Fig. 9.1
Ex-PRESS mini-glaucoma device
Initially, the device was placed directly under the conjunctiva, full thickness through the sclera near the limbus. Unfortunately, implanting the Ex-PRESS in this manner was fraught with complications. Most worrisome were erosion, profound hypotony, and extrusion of the implant [3–6]. Endophthalmitis secondary to extrusion without a scleral flap was perhaps the most severe of complications [4]. Presentation of the above was typically initially seen as hypotony, followed by erosion of the conjunctiva at the outer flange of the device.
Typical to the innovative process, old surgical vision was melded with new surgical technology as Dahan and Carmichael became the first to recommend placement of the Ex-PRESS under a scleral flap [7]. Subsequently, erosion of the device was virtually eliminated. In addition, the scleral flap was found to reduce the risk of postoperative hypotony.
Initial reports were extremely favorable as the Ex-PRESS device surpassed trabeculectomy in almost every aspect. As longer follow-up time has accrued and further research performed, early excitement has been tempered. However, the Ex-PRESS still appears to be superior to trabeculectomy in visual recovery [8–10]. Some studies observed more favorable rates of hypotony and number of interventions due to hypotony [11, 12].
9.2 Surgical Technique
The techniques used for Ex-PRESS implantation have many similarities to a traditional trabeculectomy. The Ex-PRESS device may be placed under topical, sub-tenon, or retrobulbar anesthesia. Choice of fornix- or limbal-based surgery is made according to surgeon preference. Careful cautery of the scleral bed is important for hemostasis prior to scleral flap creation. The shape of the scleral flap is not important as long as the flap has good 1 mm coverage of all sides of the device’s outer flange. This requires at least a 2.5 × 2.5 mm flap. Anti-fibrotics are administered prior to or after scleral flap creation similar to the standard trabeculectomy. A clear corneal paracentesis allows for controlled lowering of the intraocular pressure and access for reformation of the anterior chamber if necessary. However, one advantage of the Ex-PRESS is that the anterior chamber typically stays extremely stable throughout the duration of the procedure. When anti-fibrotics have been administered, the nondominant hand will lift the scleral flap with care so as to identify the trabecular meshwork at the “blue line” next to the cornea. Several different instruments can be used to enter the anterior chamber at the “blue line” including a 25-gauge needle or 25-gauge MVR blade. It is important to enter straight in at the iris plane and come straight out to ensure proper sizing of the ostium and avoid hypotony or device dislocation/instability in an ostium that is too large for the device.
The Ex-PRESS device comes on a preloaded injector. The injector has a metal shaft that holds the device at the lumen. The injector is then used to introduce the device via the created ostium. The ostium should be approached with the device’s face plate rotated in a direction 90° from its final resting place. Care should also be taken to approach at the same angle as was used to fashion the ostium. Once the face plate is flush with the sclera, the device is rotated 90° so the flow is directed posteriorly and then released by pressing the button on the injector. The device should be centered at this time and checked for anterior chamber position. Of note, no sclerostomy or iridectomy is performed.
The scleral flap is closed in desired fashion with interrupted 10-0 nylon sutures. The number of sutures and tightness of sutures should be adjusted for proper flow. The previously created paracentesis can be utilized for injection of balanced salt solution to check flow. Conjunctiva is then closed in the surgeon’s preferred technique and the wound checked with a fluorescein strip.
Several potential problems should be avoided during the Ex-PRESS implantation. Premature release of the device is possible and the provided injector is advertised as a single use system. Therefore, the assistant should be warned to not deploy the device. If it is inadvertently deployed, the surgeon can attempt to straighten the wire and reload the device.
At the time of scleral flap creation, the surgeon should be mindful of flap thickness as a thin flap could inadvertently be disinserted during device implantation. A fair amount of countertraction is needed to insert the Ex-PRESS through a properly sized ostium. Additionally, the flap should be dissected anterior into clear cornea to aid in proper device seating. If the device flange is immediately adjacent to the flap hinge, malrotation of the device and potential erosion, especially through a thin flap, may occur.
As discussed above, if the surgeon is not careful in using a properly sized needle for ostium creation, the resulting ostium can be larger than the device and lead to additional aqueous leakage around the device. Hypotony may be more likely in these cases. Also, creating the ostium and inserting the Ex-PRESS in the plane of the iris and at the “blue line” is important to avoid anterior or posterior positioning of the device. There is no evidence that anterior positioning results in endothelial cell loss. Posterior positioning may potentially result in cataract formation in phakic patients, increased inflammation due to iris chafing, and/or iris atrophy.
Subacute apparent failure of Ex-PRESS device implantation was observed in 1.7 % of patients in a large cohort [13]. These patients had flat blebs and elevated IOP during the late postoperative period. One eye had vitreous obstructing the Ex-PRESS tip. Four other patients had an inflammatory response in the anterior chamber. The Nd:YAG laser was utilized to treat the tip of these Ex-PRESS devices which resulted in an elevated bleb and lower IOP. Interestingly, the patients with the inflammatory response were not noted to have obstruction at the tip but were noted to have dispersal of white particles during the laser procedure. Before considering adding glaucoma medications, performing a bleb needling, or pursuing further glaucoma surgery, one should consider Nd:YAG to laser the tip of the Ex-PRESS, especially in patients that have had inflammation postoperatively.
Bleb needling with anti-fibrotics has become a frequently performed procedure in attempting to restore bleb function for trabeculectomy. It can be repeated as needed and there are a few sight-threatening complications reported with needle revision [14]. Unfortunately, there is no data that investigates this procedure in eyes after Ex-PRESS shunt surgery, but anecdotally, needle revision is more difficult in these eyes [15]. Friedl concluded that bleb needling in an eye with an Ex-PRESS shunt is more difficult anecdotally than in an eye without the device. The authors state that one must take care to elevate the scleral flap parallel to the limbus and never in a radial fashion to prevent dislodging the Ex-PRESS shunt into the anterior chamber. Preliminary chart review from our institution (publication pending) has demonstrated efficacy results comparable to that of bleb needling for trabeculectomy. The safety of bleb needling after Ex-PRESS shunt surgery was also demonstrated. In contrast to Friedl and colleagues, we regularly approach the Ex-PRESS shunt radially at the time of needling procedures without dislodging the shunt. We regularly needle blebs after placement of the Ex-PRESS device and view it as a safe and efficacious procedure.
9.3 Outcomes
9.3.1 Ex-PRESS Versus Trabeculectomy
One of the first groups to study the Ex-PRESS was de Jong [16]. As mentioned, initial reports were extremely favorable with the Ex-PRESS being superior in almost every category. Long-term follow-up from this group showed equivalence of the Ex-PRESS and trabeculectomy in most areas [17]. Specifically, IOP results were favorable in both the Ex-PRESS and trabeculectomy groups, but better controlled in the Ex-PRESS group from years 1 to 3 (12 mmHg and 13.5 mmHg, respectively). Interestingly, although the Ex-PRESS group’s IOP remained stable through year 5 (11.5 mmHg), average IOP decreased to 11.3 mmHg at year 5. Complete success rates were significantly higher in the Ex-PRESS group through year 3 (66.7 % to 41 %, respectively). However, after year 1, there was no difference between the groups when placed on IOP lowering medications. By year 5, there was no difference between the groups in terms of complete or qualified success, albeit with a substantial trend toward higher complete success rates in the Ex-PRESS group. Average number of medicines was similar between the two groups at year 5 (2.1 for Ex-PRESS and 2 for trabeculectomy). A smaller percentage of patients in the Ex-PRESS group required IOP lowering medicines when compared to the trabeculectomy group from years 1 to 5.
Studies have also investigated the P-200 Ex-PRESS model and specifically compared it to traditional trabeculectomy. Moisseiev and colleagues retrospectively reviewed 100 eyes, 39 of which had received the P-200 Ex-PRESS [18]. This study was particularly interesting as they did not exclude patients for “complex” glaucoma, a term they used for uveitic, neovascular, and chronic angle closure glaucomas (addressed below). Similar to de Jong et al. [17], success rates, whether complete (62.3 % for trabeculectomy and 66.6 % for Ex-PRESS) or qualified (86.9 % for trabeculectomy and 84.6 % for Ex-PRESS) were similar, as was postoperative IOP. The number of required medications, unlike the above study, was similar between the study groups. Overall complication and hypotony rates were similar (9.8 % for trabeculectomy and 7.7 % for Ex-PRESS). Four patients (two in each group) required reoperation for uncontrolled IOP. Interestingly, none of the four were from the complex glaucoma group.
9.3.2 Prospective Studies
Buys investigated the efficacy and safety of Ex-PRESS versus trabeculectomy procedures in a prospective, randomized fashion [8, 19]. The study was not masked and reported 1-year outcomes. This study again showed equivalence of trabeculectomy and the Ex-PRESS device in success rates (complete 57 % and 70 %, respectively, qualified 90 % and 83 %, respectively), postoperative IOP (11.6 and 11.3, respectively), number of medications (0.6 and 0.4, respectively), and complication rates. Postoperative hypotony rates were similar at 39 % in each group.
Two particularly interesting elements of the study were the endothelial cell counts and pachymetry readings, as this is the first information on the Ex-PRESS device’s effect on endothelial health. With the use of specular microscopy, it has been established that there is little to no endothelial cell loss especially when used prior to entry of the anterior chamber. Long-term study of the endothelium will be interesting and fortunately, at 1 year, there is no difference between trabeculectomy and Ex-PRESS groups (2,257 cells and 2,301 cells, respectively).
In both groups, vision was significantly reduced in the early postoperative period. However, the study reported that the Ex-PRESS group had faster visual recovery with no difference from preoperative acuity by postoperative month 1. In contrast, the trabeculectomy group never returned to baseline visual acuity even at last follow-up at 1 year. Median vision loss at the 6 month follow-up was 0 lines for the Ex-PRESS group and 1.5 lines for the trabeculectomy group. Forty-seven percent of patients treated with trabeculectomy experienced ≥2 Snellen lines of vision loss by their 6 month follow-up visit, whereas only 16 % of those treated with the Ex-PRESS device lost that level of vision.
It is important to pause and consider visual recovery. It is clear that transient vision loss is common after filtration surgery. Shallowing of the anterior chamber is thought to cause a myopic shift postoperatively. Tight flap suturing, scleral cautery, postoperative ptosis, and large filtration blebs may lead to changes in corneal curvature and subsequent astigmatism [20]. Other retrospective studies have been a mixed bag with differing definitions and analysis when considering visual recovery [7, 10, 16, 21–23]. However, both prospective studies that specifically analyzed visual recovery [8, 9] definitively demonstrated a quicker visual recovery in the Ex-PRESS group with Beltran-Agullo and colleagues reporting that the trabeculectomy group never returned to baseline visual acuity at 1 year follow-up. It would be interesting to understand the economic impact this has on patient job productivity as it has been previously unstudied in past economic analysis.
Perhaps one of the most important prospective, randomized trials is the XVT (Ex-PRESS versus trabeculectomy) study authored by Netland et al. [9]. In that study, 59 patients received the Ex-PRESS device, whereas 61 underwent trabeculectomy. Mean IOP at 2 years was statistically equivalent (14.7 for Ex-PRESS and 14.6 for trabeculectomy, respectively). Mean number of medications was 0.9 for the Ex-PRESS group and 0.7 for the trabeculectomy group. Visual acuity was significantly reduced for both groups at the day 1 and week 1 postoperative visits. However, that reduction disappeared for the Ex-PRESS group at the 1 month visit and required an additional 2 months for the trabeculectomy group. Qualified success was 83 % at 2 years for the Ex-PRESS group and 79 % for patients undergoing trabeculectomy. Complication rates were higher in the trabeculectomy group (36.1 % versus 17 %).
Results from a recently performed meta-analysis of all randomized, prospective studies, excluding the XVT (not published at the time of the meta-analysis) [24] confirms most of the above conclusions. Qualified success rates, mean IOP, and number of medications are equivalent between both groups. However, the Ex-PRESS was more likely to have complete success at 1 year with fewer postoperative interventions. Hyphema was also found to be less common in the Ex-PRESS group.
9.3.3 Complex Glaucomas
Trabeculectomy was long the gold standard for any glaucoma. However in recent years, adoption of glaucoma drainage implants has increased for complex glaucomas. With the advent of the Ex-PRESS shunt, some are beginning to again switch back to filtering surgery for some complex glaucomas. Although no formal studies have been conducted investigating the outcomes in such cases with the Ex-PRESS shunt, there are some data to review.
9.3.3.1 Uveitic Glaucomas
Joseph Beer first described “arthritic iritis” in 1813 in a patient that developed glaucoma and blindness after a “gray-green” deep obscuration caused by vitreous opacification. Uveitic glaucoma can be both open and closed angle with open angle being the more common. Etiology is varied. Inflammatory cells, proteins, debris, or fibrin can obstruct the trabecular meshwork. Resistance to flow can increase due to inflammatory precipitates on the meshwork and swelling or dysfunction of the trabeculum even from topical corticosteroid use. The biochemical milieu can also affect the IOP. Rho kinase can constrict the trabecular endothelium and cytokines can promote neovascularization. A fibrovascular membrane can eventually grow over the angle, fully obstructing flow. Secondary angle closure may occur in three instances: (1) pupillary block resulting in iris bombe because of posterior synechiae, (2) broad peripheral anterior synechiae, and (3) anterior rotation of the ciliary body secondary to edema and swelling.
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