Many factors involved in surgical treatment of primary open-angle glaucoma

Issue: September 2011

ByPhilippe Sourdille, MD

Philippe Sourdille

Recent developments in imaging of the optic nerve head and of retinal fibers — laser interferometry, scanning laser microscopy, adaptive optics alone or combined with microperimetry — are significant adjuncts to diagnosis of open-angle glaucoma. Treating the disease at a reversible stage, or at least consistently preventing further damage, is today’s objective.

The most accepted neuroprotection is lowering of the IOP to achieve a permanent target pressure without significant nycthemeral IOP spikes. A “pressure safety zone,” with limited variations depending on needs of individual patients, starts below 15 mm Hg and seems optimal around 10 mm Hg.

Surgical approaches

Which contemporary surgical approaches are able to reach these levels with a long-lasting effect?

Apart from valves and cyclodestructive proposals, which are to be considered in late stages of the disease, an ab externo approach, such as trabeculectomy or nonpenetrating trabecular surgery, is most frequently used. Recently, a revival of ab interno techniques, which open Schlemm’s canal with excimer laser probes or stents, has been proposed. But a permanent opening of the canal to the anterior chamber raises the issue of permanent intraocular bleeding risk.

Trabeculectomy still is the most frequent operation. It is a simple procedure, and various suturing techniques have improved subconjunctival filtration control. Treatment with adjunct antimetabolites such as perioperative mitomycin C and 5-fluorouracil seems to be more frequently used to achieve a lower IOP and a longer-lasting hypotensive result, but with the price of a significant complications rate, mainly cataract and blebitis. A combination of these antimetabolites with anti-VEGF factors has shown promising results in wound healing modulation.

Nonpenetrating trabecular surgery has benefited from the pioneering work of Robert Stegmann, MD, (viscocanalostomy) and André Mermoud, MD (deep sclerectomy). Various resorbable or nonresorbable implants have been used to maintain the “scleral lake,” according to Stegmann, and to increase aqueous access to physiological or newly formed pathways. Viscocanalostomy results highlight IOP lowering with little or no subconjunctival filtration compared with deep sclerectomy, in which slit lamp examination and high-frequency ultrasound demonstrate three possible mechanisms: subconjunctival filtration, intrascleral and uveal resorption. A lower rate of postoperative complications, as compared with trabeculectomy, is a definite benefit of nonpenetrating surgery.

In 2010, David Bellicaud and Pierre-Jean Pisella published a work on a 2- to 3-year ultrasound analysis of trabeculectomy and deep sclerectomy with an innovative conclusion: Anatomical success criteria, ie, IOP-lowering mechanisms, are identical in both penetrating and nonpenetrating techniques. They also insist on the importance of uveal resorption as a more physiological IOP-lowering mechanism. This work paves the way to a common approach of wound healing modulation in penetrating and nonpenetrating surgery.

Other considerations

A “surgical continuum,” mimicked from Robert Weinreb, MD’s, glaucoma continuum, has to be considered if the aim of a surgery is to be the first step to lower both the IOP and the surgical failure risk. This must include diagnosis and treatment of preoperative and postoperative negative prognosis factors.

Ocular surface disorders related to ocular hypertension medical treatment with preservatives have long been studied by Christophe Baudouin, MD. Limbal structures and conjunctival epithelium transformations are negative factors of postoperative wound healing. Operating on a virgin conjunctiva might therefore be a favorable condition.

A comprehensive approach of the ocular surface status and of treatments to be applied is necessary to improve our results. Dynamic and objective analysis of tear film quality (OQAS, Visiometrics) and possible corneal and conjunctival epithelium changes have to be diagnosed and treated. Non-preserved hypotensive topical drugs and ocular surface disorder treatments are prerequisites of surgical prognosis improvement. A larger consensus on this preoperative assessment and guidelines, such as the European Glaucoma Society guidelines, would be beneficial to our patients.

A number of factors are involved in wound healing evolution, especially in different phases of scarring, leading to filtration-area fibrosis. Confocal microscopy is a powerful tool to develop our knowledge of both preoperative and postoperative changes, potentially influencing success or failure. Many specific inhibitors have been used without definite success. MMC and 5-FU, as global antimetabolites, remain the most frequently used. Anti-VEGF therapy, alone or combined with MMC and 5-FU, seems to improve wound healing by decreasing fibrotic scarring. Other drug combinations and delivery modes are on their way.

Surgical technique improvement alone is not sufficient. It has to be part of a “surgical continuum,” including a comprehensive preoperative and postoperative analysis of wound healing conditions. As for surgical propositions, we must remember what John Cairns, the inventor of trabeculectomy, had in mind: to permanently establish a low IOP and to get rid of subconjunctival filtration, currently considered the most efficient IOP-lowering mechanism, and the main source of complications. Pre-existing aqueous pathways enhancement, such as suggested in viscocanalostomy, creation of a permanent significant pressure differential between the anterior chamber and the aqueous channels, and development of uveal resorption by new approaches are different and non-exclusive ways to establish surgery as a first-step treatment option.

References:

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Ciancaglini M, Carpineto P, Agnifili L, et al. Filtering bleb functionality: a clinical, anterior segment optical coherence tomography and in vivo confocal microscopy study. J Glaucoma. 2008;17(4):308-317.

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Philippe Sourdille, MD, can be reached at philippe.sourdille@wanadoo.fr.

Disclosure: Dr. Sourdille has no relevant financial disclosures.