Seminars in Ophthalmology, 2014; 29(5–6): 397–402 ! Informa Healthcare USA, Inc. ISSN: 0882-0538 print / 1744-5205 online DOI: 10.3109/08820538.2014.959199
REVIEW
Complications of Glaucoma Drainage Device Surgery: A Review Michael Giovingo
Semin Ophthalmol Downloaded from informahealthcare.com by Selcuk Universitesi on 01/29/15 For personal use only.
Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA
ABSTRACT Purpose: To review current literature on the complications of the use of glaucoma drainage device surgery. Summary: The use of glaucoma drainage devices has increased significantly in recent years for both primary treatment of glaucoma and refractory glaucoma. The efficacy and safety of glaucoma drainage devices has been well established, so they are a viable surgical option in patients who fail medical therapy. With the increased use of these devices, understanding their complications is essential in managing these patients. The prevention and management of complications associated with glaucoma drainage device insertion has some similarities to that of a trabeculectomy. The glaucoma drainage devices have additional complications associated with the fact that hardware is left within the eye. There have been no definitive answers as to the perfect surgical technique to prevent complications but careful surgical performance, tube placement and use of a double-layered graft over the tube are likely to lead to a better outcome. The rate of complications also dictates careful follow up to identify these complications early in their process as early intervention will likely lead to better outcomes. Keywords: Complications, glaucoma, glaucoma drainage device, seton, trabeculectomy
INTRODUCTION
with these devices is essential for ophthalmologists, both with and without specific glaucoma training.
Glaucoma drainage devices, or setons, were first invented in 1966 by Professor Anthony Molteno.1 Traditionally, these devices have been used for refractory cases, but recently have grown in increasing popularity due to their safe and versatile nature. Several different devices with subtypes have been developed. The current commercially available devices include the Molteno, the Baerveldt, the Ahmed, and the Krupin Implants.1 The results of the Tube versus Trabeculectomy Study have led to increasing use of these devices, even as a primary surgery. According to Medicare data between 1995 and 2004, there has been a 43% decrease in trabeculectomies and a 184% increase in tube shunt surgery.2 Although the TVT study showed a lower rate of complications with tubes compared to trabeculectomies,3 the possibilities of adverse outcomes with seton implantation still remains a possibility. Understanding the possible complications associated
CONTROVERSY There is considerable debate on the efficacy of tubes versus trabeculectomies in the management of glaucoma. Furthermore, there is additional controversy on the effectiveness of different types of glaucoma drainage devices. According to an American Academy of Ophthalmology report, the efficacy and complication rate are similar between trabeculectomy and glaucoma tube devices.4 The report further states that there have been too few quality studies comparing the efficacy and complication rate between different types of valves to make any definitive statements as to which is preferred,4 The lack of conclusive data comparing trabeculectomy with the different types of glaucoma tube devices have led to many recent studies attempting to answer these questions.
Received 29 May 2014; revised 25 June 2014; accepted 26 July 2014; published online 7 October 2014 Correspondence: Michael Giovingo, Massachussets Eye and Ear Infirmary, Glaucoma, 243 Charles Street, Boston, 02114 United States. E-mail: [email protected]
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TUBE VERSUS TRABECULECTOMY STUDY This randomized prospective study looked at the efficacy and complication rates of trabeculectomy and Baerveldt 350 mm2 placement in patients who had a previously failed trabeculectomy.3 The study found that the Baerveldt group was more likely to maintain intraocular pressure control and avoid persistent hypotony while the trabeculectomy group was less likely to need medical management.3 Postoperative analysis performed showed an overall complication rate of 34% in the Baerveldt group and 57% in the trabeculectomy group.3 The three most common complications in the trabeculectomy group were choroidal effusion (19%), wound leak (12%), and shallow or flat anterior chamber (10%),3 while the three most common complications in the Baerveldt group were choroidal effusion (16%), shallow or flat anterior chamber (11%), and persistent corneal edema.3
AHMED VERSUS BAERVELDT STUDY The Ahmed versus Baerveldt Study is a prospective multicenter trial designed to compare the efficacy and complication rates of the Ahmed FP7 and the Baerveldt 350 mm2 for the treatment of refractory glaucoma. The three-year data from this study showed a slightly lower intraocular pressure in the Baerveldt group that was not statistically significant.5 The mean number of postoperative glaucoma medications was found to be significantly less in the Baerveldt group compared to the Ahmed group.5 Complication rates were also found to be similar between the two devices: 62% for the Baerveldt and 52% for the Ahmed.5 The Baerveldt group did have a higher rate of hypotony-related vision-threatening events, which was statistically significant.5 Finally, failure rates were found to be statistically significant (p = 0.02) at 25% for the Baerveldt group and 43% for the Ahmed group.5
AHMED BAERVELDT COMPARISON (ABC) STUDY The purpose of this study was to compare the intraocular pressure, number of medications used, and complication rates between the Baerveldt 350 mm2 and the Ahmed FP7.6 Intraocular pressure was found to be statistically significantly lower in the Baerveldt group compared to the Ahmed group at one year.6 Unlike the AVB study, there was no difference noted in number of medications used at one year.5,6 The data also revealed a higher rate of early postoperative complications in the Baerveldt group (58% versus 43%).6
Despite the results of this study and the Ahmed versus Baerveldt Study, there is no clear-cut answer as to which of these two devices offers the highest benefit to risk ratio. Each device has its own unique pros and cons specific in terms of complications and pressure management. Multifactorial methods are used to determine which device would best serve each individualized patient, including patient needs, surgeon training, and personal outcomes.
COMPLICATIONS Hypotony The Tube versus Trabeculectomy Study, found that hypotony occurred at lower rates after implantation of a non-valved glaucoma drainage device (Baerveldt 350 mm2) compared to a trabeculectomy.3 Hypotony has been shown to occur in both the non-valved and valved glaucoma drainage devices.5 The non-valved devices generally depend on a ligature around the tube for initial prevention of hypotony.1 As the ligature dissolved and opens, the formation of a capsule around the reservoir helps control the flow of aqueous out of the anterior chamber.1 The valved devices depend on the valve itself to regulate the flow of aqueous humor out of the anterior chamber.1 Despite multiple measures to regulate intraocular pressure in the postoperative period in both categories of glaucoma drainage devices, hypotony is seen at a significant rate.5 In non-valved devices, hypotony may occur due to improper placement of the ligature or damage to the tube during placement of fenestrations.1 If the tube is allowed to flow prior to formation of a capsule, there is no mechanism to restrict the flow of aqueous and hypotony can ensue.7 Conservative management of hypotony includes the use of topical and oral steroids or require surgical repair.1 In cases refractory to medical management, surgical exploration and identification of the underlying cause of hypotony is necessary. Devices that employ valves can also develop hypotony for multiple different reasons. A defective valve, aggressive handling of the plate, and vigorous priming of the device are all reasons for hypotony.7 Management is similar to non-valved devices as previously described.
Encapsulation Encapsulation is a problem that is noted in both trabeculectomies and glaucoma drainage devices.3 Use of antifibrotic agents, such as mitomycin-C and 5-fluorouracil, have increased success rates when used intraoperatively and postoperatively as adjuncts Seminars in Ophthalmology
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Complications of Glaucoma Drainage Device Surgery to trabeculectomies, but there is no proven added benefit to the use of antifibrotic agents with glaucoma drainage devices and encapsulation is a very difficult problem to overcome.3 Several different materials have been looked at in an attempt to decrease the amount of fibrosis and subsequently the rate of encapsulation.8 In a rabbit model, it was shown that silicone plates (e.g., Krupin implant) showed less inflammation in postoperatively when compared to plates made with polypropylene (e.g., Molteno implant).8 Conversely, two retrospective studies found no differences in postoperative intraocular pressure, vision, or medication use when they compared the silicone Ahmed Implant (model FP7) and the polypropylene Ahmed Implant (model S2).9,10 The conflicting findings of these studies disallow any definitive statements as to which implant material poses the best overall treatment and complication profile for the patient. When occurrence does occur, digital massage has been investigated as a possible intervention to lower the pressure.11,12 Some investigation into digital ocular results has produced promising results, but overall there is no definitive way to treat an aggressive encapsulation when it occurs.11,12
Tube Erosion Erosion or extrusion of a glaucoma drainage device is a devastating complication unique to this particular surgery.7 It poses an increased risk of endophthalmitis due to the exposure of hardware that travels into the anterior chamber.13 The incidence of endophthalmitis after glaucoma drainage device implantation in one study was noted to be nine out of 542 eyes.13 Of those nine cases, six of them had tube erosion.13 In theory, the tube acts as a conduit for an infectious agent to enter the eye. In many cases, when this complication occurs, despite prior repair, the device simply needs to be removed.13,14 Tube erosion is best prevented with proper intraoperative measures. Securing the tube to the sclera with a suture at the insertion site assists in unwanted movement and possible extrusion.13 Many different materials have been used, including sclera, dura, pericardium, fascia lata, and cornea.13 None of these materials completely prevents tube erosion and none of them have been shown to be superior to the others.15 Lankaranian et al. compared the use of single-thickness pericardium patch graft versus double-thickness patch graft.16 They found erosion in 16% of eyes that had a single thickness patch graft while none of the eyes that received a double thickness graft had occurrence of erosion.16 Many treatments for tube erosion have been suggested. One case study reports successful treatment of tube erosion in a patient with an Ahmed Valve after !
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treatment with 100 mg doxycycline twice daily, prednisolone acetate eight times daily, artificial tears eight times daily, and moxifloxacin four times daily.15 The authors report complete re-epithelialization after two weeks.15 Considering this case, it is certainly reasonable to consider medical management as a first option in eyes that do not show signs of infection. Eyes that do not improve with medical management would, however, need surgical repair. In cases of recurrence, the glaucoma drainage device may need to be completely removed. Huddleston et al. looked at the different risk factors for recurrence of erosion after repair. They identified black race, diabetes mellitus, a high number of glaucoma medications before shunt implantation, a history of multiple glaucoma laser procedures, and a combination of an initial aqueous shunt implantation with another surgery as risk factors. In congruence with these findings, Trubnik et al. also found that erosion occurs at a significantly higher rate when the initial glaucoma tube surgery is combined with another procedure (i.e., cataract extraction).14
Infection As with any intraocular surgery, infection is a rare but serious complication. In the Tube versus Trabeculectomy study, the tube group had one case of endophthalmitis/blebitis (1%) and the trabeculectomy group had three cases (3%).3 An overview of prominent studies reveals an infection rate similar between trabeculectomy and glaucoma tube surgery.2,3 Al-Torbak et al. performed a regression analysis on 542 eyes where glaucoma drainage devices were placed and revealed younger age and conjunctival erosion as significant risk factors for endophthalmitis.13 Many clinicians follow the Endophthalmitis Vitrectomy Study for the treatment of endophthalmitis after glaucoma tube surgery, even though the study only included endophthalmitis after cataract surgery or secondary intraocular lens implantation.17 According to this study, patients with better than light perception vision on presentation have the same outcome in terms of visual acuity with vitreous biopsy and intravitreal injection of antibiotics as they do when they receive a pars plana vitrectomy.17 The study also showed no benefit overall in the use of systemic antibiotics.17
Corneal Decompensation Corneal decompensation is a complication that is seen with any type of intraocular surgery. In comparison with standard trabeculectomy, a glaucoma drainage device has an added risk of corneal decompensation as there is a foreign body in the anterior chamber.
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400 M. Giovingo In one retrospective study, patients underwent either a secondary Molteno Implant or a trabeculectomy.18 The study showed an occurrence of corneal edema as 50% and 0%, respectively, for these two groups.18 This rate is quite high but the number of patients was quite small. The Tube versus Trabeculectomy Study showed a much smaller occurrence in persistent corneal edema after glaucoma drainage device placement when compared with trabeculectomy; 7% and 3%, respectively.3 This complication needs even more consideration in patients with prior corneal disease due to an already compromised cornea. Individuals who have corneal disease are also more prone towards ocular hypertension and refractory glaucoma, with rates of elevated pressure after penetrating keratoplasty reaching 46.2% in one study.19 As clinicians, we need to understand the implications of glaucoma drainage devices for the patient in order to choose the correct procedure and to manage the patient postoperatively. The rate of graft failure is increased in patients who require a glaucoma drainage device after penetrating keratoplasty.20 A proposed mechanism of this complication is direct contact between the tube and the corneal endothelium, but graft failure still occurs at a rate of 41% over two years when a pars plana tube is placed.20 Another proposed mechanism is that there is a breakdown of the blood-aqueous barrier, leading to inflammation and endothelial damage.21,22 In his editorial in Cornea, Price suggests that it is unclear whether or not a glaucoma drainage device increases the rate of graft failure but that elevated intraocular pressure will certainly lead to blindness. He suggests that we need to continue to look for new methods but that, in the meantime, treatment of the intraocular pressure should continue as seen fit by the surgeon.21
Strabismus/Amblyopia Strabismus is an uncommon but serious complication22. Surgical manipulation of the muscle may play a role in the pathophysiology, as with the technique use for Baerveldt Implant insertion.23,24 Krishna et al. analyzed data from implantation of a 350 mm2 Baerveldt in 65 eyes and found two patients (3%) that experienced strabismus after the surgery.24 Strabismus is also a well-known complication when there is no muscle manipulation in the surgery (i.e., Ahmed Valve placement).23 The Tube versus Trabeculectomy Study found older age and previous eye surgery to be risk factors for postoperative diplopia after insertion of a Baerveldt 350 mm2.3 Correction of the strabismus is much more difficult than primary muscle surgery as there is extensive scarring.23 Roizen et al. looked at nine cases of glaucoma-drainage-device-associated strabismus and found that all of the cases had a dense fibrotic capsule
and extensive fibrosis around the surrounding muscle.23 They also found that they were able to achieve good surgical outcomes when the capsule and fibrosis were excised along with size reduction of the plate.23 The need to remove the scar tissue makes the repair much more extensive and complicated.23 Approximately 20% of patients who have undergone goniotomy and trabeculotomy ab externo for treatment of congenital glaucoma will need additional surgery.25 Strabismus after placement of a glaucoma drainage device is a frequent complication in the pediatric population with studies showing occurrence in 3–5% of cases.26,27 When strabismus occurs with a pediatric patient due to a glaucoma drainage device, the chance of amblyopia can be increased even more. Morad et al. found that the occurrence of postoperative motility disorders in the pediatric population was less when an Ahmed device was used in comparison with other types.27 The decreased rate of strabismus with Ahmed placement may be related to size or lack of muscle manipulation.27 The frequency of this complication, along with the potentially blinding possibility of amblyopia, dictate close follow-up by both a pediatric glaucoma specialist and a pediatric ophthalmologist. Correction of a postoperative strabismus is similar in the adult and pediatric populations. Most cases are noted to have a dense fibrous capsule around the glaucoma drainage device.2 When surgical repair occurs, it is recommended that the fibrous capsule is excised and a size reduction is performed on the implant.2
Tube Obstruction Obstruction of the tube can occur with blood, vitreous, iris, and cornea. Reports of occurrence have been as high as 11%.28,29 When the tube is obstructed, there is no flow around the plate. The lack of flow can lead to extensive subconjunctival fibrosis and subsequent failure of the tube.29 In order to prevent this complication, a clinician needs to be aware of the patient’s ocular history and do a thorough exam to choose the correct surgery. Once obstruction has occurred, it can be difficult to manage and often requires surgery. One technique suggested for treatment has been flushing the tube with balanced saline solution and a 27-gauge cannula,26 but there has been no definitive answer as to the best treatment.
OVERVIEW The use of glaucoma drainage devices has increased significantly in recent years for both primary treatment of glaucoma and refractory glaucoma.2 The efficacy and safety of glaucoma drainage devices have Seminars in Ophthalmology
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Complications of Glaucoma Drainage Device Surgery been well-established, so they are a viable surgical option in patients who fail medical therapy.3 There are many similarities between trabeculectomies and glaucoma drainage devices but there are some differences in the occurrence of complications between the two surgeries.2,3 The Tube versus Trabeculectomy Study suggests that intraocular pressures are not as low with tube surgery but that the safety profile is slightly better.3 There are many different types of glaucoma devices. These devices have changed in size, material, and design over time. There is a greater pressure reduction in valves that have larger end plates and valved implants may reduce the risk of hypotony.30 Despite many studies, however, there is definitive data to suggest using one particular device over the others.30 The choice of device should depend on many different factors, including surgeon skill and preference.7 The prevention and management of complications associated with glaucoma drainage device insertion have some similarities to those of a trabeculectomy.2,3 The glaucoma drainage devices have additional complications associated with the fact that hardware is left within the eye. There have been no definitive answers as to the perfect surgical technique to prevent complications but careful surgical performance, tube placement, and use of a double-layered graft over the tube are likely to lead to a better outcome.2,3,16 The rate of complications also dictates careful follow-up to identify these complications early in their process, as early intervention will likely lead to better outcomes.2,3,6,15
DECLARATION OF INTEREST The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
REFERENCES 1. Sarwat S. Glaucoma drainage devices. Eyewiki.aao.org. 2011. 2. Sarkisian SR. Tube shunt complications and their prevention. Curr Opin Ophthalmol 2009;20:126–130. 3. Gedde SJ, Schiffman SJ, Feuer SJ, et al. Treatment outcomes in the tube versus trabeculectomy study after five years of follow-up. Am J Ophthalmol 2012;153(5):789–803. 4. Minckler DS, Francis BS, Hodapp EA, et al. Aqueous shunts in glaucoma: A report by the American Academy of Ophthalmology. Ophthalmology 2008;115:1089–1098. 5. Christakis PG, Tsai JC, Kalenak JW, et al. The Ahmed versus Baerveldt study. Ophthalmology 2013; 120(11):2232–2240. 6. Barton K, Gedde SJ, Budenz DL, et al. The Ahmed Baerveldt Comparison study. Ophthalmology 2011; 118(3):435–442. !
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7. Bailey AK, Sarkisian SR. Complications of tube implants and their management. Curr Opin Ophthalmol 2014;24: 148–153. 8. Ayyala RS, Michelini-Norris B, Flores A, et al. Comparison of different biomaterials for glaucoma drainage devices: Part 2. Arch Ophthalmol 2000;118(8):1081–1084. 9. Mackenzie PJ, Schertzer RM, Isbister CM. Comparison of silicone and polypropylene ahmed glaucoma valves: Twoyear follow up. Can J Ophthalmol 2007;42(2):227–232. 10. Brasil MV, Rockwood EJ, Smith SD. Comparison of silicone and polypropylene Ahmed glaucoma valve implants. Journal of Glaucoma 2007;16(1):36–41. 11. McIlraith I, Buys Y, Campbell RJ, Trope GE. Ocular massage for intraocular pressure control after Ahmed valve insertion. Can J Ophthalmol 2008; 43(1):48–52. 12. Smith M, Geffen N, Alasbali T, et al. Digital ocular massage for hypertensive phase after Ahmed valve surgery. J Glaucoma 2010;19:11–14. 13. Al-Torbak AA, Al-Shahwan S, Al-Jadaan I, et al. Endophthalmitis associated with the Ahmed valve implant. Br J Ophthalmol 2005;89(4):454–458. 14. Trubnik V, Zangalli C, Moster MR, et al. Evaluation of risk factors for glaucoma drainage device-related erosions: A retrospective case-control study. J Glaucoma 2013 [epub ahead of print]. 15. Dubey S, Prasanth B, Acharya MC, Narula R. Conjunctival erosion after glaucoma drainage device surgery: A feasible option. Indian J Ophthalmol 2013;6(7):355–357. 16. Lankaranian D, Reis R, Henderer JD, et al. Comparison of single thickness and double thickness processed pericardium patch graft in glaucoma drainage device surgery: A single surgeon comparison of outcome. Journal of Glaucoma 2008;17(1):48–51. 17. Endophthalmitis Vitrectomy Study Group. Results of the Endophthalmitis Vitrectomy Study: A randomized trial of immediate vitrectomy and of intravenous antibiotics for the treatment of postoperative bacterial endophthalmitis. Arch Ophthalmol 1995;113(12):1479–1496. 18. Zalloum JN, Ahuja RM, Shin D, Weiss JS. Assessment of corneal decompensation in eyes having undergone molteno shunt procedures compared to eyes having undergone trabeculectomy. Contact Lens Association of Ophthalmologists Journal 1999;25(1):57–60. 19. Zhang YM, Wu SQ, Yao YF. Long-term comparison of fullbed deep anterior lamellar keratoplasty and penetrating keratoplasty in treating keratoconus. J Zhejiang Univ 2013; 14(5):438–450. 20. Ritterband DC, Shapiro D, Trubnik V, et al. Penetrating keratoplasty with pars plana glaucoma drainage devices. Cornea 2007;26:1060–1066. 21. Price FW, Price MO. Is it worthwhile to combine penetrating keratoplasty with glaucoma drainage implants? Cornea 2008;27:261–262. 22. Kirkness CM. Penetrating keratoplasty, glaucoma and silicone drainage tubing. Dev Ophthalmol 1987;14:161–165. 23. Roizen A, Ela-Dalman N, Velez FG, et al. Surgical treatment of strabismus secondary to glaucoma drainage device. Arch Ophthalmol 2008;126:480–486. 24. Krishna R, Godfrey DG, Budenz DL, et al. Intermediateterm outcomes of 350-mm2 Baerveldt glaucoma implants. Ophthalmology 2001;108:621–626. 25. Nassiri N, Nouri-Mahdavi K, Coleman AL. Ahmed glaucoma valve in children: A review. Saudi Journal of Ophthalmology 2011;25:317–327. 26. Coleman AL, Smyth RJ, Wilson MR, Tam M. Initial clinical experience with the Ahmed glaucoma valve implant in pediatric patients. Arch Ophthalmol 1997; 115(2):186–191.
402 M. Giovingo 30. Schwartz KS, Lee RK, Gedde SJ. Glaucoma drainage implants: A Critical comparison of types. Curr Opin Ophthalmol 2006;17:181–189. 31. Munoz M, Parrish RK. Strabismus following implantation of Baerveldt drainage devices. Arch Ophthalmol 1993; 111(8):1096–1099.
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27. Morad Y, Dondaldson CE, Kim YM, et al. The Ahmed drainage implant in the treatment of pediatric glaucoma. Am J Ophthalmol 2003;135:821–829. 28. Huang MC, Netland PA, Coleman AL, et al. Intermediateterm clinical experience with the Ahmed glaucoma valve implant. Am J Ophthalmol 1999;127(2):172–174. 29. Chen T (ed.). Surgical Techniques in Ophthalmology: Glaucoma Surgery; Boston, MA: Saunders Elsevier, 2008.
Seminars in Ophthalmology
REVIEW
Complications of Glaucoma Drainage Device Surgery: A Review Michael Giovingo
Semin Ophthalmol Downloaded from informahealthcare.com by Selcuk Universitesi on 01/29/15 For personal use only.
Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA
ABSTRACT Purpose: To review current literature on the complications of the use of glaucoma drainage device surgery. Summary: The use of glaucoma drainage devices has increased significantly in recent years for both primary treatment of glaucoma and refractory glaucoma. The efficacy and safety of glaucoma drainage devices has been well established, so they are a viable surgical option in patients who fail medical therapy. With the increased use of these devices, understanding their complications is essential in managing these patients. The prevention and management of complications associated with glaucoma drainage device insertion has some similarities to that of a trabeculectomy. The glaucoma drainage devices have additional complications associated with the fact that hardware is left within the eye. There have been no definitive answers as to the perfect surgical technique to prevent complications but careful surgical performance, tube placement and use of a double-layered graft over the tube are likely to lead to a better outcome. The rate of complications also dictates careful follow up to identify these complications early in their process as early intervention will likely lead to better outcomes. Keywords: Complications, glaucoma, glaucoma drainage device, seton, trabeculectomy
INTRODUCTION
with these devices is essential for ophthalmologists, both with and without specific glaucoma training.
Glaucoma drainage devices, or setons, were first invented in 1966 by Professor Anthony Molteno.1 Traditionally, these devices have been used for refractory cases, but recently have grown in increasing popularity due to their safe and versatile nature. Several different devices with subtypes have been developed. The current commercially available devices include the Molteno, the Baerveldt, the Ahmed, and the Krupin Implants.1 The results of the Tube versus Trabeculectomy Study have led to increasing use of these devices, even as a primary surgery. According to Medicare data between 1995 and 2004, there has been a 43% decrease in trabeculectomies and a 184% increase in tube shunt surgery.2 Although the TVT study showed a lower rate of complications with tubes compared to trabeculectomies,3 the possibilities of adverse outcomes with seton implantation still remains a possibility. Understanding the possible complications associated
CONTROVERSY There is considerable debate on the efficacy of tubes versus trabeculectomies in the management of glaucoma. Furthermore, there is additional controversy on the effectiveness of different types of glaucoma drainage devices. According to an American Academy of Ophthalmology report, the efficacy and complication rate are similar between trabeculectomy and glaucoma tube devices.4 The report further states that there have been too few quality studies comparing the efficacy and complication rate between different types of valves to make any definitive statements as to which is preferred,4 The lack of conclusive data comparing trabeculectomy with the different types of glaucoma tube devices have led to many recent studies attempting to answer these questions.
Received 29 May 2014; revised 25 June 2014; accepted 26 July 2014; published online 7 October 2014 Correspondence: Michael Giovingo, Massachussets Eye and Ear Infirmary, Glaucoma, 243 Charles Street, Boston, 02114 United States. E-mail: [email protected]
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TUBE VERSUS TRABECULECTOMY STUDY This randomized prospective study looked at the efficacy and complication rates of trabeculectomy and Baerveldt 350 mm2 placement in patients who had a previously failed trabeculectomy.3 The study found that the Baerveldt group was more likely to maintain intraocular pressure control and avoid persistent hypotony while the trabeculectomy group was less likely to need medical management.3 Postoperative analysis performed showed an overall complication rate of 34% in the Baerveldt group and 57% in the trabeculectomy group.3 The three most common complications in the trabeculectomy group were choroidal effusion (19%), wound leak (12%), and shallow or flat anterior chamber (10%),3 while the three most common complications in the Baerveldt group were choroidal effusion (16%), shallow or flat anterior chamber (11%), and persistent corneal edema.3
AHMED VERSUS BAERVELDT STUDY The Ahmed versus Baerveldt Study is a prospective multicenter trial designed to compare the efficacy and complication rates of the Ahmed FP7 and the Baerveldt 350 mm2 for the treatment of refractory glaucoma. The three-year data from this study showed a slightly lower intraocular pressure in the Baerveldt group that was not statistically significant.5 The mean number of postoperative glaucoma medications was found to be significantly less in the Baerveldt group compared to the Ahmed group.5 Complication rates were also found to be similar between the two devices: 62% for the Baerveldt and 52% for the Ahmed.5 The Baerveldt group did have a higher rate of hypotony-related vision-threatening events, which was statistically significant.5 Finally, failure rates were found to be statistically significant (p = 0.02) at 25% for the Baerveldt group and 43% for the Ahmed group.5
AHMED BAERVELDT COMPARISON (ABC) STUDY The purpose of this study was to compare the intraocular pressure, number of medications used, and complication rates between the Baerveldt 350 mm2 and the Ahmed FP7.6 Intraocular pressure was found to be statistically significantly lower in the Baerveldt group compared to the Ahmed group at one year.6 Unlike the AVB study, there was no difference noted in number of medications used at one year.5,6 The data also revealed a higher rate of early postoperative complications in the Baerveldt group (58% versus 43%).6
Despite the results of this study and the Ahmed versus Baerveldt Study, there is no clear-cut answer as to which of these two devices offers the highest benefit to risk ratio. Each device has its own unique pros and cons specific in terms of complications and pressure management. Multifactorial methods are used to determine which device would best serve each individualized patient, including patient needs, surgeon training, and personal outcomes.
COMPLICATIONS Hypotony The Tube versus Trabeculectomy Study, found that hypotony occurred at lower rates after implantation of a non-valved glaucoma drainage device (Baerveldt 350 mm2) compared to a trabeculectomy.3 Hypotony has been shown to occur in both the non-valved and valved glaucoma drainage devices.5 The non-valved devices generally depend on a ligature around the tube for initial prevention of hypotony.1 As the ligature dissolved and opens, the formation of a capsule around the reservoir helps control the flow of aqueous out of the anterior chamber.1 The valved devices depend on the valve itself to regulate the flow of aqueous humor out of the anterior chamber.1 Despite multiple measures to regulate intraocular pressure in the postoperative period in both categories of glaucoma drainage devices, hypotony is seen at a significant rate.5 In non-valved devices, hypotony may occur due to improper placement of the ligature or damage to the tube during placement of fenestrations.1 If the tube is allowed to flow prior to formation of a capsule, there is no mechanism to restrict the flow of aqueous and hypotony can ensue.7 Conservative management of hypotony includes the use of topical and oral steroids or require surgical repair.1 In cases refractory to medical management, surgical exploration and identification of the underlying cause of hypotony is necessary. Devices that employ valves can also develop hypotony for multiple different reasons. A defective valve, aggressive handling of the plate, and vigorous priming of the device are all reasons for hypotony.7 Management is similar to non-valved devices as previously described.
Encapsulation Encapsulation is a problem that is noted in both trabeculectomies and glaucoma drainage devices.3 Use of antifibrotic agents, such as mitomycin-C and 5-fluorouracil, have increased success rates when used intraoperatively and postoperatively as adjuncts Seminars in Ophthalmology
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Complications of Glaucoma Drainage Device Surgery to trabeculectomies, but there is no proven added benefit to the use of antifibrotic agents with glaucoma drainage devices and encapsulation is a very difficult problem to overcome.3 Several different materials have been looked at in an attempt to decrease the amount of fibrosis and subsequently the rate of encapsulation.8 In a rabbit model, it was shown that silicone plates (e.g., Krupin implant) showed less inflammation in postoperatively when compared to plates made with polypropylene (e.g., Molteno implant).8 Conversely, two retrospective studies found no differences in postoperative intraocular pressure, vision, or medication use when they compared the silicone Ahmed Implant (model FP7) and the polypropylene Ahmed Implant (model S2).9,10 The conflicting findings of these studies disallow any definitive statements as to which implant material poses the best overall treatment and complication profile for the patient. When occurrence does occur, digital massage has been investigated as a possible intervention to lower the pressure.11,12 Some investigation into digital ocular results has produced promising results, but overall there is no definitive way to treat an aggressive encapsulation when it occurs.11,12
Tube Erosion Erosion or extrusion of a glaucoma drainage device is a devastating complication unique to this particular surgery.7 It poses an increased risk of endophthalmitis due to the exposure of hardware that travels into the anterior chamber.13 The incidence of endophthalmitis after glaucoma drainage device implantation in one study was noted to be nine out of 542 eyes.13 Of those nine cases, six of them had tube erosion.13 In theory, the tube acts as a conduit for an infectious agent to enter the eye. In many cases, when this complication occurs, despite prior repair, the device simply needs to be removed.13,14 Tube erosion is best prevented with proper intraoperative measures. Securing the tube to the sclera with a suture at the insertion site assists in unwanted movement and possible extrusion.13 Many different materials have been used, including sclera, dura, pericardium, fascia lata, and cornea.13 None of these materials completely prevents tube erosion and none of them have been shown to be superior to the others.15 Lankaranian et al. compared the use of single-thickness pericardium patch graft versus double-thickness patch graft.16 They found erosion in 16% of eyes that had a single thickness patch graft while none of the eyes that received a double thickness graft had occurrence of erosion.16 Many treatments for tube erosion have been suggested. One case study reports successful treatment of tube erosion in a patient with an Ahmed Valve after !
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treatment with 100 mg doxycycline twice daily, prednisolone acetate eight times daily, artificial tears eight times daily, and moxifloxacin four times daily.15 The authors report complete re-epithelialization after two weeks.15 Considering this case, it is certainly reasonable to consider medical management as a first option in eyes that do not show signs of infection. Eyes that do not improve with medical management would, however, need surgical repair. In cases of recurrence, the glaucoma drainage device may need to be completely removed. Huddleston et al. looked at the different risk factors for recurrence of erosion after repair. They identified black race, diabetes mellitus, a high number of glaucoma medications before shunt implantation, a history of multiple glaucoma laser procedures, and a combination of an initial aqueous shunt implantation with another surgery as risk factors. In congruence with these findings, Trubnik et al. also found that erosion occurs at a significantly higher rate when the initial glaucoma tube surgery is combined with another procedure (i.e., cataract extraction).14
Infection As with any intraocular surgery, infection is a rare but serious complication. In the Tube versus Trabeculectomy study, the tube group had one case of endophthalmitis/blebitis (1%) and the trabeculectomy group had three cases (3%).3 An overview of prominent studies reveals an infection rate similar between trabeculectomy and glaucoma tube surgery.2,3 Al-Torbak et al. performed a regression analysis on 542 eyes where glaucoma drainage devices were placed and revealed younger age and conjunctival erosion as significant risk factors for endophthalmitis.13 Many clinicians follow the Endophthalmitis Vitrectomy Study for the treatment of endophthalmitis after glaucoma tube surgery, even though the study only included endophthalmitis after cataract surgery or secondary intraocular lens implantation.17 According to this study, patients with better than light perception vision on presentation have the same outcome in terms of visual acuity with vitreous biopsy and intravitreal injection of antibiotics as they do when they receive a pars plana vitrectomy.17 The study also showed no benefit overall in the use of systemic antibiotics.17
Corneal Decompensation Corneal decompensation is a complication that is seen with any type of intraocular surgery. In comparison with standard trabeculectomy, a glaucoma drainage device has an added risk of corneal decompensation as there is a foreign body in the anterior chamber.
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400 M. Giovingo In one retrospective study, patients underwent either a secondary Molteno Implant or a trabeculectomy.18 The study showed an occurrence of corneal edema as 50% and 0%, respectively, for these two groups.18 This rate is quite high but the number of patients was quite small. The Tube versus Trabeculectomy Study showed a much smaller occurrence in persistent corneal edema after glaucoma drainage device placement when compared with trabeculectomy; 7% and 3%, respectively.3 This complication needs even more consideration in patients with prior corneal disease due to an already compromised cornea. Individuals who have corneal disease are also more prone towards ocular hypertension and refractory glaucoma, with rates of elevated pressure after penetrating keratoplasty reaching 46.2% in one study.19 As clinicians, we need to understand the implications of glaucoma drainage devices for the patient in order to choose the correct procedure and to manage the patient postoperatively. The rate of graft failure is increased in patients who require a glaucoma drainage device after penetrating keratoplasty.20 A proposed mechanism of this complication is direct contact between the tube and the corneal endothelium, but graft failure still occurs at a rate of 41% over two years when a pars plana tube is placed.20 Another proposed mechanism is that there is a breakdown of the blood-aqueous barrier, leading to inflammation and endothelial damage.21,22 In his editorial in Cornea, Price suggests that it is unclear whether or not a glaucoma drainage device increases the rate of graft failure but that elevated intraocular pressure will certainly lead to blindness. He suggests that we need to continue to look for new methods but that, in the meantime, treatment of the intraocular pressure should continue as seen fit by the surgeon.21
Strabismus/Amblyopia Strabismus is an uncommon but serious complication22. Surgical manipulation of the muscle may play a role in the pathophysiology, as with the technique use for Baerveldt Implant insertion.23,24 Krishna et al. analyzed data from implantation of a 350 mm2 Baerveldt in 65 eyes and found two patients (3%) that experienced strabismus after the surgery.24 Strabismus is also a well-known complication when there is no muscle manipulation in the surgery (i.e., Ahmed Valve placement).23 The Tube versus Trabeculectomy Study found older age and previous eye surgery to be risk factors for postoperative diplopia after insertion of a Baerveldt 350 mm2.3 Correction of the strabismus is much more difficult than primary muscle surgery as there is extensive scarring.23 Roizen et al. looked at nine cases of glaucoma-drainage-device-associated strabismus and found that all of the cases had a dense fibrotic capsule
and extensive fibrosis around the surrounding muscle.23 They also found that they were able to achieve good surgical outcomes when the capsule and fibrosis were excised along with size reduction of the plate.23 The need to remove the scar tissue makes the repair much more extensive and complicated.23 Approximately 20% of patients who have undergone goniotomy and trabeculotomy ab externo for treatment of congenital glaucoma will need additional surgery.25 Strabismus after placement of a glaucoma drainage device is a frequent complication in the pediatric population with studies showing occurrence in 3–5% of cases.26,27 When strabismus occurs with a pediatric patient due to a glaucoma drainage device, the chance of amblyopia can be increased even more. Morad et al. found that the occurrence of postoperative motility disorders in the pediatric population was less when an Ahmed device was used in comparison with other types.27 The decreased rate of strabismus with Ahmed placement may be related to size or lack of muscle manipulation.27 The frequency of this complication, along with the potentially blinding possibility of amblyopia, dictate close follow-up by both a pediatric glaucoma specialist and a pediatric ophthalmologist. Correction of a postoperative strabismus is similar in the adult and pediatric populations. Most cases are noted to have a dense fibrous capsule around the glaucoma drainage device.2 When surgical repair occurs, it is recommended that the fibrous capsule is excised and a size reduction is performed on the implant.2
Tube Obstruction Obstruction of the tube can occur with blood, vitreous, iris, and cornea. Reports of occurrence have been as high as 11%.28,29 When the tube is obstructed, there is no flow around the plate. The lack of flow can lead to extensive subconjunctival fibrosis and subsequent failure of the tube.29 In order to prevent this complication, a clinician needs to be aware of the patient’s ocular history and do a thorough exam to choose the correct surgery. Once obstruction has occurred, it can be difficult to manage and often requires surgery. One technique suggested for treatment has been flushing the tube with balanced saline solution and a 27-gauge cannula,26 but there has been no definitive answer as to the best treatment.
OVERVIEW The use of glaucoma drainage devices has increased significantly in recent years for both primary treatment of glaucoma and refractory glaucoma.2 The efficacy and safety of glaucoma drainage devices have Seminars in Ophthalmology
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Complications of Glaucoma Drainage Device Surgery been well-established, so they are a viable surgical option in patients who fail medical therapy.3 There are many similarities between trabeculectomies and glaucoma drainage devices but there are some differences in the occurrence of complications between the two surgeries.2,3 The Tube versus Trabeculectomy Study suggests that intraocular pressures are not as low with tube surgery but that the safety profile is slightly better.3 There are many different types of glaucoma devices. These devices have changed in size, material, and design over time. There is a greater pressure reduction in valves that have larger end plates and valved implants may reduce the risk of hypotony.30 Despite many studies, however, there is definitive data to suggest using one particular device over the others.30 The choice of device should depend on many different factors, including surgeon skill and preference.7 The prevention and management of complications associated with glaucoma drainage device insertion have some similarities to those of a trabeculectomy.2,3 The glaucoma drainage devices have additional complications associated with the fact that hardware is left within the eye. There have been no definitive answers as to the perfect surgical technique to prevent complications but careful surgical performance, tube placement, and use of a double-layered graft over the tube are likely to lead to a better outcome.2,3,16 The rate of complications also dictates careful follow-up to identify these complications early in their process, as early intervention will likely lead to better outcomes.2,3,6,15
DECLARATION OF INTEREST The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.
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7. Bailey AK, Sarkisian SR. Complications of tube implants and their management. Curr Opin Ophthalmol 2014;24: 148–153. 8. Ayyala RS, Michelini-Norris B, Flores A, et al. Comparison of different biomaterials for glaucoma drainage devices: Part 2. Arch Ophthalmol 2000;118(8):1081–1084. 9. Mackenzie PJ, Schertzer RM, Isbister CM. Comparison of silicone and polypropylene ahmed glaucoma valves: Twoyear follow up. Can J Ophthalmol 2007;42(2):227–232. 10. Brasil MV, Rockwood EJ, Smith SD. Comparison of silicone and polypropylene Ahmed glaucoma valve implants. Journal of Glaucoma 2007;16(1):36–41. 11. McIlraith I, Buys Y, Campbell RJ, Trope GE. Ocular massage for intraocular pressure control after Ahmed valve insertion. Can J Ophthalmol 2008; 43(1):48–52. 12. Smith M, Geffen N, Alasbali T, et al. Digital ocular massage for hypertensive phase after Ahmed valve surgery. J Glaucoma 2010;19:11–14. 13. Al-Torbak AA, Al-Shahwan S, Al-Jadaan I, et al. Endophthalmitis associated with the Ahmed valve implant. Br J Ophthalmol 2005;89(4):454–458. 14. Trubnik V, Zangalli C, Moster MR, et al. Evaluation of risk factors for glaucoma drainage device-related erosions: A retrospective case-control study. J Glaucoma 2013 [epub ahead of print]. 15. Dubey S, Prasanth B, Acharya MC, Narula R. Conjunctival erosion after glaucoma drainage device surgery: A feasible option. Indian J Ophthalmol 2013;6(7):355–357. 16. Lankaranian D, Reis R, Henderer JD, et al. Comparison of single thickness and double thickness processed pericardium patch graft in glaucoma drainage device surgery: A single surgeon comparison of outcome. Journal of Glaucoma 2008;17(1):48–51. 17. Endophthalmitis Vitrectomy Study Group. Results of the Endophthalmitis Vitrectomy Study: A randomized trial of immediate vitrectomy and of intravenous antibiotics for the treatment of postoperative bacterial endophthalmitis. Arch Ophthalmol 1995;113(12):1479–1496. 18. Zalloum JN, Ahuja RM, Shin D, Weiss JS. Assessment of corneal decompensation in eyes having undergone molteno shunt procedures compared to eyes having undergone trabeculectomy. Contact Lens Association of Ophthalmologists Journal 1999;25(1):57–60. 19. Zhang YM, Wu SQ, Yao YF. Long-term comparison of fullbed deep anterior lamellar keratoplasty and penetrating keratoplasty in treating keratoconus. J Zhejiang Univ 2013; 14(5):438–450. 20. Ritterband DC, Shapiro D, Trubnik V, et al. Penetrating keratoplasty with pars plana glaucoma drainage devices. Cornea 2007;26:1060–1066. 21. Price FW, Price MO. Is it worthwhile to combine penetrating keratoplasty with glaucoma drainage implants? Cornea 2008;27:261–262. 22. Kirkness CM. Penetrating keratoplasty, glaucoma and silicone drainage tubing. Dev Ophthalmol 1987;14:161–165. 23. Roizen A, Ela-Dalman N, Velez FG, et al. Surgical treatment of strabismus secondary to glaucoma drainage device. Arch Ophthalmol 2008;126:480–486. 24. Krishna R, Godfrey DG, Budenz DL, et al. Intermediateterm outcomes of 350-mm2 Baerveldt glaucoma implants. Ophthalmology 2001;108:621–626. 25. Nassiri N, Nouri-Mahdavi K, Coleman AL. Ahmed glaucoma valve in children: A review. Saudi Journal of Ophthalmology 2011;25:317–327. 26. Coleman AL, Smyth RJ, Wilson MR, Tam M. Initial clinical experience with the Ahmed glaucoma valve implant in pediatric patients. Arch Ophthalmol 1997; 115(2):186–191.
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27. Morad Y, Dondaldson CE, Kim YM, et al. The Ahmed drainage implant in the treatment of pediatric glaucoma. Am J Ophthalmol 2003;135:821–829. 28. Huang MC, Netland PA, Coleman AL, et al. Intermediateterm clinical experience with the Ahmed glaucoma valve implant. Am J Ophthalmol 1999;127(2):172–174. 29. Chen T (ed.). Surgical Techniques in Ophthalmology: Glaucoma Surgery; Boston, MA: Saunders Elsevier, 2008.
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