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In the past 5 years, the Ex-PRESS drainage device has been mentioned in the discussions of glaucoma surgeons. Its place in the surgical management of glaucoma has not been clear so far and much contradictory information and controversy have been circulated.
In this issue of the BJO (p 425) is presented the first written clinical report on the Ex-PRESS tube used in combined cataract and glaucoma surgery.
Glaucoma drainage devices (GDDs) were first introduced a century ago. Much experience has been gained in the use of these devices, and has led to many modifications in design, construction, and implantation techniques.1 In 1969 Molteno launched the concept of a tube and plate for glaucoma drainage, in which the plate is secured onto the episclera, helping with the formation of a posterior orbital filtering bleb.2,3 Contemporary GDDs, which dominate the market are the Molteno, Krupin, Baerveldt, Ahmed, and OptiMed devices, which all share the essential design concept of posterior filtration via a tube (outer diameter 0.56–0.63 mm) from the anterior chamber to a plate element secured to the episclera; they differ in plate design and size (135–500 mm2) and their provision for a flow control mechanism.1
If glaucoma drainage devices do offer substantial surgical possibilities for refractory glaucoma they also present disadvantages, either overflow of aqueous onto the anterior chamber or poor filtration with IOP elevation.
Contact between the tube and the corneal endothelium may also induce a long term corneal decompensation.4 To minimise the rate of early postoperative hypotony, some of the devices contain a valve mechanism that restricts the aqueous outflow.5–7 However, owing to the relatively high postoperative complication rates and the relatively difficult and traumatic implantation procedure, the use of GDDs is usually limited to complicated cases after other modes of treatment, both surgical and non-surgical, have failed.8
Past experience with GDDs reveals that material composition, implant design, physicochemical surface properties, condition of the host bed, surgical technique, and mechanical properties influence the eye’s response to the device. All of these factors may influence the overall performance and surgical outcome.9,10
The Ex-PRESS implant is a miniature unvalved glaucoma implant. It was developed as an alternative procedure to trabeculectomy and to the other types of glaucoma filtering surgery for patients with primary open angle glaucoma (POAG). The device is a 3 mm long stainless steel tube (outer diameter 400 μm (27 gauge)) with a bevelled, sharpened, rounded tip, a disc-like flange (<1 mm2) at the device proximal end, and a spur-like projection that prevents its extrusion. The external flange and inner spur are angled to conform to the anatomy of the sclera, and the distance between them corresponds to the scleral thickness at the site of implantation.11
Originally, the device was designed to be inserted at the limbus directly under the conjunctiva. In this case, a subconjunctival bleb is formed and serves as a flow modulator. This technique is relatively simple and can be performed in a few minutes, either on its own or in combination with phacoemulsification.
The paper by Traverso et al in this issue of the journal summarises a 3 year follow up with the device. Success rate and short term complications, such as a shallow or flat anterior chamber and hyphaema compare favourably with data reported in the literature for trabeculectomy.
However, some physicians encountered poor conjunctival covering of the device. Several conjunctival erosions were noted over the external flange. Conjunctivoplasty or tube removal had to be performed to avoid secondary infection. On the other hand, several patients showed conjunctival scarring with subsequent decreased aqueous humour filtration.
To overcome this complication of conjunctival erosion and bleb fibroses, Dahan and Carmichel recently suggested implanting the device under a limbus based 50% deep scleral flap extending into clear cornea. This operation is similar to standard trabeculectomy without the need of an iridectomy or scleral removal.12 This may offer an advantage over standard trabeculectomy. Early findings from Sherwood on rabbits (Ex-PRESS filtering shunt bleb TGF-β levels in rabbit model, personal communication, October 2004) reveal that the “less invasive technique reduces ocular inflammation by decreasing TGF-β level in aqueous humour.” The rationale behind this surgical modification is to increase the resistance to aqueous flow in the early postoperative stages as well as to reduce the development of late conjunctival erosion. This technique therefore potentially reduces the complications of hypotony, especially in patients at high risk of surgical failure.12 Furthermore, the 2 year postoperative reduction in IOP in the study of Dahan et al was >40% and only 10% of the patients required further medical therapy.12
This tube may also be used in deep sclerectomy to simplify the difficult dissection of Schlemm’s canal and trabeculo-Descemet’s membrane. In an unpublished study, we found that by performing a partial posterior deep sclerectomy and inserting an Ex-PRESS implant into the anterior portion under the superficial scleral flap, we obtained excellent IOP reduction with very few postoperative complications. This technique drastically simplifies the surgical dessection of deep sclerectomy and yet still provides its outflow advantage including the drainage of the aqueous to (1) a subconjunctival bleb, (2) an intrascleral bleb, and (3) the subchoroidal space.
Used in deep sclerectomy, the Ex-PRESS tube also avoids the late need for goniopuncture (Mermoud et al, unpublished data).
Initial doubt about the Ex-PRESS implant are decreasing with recent advances offering possibly a wider spectrum of indications while diminishing the potential complications.
The Ex-PRESS implant was introduced to offer a quick and simple alternative to glaucoma surgery. The procedure is indeed rapid; however, it may be associated with new complications such as conjunctival erosion and risk of subsequent infection. The modification in the technique by introducing the tube under a superficial scleral flap seems to overcome these complications.
Further research and clinical studies will allow us to discover whether the Ex-PRESS tube will definitely change our approach to glaucoma surgery.
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