patients with a preexisting episcleral encircling element who underwent implantation of a silicone agv to treat intractable glaucoma during january 2009 to september 2010 at a large , tertiary care ophthalmic hospital were identified by means of operative records . postsurgical follow - up of less than 6 weeks and inability to measure intraocular pressure ( iop ) were the exclusion criteria . the conjunctival incision was made at the corneal limbus or at 4 - 5 mm behind and parallel to the limbus , at the operating surgeon 's discretion , for approximately 100 in the supero - temporal quadrant . the agv ( model fp7 , new world medical , rancho cucamonga , la , usa ) was primed by injecting 1 - 2 ml balanced salt solution . the plate of agv was placed over the episcleral encircling element ; either encircling band or scleral buckle [ figure 1 ] . the plate was secured to the underlying sclera with 8 - 0 nylon suture material ( m / s gn corporation ltd . , yamanashi , japan ) such that its anterior edge lied 8 mm behind the corneal limbus . this was followed by placement of the silicone tube into anterior chamber or pars plana region through a 23-gauge needle track . the anterior part of the tube was covered with previously prepared human donor scleral patch graft . fibrin sealant ( tisseel kit , baxter ag , vienna , austria ) or 8 - 0 nylon suture material was used to secure the scleral patch graft . the overlying conjunctiva was sutured with 8 - 0 polyglactin suture material ( ethicon inc . , if there was limited mobility of the conjunctiva due to prior surgeries , relaxing incisions were given in the conjunctiva and/or amniotic membrane transplantation was considered . the eye was inspected for any leaks after the anterior chamber was inflated using balanced salt solution . the base plate of ahmed glaucoma valve being placed over the episcleral encircling element that is indicated by arrows the donor scleral tissue preserved in absolute alcohol was used in every case . the tissue was cleaned of all the uveal tissue attachments , washed thoroughly with balanced salt solution and cut into the desired size ( 4 - 5  4 - 5 mm ) . the data collection included information on patient demography , diagnosis of glaucoma , prior ocular surgeries , measurement of visual acuity , iop , number of antiglaucoma medications at pre - agv and every post - agv follow - up visit , duration between placement of episcleral encircling element and agv , and complications , if any . we measured iop either by applanation tonometer , namely , goldmann tonometer ( haag - streit , switzerland ) , a hand - held perkin 's tonometer ( haag - streit , essex , uk ) , or by tonopen xl ( reichert ophthalmic instruments , walden ave . the cause ( s ) for low vision and postoperative reduction in visual acuity , if any , were also recorded . surgical success was defined as a final iop between 5 and 22 mmhg without ( complete success ) or with topical antiglaucoma medication ( s ) ( qualified success ) and without any vision threatening complication . paired t - test was used to compare measurements of iop and number of antiglaucoma medications at the preoperative and the final visits . data analysis was done using spss software version 15.0 for windows ( spss inc . , patients with a preexisting episcleral encircling element who underwent implantation of a silicone agv to treat intractable glaucoma during january 2009 to september 2010 at a large , tertiary care ophthalmic hospital were identified by means of operative records . postsurgical follow - up of less than 6 weeks and inability to measure intraocular pressure ( iop ) were the exclusion criteria . the conjunctival incision was made at the corneal limbus or at 4 - 5 mm behind and parallel to the limbus , at the operating surgeon 's discretion , for approximately 100 in the supero - temporal quadrant . the agv ( model fp7 , new world medical , rancho cucamonga , la , usa ) was primed by injecting 1 - 2 ml balanced salt solution . the plate of agv was placed over the episcleral encircling element ; either encircling band or scleral buckle [ figure 1 ] . the plate was secured to the underlying sclera with 8 - 0 nylon suture material ( m / s gn corporation ltd . , yamanashi , japan ) such that its anterior edge lied 8 mm behind the corneal limbus . this was followed by placement of the silicone tube into anterior chamber or pars plana region through a 23-gauge needle track . the anterior part of the tube was covered with previously prepared human donor scleral patch graft . fibrin sealant ( tisseel kit , baxter ag , vienna , austria ) or 8 - 0 nylon suture material was used to secure the scleral patch graft . the overlying conjunctiva was sutured with 8 - 0 polyglactin suture material ( ethicon inc . , aurangabad , india ) . if there was limited mobility of the conjunctiva due to prior surgeries , relaxing incisions were given in the conjunctiva and/or amniotic membrane transplantation was considered . the eye was inspected for any leaks after the anterior chamber was inflated using balanced salt solution . the base plate of ahmed glaucoma valve being placed over the episcleral encircling element that is indicated by arrows the tissue was cleaned of all the uveal tissue attachments , washed thoroughly with balanced salt solution and cut into the desired size ( 4 - 5  4 - 5 mm ) . the data collection included information on patient demography , diagnosis of glaucoma , prior ocular surgeries , measurement of visual acuity , iop , number of antiglaucoma medications at pre - agv and every post - agv follow - up visit , duration between placement of episcleral encircling element and agv , and complications , if any . we measured iop either by applanation tonometer , namely , goldmann tonometer ( haag - streit , switzerland ) , a hand - held perkin 's tonometer ( haag - streit , essex , uk ) , or by tonopen xl ( reichert ophthalmic instruments , walden ave . the cause ( s ) for low vision and postoperative reduction in visual acuity , if any , were also recorded . surgical success was defined as a final iop between 5 and 22 mmhg without ( complete success ) or with topical antiglaucoma medication ( s ) ( qualified success ) and without any vision threatening complication . paired t - test was used to compare measurements of iop and number of antiglaucoma medications at the preoperative and the final visits . data analysis was done using spss software version 15.0 for windows ( spss inc . , fourteen patients underwent implantation of agv in eyes with a preexisting episcleral encircling element during the study period . two eyes ( 16.6% ) had undergone placement of a circumferential scleral buckle in the supero - temporal quadrant . in one of these eyes with scleral buckle the shunt plate was additionally covered with two layers of cryo - preserved human amniotic membrane to reduce the chances of exposure of this implant in the postoperative period . the mean ( standard deviation ) duration between placement of episcleral encircling element and implantation of agv was 30.5 ( 33.8 ) months ; median , 11.5 months . the mean follow - up was 37.4 ( 22.9 ) weeks ; median , 33.5 weeks . the mean preoperative iop was 31.4 ( 7.9 ) mmhg ; median , 32mmhg with an average of 2.8 ; median , 3 medications . at last postoperative follow - up , the mean iop decreased to 12.5 ( 3.5 ) mmhg the postoperative reduction in iop and in number of antiglaucoma medications was statistically significant ( p < 0.001 , paired t - test ) . demographic / pre - operative data corneal graft failure occurred in three eyes in late postoperative period following implantation of agv ( cases 4 , 7 , 9 ) . in one of these eyes , the agv tube was placed in the pars plana region . in the remaining two eyes , the agv tube was placed in the anterior segment , however , there was no tube - cornea touch . the mean duration between placement of agv and corneal graft failure was 7.3 ( 5.3 ) months ; median , 8.5 months . tube erosion occurred in another two eyes in late postoperative period ( cases 10 , 11 ) . case 12 reported reduced vision at sixth postoperative week and was found to have a rhegmatogenous retinal detachment . in this series , we describe implantation of the silicone plate agv in eyes with a preexisting episcleral encircling element . this novel use of ahmed valve can be helpful in the management of intractable glaucoma after the encircling procedure . described the use of a silicone tube to shunt aqueous from the anterior segment to the fibrous capsule surrounding a previously placed episcleral encircling element . using the existent fibrous capsule around the encircling element as an aqueous reservoir obviated the need for temporary restriction of the aqueous flow to allow encapsulation . early postoperative complications attributable to hypotony were few and self - limiting . however , eight instances of fibrous obstruction of the distal tube opening occurred within 4 months of the initial procedure . suh et al . also reported high overall success rate with the same technique , but they studied only seven eyes . modified the technique by using a valved ( plate less ) krupin - denver tube . no case of early postoperative hypotony occurred , although two ( 29% ) of seven eyes experienced distal tube occlusion necessitating surgical revision . scott et al . described an alternative approach to manage refractory glaucoma in eyes with a preexisting encircling band . they inserted 250- ( 7 eyes [ 44% ] ) or 350-mm ( 9 eyes [ 56% ] ) baerveldt drainage devices behind or over a preexisting encircling band and over the adjacent recti muscles . the fibrous capsule overlying the encircling band was excised in the quadrant of surgical implantation . nine patients ( 56% ) achieved complete success and seven patients ( 44% ) achieved qualified success at 1 year postoperatively . implant migration or exposure and diplopia did not develop in any patient over the median follow - up of 22.9 months . however , it might be unsafe to insert a large sized implant in the presence of an encircling band in all four quadrants due to the effects of crowding . it may be that this study with limited number of patients does not reflect the true outcome . the incidence of postoperative diplopia has been shown to be significantly higher with the baerveldt than any other implant . this is the reason smith et al . trimmed the wings of baerveldt implants to debulk them before insertion in eyes with a preexisting episcleral encircling element . the valve abutted against the anterior portion of the scleral band and was sutured into position . the valve function of the implant was retained to reduce postoperative hypotony . however , the reduction in the surface area of the trimmed drainage implant is of concern as the extent of iop reduction with glaucoma drainage implants has been demonstrated to be directly proportional to the surface area of the fibrous capsule . additionally , it may be difficult to mobilize adequate conjunctiva to cover the implant in eyes with a preexisting episcleral encircling element , especially a scleral buckle . an implant with minimum - sized end - plate that is sufficient to achieve iop control is preferable in such eyes . increasing the surface area of a randomized controlled clinical trial showed comparable failure rates at 1-year for both agv and 350 mm baerveldt implants . therefore , agv should be preferred over baerveldt implant in eyes with a preexisting episcleral encircling element . moreover , the base plate of the newer silicone ahmed valve ( model fp7 ) is thinner ( 0.9 mm ) and has the same surface area ( 184 mm ) compared with the earlier polypropylene model s2 ( thickness 1.9 mm ) . the silicone base plate is also flexible and has a tapered profile for easy insertion . these features allowed us to insert a silicone agv over the episcleral element in our patients . one can also make use of a long , curved surgical scissor for better access to the supero - temporal quadrant , and guide the base plate of the agv into position over the partly open blades of the scissor . two patients in our series had preexisting scleral buckle in the supero - temporal quadrant ( cases 8 and 12 ) . however , the procedure was difficult in one eye ( case 12 ) due to multiple prior surgeries . we gave a couple of relaxing incisions in the surrounding conjunctiva for adequate wound closure . the shunt plate was additionally covered with two layers of cryo - preserved human amniotic membrane , as described by amini et al . to reduce the chances of exposure of the implant in the postoperative period . despite these efforts , the anterior edge of the scleral patch graft covering the implant tube did expose in the early postoperative period one of them had prior corneal graft failure ( case 9 ) . in two of these three eyes , the agv tube was placed in the anterior segment , however , there was no demonstrable tube - cornea touch . found corneal graft failure in 24 ( 43.6% ) out of 55 eyes that had undergone both penetrating keratoplasty ( pk ) and either baerveldt or ahmed glaucoma implant . also found poor long - term survival of corneal grafts in their study of 77 eyes that underwent pk following agv implantation . the grafted corneas failed in 46 [ 59.1% , ( 95% confidence interval : 47.5 - 71.2% ) ] eyes at 3 years . prior pk and stromal vessels , but not tube - cornea touch , did increase the risk of graft failure . erosion of drainage tube through the overlying conjunctiva was seen in two eyes despite meticulous conjunctival closure and the use of a scleral patch graft . both eyes underwent early repair as tube erosion carries with it increased risk of endophthalmitis . he was a high myope , suffered from posttraumatic retinal detachment and developed secondary glaucoma following retinal detachment repair . retinal detachment as a complication of glaucoma drainage device has been reported in as many as 16% cases with varied risk factors . nevertheless , considering the presence of multiple risk factors for retinal detachment , the complication may not necessarily be related to the implantation of agv in our case . conventional filtration surgery such as trabeculectomy was either not possible or carried an unacceptably high risk of failure in these eyes . known frequent complications such as early postoperative hypotony , shallow anterior chamber , tube obstruction , and conjunctival wound leak were not detected in this series . even so , the overall postsurgical complications do appear frequent in this series ; however , many patients maintained useful vision that they could potentially have lost since all had uncontrolled glaucoma prior to surgery . the retrospective design and the heterogeneity of the cases are major limitations of this study . the sample size is small and therefore , we did not analyze complete and qualified success separately . however , the clinical situations in which the procedures were done were extremely severe and until now none of the proposed treatments have gained general acceptance . this study , for the first time , shows that the silicone , flexi - plate ahmed valve can be effectively implanted in eyes with a preexisting episcleral encircling element keeping in mind the possibility of significant postoperative complications .
background : to describe the use of ahmed glaucoma valve ( agv ) in the management of intractable glaucoma in eyes with a preexisting episcleral encircling element.materials and methods : this is a retrospective , consecutive , noncomparative study . 
 the study included 12 eyes of 12 patients with a preexisting episcleral encircling element that underwent implantation of silicone agv to treat intractable glaucoma during january 2009 to september 2010.results:the mean patient age was 25.6 ( standard deviation 17.1 ) years . 
 five ( 41.6% ) patients were monocular . 
 the indications for agv were varied . 
 the mean duration between placement of episcleral encircling element and implantation of agv was 30.5 ( 33.8 ) months . 
 the mean follow - up was 37.4 ( 22.9 ) weeks . 
 preoperatively , the mean intraocular pressure ( iop ) was 31.4 ( 7.9 ) mmhg and the mean antiglaucoma medications were 2.8 . at the final postoperative follow - up , the mean iop was 12.5 ( 3.5 ) mmhg and the mean number of antiglaucoma medications was 0.8 ( p < 0.001 ) . 
 the complications observed over the follow - up period did include corneal graft failure in three eyes , tube erosion in two eyes and rhegmatogenous retinal detachment in one eye.conclusion:agv is an effective option in the management of intractable glaucoma in eyes with a preexisting episcleral encircling element keeping in mind the possibility of significant postoperative complications .