|Year : 2020 | Volume
| Issue : 1 | Page : 16
Pars plana Ahmed glaucoma valve implantation in refractory glaucoma: Surgical technique and long-term outcomes
Harsh Kumar, Avnindra Gupta, Suman Bandil, Mithun Thulasidas
Centre for Sight, New Delhi, India
|Date of Submission||14-Apr-2020|
|Date of Acceptance||08-May-2020|
|Date of Web Publication||24-Jun-2020|
Dr. Mithun Thulasidas
Centre for Sight, B-5/24, Safdarjung Enclave, New Delhi - 110 029
Source of Support: None, Conflict of Interest: None
Purpose: The aim of this study was to evaluate the long-term efficacy of intraocular pressure (IOP) control and complications of pars plana Ahmed glaucoma valve (AGV) implantation in refractory glaucoma patients. Design: This was a prospective interventional study. Materials and Methods: We conducted a single-center study, involving eyes with refractory glaucoma. Study variables were IOP, the number of glaucoma medications, and corrected distance visual acuity (CDVA) evaluated preoperatively and postoperatively at 1 day, 1 week, 1 month, 3 months, 6 months, and every 6 months till the last follow-up. Complete success was defined as absolute if IOP was between 6 and 21 mmHg in the absence of any glaucoma medication and qualified success if IOP was between 6 and 21 mmHg with medication at the last follow-up. Results: The study included 27 patients (29 eyes) with a mean age of 54.28 (standard deviation [SD]: 16.76; range: 11–73) years and a mean follow-up of 21.31 (SD: 20.38; range: 6–60) months. The mean IOP reduced from 38.14 (SD: 7.4; range: 25–50) mmHg preoperatively to 12.76 (SD: 3.92; range: 6–20) mmHg at the last follow-up (P <0.001). CDVA improved in 16 (55.2%) eyes, remained the same in 10 (34.5%) eyes, and worsened in 3 (10.3%) eyes. There was a mean reduction of antiglaucoma medications from 4.07 (SD: 0.26) preoperatively to 0.93 (SD: 1.31) postoperatively (P <0.001). The absolute success rate was 62%, reaching 100% in terms of qualified success. Postoperative complications included vitreous hemorrhage in 4 (13.8%) eyes, transient hypotony in 3 (10.3%) eyes, hyphema in 2 (6.9%) eyes, tube exposure in 2 (6.9%) eyes, and development of a small iris cyst in 1 (3.4%) eye. Conclusion: Pars plana implantation of AGV is a viable option in refractory glaucoma eyes where other surgical options are precluded, as it provides a good success rate with fewer postoperative complications. One must still keep a watch for tube exposure, vitreous incarceration in the tube, vitreous hemorrhage, and future retinal complications.
Keywords: Ahmed glaucoma valve, pars plana, pars plana vitrectomy, refractory glaucoma, tube exposure
|How to cite this article:|
Kumar H, Gupta A, Bandil S, Thulasidas M. Pars plana Ahmed glaucoma valve implantation in refractory glaucoma: Surgical technique and long-term outcomes. Pan Am J Ophthalmol 2020;2:16
|How to cite this URL:|
Kumar H, Gupta A, Bandil S, Thulasidas M. Pars plana Ahmed glaucoma valve implantation in refractory glaucoma: Surgical technique and long-term outcomes. Pan Am J Ophthalmol [serial online] 2020 [cited 2021 Dec 7];2:16. Available from: https://www.thepajo.org/text.asp?2020/2/1/16/287690
| Introduction|| |
Glaucoma is considered as the leading cause of irreversible blindness worldwide. Intraocular pressure (IOP) reduction in glaucoma patients can be achieved with medical, laser, or surgical management. Medical treatment is generally the first choice due to less side effects. However, when target IOP is not achieved, laser or surgical modality should be chosen.
Neovascular glaucoma, uveitic, iridocorneal endothelial syndrome, epithelial ingrowth, postpenetrating keratoplasty, angle recession, and other secondary glaucomas defined as refractory glaucomas, usually are unresponsive to medical therapy or challenging to manage with conventional surgical modalities.,, Glaucoma drainage devices (GDDs) have been used extensively for the management of such cases of refractory glaucoma, especially in patients whose previous partial-thickness filtering procedures have failed or are expected to have a low chance of success.,
GDD was first described by Molteno in 1969. The Ahmed glaucoma valve (AGV; New World Medical, Inc., Rancho Cucamonga, California, USA), a valvular tube shunt with a restriction flow mechanism, is the most frequently used due to less complications.,, GDD tube is placed either into the anterior chamber or into the vitreous cavity. In cases where corneal endothelium is compromised, the angle is vascularized or obliterated because of peripheral anterior synechiae and eye is small with inadequate anterior chamber depth, placement of the tube in the anterior chamber is extremely difficult.,, In these situations, pars plana tube placement is the preferred approach. However, pars plana placement of GDD tubes has complications too, including vitreous incarceration of the tube, vitreous hemorrhage, and retinal detachment.
The purpose of this study was to compare the long-term efficacy and complications in refractory glaucoma patients undergoing pars plana implantation of AGV.
| Materials and Methods|| |
A single-center, prospective study was conducted at Centre for Sight, India, between January 2012 and August 2019. The study was approved by the ethics committee and adhered to the tenets of the Declaration of Helsinki. Informed consent was obtained from all patients before undergoing surgery.
Inclusion criteria included patients who had refractory glaucoma, with an IOP >21 mmHg with maximally tolerated glaucoma medications, failed surgeries, or both. Exclusion criteria included patients with <6 months of follow-up and previous GDD placement. A complete ophthalmologic examination including corrected distance visual acuity (CDVA) measured as logarithm of the minimum angle of resolution (logMAR) scale, slit-lamp biomicroscopic examination, IOP measurement using Goldmann applanation tonometer, dilated fundus examination using 90 diopter lens, and indirect ophthalmoscopy was performed. All surgeries were performed by a single glaucoma surgeon and pars plana vitrectomy by a single vitreoretinal surgeon. AGV flexible plate (FP-7) model (New World Medical, Inc., Rancho Cucamonga, California, USA; FDA approved) made of medical-grade silicone with valve/plate specifications (thickness: 2.1 mm, width: 13.0 mm, length: 16.0 mm, and surface area: 184.0 mm2) and tube specifications (length: 25.4 mm, inner diameter: 0.305 mm, and outer diameter: 0.635 mm) was used in all cases.
Demographic characteristics for each patient, including age, gender, preoperative lens status, cornea status, and glaucoma diagnosis, were recorded. Study variables were postoperative IOP, CDVA, the number of glaucoma medications, surgical complications, and success at the last follow-up examination. Complete success was defined as absolute if IOP was between 6 and 21 mmHg in the absence of any glaucoma medication and qualified success if IOP was between 6 and 21 mmHg with medication at the last follow-up visit. Failure was defined as IOP >21 mmHg on medical therapy, IOP <6 mmHg on 2 consecutive visits after 3 months, loss of light perception, additional glaucoma surgery for IOP control, and explantation of implant. Examinations were performed preoperatively and postoperatively at 1 day, 1 week, 1 month, 3 months, 6 months, and every 6 months after that.
Before proceeding for the surgery, careful planning was done in each case regarding the quadrant available for tube placement. Inferotemporal quadrant was preferred in cases with previous superior quadrant surgeries, extensive conjunctival scarring, or scleral thinning in the superior quadrant and silicone oil-induced glaucoma. The peribulbar block was the chosen technique of anesthesia, which could always be augmented by injecting the anesthetic posteriorly from the fornix-based conjunctival flap. After putting a 6-0 vicryl corneal traction suture to rotate the globe, a fornix-based conjunctival flap was fashioned in the quadrant of choice. AGV (FP-7 model) priming was done by irrigating the tube through the 30G needle or cannula using a sterile balanced salt solution. The initial pressure through a 5-ml syringe was forceful to open the silicone membrane valve, followed by a gentle pressure to check if the valve was opening at a lower pressure. An 8-0 silk suture was passed through the eyelet of the valve plate to hold the valve to prevent posterior displacement, and the tubing was trimmed to extend into the vitreous cavity for 5–6 mm before insertion with bevel up. The plate was placed in the requisite quadrant with its anterior edge 8 mm posterior to the corneoscleral limbus. The plate was sutured to the episclera with 2 interrupted 8-0 silk sutures on a reverse cutting needle. Cautery was done, and a 5 mm × 5 mm partial-thickness limbus-based scleral flap was created.
Simultaneously, a three-port 23G pars plana vitrectomy was performed by the vitreoretinal surgeon. It was ensured that a complete vitrectomy was carried out, including the posterior hyaloid removal by triamcinolone staining of vitreous. The tube was then inserted through a scleral fistula that was created with a 23G needle. The fistula was created approximately 2–3 mm posterior to the surgical limbus and advanced 5 mm into the vitreous cavity. The position of the tube inside the eye was confirmed by direct visualization. An interrupted suture 10-0 was placed to secure the tube's course and to prevent kinking because of an acute angle of entry in these cases. The scleral flap was sutured with 10-0 nonabsorbable suture.
After performing the conventional technique in 11 eyes, we noticed mild tube exposure in 2 eyes at a site just beyond the scleral pocket where the tube was covered only by the conjunctiva. We used a 5 mm × 4 mm donor scleral patch graft to cover the posterior portion of the tube, i.e., around 5 mm posterior to the surgical limbus, and continued to do the same in the subsequent 18 eyes. Thus, the entire length of the tube from the plate till the entry into the vitreous cavity was covered by the donor sclera. The posterior apex of the scleral flap was sutured to the donor scleral patch using a 10-0 nonabsorbable suture, leaving no exposed area between the flaps. In one case, only a scleral donor patch graft was used as the scleral pocket could not be fashioned due to thin sclera.
The conjunctiva and Tenon capsule were closed with 10-0 or 8-0 vicryl sutures using both interrupted and running techniques. Postoperative management included the use of topical corticosteroid in tapering dosage for 6 weeks, a topical antibiotic for 2 weeks, cycloplegics, and antiglaucoma medications as required. Postoperative complications were defined as early (till 3 weeks) and late (after 3 weeks).
Continuous variables were presented as mean ± standard deviation. Categorical variables were presented as frequency and percentage. Normality of data was tested by Kolmogorov–Smirnov test. Paired Student's t-test was applied to see the relative change with time. P < 0.05 considered statistically significant at 95% confidence level. The statistical software SPSS version 24.0 was used in the analysis.
| Results|| |
Twenty-nine eyes of 27 patients were included in this study. The demographic characteristics and type of glaucoma are shown in [Table 1] and [Table 2]. The mean age was 54.28 ± 16.76 years, ranging from 11 to 73 years. Sixteen (59.3%) patients were male. Neovascular glaucoma (20.7%) was the most common type of glaucoma. The mean preoperative and final follow-up postoperative data are displayed in [Table 3], while the mean postoperative IOP at every visit is displayed in [Figure 1]. Preoperatively, all patients, despite being on maximal medical therapy, had an IOP of 25 mmHg or higher (range, 25–50 mmHg) and were associated with advanced glaucomatous cupping. The mean follow-up time was 21.31 ± 20.38 months, ranging from 6 to 60 months.
|Figure 1: Preoperative and postoperative mean intraocular pressure values|
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At the last follow-up, the mean IOP had decreased significantly from 38.14 ± 7.4 mmHg to 12.76 ± 3.92 mmHg (P <0.001). Postoperatively, IOP decreased in all cases in comparison with preoperative values. The mean number of glaucoma medications decreased significantly from 4.07 ± 0.26 preoperatively to 0.93 ± 1.31 at the final follow-up (P <0.001). The absolute success rate was 62%, reaching 100% in terms of qualified success (glaucoma medication was necessary for 11 eyes to achieve normal IOP levels). [Figure 2] shows the postoperative image of an eye with the visualization of the tube in the vitreous cavity and a donor scleral patch graft at the site beyond the autoscleral pocket, covering the posterior portion of the tube in the superotemporal quadrant.
|Figure 2: (a) Postoperative image of an eye with the visualization of the tube in the vitreous cavity. (b) A donor scleral patch graft at the site beyond the autoscleral pocket, covering the posterior portion of the tube in the superotemporal quadrant|
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The mean preoperative logMAR CDVA improved from 0.83 ± 0.66–0.58 ± 0.52 at the last follow-up (P = 0.007). Eleven (37.9%) eyes had a gain of ≥2 lines of visual acuity. CDVA improved in 16 (55.2%) eyes, remained the same in 10 (34.5%) eyes, and worsened in 3 (10.3%) eyes. No patients reported postoperative loss of light perception.
No significant intraoperative complications of pars plana AGV implantation were observed. Postoperative complications were defined as early (till 3 weeks) and late (after 3 weeks). The postoperative complications are given in [Table 4]. The most common early postoperative complication was vitreous hemorrhage in 4 (13.8%) eyes, of which 3 eyes had neovascular glaucoma and 1 eye had acute angle-closure glaucoma, which cleared within 2 weeks of surgery with preoperative vision. Transient hypotony due to choroidal effusion occurred in 3 (10.3%) eyes, which was an expected sequela after any pressure-lowering surgery. Mild-to-moderate hyphema was observed in 2 (6.9%) eyes, both of which were cases of neovascular glaucoma and the hyphema absorbed spontaneously. Late postoperative complications occurred in the form of tube exposure in 2 (6.9%) eyes where the posterior portion of the tube was covered only by conjunctiva and was repaired with scleral allograft and conjunctival autograft. One eye had developed a small iris cyst at 6-month follow-up and is under observation.
| Discussion|| |
The AGV, since its initial description in 1995, has shown an improvement in surgical success rates and has reduced the complication rate compared to other surgical techniques previously used in refractory glaucoma. However, implantation of the tube into the anterior chamber can potentially cause significant anterior segment complications including corneal decompensation because of the tube-endothelial touch, corneal graft failure, dellen formation, limbal erosion over the tube's entry site and adjacent conjunctiva, iris plugging of the tube, progression of cataract, and aqueous misdirection.,,,,,,, Furthermore, a shallow anterior chamber, abnormalities of the iridocorneal angle, angle neovascularization, preexisting peripheral anterior synechiae, or advancing peripheral synechiae secondary to inflammation may make anterior segment tube placement difficult.,, Pars plana placement of the tube has been preferred for such cases. Numerous studies have produced clinical data on the use of pars plana AGV implantation in various types of intractable glaucoma.,,,,,,,,,,, Here, we present a prospective long-term (maximum of 5 years) clinical study on patients with refractory glaucoma with pars plana AGV implantation.
Regarding the type of glaucoma, the present study reported neovascular glaucoma (20%) as the most common indication, followed by other refractory secondary glaucomas, similar to the studies by de Frutos-Lezaun et al. and Diaz-Llopis et al., Maris et al. reported a 25.8% rate of primary open-angle glaucoma, whereas Parihar et al. excluded patients with neovascular glaucoma or retinal diseases.,
It is challenging to compare surgical success rates from various published studies because of the differences in the study population, types of implants used, and duration of follow-up. In the present study, the absolute success rate was 62% at the last follow-up, reaching 100% in terms of qualified success. This is in comparison with the data reported by de Frutos-Lezaun et al. (60% absolute success and 100% qualified success) and Diaz-Llopis et al.(70% absolute success and 90% qualified success) at 12-month follow-up., Qin et al. reported a success rate of 86% with pars plana GDD implantation at the end of 5 years. Maris et al. have reported a success rate of 83.9% at 48 months, and Parihar et al. have reported a complete success rate of 72% at 24-month follow-up., The absolute and qualified success rates reported by Dada et al. at 12 months were 54.5% and 81.8%, respectively.
In this study, the mean preoperative IOP (38.14 ± 7.4 mmHg) showed a reduction of 67% postoperatively (12.76 ± 3.92 mmHg) at the last follow-up, which is comparable to other studies.,, The intervening postoperative IOP ranged from 6 to 19 mmHg during the entire postoperative period and was significantly reduced compared to baseline (P <0.001). We found that IOP was relatively high at 1–3 months postsurgery and then remained steady afterward [Figure 1]. IOP was controlled in all the patients (100%). Eighteen patients (62%) did not require any glaucoma medication postoperatively. There was a significant reduction in the number of medications from 4.07 ± 0.26 preoperatively to 0.93 ± 1.31 at the final follow-up (P <0.001).
Visual acuity after glaucoma surgery can be affected by multiple factors such as the stage/severity of glaucoma, surgical complications, and other ocular comorbidities. Furthermore, the different preoperative stage of glaucoma among various studies makes comparison challenging. In this study, although most of the patients with advanced refractory glaucoma had a guarded visual prognosis, there was a significant improvement in CDVA from 0.83 ± 0.66 preoperatively to 0.58 ± 0.52 at the last follow-up (P = 0.007). Twenty-six (89.7%) eyes improved or maintained the CDVA, whereas three (10.3%) eyes worsened due to the development of after-cataract. Performing cataract surgery in the same sitting is preferred in case of pars plana AGV implantation, provided the cataract is visually significant. No postoperative loss of light perception was observed. A wide range of visual acuity outcomes has been reported after pars plana implantation of GDDs, with improved or stable visual acuity reported in 27.7% to 100% of cases.,,,,,,,,
In the present study, three eyes had a previous corneal graft, and they remained clear until the last follow-up at 24 months. One eye had undergone penetrating keratoplasty with simultaneous pars plana AGV implantation, and the graft remained clear at the end of 36-month follow-up. Various studies have reported a 24-month graft survival rate ranging from 41% to 76% with penetrating keratoplasty and pars plana GDD placement.,,, Although the placement of a GDD tube through the pars plana approach may reduce direct mechanical endothelial trauma to the graft, other factors, such as blood–aqueous barrier breakdown as well as a history of multiple previous and concurrent intraocular surgeries, predispose these patients to increased postoperative inflammation, corneal endothelial cell loss, and immunologic graft rejection.,
No significant intraoperative complications were noted in the present study. The most common postoperative complication was vitreous hemorrhage (13.8%), which cleared subsequently within 2 weeks. Three out of four eyes with vitreous hemorrhage had neovascular glaucoma. This shows the risk of vitreous hemorrhage postoperatively in cases of neovascular glaucoma, which is observed in different studies as well.,, Other early postoperative complications included transient hypotony (10.3%) and hyphema (6.9%), which are consistent with other studies.,, None of the complications affected the final surgical outcome or success.
Late postoperative complications included tube exposure (6.9%) and the development of a small iris cyst (3.4%). The incidence of tube exposure in this study is consistent with the exposure rates reported in other studies, and this complication appears to occur whether the tube is placed in the anterior chamber or through the pars plana., Tube exposure may lead to inflammation-mediated melting of self-tissue or the donor graft and subsequent mechanical damage to the overlying conjunctiva over the area of the protrusion by the underlying valve tube. It is understood that poorly managed cases of tube exposure may lead to endophthalmitis with poor visual prognosis. In the present study, tube exposure occurred in two eyes but was noticed on time and treated immediately before the development of a further complication. We used a donor scleral patch graft at the site beyond the autoscleral pocket, where the tube was covered only by the conjunctiva and continued to do the same in remaining cases. Furthermore, the donor scleral flap was used in a case where the sclera was thin, and it was prudent not to try a scleral pocket in this. Partial-thickness scleral flaps alone have been reported to have a higher rate of tube erosion, similar to what we observed in our initial cases. We found that the combination of a partial-thickness limbus-based scleral flap with donor scleral patch graft covered the entire length of the tube effectively, enhanced the cosmetic outcome, and eliminated the chance of erosion. A small iris cyst developed in one patient at 6-month follow-up and is under observation.
Pars plana implantation of GDD tubes has complications as well, such as vitreous incarceration of the tube and retinal detachment. A complete peripheral vitrectomy is important as the tube can be occluded by vitreous and cause a failure in the control of IOP, or traction can be exerted on the retina leading to a tear. None of our cases had these risks. Cases that were thought inoperable because of failed filtering surgery, extensive peripheral anterior synechiae, and weak corneas were taken up as the last choice to retain vision and managed successfully. Many of these patients had only one functional eye. AGV placement at the level of the pars plana should not be limited exclusively to aphakic or pseudophakic eyes, provided phakic eyes can undergo cataract surgery in the same sitting, as was achieved in all of our phakic patients. Every glaucoma surgeon must acquire the skill to perform pars plana AGV implantation and combined technique of partial-thickness scleral flap with donor scleral patch graft to avoid the complication of tube erosion.
The strengths of our study include its prospective design, longer follow-up though it is heterogeneous, and the description of surgical technique including the combined technique of partial-thickness autoscleral flap with scleral allograft. Limitations of our study include its small sample size and variable severity of glaucoma. Further prospective studies with a larger sample size may provide more meaningful results.
| Conclusion|| |
Our study demonstrates that AGV implantation through pars plana can be a secure and successful option in patients with refractory glaucoma and increased risk of surgical failure. It effectively lowers the IOP and reduces the number of glaucoma medications. The possibility of complications such as tube exposure, tube blockage due to vitreous incarceration, and other retinal problems such as vitreous hemorrhage must be kept in mind.
We thank Sanjay Tanwar for assistance in the statistical analysis of the manuscript.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
| References|| |
Quigley HA, Broman AT. The number of people with glaucoma worldwide in 2010 and 2020. Br J Ophthalmol 2006;90:262-7.
Das JC, Chaudhuri Z, Sharma P, Bhomaj S. The Ahmed Glaucoma Valve in refractory glaucoma: experiences in Indian eyes. Eye (Lond) 2005;19:183-90.
Lima FE, Magacho L, Carvalho DM, Susanna R Jr., Avila MP. A prospective, comparative study between endoscopic cyclophotocoagulation and the Ahmed drainage implant in refractory glaucoma. J Glaucoma 2004;13:233-7.
Schwartz K, Budenz D. Current management of glaucoma. Curr Opin Ophthalmol 2004;15:119-26.
Wilson MR, Mendis U, Smith SD, Paliwal A. Ahmed glaucoma valve implant vs trabeculectomy in the surgical treatment of glaucoma: a randomized clinical trial. Am J Ophthalmol 2000;130:267-73.
Molteno AC. New implant for drainage in glaucoma. Animal trial. Br J Ophthalmol 1969;53:161-8.
Coleman AL, Smyth RJ, Wilson MR, Tam M. Initial clinical experience with the Ahmed Glaucoma Valve implant in pediatric patients. Arch Ophthalmol 1997;115:186-91.
Law SK, Nguyen A, Coleman AL, Caprioli J. Comparison of safety and efficacy between silicone and polypropylene Ahmed glaucoma valves in refractory glaucoma. Ophthalmology 2005;112:1514-20.
Joos KM, Laviña AM, Tawansy KA, Agarwal A. Posterior repositioning of glaucoma implants for anterior segment complications. Ophthalmology 2001;108:279-84.
Nguyen QH. Avoiding and managing complications of glaucoma drainage implants. Curr Opin Ophthalmol 2004;15:147-50.
Gedde SJ, Schiffman JC, Feuer WJ, Herndon LW, Brandt JD, Budenz DL, et al
. Treatment outcomes in the Tube Versus Trabeculectomy (TVT) study after five years of follow-up. Am J Ophthalmol 2012;153:789-80300.
Varma R, Heuer DK, Lundy DC, Baerveldt G, Lee PP, Minckler DS. Pars plana Baerveldt tube insertion with vitrectomy in glaucomas associated with pseudophakia and aphakia. Am J Ophthalmol 1995;119:401-7.
Lloyd MA, Heuer DK, Baerveldt G, Minckler DS, Martone JF, Lean JS, et al
. Combined Molteno implantation and pars plana vitrectomy for neovascular glaucomas. Ophthalmology 1991;98:1401-5.
Ritterband DC, Shapiro D, Trubnik V, Marmor M, Meskin S, Seedor J, et al
. Penetrating keratoplasty with pars plana glaucoma drainage devices. Cornea 2007;26:1060-6.
Lieberman RA, Maris PJ Jr., Monroe HM, Al-Aswad LA, Bansal R, Lopez R, et al
. Corneal graft survival and intraocular pressure control in coexisting penetrating keratoplasty and pars plana Ahmed Glaucoma Valves. Cornea 2012;31:350-8.
Parihar JK, Jain VK, Kaushik J, Mishra A. Pars plana-modified versus conventional ahmed glaucoma valve in patients undergoing penetrating keratoplasty: A Prospective comparative randomized study. Curr Eye Res 2017;42:436-42.
Greenfield DS, Tello C, Budenz DL, Liebmann JM, Ritch R. Aqueous misdirection after glaucoma drainage device implantation. Ophthalmology 1999;106:1035-40.
Rotsos T, Tsioga A, Andreanos K, Diagourtas A, Petrou P, Georgalas I, et al
. Managing high risk glaucoma with the Ahmed valve implant: 20 years of experience. Int J Ophthalmol 2018;11:240-4.
de Frutos-Lezaun M, Rodriguez-Agirretxe I, Eder Labairu F, Irigoyen C. Vitrectomy combined with posterior-segment Ahmed valve implant: A case series study. Saudi J Ophthalmol 2018;32:180-7.
Qin VL, Kaleem M, Conti FF, Rockwood EJ, Singh A, Sood-Mendiratta S, et al
. Long-term Clinical Outcomes of Pars Plana Versus Anterior Chamber Placement of Glaucoma Implant Tubes. J Glaucoma 2018;27:440-4.
Maris PJ Jr., Tsai JC, Khatib N, Bansal R, Al-Aswad LA. Clinical outcomes of Ahmed Glaucoma valve in posterior segment versus anterior chamber. J Glaucoma 2013;22:183-9.
Wallsh JO, Gallemore RP, Taban M, Hu C, Sharareh B. Pars plana Ahmed valve and vitrectomy in patients with glaucoma associated with posterior segment disease. Retina 2013;33:2059-68.
Jeong HS, Nam DH, Paik HJ, Lee DY. Pars plana Ahmed implantation combined with 23-gauge vitrectomy for refractory neovascular glaucoma in diabetic retinopathy. Korean J Ophthalmol 2012;26:92-6.
Diaz-Llopis M, Salom D, García-Delpech S, Udaondo P, Millan JM, Arevalo JF. Efficacy and safety of the pars plana clip in the Ahmed valve device inserted via the pars plana in patients with refractory glaucoma. Clin Ophthalmol 2010;4:411-6.
Dada T, Bhartiya S, Vanathi M, Panda A. Pars plana Ahmed glaucoma valve implantation with triamcinolone-assisted vitrectomy in refractory glaucomas. Indian J Ophthalmol 2010;58:440-2.
] [Full text]
Faghihi H, Hajizadeh F, Mohammadi SF, Kadkhoda A, Peyman GA, Riazi-Esfahani M. Pars plana Ahmed valve implant and vitrectomy in the management of neovascular glaucoma. Ophthalmic Surg Lasers Imaging 2007;38:292-300.
Schlote T, Ziemssen F, Bartz-Schmidt KU. Pars plana-modified Ahmed Glaucoma Valve for treatment of refractory glaucoma: a pilot study. Graefes Arch Clin Exp Ophthalmol 2006;244:336-41.
Kirkness CM, Moshegov C. Post-keratoplasty glaucoma. Eye (Lond) 1988;2 Suppl: S19-26.
Rachmiel R, Trope GE, Buys YM, Flanagan JG, Chipman ML. Intermediate-term outcome and success of superior versus inferior Ahmed Glaucoma Valve implantation. J Glaucoma 2008;17:584-90.
Heuer DK, Budenz D, Coleman A. Aqueous shunt tube erosion. J Glaucoma 2001;10:493-6.
[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]