Glaucoma
Are There Problems with Non-penetrating Glaucoma Surgery? Vincent Dubois, MB BS, FRCOphth1
and Ivan Goldberg, AM, MB BS, FRANZCO, FRACS1
1. Glaucoma Fellow, Sydney Eye Hospital; 2. Head, Glaucoma Unit, Sydney Eye Hospital and Clinical Associate Professor, Discipline of Ophthalmology, University of Sydney and Director, Eye Associates
Abstract
Non-penetrating glaucoma surgery (NPGS) has been around in various guises for 50 years, yet its acceptability among the ophthalmological community is variable. This article aims to debunk some of the myths associated with NPGS and to explain the differences in NPGS techniques. Once these differences have been explained, we scrutinize and meaningfully compare the good-quality research that has been published on the subject. In doing so, we aim to help readers determine which techniques work best and why. Finally, we hope to show the readers where NPGS has a place in the glaucomatologist’s armamentarium.
Keywords
Deep sclerectomy, viscocanalostomy, canaloplasty, collagen implant, non-penetrating glaucoma surgery, ab externo canal surgery, combined glaucoma surgery
Disclosure: The authors have no conflicts of interest to declare. Received: October 17, 2011 Accepted: December 19, 2011 Citation: US Ophthalmic Review, 2012;5(1):27–32 Correspondence: Ivan Goldberg, AM, MB BS, FRANZCO, FRACS, Head, Glaucoma Unit, Sydney Eye Hospital, Clinical Associate Professor, Discipline of Ophthalmology, University of Sydney, Eye Associates, Floor 4, Macquarie Street, Sydney 2000, Australia. E:
eyegoldberg@gmail.com
In the 1960s, Krasnov1
began to develop what became known as
‘non-penetrating glaucoma surgery’ (NPGS). The ‘sinusotomy’ he described consisted of de-roofing Schlemm’s canal from 10–2 o’clock via an external approach and then covering the canal with conjunctiva. With little post-operative detail in the report, plus the need for an operating microscope, the procedure was never accepted.
In 1989, Koslov et al.2 described ‘deep sclerectomy’ (DS): an ‘en-bloc’
resection of the external wall of Schlemm’s canal, along with corneal stroma adjacent to the anterior trabeculum and, more anteriorly, exposure of Descemet’s membrane over 4–5 mm. These structures were removed with a slice of sclera beneath a superficial scleral flap: hence the term deep sclerectomy. In 1998, Vaudaux et al.3 demonstrated increased aqueous humor outflow, while protecting the eye from hypotony-related complications. At that time, Watson et al.’s trabeculectomy complications4
included 28 % with iridocorneal touch, a
further 1 % with lenticulo-corneal touch, and early intraocular pressures (IOPs) of ≤5 mmHg in 25 % of eyes; Popovic’s series5
had IOPs ≤5 mmHg
in one in three patients at one week post-operatively; Migdal and Hitchings6
reported that 29 % of patients had IOPs ≤8 mmHg for over two weeks post-operatively; Stewart et al.’s results7
showed 76 % with IOP
<5 mmHg and 47 % with iridocorneal touch, both at two days post-operatively. Despite these rates of complications occurring early in the post-operative period, trabeculectomy became established as the technique of choice for glaucoma. It was considerably safer than its predecessors, namely anterior and posterior lip sclerectomy, iridencleisis, and posterior lip sclerectomy with or without cautery.
© TOUCH BRIEFINGS 2012
Today, post-trabeculectomy complication rates are far less high than these owing to improvements in surgical technique. At the time, however, they were the benchmark, driving the search for an alternative. Koslov’s deep sclerectomy was appealing.
Ideal surgery would create consistently an immediate, controlled IOP reduction with stable visual acuity and a minimal surgical learning curve. A realistic goal would be an operation that did not give rise to problems associated with early hypotony, late leaks, cataract formation or endophthalmitis, one that necessitated infrequent follow-up and was not bleb-dependent for success. DS and viscocanalostomy (VC) represent attempts to achieve this goal. In particular, VC aims to be bleb-free. Both operations may provoke less post-operative inflammation than trabeculectomy surgery,8
with smaller amounts of
post-operative steroids required. These advantages translate into less intensive follow-up than following trabeculectomy.9
Where are the Problems with Non-penetrating Glaucoma Surgery?
NPGS may be less effective to control IOP than trabeculectomy. Another challenge is the relative complexity of these procedures compared with trabeculectomy. A high level of skills is required to dissect a longer scleral flap of uniform thickness and to create a trabeculo-Descemet window (TDW) without entering the anterior chamber. Another problem is the very general appellation ‘NPGS’: there are many surgical variations all grouped under the same umbrella term. To many ophthalmologists, this acronym suggests one type of operation, perhaps with a few
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