Ординатура / Офтальмология / Английские материалы / Glaucoma Surgery_Bettin, Khaw_2012

that the Ex-PRESS Mini-Glaucoma Device has been introduced to the trabeculectomy and glaucoma filtering surgery.

Overview of the Ex-PRESS

The Ex-PRESS Mini-Glaucoma Device is a nonvalved, MRI-compatible stainless steel device designed by Optonol Ltd. (Neve Ilan, Israel) to shunt aqueous underneath the conjunctiva and control the intraocular pressure. The device is 3 mm in length with a 400-μm external diameter. Currently, models of the shunt are available with 50 or 200-μm internal lumens (fig. 1). The company was acquired by Alcon (Ft Worth, Tex., USA) in 2010, and the name was changed from the Ex-PRESS Mini-Glaucoma Shunt, to the Ex-PRESS Mini-Glaucoma Device to avoid confusion with more traditional glaucoma drainage devices that are typically referred to as ‘shunts’. Biocompatibility of the Ex-PRESS has been proven through implantation in rabbits which showed virtually no inflammation associated with the device [2].

The device was initially designed to be placed directly underneath the conjunctiva through the full thickness of the sclera near the limbus. This implantation was soon met with multiple problems including erosion, hypotony and extrusion of the implant [3–13]. Extrusion of the implant when implanted without a flap has even been associated with endophthalmitis [8]. The typical complicated case presents with

initial hypotony followed by erosion of the outer flange of the device through the conjunctiva.

Dahan and Carmichael [14] were the first to present a successful alternative to the direct subconjunctival implantation by combining old surgical insight with new surgical technology. They proposed placing the Ex-PRESS underneath a scleral flap as in standard trabeculectomy. This change has led to almost complete elimination of erosion with the Ex-PRESS. In addition, it seems to have provided an improvement in hypotony when compared with the standard trabeculectomy [15]. A retrospective case series comparing 50 eyes treated with the Ex-PRESS underneath a scleral flap versus 50 eyes treated with trabeculectomy found similar reduction in intraocular pressure and glaucoma medications at 3 months. However, choroidal effusion and hypotony were much more significant after trabeculectomy than with implantation of the Ex-PRESS. Maris et al. [15] found a 32% hypotony rate in trabeculectomy patients compared with 4% hypotony with the Ex-PRESS shunt. It is thought that this reduction in hypotony is due to the additional resistance to flow through the 50-μm lumen of the shunt. The scleral sutures of the flap obviously provide the majority of the resistance in the surgery, but the combination of scleral flap and implant resistance gives extra stability to the surgery. Due to these factors, placing the Ex-PRESS underneath a scleral flap has become the recommended technique to implant the ExPRESS device.

Surgical Technique

Surgical technique for implantation of the Ex-PRESS shares many similarities with the standard trabeculectomy. Retrobulbar or topical anesthesia is chosen based upon discussion and preference of the surgeon and patient. A standard fornix-based or limbal-based conjunctival flap is then created to provide access to the scleral bed at the limbus. Careful cautery of the scleral bed should then be performed before proceeding with flap formation. A blade of the surgeon’s choice is then used to create a standard scleral flap as with trabeculectomy. Shape of the flap is not as important as paying close attention to dissecting completely to clear cornea; however, the flap should be at least approximately 2.5 × 2.5 mm to be certain the implant is well covered by at least 1 mm all around the plate. Antifibrotics may be used at this juncture before or after the creation of the scleral flap in the usual manner for trabeculectomy. A clear corneal paracentesis should be created at this point to lower the intraocular pressure and provide access for reformation of the anterior chamber during the remainder of the case. After antifibrotics, the scleral flap is then lifted and the surgeon should identify the ‘blue line’ next to clear cornea that identifies the trabecular meshwork. A 25-gauge needle (27 G for the R version of the shunt) is then used to enter the anterior chamber at the ‘blue line’ parallel to the iris plane. Alternatively, a 25-gauge MVR blade is preferred as it allows for a tighter fit around the implant preventing

aqueous from going around the implant causing unnecessary hypotony. The needle is removed after creating the ostium in the sclera. Do not use a larger needle as this may cause the Ex-PRESS to dislocate into the anterior chamber. The Ex-PRESS is then removed from the packaging on its preloaded injector. The injector has a metal shaft which inserts through the lumen of the Ex-PRESS. The injector is used to introduce the shunt through the ostium created in the previous step. Attention should be paid to entering the anterior chamber at the same angle used with the 25-gauge needle and inserting the shunt until the face plate is flush with the scleral bed. The injector has a button in the center of the device which releases the shunt from the metal shaft when depressed. At this time, the shunt should be adjusted to assure that it is well centered and in the desired position in the anterior chamber.

Next, the scleral flap is sutured with 10-0 nylon suture on a spatulated needle as with a standard trabeculectomy. Two or more interrupted sutures should be placed through the flap and adjusted according to flow from beneath the flap. Flow can be tested by injecting balanced salt solution through the previously created corneal paracentesis. The conjunctiva is then closed with the suture using the technique (continuous or interrupted) of the surgeon’s choice to make the area water tight. A fluorescein strip can be used to assure the integrity of the wound closure.

Standard postoperative care is similar to posttrabeculectomy care. Patients should be treated with anti-inflammatory steroid and antibiotic drops. With the technique described, laser suture lysis should be completed if intraocular pressure rises above desired parameters.

Discussion

The Ex-PRESS Mini-Glaucoma Device has been a promising development in the field of glaucoma surgery. The most complete evaluation of patients receiving the shunt to this point was reported in the Journal of Glaucoma in 2009. This case series of 345 patients was divided with 231 receiving Ex-PRESS beneath a scleral flap alone and 114 eyes receiving Ex-PRESS beneath scleral flap with phacoemulsification [16]. Surgical success at 3 years was found to be 94.8 and 95.6%, respectively. The change from baseline intraocular pressure and number of glaucoma medications was significantly decreased in both groups. Ex-PRESS implant alone without phacoemulsification showed the most significant drop in intraocular pressure in this particular study. The most common complication in this study was elevation of intraocular pressure due to plugging of the shunt tube opening. This occurred in approximately 1.7% of cases, but was successfully treated by using the Nd:YAG laser on the tip. The shunt opening was blocked by fibrin and not by iris tissue as might be expected. The eyes that suffered this complication had previous inflammation before the surgery.

Good and Kahook [17] have recently reported further benefits of the Ex-PRESS shunt with their retrospective study comparing consecutive results of Ex-PRESS

implantation versus trabeculectomy. This report, which placed 35 patients in each of the two arms of the study, revealed similar surgical success numbers between the two groups. Unqualified success was 77.14% in the Ex-PRESS group versus 74.29% in the trabeculectomy group. Follow-up for the group averaged 28 months. Over this time, a slightly higher intraocular pressure was found in the Ex-PRESS group. While statistically significant, this difference may not be clinically significant. Long-term bleb morphology scores were comparable. This study also attempted to look at clinical variations between the two groups in the postoperative data. Interestingly, these data revealed a difference in the postoperative visual recovery between the two groups. Patients in the Ex-PRESS group tended to regain their baseline visual acuity by the one-week postoperative visit, while the trabeculectomy group reached this baseline by the one-month visit. In addition, postoperative visits were reduced in the Ex-PRESS group compared to the trabeculectomy group. The Ex-PRESS does seem to offer distinct advantages in the recovery period after surgery as evidenced by these findings.

In our practice, the Ex-PRESS is the procedure of choice in any patient who would otherwise require a trabeculectomy, with the exception of children, or in the very rare patient with narrow angle in whom lensectomy is not a consideration. Moreover, it may offer advantages in patients in whom a glaucoma drainage implant may have been a first choice in the past. In patients with neovascular, uveitic, aphakic or traumatic glaucoma, we have found the Ex-PRESS to be an excellent alternative to either trabeculectomy or tube shunts. The Ex-PRESS has advantages in patients with ICE syndrome as well, since there is no fistula to be occluded by the endothelial membrane in this disease. If the Ex-PRESS does get occluded, the tip is easily visualized and lasered. The same benefit of the Ex-PRESS exists in cases in which the surgeon may fear vitreous or silicone oil occluding a slerostomy. However, in cases in which the conjunctiva has significant scarring and there is no area of mobility, neither the Ex-PRESS, nor a trabeculectomy is indicated.

Many glaucomologists would agree that the Ex-PRESS Mini-Glaucoma Device has been a major advancement in glaucoma filtering surgery. There appears to be many advances on the near horizon in glaucoma surgery. Many of these surgeries will focus on the restoration of the natural outflow working of the Schlemm’s canal. These surgeries have been helpful in treating earlier phases of glaucoma. However, for more advanced cases of the disease, they have not had the amount of intraocular pressure lowering success that the Ex-PRESS device has shown thus far. The Ex-PRESS is small incision glaucoma surgery on par with the microincisional emphasis of 25-gauge vitrectomy and foldable intraocular lenses implanted through sub-2-mm incisions. It allows reduction in intraocular pressure with less chance of hypotony and more visual stability and is an important evolutionary change in glaucoma filtration surgery.

Although there are significant data demonstrating the safety and efficacy of the ExPRESS, a large prospective, multicenter, randomized trial comparing the Ex-PRESS versus trabeculectomy (both arms with MMC) is underway and has finished recruiting. The study (XVT study) is still collecting data at the time of this publication.

Prof. Steven R. Sarkisian, Jr., MD

Dean McGee Eye Institute, Department of Ophthalmology University of Oklahoma College of Medicine

608 Stanton Young Boulevard Oklahoma City, Oklahoma 73104 (USA) E-Mail steven-sarkisian@dmei.org

purity, size, concentration, and shape, which amplifies the beam by the process of stimulated emission. It can be of any state: gas, liquid, solid or plasma.

Laser effects in biological tissues can be divided into three categories: photochemical, thermal, and ionizing. Lasers can be used for photoradiation, for photoablation, when tissue is removed in some way by light (i.e. excimer laser), for photocoagulation (argon, krypton, diode, or neodymium (Nd):yttrium aluminum garnet, YAG) which causes denaturation of biomolecules when temperatures are sufficiently high (≥600 °C). Lasers can also be used for photovaporization that occurs when the tissue temperature quickly reaches the boiling point of water, causing disruption (evaporation) before denaturation photocoagulation. In photodisruption (i.e. Q-switched and pulsed Nd:YAG laser), short-pulsed, high-power lasers disrupt tissues by delivering enormous irradiance to tissue targets. The high level of irradiance ionizes molecules in a small volume of space at the focal point of the laser beam, disintegrating into collections of ions and electrons called plasma. This plasma expands rapidly, producing shock and acoustic waves that mechanically disrupt tissues adjacent to the region of laser focus [4].

Using different types of lasers allows utilizing lasers in the treatment and diagnostics of many eye disorders [5]. Absorption of certain light frequencies is high in pigmented trabecular meshwork, iris, ciliary body, and retinal pigment epithelium (owing to melanin), and in the blood vessels (owing to hemoglobin). The use of lasers is slowly pervading all subspecialties of Ophthalmology, especially glaucoma, and lasers are slowly replacing many glaucoma surgeries. Incisional operation most frequently used for chronic forms of glaucoma, especially in adults, is referred to as a filtering procedure. Filtering procedures can be divided into penetrating and nonpenetrating. The availability of a variety of ophthalmic lasers, ranging from ultraviolet to mid-infrared wavelengths, and the vast improvement in laser delivery technology have generated great interest in using laser in filtering surgery.

Laser-Assisted Techniques for Penetrating Filtering Surgery

There is a variety of penetrating filtering procedures, but all share the same basic mechanism of action and general surgical principles. The basic mechanism of all filtering procedures is the creation of an opening, or fistula, at the limbus, which allows the aqueous to drain. The aqueous flows directly or indirectly from the anterior chamber into subconjunctival spaces, and it is then removed by one or more routes. The various types of filtering surgeries differ primarily according to the method used to create the drainage fistula, but all show a gradual decline in the probability of successful intraocular pressure (IOP) control over time, although the actual numbers vary considerably [6–8]. The most common cause of failure in filtering surgery is cell proliferation and scar formation at the filtering site [9]. To increase the success rate of filtering surgery, antimetabolites may be used to achieve a functioning filter [10–

12]. Major hazards associated with its employment include persistent ocular hypotony, conjunctival wound leak and endophthalmitis [13]. Another approach consists in reducing injury to subconjunctival and episcleral tissues. Based on this approach, laser sclerostomy, using various kinds of lasers, was believed to be minimally invasive [14]. It was suggested that when the radiation energy is properly delivered, laser sclerostomy can create a small, neatly cut, and appropriately placed fistula with minimal complications, thereby increasing the rate of success.

Penetrating laser sclerostomy can be achieved either via an ab interno or an ab externo procedure. The ab externo perforates from the external surface into the anterior chamber, whereas the ab interno includes a perforation from the internal surface outwards. Gaasterland et al. [15] tried to compare the two approaches. They investigated the creation of filtering tracts using an argon laser gas laser emitting radiation lines in the ultraviolet (333–363 nm) wavelengths. This system was used to perforate the corneoscleral limbal tissue of enucleated bovine eyes to create a filtering fistula. The investigators compared the energy required for perforation in the two approaches and found no difference.

The main advantage of the ab interno over the ab externo procedure is the fact that it avoids injury to the conjunctival tissue [16]. Ab externo also involves a risk of photochemical damage to the iris induced by cavitation bubbles that penetrate the anterior chamber before the fistula is completed [17]. As opposed to ab externo, ab interno approach also reduces the risk of damaging anterior chamber structures when the probe reaches the anterior chamber at the end of the procedure. On the other hand, Ab interno with endoscopic guidance [18] is more invasive than an ab externo approach, and there is a risk of injury to the crystalline lens.

Various lasers were examined for laser sclerostomy with limited success. The rationale behind testing an increasing number of different radiation sources has been the concept that if a wavelength with high water-absorbing and low light-scattering properties is employed, the extent of collateral thermal damage incurred will be reduced. Collateral thermal damage adjacent to the sclerostomy site is believed to be detrimental to the long-term success and the long-term maintenance of fistula patency [16].

The pulsed Nd:YAG laser (1.06 μm) may be used in a variety of ways for the treatment of glaucoma. Its use include: peripheral iridotomy, reopening of trabeculotomy, graded trabeculectomy, lysis of synechiae, cyclodialysis, goniotomy, and internal trabeculotomy. Higginbotham et al. [19] used the Nd:YAG to create an internal laser sclerostomy (sclerostomy ab interno) in a rabbit model. A synthetic sapphire contact Nd:YAG laser was used. The probe connected to a laser source was inserted into the anterior chamber via preplaced paracentesis tract, and positioned within the eye at the trabecular meshwork. Full sclerostomy was achieved in all cases in this trial, bypassing the need for conjunctival dissection, presumably minimizing the stimulus for conjunctival proliferation.

Latina et al. [20] used a ‘flash-lamp pumped pulse-dye laser’ to create a gonioscopic ab interno penetrating laser sclerostomy (GLS). The GLS is a ‘one step’ procedure