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  Table of Contents 
ORIGINAL ARTICLE
Year : 2016  |  Volume : 23  |  Issue : 1  |  Page : 110-114  

EX-PRESS® Implant position and function: Comparative evaluation with ultrasound biomicroscopy and optical coherence tomography


1 Department of Ophthalmology, University Hospital of Heraklion, Heraklion; Department of Refractive Surgery, Institute of Vision and Optics, Crete, Greece
2 Department of Refractive Surgery, Institute of Vision and Optics, Crete, Greece
3 Department of Ophthalmology, University Hospital of Heraklion, Heraklion, Greece

Date of Web Publication4-Jan-2016

Correspondence Address:
Efstathios T Detorakis
Department of Ophthalmology, University Hospital of Heraklion, 71110, Heraklion, Crete
Greece
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0974-9233.171774

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   Abstract 


Purpose: This study evaluated the feasibility of anterior segment optical coherence tomography (OCT) and ultrasound biomicroscopy (UBM) for the imaging of EX-PRESS® implant.
Materials and Methods: This nonrandomized comparative case series was performed at the Department of Ophthalmology of the University Hospital of Heraklion, Crete, Greece. The Ellex Eye Cubed (40 MHz) UBM and the Zeiss Visante OCT systems were used. The filtering bleb morphology (BL), aqueous outflow (AS), and tube position (TB) were evaluated by two independent observers using a quality scale of 1 (worst) to 4 (best). Data were also collected on corneal and iris clearance from the tip of the tube (CC and IC, respectively). Data from both the devices were statistically analyzed. P < 0.05 was considered as statistically significant.
Results: Ten eyes of 10 patients (6 males) with EX-PRESS® implant were examined. TB, AS, and BL scores using UBM were 2.40 ± 0.39, 3.45 ± 0.72, and 2.45 ± 0.64, respectively. TB, AS, and BL scores for OCT were 3.35 ± 0.41, 1.55 ± 0.43, and 2.55 ± 0.55, respectively. AS was significantly higher with UBM whereas the opposite was true for TB. Differences in BL between OCT and UBM were not statistically significant (P > 0.05).
Conclusion: Imaging of the EX-PRESS® implant is feasible with both UBM and OCT. Both modalities allow visualization of the position of the implant tube in relation to the iris or cornea and delineate the internal structure of the filtering bleb.

Keywords: Anterior Chamber, Cornea, EX-PRESS®, Iris, Optical Coherence Tomography, Ultrasound Biomicroscopy


How to cite this article:
Detorakis ET, Stojanovic N, Chalkia A, Pallikaris IG. EX-PRESS® Implant position and function: Comparative evaluation with ultrasound biomicroscopy and optical coherence tomography. Middle East Afr J Ophthalmol 2016;23:110-4

How to cite this URL:
Detorakis ET, Stojanovic N, Chalkia A, Pallikaris IG. EX-PRESS® Implant position and function: Comparative evaluation with ultrasound biomicroscopy and optical coherence tomography. Middle East Afr J Ophthalmol [serial online] 2016 [cited 2021 Oct 26];23:110-4. Available from: http://www.meajo.org/text.asp?2016/23/1/110/171774




   Introduction Top


The EX-PRESS ® implant (Alcon Laboratories Inc., Fort Worth, TX, USA) is becoming increasingly popular for patients undergoing glaucoma surgery.[1],[2] Some consider this implant as an integral component of modified “trabeculectomy.” In “modified trabeculectomy” iridectomy is not performed. All trabecular tissue remains in place and aqueous outflow is maintained through the lumen of the implant.

Although the implantation of EX-PRESS ® is fairly straightforward, there are some key technical aspects for correct implant position in the anterior chamber, including adequate tube clearance from the cornea and iris. Furthermore, it is beneficial for the examiner to be able to confirm satisfactory aqueous outflow from the anterior chamber below the superficial scleral flap.[1],[3] Ultrasound biomicroscopy (UMB) and anterior segment optical coherence tomography (OCT) are both well-established imaging modalities of the anterior ocular segment, including various forms of glaucoma.[4],[5],[6] Previous studies have employed UBM and OCT to evaluate filtering bleb features following trabeculectomy.[7],[8] This study examines the feasibility of using these imaging modalities to examine the position and function of the EX-PRESS ® and compares the two modalities by applying them on the same case series.


   Materials and Methods Top


This is a comparative case series study, performed at the Department of Ophthalmology of the University Hospital of Heraklion, Crete, Greece. All consecutive patients were included who underwent implantation of an EX-PRESS ® implant for the surgical management of open-angle glaucoma with medically uncontrolled intraocular pressure (IOP) during a 6-month period (November 2011–May 2012). Preoperatively, all eyes included in this study were on maximum tolerated topical therapy (prostaglandin analogs, b-blockers, and a-agonists) and oral acetazolamide. The 200 μm lumen EX-PRESS ® (P200) was implanted in all cases. Participating patients signed an informed consent form. This study was approved by the Ethics Committee of the Hospital and adhered to the tenets of the declaration of Helsinki.

The implantation of the EX-PRESS ® was performed in a standard fashion in all cases.[3] Briefly, under topical (subconjunctival) anesthesia; a traction suture (7.0 vicryl) was inserted through the superior corneal stroma to infraduct the globe. A small radial incision was created at the superior conjunctiva, and then a fornix-based conjunctival flap was prepared. Following the removal of Tenon's capsule and hemostasis, a sponge soaked in 0.2% mitomycin-C was applied locally for 2 min. A partial-thickness rectangular scleral flap, approximately 5 mm × 5 mm was then raised. When clear cornea was reached, a side port was fashioned, in order to be able to reform the chamber in case loss of chamber depth occurred intraoperatively. A 25G needle was then used for anterior chamber entry at the scleral spur (visible as a “blue-line”). The course of the needle was parallel to the iris plane for adequate clearance from both iris and cornea. The needle was then removed, and the EX-PRESS ® implant was soaked in balanced salt solution (BSS) and inserted through the needle entrance. The implant was released based on the manufacturer instructions by depressing the inserter when the implant flange was in place. Adequate aqueous outflow was then verified with a sponge, and the superficial scleral flap was sutured with 2 10.0 nylon sutures, providing apposition but not compression. The conjunctiva was then sutured with 7.0 vicryl implants and wound leakage was checked with a sponge. Finally, all patients received a subconjunctival injection of gentamycin and dexamethasone. All patients were discharged on the 3rd postoperative day and examined at weekly intervals for the first postoperative month. At the time of UBM/OCT imaging studies, no patient was on glaucoma medications in the operated eye. Slit lamp examination indicated one case with implant tip that was in close proximity to the anterior iris surface.

At least 2 months postoperatively (to ensure complete wound healing), the operated eyes were examined with UBM and OCT. UBM was performed with the 40 MHz Ellex Eye Cubed system (Ellex Medical Pty. Ltd., Adelaide, SA 5000 Australia). OCT was performed with the Zeiss Visante system (Carl Zeiss Meditec, Inc., Dublin, CA, USA). The Ellex Eye Cubed system has an axial resolution of 23 μm, a lateral resolution of 33 μm, and a 13 frames-per-second image acquisition rate (http://www.ellex.com/). The spectral-domain Zeiss Visante OCT system employs a superluminescent LED laser at 1310 nm producing 512 scans in 250 ms in a transverse fashion. The axial optical resolution is 18 μm and the transverse (center) resolution is 60 μm (http://www.meditec.zeiss.com).

For UBM examination, patients were examined in the supine position. Following the instillation of anesthetic eye drops, a purpose-designed eyecup was inserted behind the superior and inferior eyelid margins and filled with BSS. The oscillating UMB probe was then covered with a soft plastic cup filled with BSS. The covered probe was then dipped into the cup and aligned with the meridian along which the EX-PRESS ® had been implanted to obtain images of the implant and its position in the anterior chamber. As the implant was inserted in the superior limbal sector in all the eyes, the patients were asked to look down during UBM imaging to achieve better exposure of the potential space underneath the superficial flap, corresponding to aqueous outflow. An amplification setting of 90 dB was used in all cases. For OCT examination, the patients were examined in the sitting position per manufacturer instructions. The meridian along which the EX-PRESS ® had been implanted was the input into the software of the system and optical sections of the anterior segment with the Enhanced Anterior Segment Protocol were obtained. All examinations were performed with the same technique and by the same examiner (NS) who is experienced with both imaging modalities. UBM and OCT images of a filtering bleb created by an EX-PRESS ® implant are presented in [Figure 1]a and [Figure 1]b, respectively.
Figure 1: Ultrabiomicroscopy (a) and optical coherence tomography (b) images of an implanted EX-PRESS® implant. The area of aqueous outflow under the scleral flap is shown with “+” in both cases. Subconjunctival cystic spaces are also detected with both modalities

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Parameters examined were the delineation of the implant tube in the anterior chamber (TB), delineation of the filtrating bleb created by the implant (BL), delineation of the potential aqueous space underneath the superficial scleral flap (AS), clearance of the tip of the implant tube from corneal endothelium (CC), and clearance of the tip of the implant tube from iris (IC). BL, TB, and AS measurements were based on the average subjective evaluation of two independent observers (ETD, IGP), masked to each other's score. The observers used a quality scale of 1 (worst) to 4 (best), based on how clear, informative, and noise-free the images were. CC and IC were measured by using the incorporated software analysis of both Visante and Eye Cubed systems. OCT and UBM images of the case with contact between the tip of the EX-PRESS ® tube and the iris are presented in [Figure 2]a and [Figure 2]b, respectively.
Figure 2: Optical coherence tomography (a) and ultrasound biomicroscopy (b) images of a case with contact between the implant tube and iris, creating a kink in the iris contour (shown with an arrow) in both cases. The tube of the implant is shown with “*” in both cases

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Data were statistically analyzed with SPSS Software, version 8.0 (IBM Corp., New York, NY, USA). Statistical significance was set as 0.05. The level of agreement between the observers concerning BL, AS, and TB (examined by OCT) and BL, AS, and TB (examined by UBM) were evaluated with the Cohen's kappa coefficient. In the case of unequal score ranges, kappa was calculated by weighting the observations as previously described (http://www.ats.ucla.edu/stat/spss/faq/kappa.htm). The mean values of the UBM scores of the observers for BL, AS, and TB and the respective means for OCT scores were calculated, and the differences between the mean values of the parameters recorded by the two modalities were examined with paired samples t-test.


   Results Top


Overall, 10 patients were included (6 males). The average age (mean ± standard deviation, range) was 66.66 ± 7.08 years (range, 60–79 years) for males and 60.75 ± 10.04 years (range, 55–78 years) for females. All patients were pseudophakic, having previously undergone uncomplicated phacoemulsification. Previous glaucoma surgery had been performed in three cases (a trabeculectomy, enhanced with mitomycin-C in all three cases). The demographic characteristics and preoperative and postoperative IOP are presented in [Table 1].
Table 1: Demographic characteristics of the patients included as well as the preoperative and postoperative levels of IOP (recorded on the last preoperative visit and on the 2 months postoperative visit, respectively)

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The value of Cohen's kappa coefficient and the respective values for respective approximate standard error and approximate level of statistical significance for the examined parameters are presented in [Table 2]. The mean UBM score was statistically and significantly higher than the OCT score for AS (paired samples t-test). The mean OCT score was statistically and significantly higher for TB (paired samples t-test). The tube of the implant created an acoustic (A) and optical (B) shadow of the underlying iris, which was more pronounced in OCT [Figure 1], shown with a dashed line in both cases]. For BL, IC, and CC, the differences between the mean UBM and OCT scores were not statistically significant, although in CC, the difference approached (but did not exceed) statistical significance (paired samples t-test). Average scores for all parameters examined for both OCT and UBM and respective scores of the paired t-test and levels of statistical significance are presented in [Table 3].
Table 2: Values of kappa coefficient and respective values for approximate SE and approximate level of statistical significance for the examined parameters

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Table 3: Average scores (mean±SD, range) of TB, BL, and AS as well as CC (mm) and IC (mm) and respective levels of statistical significance for differences between UBM and OCT (paired samples t-test)

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   Discussion Top


The EX-PRESS ® implant in its current design (placed under a superficial scleral flap) is considered as a significant addition to the surgical options for treating medically uncontrolled glaucoma.[1],[2],[3],[9] The examination of implant position is usually performed by slit lamp biomicroscopy and gonioscopy. However, it would be clinically beneficial to observe the position of the implant tube and the clearance from the anterior iris surface and cornea, especially in cases with large filtering blebs over-hanging the cornea or in cases with opacified superior cornea. Findings from this study imply that UBM and OCT are both feasible imaging techniques for this purpose. The capability to display tube-iris contact and associated iris surface kinking, which may not be directly observed by slit lamp biomicroscopy or gonioscopy, may be another advantage for employing imaging modalities for the EX-PRESS ® implant. However, UBM and OCT suffer from artifacts such as acoustic or optical shadows created by the intensely refractile and opaque implant tube, which may compromise the accuracy of imaging.

A previous comparison of UBM (D1000; Tomey Corp., Nagoya, Japan) and OCT (SL [slit lamp] - OCT; Heidelberg Engineering GmbH, Heidelberg, Germany) to evaluate bleb function in trabeculectomy concluded that these imaging modalities can provide objective data for evaluating the outcome of glaucoma surgery or the need for a second procedure.[7] Findings from this study also show that the delineation of the internal structure of the filtering bleb following EX-PRESS ® implantation is possible with UBM and OCT. SL-OCT has previously been reported to have greater sensitivity and specificity than UBM in evaluating filtering bleb function following trabeculectomy.[7] In the present study, the lack of statistical difference between BL-OCT and BL-UBM scores, indicates that both modalities are equally capable of imaging bleb features. Furthermore, findings from this study imply that the UBM system employed in this study may be advantageous in delineating deeper filtration features such as the aqueous outflow pocket underneath the scleral flap, as derived from the statistically and significantly higher AS-UBM score, compared to the AS-OCT score. In the current study, the higher resolution of the OCT system compared to the UBM system and the fact that OCT is a noncontact technique, are the advantages of OCT.[7] However, light transmission through opaque tissues is limited, compared with the propagation of sound waves, implying that UBM may have advantages in the imaging of structures lying underneath opaque tissues.[10] It has been previously reported that aqueous humor in filtering blebs absorbs the reflection signal at a wavelength of 1310 nm, creating an attenuation of the scleral reflection behind the filtering zone, termed as the “shading phenomenon.”[11] This could possibly explain the significantly better score of UBM, compared with OCT, for the imaging of the aqueous outflow pocket in the present study. In the present study, shadowing of the iris under the EX-PRESS ® tube which obscured details was noted for both UBM and OCT images, but was more pronounced in the latter.

There are some drawbacks to the present study, including the relatively small number of patients examined, the fact that scoring for AS, BL, and TB was subjective as well as the fact that results may have been affected by the technical profile of the specific OCT and UBM systems employed. Furthermore, we limited cases to successful EX-PRESS ® implantation; hence, sensitivity and specificity of UBM and OCT in assessing implant function could not be evaluated. However, some of the drawbacks are mitigated by using one experience examiner to perform all imaging studies and using 2 independent masked observers for the scoring whose levels of agreement were moderate to substantial. The purpose of this study was to display the feasibility of these techniques, to obtain the images of EX-PRESS ® implants, and to explore potential advantages of each modality against the other, rather than to provide sensitivity and specificity data on their performance. Future studies should enroll a larger sample size and include failed or partly functioning cases to fully explore and quantitatively assess the role of these imaging modalities for evaluating the EX-PRESS ® implant.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
   References Top

1.
Freidl KB, Moster MR. EX-PRESS ® shunt surgery: Preferred glaucoma surgery in residency training? Surv Ophthalmol 2012;57:372-5.  Back to cited text no. 1
    
2.
Maris PJ Jr, Ishida K, Netland PA. Comparison of trabeculectomy with ex-press miniature glaucoma device implanted under scleral flap. J Glaucoma 2007;16:14-9.  Back to cited text no. 2
    
3.
Sarkisian SR. The ex-press mini glaucoma shunt: Technique and experience. Middle East Afr J Ophthalmol 2009;16:134-7.  Back to cited text no. 3
[PUBMED]  Medknow Journal  
4.
Dada T, Gadia R, Sharma A, Ichhpujani P, Bali SJ, Bhartiya S, et al. Ultrasound biomicroscopy in glaucoma. Surv Ophthalmol 2011;56:433-50.  Back to cited text no. 4
    
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Konstantopoulos A, Hossain P, Anderson DF. Recent advances in ophthalmic anterior segment imaging: A new era for ophthalmic diagnosis? Br J Ophthalmol 2007;91:551-7.  Back to cited text no. 5
    
6.
Silverman RH. High-resolution ultrasound imaging of the eye: A review. Clin Experiment Ophthalmol 2009;37:54-67.  Back to cited text no. 6
    
7.
Zhang Y, Wu Q, Zhang M, Song BW, DU XH, Lu B. Evaluating subconjunctival bleb function after trabeculectomy using slit-lamp optical coherence tomography and ultrasound biomicroscopy. Chin Med J (Engl) 2008;121:1274-9.  Back to cited text no. 7
    
8.
Singh M, Chew PT, Friedman DS, Nolan WP, See JL, Smith SD, et al. Imaging of trabeculectomy blebs using anterior segment optical coherence tomography. Ophthalmology 2007;114:47-53.  Back to cited text no. 8
    
9.
Hendrick AM, Kahook MY. Ex-press mini glaucoma shunt: Surgical technique and review of clinical experience. Expert Rev Med Devices 2008;5:673-7.  Back to cited text no. 9
    
10.
Garcia JP Jr, Rosen RB. Anterior segment imaging: Optical coherence tomography versus ultrasound biomicroscopy. Ophthalmic Surg Lasers Imaging 2008;39:476-84.  Back to cited text no. 10
    
11.
Theelen T, Wesseling P, Keunen JE, Klevering BJ. A pilot study on slit lamp-adapted optical coherence tomography imaging of trabeculectomy filtering blebs. Graefes Arch Clin Exp Ophthalmol 2007;245:877-82.  Back to cited text no. 11
    


    Figures

  [Figure 1], [Figure 2]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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