The goals of glaucoma-filtering procedures are to lower intraocular pressures (IOP) and maintain visual acuity (VA) while reducing the risk of further glaucomatous visual field progression and to avoid adverse side effects.1–7 Clinical observations suggest that optimal visual field preservation often requires maintaining IOP in the lower range of the normal distribution.5 Although trabeculectomy with intraoperative Mitomycin C (MMC) application often achieves such a result in primary surgery, skill is required to achieve the appropriate scleral flap resistance and avoid the potential complications associated with hypotony.
Our goals and rationales are as follows: (1) to provide a simple bleb-based procedure that does not require a scleral flap. We developed a soft, conforming, microlumen tube (Fig. 1) made from an inert biocompatible biomaterial called poly(styrene-block-isobutylene-block-styrene), or “SIBS.”8,9 The device is placed through a 3-mm-long 25-G needle tract formed under the limbus to shunt aqueous humor from the anterior chamber to the potential space under Tenon’s capsule. This device obviates the need for the scleral flap, sclerostomy, iridotomy, and tensioning sutures used in trabeculectomy. (2) Confirm that (i) the implant procedure developed in rabbit eye studies is applicable in human eyes; (ii) that the fins on the microtube serve as a stopper to prevent aqueous humor from leaking around the tube; (iii) that the fins tucked in a scleral pocket prevent device migration; and (iv) that a scleral patch to prevent erosion of the device through the conjunctiva is unnecessary. We hypothesize that the soft, conforming shunt, combined with placement beyond the eyelid excursion will minimize tissue erosion. (3) Yield a predictable transscleral pressure gradient without relying upon subjective suture tension. The lumen geometry (70 μm diameter, 8.5 mm long) of the MicroShunt acts as a flow resistor to maintain long-term transscleral pressure above 5 mm Hg; provided that aqueous production is >2 μL/min.10 (4) Determine the nature of postoperative interventions and adverse events. The device itself obviates suture lysis. We expect that the elimination of the scleral flap, sclerostomy, iridotomy, and tensioning sutures should reduce scar formation within the bleb and inflammation in the anterior chamber, which might reduce cataract progression. The use of a wide and deep fornix-based subconjunctival/Tenon’s flap with the wide placement of MMC should provide less problematic diffuse blebs.11
MATERIALS AND METHODS
The study is a nonrandomized prospective observational study of the InnFocus MicroShunt (MicroShunt). MMC was used in these patients based upon literature reports of its effectiveness in maintaining successful trabeculectomy-based blebs as compared with trabeculectomy alone.11,12 This device is experimental and at the time of this writing was not cleared for sale by the FDA but is approved for a US Investigational Device Exception clinical trial in the USA. It has also received a CE-Mark in Europe.
The study was conducted at Centro Láser, Santo Domingo, Dominican Republic (21 cases by J.F.B., 2 cases by R.A.). After approval of the implant protocol (ID 002-2007) by CONABIOS, the Dominican Republic National Counsel of Bioethics and Health, the study was initiated on February 1, 2010. The study is also listed as protocol NCT00772330 in http://www.clinicaltrials.gov.
Patients were screened and recruited from the glaucoma clinic at Centro Láser and the Elías Santana Hospital in Santo Domingo (Dominican Republic). Primary open-angle glaucoma patients that were not controlled with maximum tolerated glaucoma medication, demonstrating glaucomatous neuropathy progression were considered as potential subjects for the study. Neuropathy progression was determined by deterioration in visual fields (obtained by Humphrey Visual Field Analyzer) or in optic disc changes as estimated in images obtained by OCT (Cirrus; Zeiss). Likewise, patients who had both cataracts and glaucoma, where combined cataract and glaucoma procedures were indicated, were also considered for the study. All patients were carefully instructed about the new device and the study protocol and all required signing an informed consent form that was approved by the Dominican Republic National IRB. The first 23 consecutive patients who agreed to participate in the study were subsequently enrolled. Inclusion and exclusion criteria are listed in Table 1. The baseline examination included measures of best-corrected VA, visual field, gonioscopy, IOP, slit-lamp examination of the anterior chamber, and optic disc and fundus examination.
The criteria for “complete success” and “qualified success” were adopted from the Tube versus Trabeculectomy (TVT) Study.13–15 Complete success requires all of the following: (1) IOP≤21 mm Hg; (2) IOP reduction from baseline of ≥20%; (3) no reoperation for glaucoma (defined as requiring a procedure in an operating room); (4) no loss of light perception vision; (5) no chronic hypotony defined as IOP≤5 mm Hg on 2 consecutive follow-up visits after 3 months; and (6) no use of supplemental glaucoma medication. (Needling of the bleb or postsurgical injection of an antifibrotic is not considered failures unless performed in an operating room setting.) Qualified success is the same as “complete success,” but with use of supplemental glaucoma medication. Qualified success with the same criteria as above, except with IOP≤18, 16, 15, 14, and 12 mm Hg will also be reported.
A masked observer measured IOP using the Goldmann applanation tonometry technique.13 The IOP was measured at baseline while patients were self-administering their habitual glaucoma medications. Glaucoma medications were discontinued immediately after surgery and were introduced at the surgeon’s discretion if the IOP was not adequately controlled.
The MicroShunt was provided by InnFocus Inc. (Miami, FL) in a sterile packaged kit containing: (1) three 7 mm diameter, 1-mm thick, polyvinyl alcohol LASIK shields (Hurricane Medical Inc., Bradenton, FL); (2) a gentian violet marker pen (Hurricane Medical Inc.); (3) a 3-mm marker/ruler (custom made by InnFocus Inc.); (4) a flat 1 mm wide×1 mm long Mani angled knife blade (Mani ophthalmic knife, MSL10 Slit Angled 1.0 mm; Mani Inc., Utsunomiya, Tochigi, Japan); and (5) a 25- or 27-G needle (Precision Glide Needle; Becton & Dickinson & Co, Franklin Lakes). Lidocaine with epinephrine was from Ropsohn, Bogotá, Colombia. Intracameral lidocaine was from Hospira Inc., Lake Forest, IL. The bipolar diathermy unit was from Radionic by Mentor, Model 440E, Santa Barbara, CA.
Phacoemulsification and intraocular lens (IOL) insertion, if required, was performed first with suturing of the clear corneal incision. The MicroShunt was implanted as illustrated in Figure 2. (1) A mixture of 0.1 mL of 0.1% lidocaine and 0.1 mL of 0.5% epinephrine was injected (30-G needle) under the conjunctiva and the conjunctival elevated to include 2 quadrants. Intracameral lidocaine (0.1 to 0.5 mL) was injected through a temporal corneal paracentesis tract. (2) A 6- to 8-mm-wide incision was made through the insertions of the conjunctiva and Tenon’s capsule at the corneoscleral junction in the superior temporal quadrant to form a fornix-based subconjunctival/Tenon’s flap. The flap was dissected posteriorly with blunt-tipped scissors to approximately the equator and laterally 3 to 4 mm on each side of the incision. Hemostasis was achieved with bipolar diathermy. (3) Three LASIK shields saturated in 0.4 mg/mL MMC were placed in the flap for 3 minutes (±15 s) followed by irrigation with sterile saline solution (>25 mL). (4) A point on the sclera was marked 3 mm posterior to the limbus with the inked marker/ruler and a radial, shallow scleral pocket, approximately 1 mm wide×1 mm in length, triangular pocket was made at the marked point with the Mani knife. (5) A 25- or 27-G needle was advanced through the apex of the scleral pocket into the anterior chamber above the iris plane. The course of the drainage tube approximately bisected the angle that was formed between the iris and cornea. (6) The MicroShunt was maneuvered through the scleral pocket and needle tract with a forceps and the fins of the device wedged snugly into the scleral pocket. The proximal end of the shunt extended 2 to 3 mm into the anterior chamber. (7) Flow of aqueous humor was confirmed by observing drop formation at the distal end of the tube. (8) The distal end of the device was tucked under the subconjunctival Tenon’s capsule flap to lie flush with the sclera, and the flap closed with multiple interrupted 10 to 0 nylon sutures on a spatula needle.
A light-pressure patch was used the day after surgery and nightly for 5 days thereafter. Topical Tobradex (Alcon Laboratories Inc, Fort Worth, TX), or Zymar and Predsol Forte (both from Allergan Inc., Irvine, CA) were instilled for 3 weeks or until the anterior chamber reaction and conjunctival hyperemia had resolved.
Subjects were examined at 1 day, 1 week, 1 month, 3 months, 6 months, and at 1, 2, and 3 years for protocol-based examinations. Best-corrected VA, IOP, slit-lamp examination including gonioscopy and fundus were assessed at each visit and visual fields annually. Anterior chamber and bleb slit-lamp photography was performed at 1, 3, 6 months, and annually. Blebs were rated annually using the Indiana Bleb Appearance Grading Scale.16
Baseline demographic characteristics are described in Table 2. Postoperative data were available for 23 patients at 1 year and 22 patients thereafter as 1 patient was lost to follow-up. Fourteen patients underwent MicroShunt implantation alone and 9 underwent combined MicroShunt insertion and phacoemulsification with subsequent IOL implantation. All patients presented with open-angle glaucoma with angles >30 degrees as determined by gonioscopy.
The first 20 insertions of the MicroShunt were performed successfully with the needle tract formed with the 27-G needle. However, the surgeon suggested that insertion of the MicroShunt could be facilitated if a larger 25-G needle was used for this purpose. The last 3 cases were performed with the 25-G needle and the insertion was indeed found to be easier and quicker with no observable periannular leakage. The MicroShunt was implanted successfully in all cases, thereby confirming that the procedure established in rabbit eyes can be reproduced in human eyes. Flow through the tube was observed after implantation, and there were no observable leaks around the tube. No device migration or erosion occurred throughout the 3-year study.
The mean percent reduction in IOP from baseline (23.8±5.3 mm Hg) at 1, 2, and 3 years was 55%, 50%, and 55%, respectively (Fig. 3). The mean IOP were 10.7±2.8, 11.9±3.7, and 10.7±3.5 mm Hg, respectively.
The number and percent of patients at various IOP intervals (≤21, 18, 14, etc.) at 0.5, 1, 2, and 3 years are reported in the upper section of Table 3. At 0.5, 1, 2, and 3 years there were 0, 0, 2, and 1 eye, respectively, with IOP reduction from baseline <20%; that is, only 3 of the 23 eyes in the study did not demonstrate a reduction in IOP from baseline of ≥20%. The IOP for the 2 patients at 2 years with IOP reduction from baseline <20% were 18 and 19 mm Hg, respectively. The 1 patient at 3 years with IOP reduction from baseline <20% had an IOP of 15.5 mm Hg. The data in the lower section of Table 3 combine the IOP from the upper section of Table 3 with the 3 failures where IOP was not reduced ≥20%. Therefore, for example, reading from Table 3 (lower), if the qualified success rate was defined as IOP≤14 mm Hg and ≥20% reduction in IOP from baseline, the result would be 100%, 100, 91%, and 95% at 0.5, 1, 2, and 3 years, respectively. The reason for the increased qualified success rate from 2 to 3 years is due to one of the failed cases being placed back on glaucoma medication.
One operation failed at 27 months due to the formation of an encapsulated bleb and an IOP that could not be controlled with medication. The patient underwent reoperation with a second MicroShunt, with the first device remaining in place. The IOP at the time of this writing with the second shunt is 12.5 mm Hg. This patient was considered a failure and the data not censored from the study.
Two patients had elevated IOP in the immediate postoperative period. In 1 combined surgery case, elevated IOP on day 1 was likely due to fibrin that was observed to block the MicroShunt lumen. The surgeon used a 27-G needle to perform an anterior chamber paracentesis through a clear cornea incision to flush the debris from the lumen and the IOP was thereafter controlled. In the second case, the surgeon used a 25-G needle to perforate an encysted bleb on postoperative day 90 when the pressure rose to 34 mm Hg, after which the IOP was controlled. Both of these interventions were considered serious adverse events.
The change in glaucoma medication use and the percent of patients off medication are reported in Table 4. The Kaplan-Meier survival curves showing both the complete and qualified success rates are presented in Figure 4.
Blebs and anterior chambers for tube placement were photographed and later rated according to the Indiana Bleb Appearance Grading Scale by a masked reviewer (P.P.).16 The average rated height, area, and vascularity at year 2 (n=23) of the blebs were H2.0±0.6 (range, 1 to 3), A2.5±1.0 (range, 1 to 4), and V1.3±0.5 (range, 1 to 2), respectively. The average rated height, area, and vascularity at year 3 (n=22) of the blebs were H1.0±0.7 (range, 0 to 2), A0.8±0.7 (range, 0 to 2), and V2.0±1.2 (range, 0 to 3), respectively. Figure 5 shows a typical bleb progression at 1, 2, and 3 years. No tubes were observed to be in contact with the corneal endothelium, and no focal corneal opacities were noted.
Filtering blebs were observed at the slit lamp in 21 of 23 eyes at 1 year. Two of the 23 eyes had no discernible bleb; however, the IOP was controlled. At 3 years, 3 more patients (5 in total) were observed to have no discernable bleb, also with IOP controlled. None of the flat blebs had angle closure by Van Herick or gonioscopic examination. One patient had an early bleb leak that spontaneously resolved within 2 weeks. No late bleb leaks were observed, and there were no cases of bleb infection. In addition, there was no observed “tenting” of the conjunctiva over the MicroShunt in eyes with blebs. In eyes with flat blebs, the outline of the MicroShunt could be discerned under the Tenon’s; however, the MicroShunt tended to remain flat on the scleral surface in all cases as opposed to lifting from the sclera.
There were no VA losses or gains >1 line in any of the patients who had glaucoma surgery alone over the 3-year timeframe tested. There were 3 patients who gained 2 or more lines at 1 and 3 years, and 4 patients at 2 years, after implantation of a MicroShunt in combination with phacoemulsification and implantation of an IOL.
A summary of 21 postpostoperative adverse events directly related to the MicroShunt are presented in Table 5. Of these 21 adverse events, 14 patients experienced no adverse events. Two of the 7 patients with adverse events endured multiple adverse events which included hypotony, shallow anterior chamber, iris touch, and choroidal detachment.
Shallow anterior chambers were observed in 3/23 (13.0%) patients, 1 from the device only group and 2 from the combined group and occurred during the first 3 weeks after surgery. All were managed expectantly without secondary procedures or special maneuvers. Atropine, viscoelastic, and patching were not used in any of these cases. There were no bleb leaks. One of the combined cases presented with their intraocular lens captured in the pupil but with an excellent bleb and good VA. The IOL was repositioned in a subsequent intervention. No patient required reformation of the anterior chamber or drainage of a choroidal effusion. One shallow anterior chamber spontaneously deepened to normal depth by 14 days and the other 2 resolved spontaneously by the day 21 of the follow-up. There were no associated adverse events such as cataract formation, corneal edema, or development of peripheral anterior synechiae from these 3 patients with shallow chambers.
Choroidal detachment was observed in 2 patients (8.7%) from the combined group and were documented by indirect ophthalmoscopy and in some cases by B-ultrasound. In 1 patient with transient hypotony, who also experienced a shallow chamber, the IOP returned to 6 mm Hg by the 6-week follow-up and the detachment resolved spontaneously by the 12-week follow-up. In the second patient, the IOP dropped to 6 mm Hg at the 3-week follow-up and increased to 8 mm Hg at 6 weeks, at which time the choroidal detachment had resolved spontaneously. Topical steroids and antibiotics were used in these patients—oral steroids were not used. There were no cases of chronic hypotony, late bleb leak, endophthalmitis, or cataract progression in these 2 patients.
Adverse events related to cataract surgery included; transient corneal edema (4 patients), posterior capsular opacities (2 patients) which were successfully treated with a Nd:YAG laser and posterior synechiae (2 patients). Intraocular lens pupillary capture (1 patient) was corrected by repositioning. Vitreous hemorrhage resolved on its own in 1 patient and fibrin in the aqueous resolved in another patient on its own. Other individual adverse events included tearing, dry eye, and pain.
This small nonrandomized observational study was designed to confirm the implant procedure in humans and to gather some information on the long-term safety and efficacy of the device. The average IOP at 3 years was 10.7±3.5 mm Hg with a reduction in IOP from baseline of 53% and was similar in patients undergoing device implantation alone or device implantation combined with phacoemulsification and IOL implantation. These data are similar to those reported for bleb-based procedures with MMC; that is, primary trabeculectomy alone and primary trabeculectomy with the Ex-Press Shunt (Alcon Laboratories Inc., Optonol, Fort Worth, TX),12–15,17–19 with 1-year mean IOP varying within a range of 11 to 15 mm Hg.
Over 80% of the patients in this study have an IOP≤14 mm Hg (Table 3) which suggests sufficient IOP lowering to limit vision loss based upon data from the AGIS study.5 Two thirds of the patients did not require glaucoma medication at the third year of the study and the overall mean reduction in glaucoma medication was 71% to 0.7±1.1 medications/patient (Table 4) at 3 years.
Bleb appearance trended toward shrinkage in volume (decreased height and decreased area) and increased vascularity with time. The IOP remained in the low teens in the 5 patients at 3 years with flat blebs, suggesting that drainage from these blebs was occurring, possibly through lymphatic channels in the area of the bleb.
The adverse events observed in this study are either comparable to or less than those observed in other surgical procedures and devices reported in the literature.12–15,17–20 The failure rate and need for supplemental medication seem favorable in comparison to trabeculectomy with MMC. In contrast to results for tube-to-plate aqueous drainage implants, no cases of persistent corneal edema or of motility disturbance were observed.14,15,20
The initial safety profile of the MicroShunt may have advantages over trabeculectomy in that patients did not demonstrate hypotony-related complications that required surgical intervention. The incidence of transient hypotony observed in this study was in the range of that reported by various investigators with the Ex-Press shunt (7.5% to 15.6%) and with trabeculectomy (8% to 32%).12–15,17–19 The incidence of combined shallow anterior chambers and choroidal effusions reported by Netland et al19 was 6.8% and 11.5% in the Ex-Press and trabeculectomy groups, respectively. The small lumen diameter and long length of the rubbery tube, combined with sealing of the peritubular space with the fins of the device, prevents sudden changes from occurring in aqueous humor volume in the eye which may play a role in limiting choroidal hemorrhage and other severe adverse sequelae.
No cases of late tube-corneal touch, migration, or erosion were observed in this study. The lack of tube exposure may be due to use of a 3-mm-long scleral needle track with surfacing of the tube above the scleral surface behind the excursion of the upper eyelid. Placement of the tube in this manner has been shown to markedly reduce tube erosions for Ahmed implants, as described by Albis-Donato et al.21 These results suggest that use of covering patch material, such as sclera, cornea, pericardium, or amniotic membrane is unnecessary with this device.
To summarize relative to the goals outlined in the introduction: (1) the InnFocus MicroShunt is simple to implant, without the need for scleral dissection, sclerostomy, iridotomy, and tensioning sutures. With practice, the procedural time was reduced to <12 minutes. Although not explored in this study, we believe that the procedure can be performed <9 minutes if MMC were injected before surgery. (2) The MicroShunt was implanted successfully in all cases, thereby confirming that the procedure established in rabbit eyes can be reproduced in human eyes. The establishment of flow through the device at the end of the procedure, as determined by observing drop formation at the exit of the device, suggests that the tube and fins effectively sealed the needle tract (flow would not occur through the small lumen of the device if there was substantial periannular leakage). There were no observations of device migration or erosion through the conjunctiva throughout the 3-year study, thereby confirming that a scleral patch is not required. (3) IOP is controlled in the long term. Although there was some acute hypotony, all resolved spontaneously without intervention. Early hypotony was expected until the effect on aqueous flow of prior medical therapy abated. The device was effective in lowering IOP by 50% to 55%, with control of IOP to a level <14 mm Hg in over 80% of patients. (4) Postoperative intervention included only 1 bleb needling and 1 failure over the 3-year study. Suture lysis was eliminated and there were no incidences of late bleb leaks, endophthalmitis, or any other long-term sight-threatening adverse events. There was no noted progression of cataracts in any of the phakic patients.
This observational study was conducted on a small number (23) of patients and was not powered or randomized to provide conclusive results on its effectiveness in relation to more conventional procedures such as trabeculectomy. However, the data did provide a level of confidence to proceed to larger controlled studies. The InnFocus MicroShunt was CE Marked on January 9, 2012 in Europe where several other clinical studies are under way to increase the number of patients followed and to find the limitations of the device. In addition, a US Investigational Device Exception was granted by the FDA in May 2013 and a multicenter clinical trial comparing the MicroShunt to primary trabeculectomy in patients refractory to medication is under way.
The authors wish to acknowledge Maria Consuelo Varela as the clinical coordinator in the study and John B. Martin, Jr for building the pilot plant to make the devices. The authors would like to dedicate this publication to Francisco Fantes, MD, coinventor of the MicroShunt and the inspiration behind its development, who sadly passed away in the third year of this study.
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Keywords:Copyright © 2016 Wolters Kluwer Health, Inc. All rights reserved.
glaucoma; glaucoma drainage tube; treatment surgery; aqueous humor; minimally invasive surgery; shunt