucomatous normals

    Arch Ophthalmol

    (1986)
  • A. Ambresin et al.

    Deep sclerectomy with collagen implant in one eye compared with trabeculectomy in the other eye of the same patient

    J Glaucoma

    (2002)
  • N. Anand et al.

    Deep sclerectomy augmented with mitomycin C

    Eye (Lond)

    (2005)
  • S.V. Araujo et al.

    A ten-year follow-up on a prospective, randomized trial of postoperative corticosteroids after trabeculectomy

    Ophthalmology

    (1995)
  • S. Arnavielle et al.

    Corneal endothelial cell changes after trabeculectomy and deep sclerectomy

    J Glaucoma

    (2007)
  • K.W. Ascher

    Aqueous veins; their status eleven years after their detection

    AMA Arch Ophthalmol

    (1953)
  • I. Ashkenazi et al.

    Risk factors associated with late infection of filtering blebs and endophthalmitis

    Ophthalmic Surg

    (1991)
  • N.N. Ashraff et al.

    Transconjunctival suture adjustment for initial intraocular pressure control after trabeculectomy

    J Glaucoma

    (2005)
  • A. Azuara-Blanco et al.

    Encapsulated filtering blebs after trabeculectomy with mitomycin-C

    Ophthalmic Surg Lasers

    (1997)
  • A. Azuara-Blanco et al.

    Dysfunctional filtering blebs

    Surv Ophthalmol

    (1998)
  • S. Babighian et al.

    Excimer laser trabeculotomy vs 180 degrees selective laser trabeculoplasty in primary open-angle glaucoma. A 2-year randomized, controlled trial

    Eye (Lond)

    (2010)
  • K. Barton

    Bleb dysesthesia

    J Glaucoma

    (2003)
  • A.D. Beck et al.

    Trabeculectomy with mitomycin-C in pediatric glaucomas

    Ophthalmology

    (2001)
  • A.D. Beck et al.

    Trabeculectomy with adjunctive mitomycin C in pediatric glaucoma

    Am J Ophthalmol

    (1998)
  • B. Becker

    The decline in aqueous secretion and outflow facility with age

    Am J Ophthalmol

    (1958)
  • A.R. Bellows et al.

    Endophthalmitis in aphakic patients with unplanned filtering blebs wearing contact lenses

    Ophthalmology

    (1981)
  • D.A. Belyea et al.

    Late onset of sequential multifocal bleb leaks after glaucoma filtration surgery with 5-fluorouracil and mitomycin C

    Am J Ophthalmol

    (1997)
  • P. Ben-Av et al.

    Induction of vascular endothelial growth factor expression in synovial fibroblasts by prostaglandin E and interleukin-1: a potential mechanism for inflammatory angiogenesis

    FEBS Lett

    (1995)
  • T.L. Beyer et al.

    Role of the posterior capsule in the prevention of postoperative bacterial endophthalmitis: experimental primate studies and clinical implications

    Br J Ophthalmol

    (1985)
  • A. Bill et al.

    Production and drainage of aqueous humor in the cynomolgus monkey (Macaca irus)

    Invest Ophthalmol

    (1965)
  • P. Brincker et al.

    Limbus-based versus fornix-based conjunctival flap in glaucoma filtering surgery

    Acta Ophthalmol (Copenh)

    (1992)
  • C.A. Bruno et al.

    Subconjunctival placement of human amniotic membrane during high risk glaucoma filtration surgery

    Ophthalmic Surg Lasers Imaging

    (2006)
  • D.L. Budenz et al.

    Glaucoma filtering bleb dysesthesia

    Am J Ophthalmol

    (2001)
  • J.C. Burchfield et al.

    Endophthalmitis following trabeculectomy with releasable sutures

    Arch Ophthalmol

    (1996)
  • E.N. Burney et al.

    Hypotony and choroidal detachment as late complications of trabeculectomy

    Am J Ophthalmol

    (1987)
  • S. Bylsma

    Nonpenetrating deep sclerectomy: collagen implant and viscocanalostomy procedures

    Int Ophthalmol Clin

    (1999)
  • J.E. Cairns

    Clear cornea trabeculectomy

    Trans Ophthalmol Soc UK

    (1985)
  • J.E. Cairns

    Surgical treatment of primary open-angle glaucoma

    Trans Ophthalmol Soc UK

    (1972)
  • J.E. Cairns

    Symposium: microsurgery of the outflow channels

    Trabeculectomy. Trans Am Acad Ophthalmol Otolaryngol

    (1972)
  • J.E. Cairns

    Trabeculectomy. Preliminary report of a new method

    Am J Ophthalmol

    (1968)
  • J.A. Campagna et al.

    Tenon’s cyst formation after trabeculectomy with mitomycin C

    Ophthalmic Surg

    (1995)
  • R.G. Carassa et al.

    Viscocanalostomy versus trabeculectomy in white adults affected by open-angle glaucoma: a 2-year randomized, controlled trial

    Ophthalmology

    (2003)
  • A.C. Castelbuono et al.

    Histopathologic features of trabeculectomy surgery

    Trans Am Ophthalmol Soc

    (2003)
  • C. Chai et al.

    Meta-analysis of viscocanalostomy versus trabeculectomy in uncontrolled glaucoma

    J Glaucoma

    (2010)
  • C.W. Chen et al.

    Trabeculectomy with simultaneous topical application of mitomycin-C in refractory glaucoma

    J Ocul Pharmacol

    (1990)
  • H.S. Chen et al.

    Control of filtering bleb structure through tissue bioengineering: An animal model

    Invest Ophthalmol Vis Sci

    (2006)
  • Cheng JW, Xi GL, Wei RL, et al. Efficacy and tolerability of nonpenetrating filtering surgery in the treatment of...
  • J.W. Cheng et al.

    Efficacy and tolerability of nonpenetrating glaucoma surgery augmented with mitomycin C in treatment of open-angle glaucoma: a meta-analysis

    Can J Ophthalmol

    (2009)
  • D. Chiselita

    Non-penetrating deep sclerectomy versus trabeculectomy in primary open-angle glaucoma surgery

    Eye (Lond)

    (2001)
  • S. Cillino et al.

    Deep sclerectomy versus trabeculectomy with low-dosage mitomycin C: four-year follow-up

    Ophthalmologica

    (2008)
  • S. Cillino et al.

    Deep sclerectomy versus punch trabeculectomy: effect of low-dosage mitomycin C

    Ophthalmologica

    (2005)
  • L.B. Cohen et al.

    Beta radiation; as an adjunct to glaucoma surgery in the Negro

    Am J Ophthalmol

    (1959)
  • V.P. Costa et al.

    Effects of topical mitomycin C on primary trabeculectomies and combined procedures

    Br J Ophthalmol

    (1993)
  • V.P. Costa et al.

    Hypotony maculopathy following the use of topical mitomycin C in glaucoma filtration surgery

    Ophthalmic Surg

    (1993)
  • A.S. Crandall

    Nonpenetrating filtering procedures: viscocanalostomy and collagen wick

    Semin Ophthalmol

    (1999)
  • E. Dahan et al.

    Nonpenetrating filtration surgery for glaucoma: control by surgery only

    J Cataract Refract Surg

    (2000)
  • Cited by (106)

    • Glaucoma: now and beyond

      2023, The Lancet
    • Spurectomy: A novel modification of non-penetrating deep sclerectomy

      2021, Archivos de la Sociedad Espanola de Oftalmologia
    • Personalising surgical treatments for glaucoma patients

      2021, Progress in Retinal and Eye Research
      Citation Excerpt :

      Alternative treatments have been proposed such as bevacizumab (Vandewalle et al., 2014a), but these agents seem less effective than MMC (Xiong et al., 2014), and taking into consideration their cost/efficacy ratio, there is no robust evidence for their routine use in the context of trabeculectomy (Mathew and Barton, 2011). In fact, trabeculectomy is conceptually a guarded-filtration fistula between the anterior chamber and the subconjunctival space, resulting in a safer procedure compared with previously used techniques (Razeghinejad et al., 2012). In practice, many variations of the conventional technique have been described, making comparison among studies difficult.

    • Epigallocatechin-3-gallate (EGCG) inhibits myofibroblast transformation of human Tenon's fibroblasts

      2020, Experimental Eye Research
      Citation Excerpt :

      To alleviate the fibrosis of the glaucoma filtering bleb, the antifibrotic agents, such as 5-fluorouracil (5-FU) and mitomycin C (MMC), have been introduced in the surgery (Al Habash et al., 2015; Kilic et al., 2016). However, these antifibrotic agents are associated with reported side-effects, including corneal toxicity, wound leakage, blebitis, dysesthesia, and endophthalmitis (Razeghinejad et al., 2012). Epigallocatechin-3-gallate (EGCG), the most abundant catechins from green tea, is not only a strong antioxidant but also a multi-target therapeutic agent (Gu et al., 2013; Singh et al., 2011; Zeng et al., 2014).

    View all citing articles on Scopus
    View full text