Non-Penetrating to Minimally Penetrating Glaucoma Surgery
Dr. Elie Dahan
University of the Witwatersrand
In the management of glaucoma patients, there
are instances when surgery becomes the only option. These occur in young
patients with very high intraocular pressures (IOP), in terminal glaucoma patients
with poor compliance, and in patients who cannot tolerate or afford medical
When surgery becomes the only option, it has to be safe and effective. Nonpenetrating Glaucoma Surgery (NPGS) allows a slow and controlled filtration through a naturally occurring membrane: the Trabecular Meshwork.
Therefore, the dangers of early excessive filtration are lower in
NPGS than in trabeculectomy. NPGS, also known as “Deep Sclerectomy”, is less
“bleb dependant” than trabeculectomy because most of the aqueous re-absorption
occurs intra-sclerally. The NPGS opponents claim that its medium and long term
results are inferior to those of the classic trabeculectomy.
NPGS is safer but in order to become as effective, it has to be performed meticulously. The surgeon has to expose a wide Trabeculo-Descemetic window without rupturing it. In order to restore sufficient filtration, the diseased trabecular meshwork has to be thinned out by peeling and/or scraping - a delicate and difficult procedure. Its learning curve is very long and it is believed that it takes 200 NPGS operations, under experienced supervision, to achieve an acceptable level of proficiency.
Modern NPGS has evolved since the early ‘90s in
South Africa and Europe but its popularity in the USA
is still lingering. In the literature, mediocre reports on NPGS are published
by those who are still in their learning curve, whereas good results are reported
by those who have mastered the technique (1-4).
The practical conclusion is that NPGS is a too demanding surgical technique. Thus, its chances to be popularized are very slim.
During the late ‘90s, Glovinsky and Optonol, an Israeli Startup Company, developed the ExPRESS (Figure 1); a trans-limbal mini-shunt that provides controlled filtration through a restricted lumen. The idea was to provide a rapid and simple filtering operation that could be performed by surgeons with little glaucoma surgery experience. The early trials were done implanting the mini-shunt trans-limbally, just under the conjunctiva.
Early excessive filtration and late conjunctival erosion over the device
jeopardised the project. Dahan and Carmichael, who participated in the early “under conjunctiva” clinical trials in Johannesburg,
suggested implanting the ExPRESS mini-shunt Under a Scleral Flap
(USF). The aim was to reduce the
risks of early excessive filtration and late conjunctival erosion. Initially, their
suggestion was not welcomed by the developers. The Optonol team claimed that
implanting the ExPRESS USF defeated the point and changed the whole essence of
the project. The USF technique lengthened the operation and at first glance,
did not offer anything more than a classic trabeculectomy.
Finally, Dahan and Carmichael were allowed to implant the Ex-PRESS USF (Figure 2) in a small prospective pilot study involving severe glaucoma patients who failed previous glaucoma surgery. The pilot study on the Ex-PRESS USF started in September 2000 and yielded surprisingly good results (5). This has prompted Optonol to abandon the “under conjunctiva” technique and concentrate on the USF technique only.
In March 2002, the Ex-PRESS mini-shunt obtained FDA approval and CE mark. To date, more than 10,000 Ex-PRESS devices were implanted in the USA, Europe
and South Africa by leading glaucoma surgeons. The users report a surprisingly quiet eye on “Day one” because of minimal tissue manipulation. Unlike trabeculectomy, the Ex-PRESS USF does not require scleral punching or iridectomy and is feasible also in aphakia, when there is vitreous under the iris plane.
After having performed more than 2000 NPGS and a few hundred of ExPRESS USF, Dahan and Mermoud have second thoughts of popularizing NPGS. They have realized that the Ex-PRESS USF might be the right compromise between NPGS and trabeculectomy. The Ex-PRESS USF, like NPGS, offers a safe and controlled filtration and it has a shorter learning curve (Figures 2 & 3).
In other words, the ExPRESS USF combines the advantages of both NPGS and trabeculectomy without their inconveniences. It can be described as a Minimally Penetrating Glaucoma Surgery (MPGS). It mimics NPGS in its mode of action and it
is as easy, if not simpler, than the classic trabeculectomy. Controlled
randomized prospective clinical trials are being conducted in the USA, Europe and South Africa to compare the ExPRESS USF (MPGS) and trabeculectomy.
Dahan E, Drusedau MU. Nonpenetrating
filtration surgery for glaucoma: control by surgery only. J Cataract
Refract Surg. 2000;26(5):695-701.
Shaarawy T, Nguyen C, Schnyder C, Mermoud A. Comparative study between deep sclerectomy
with and without collagen implant: long-term follow-up. BJO 2004;
Tan JC, Hitchings RA.
Non-penetrating glaucoma surgery: the state of play. Br J Ophthalmol 2001 Feb ;
85(2) : 234-237
Jonescu-Cuypers C, Jacobi
PC, Konen W, Krieglstein GK. Primary viscocanalostomy versus trabeculectomy
in white patients with open-angle glaucoma. A randomised clinical trial.
Ophthalmology 2001 ; 108 : 254-258
Dahan E, Carmichael
TR. Implantation of a miniature glaucoma device under a scleral flap. J
Glaucoma 2005; 14:98-102