Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
The Ex-PRESS™ Miniature Glaucoma Implant
* Deceased. The editors and Elsevier note with sadness the untimely death of Elie Dahan who co-authored the first edition of this chapter.
Summary
The Ex-PRESS™ glaucoma implant is a miniature stainless steel device that offers a simple and safe alternative to the classic trabeculectomy. MPGS with the Ex-PRESS™ can be perceived as a standardized trabeculectomy because of the predetermined size of the implant lumen. The rate of postoperative complications is lower than with trabeculectomy.
It does not require removal of scleral tissue or iridectomy, hence the appearance of a quiet AC on day 1. MPGS mimics NPGS because it allows a controlled flow of aqueous from the AC to the subscleral and subconjunctival spaces. MPGS is faster to perform and has a shorter learning curve than NPGS. Surgeons who are familiar with trabeculectomy or with NPGS can easily convert their filtering operations to MPGS with the Ex-PRESS™.
Introduction
The Ex-PRESS™ glaucoma implant is a miniature stainless steel device that was designed with the intention of offering a simple and safe alternative to the classic trabeculectomy. The inventors (Belkin and Glovinsky) and the original manufacturers initially suggested that the implant be inserted at the limbus under a conjunctival flap. This technique was soon abandoned for a safer and more efficient technique of implantation under a scleral flap.
This chapter will deal only with the under-flap implantation technique.
The Ex-PRESS™ device is a nonvalved implant made of medical-grade implantable stainless steel (316LVM) identical to the material used worldwide for cardiac stents. The material is Food and Drug Administration-approved for ophthalmic applications and is magnetic resonance imaging (MRI)-compatible. At present, two models of the Ex-PRESS™ implants are available ( Fig. 126-1 ). The basic design is of a 27-gauge (0.4 mm external diameter) tube the length of which varies from 2.4 mm to 3.0 mm. The internal diameter of the device can be 50 µm or 200 µm. The distal end can be beveled and sharp or rounded off according to the device model (see Fig. 126-1 ). The proximal end has a disc-like flange that limits the device penetration into the anterior chamber (AC). A spur-like projection is situated on the lower external surface of the tube to prevent extrusion once the device has been implanted. Both the flange and the spur are angled to conform to the anatomy of the sclera and the distance between them corresponds to the scleral thickness at the limbus. The distal end has extra holes to provide alternative routes for the aqueous humor in case the main hole becomes obstructed.
The main concept of the Ex-PRESS™ glaucoma implant is to allow a controlled aqueous humor flow from the AC to the intrascleral and subconjunctival spaces ( Fig. 126-2 ). The restricted internal diameter (50 or 200 µm) of the device provides a certain consistency and standardization to the filtration procedure. In the classic trabeculectomy, wide variations occur not only between different surgeons but also in the hands of the same surgeon. These variations occur during the sclerostomy that is done either by manual incisions or by punch. The Ex-PRESS™ implantation does not require any tissue excision or removal, whereas in trabeculectomy, a sclerostomy and generally an iridectomy are mandatory.
Therefore, the Ex-PRESS™ implantation can be described as a minimally penetrating glaucoma surgery. Both the device and the required incision into the AC are miniaturized. Reflecting upon the two approaches of glaucoma surgery, penetrating and nonpenetrating, the Ex-PRESS™ device offers a valid compromise between these two opposites. Trabeculectomy (penetrating), considered as the gold standard, has shortcomings because of its higher immediately postoperative risk. Nonpenetrating glaucoma surgery (NPGS) is recognized as a safe filtering procedure but it has a long learning curve and the reputation of being difficult to master. A glaucoma intervention with the Ex-PRESS™, being similar to trabeculectomy, has a short learning curve and at the same time mimics NPGS with its restricted flow and reduced intraocular manipulation.
Indications and Contraindications for Minimally Penetrating Glaucoma Surgery with the Ex-PRESS™ Implant
Indications
In general, the indications are wider and more inclusive than those for classic trabeculectomy, for two reasons: (1) MPGS is safer but not less efficient than trabeculectomy; and (2) MPGS is indicated in certain types of glaucoma where trabeculectomies normally fail or are not feasible. Until the advent of MPGS, penetrating glaucoma surgery was generally regarded as the last resort in the treatment of glaucoma. When medical therapy and laser failed to lower intraocular pressure (IOP) to an acceptable level, glaucomatologists explained to their patients that an operation was necessary to halt the progression of the disease. MPGS, with its lower complication rate, can be offered earlier in the course of the disease.
In fact, MPGS can be offered as a first-line treatment in cases where it is obvious that medical treatment will not lower IOP to acceptable levels. This factor is particularly important in glaucoma patients under 50 years of age who have a longer lifespan. Furthermore, glaucoma surgery in general and MPGS in particular is more successful in glaucoma patients who were not exposed to medical treatment. The noxious effects of topical medications on the conjunctiva are well documented (see Chapter 58 ). The conjunctival tissues undergo scarring processes when exposed to certain topical medications. Scarred conjunctiva, as found in patients who have been medically treated for years, is less amenable to the formation of a healthy diffuse bleb than a ‘virgin’ conjunctiva. It is therefore logical to propose MPGS earlier, when the chances of favorable outcomes are greater, rather than later. The previous teaching of ‘first medical and laser treatment and then surgical treatment’ has to be reviewed in the advent of the promising outcomes of MPGS.
Open-Angle Glaucoma
Open-angle glaucoma is the commonest type of glaucoma and is the best indication for MPGS. MPGS bypasses the presumed site of pathology, namely the trabecular meshwork (TM). During MPGS the limbus is incised at the level of the TM and the Ex-PRESS™ implant is inserted into the AC to allow a controlled flow of aqueous from the AC to the intrascleral and subconjunctival spaces. MPGS may have the advantage of being less cataractogenic than trabeculectomy because of its lower rate of immediate postoperative complications. Furthermore, the eye is less inflamed following MPGS because of the lower concentration of transforming growth factors.
Pigmentary and Pseudoexfoliation Glaucoma
Minimally penetrating glaucoma surgery is indicated for pigmentary glaucoma because of its greater resistance to medical treatment. Pigmentary glaucoma occurs more frequently in young myopic male adults, and it is often better to offer a safe surgical solution without depending on a complex combination of medical treatment. MPGS bypasses the site of pathology, namely the pigment-loaded trabecular meshwork. Pseudoexfoliation glaucoma is a form of open-angle glaucoma where there is accumulation of exfoliation material along all the aqueous outflow pathways. Since the exfoliation material is found especially in the TM and Schlemm's canal, MPGS is the treatment of choice for this condition because the blocked TM is bypassed during this procedure. MPGS can be done alone or in conjunction with cataract extraction according to patient age, cataract status, and refractive error.
Aphakic Glaucoma
Formerly, glaucomatologists relied heavily on medication to lower IOP to acceptable levels in aphakic glaucoma. Progressive loss of visual field and eventual loss of vision were often the rule. Trabeculectomies were not regarded as a valid proposition because they necessitate peripheral iridectomies. In aphakic glaucoma, iridectomy is not desirable because the vitreous may move forwards through the iridectomy and block the filtration site. Extensive basal vitrectomy is needed to prevent blockage, but it is difficult to accomplish. The ever-present residual vitreous often finds its way to the filtration site and blocks it. Traction retinal detachment is not an uncommon complication in these combined vitrectomy–trabeculectomies. MPGS does not require iridectomy; therefore, it is particularly indicated in aphakic glaucoma. When aphakia has been longstanding, the TM is often collapsed and scarred. MPGS bypasses the nonfunctional TM.
Sturge–Weber Syndrome
Sturge–Weber syndrome, a cutaneous hemangiomatous disorder, is often associated with congenital or developmental glaucoma. The greater numbers and tortuosity of the conjunctival blood vessels can be an indicator of glaucoma. Minor angle abnormalities, heterochromia, and choroidal hemangioma are often present in Sturge–Weber syndrome patients with glaucoma. Since choroidal effusions following fistulizing surgery are not uncommon in these patients, MPGS offers a safer alternative because only a small needle track opening is made into the anterior chamber.
Glaucoma Secondary to Uveitis
Glaucoma surgery is indicated when elevated IOP persists after the uveitis has subsided. MPGS can offer efficient IOP reduction in these cases because it bypasses the inflamed nonfunctional TM. Furthermore, since its postoperative course is quieter than in trabeculectomies, MPGS has an advantage over the classic trabeculectomy.
Nevertheless, in cases where multiple peripheral anterior synechiae are present, the surgeon has to take special care when positioning the Ex-PRESS™ in order to avoid iris tissue touch.
Post-Trauma Angle-Recession Glaucoma
In angle-recession glaucoma, the trabecular meshwork has been damaged and may not recover. MPGS with the Ex-PRESS™ implant is feasible because of its minimal tissue manipulation.
You're Reading a Preview
Become a Clinical Tree membership for Full access and enjoy Unlimited articles
If you are a member. Log in here