globally , glaucoma is the leading cause of irreversible blindness , and this is especially relevant to complicated , refractory cases of glaucoma.1 glaucoma drainage devices ( gdd ) are frequently used for the management of refractory glaucoma cases , and as a secondary choice following failure of other surgeries .
additionally , several studies have reported favorable results with gdd implantation as the primary surgical option in glaucoma patients.234 the ahmed glaucoma valve ( agv ; new world medical , inc . , rancho cucamonga , california , usa )
was introduced into the market at 1993 and has a built - in silicone venturi valve to restrict aqueous outflow and prevent postoperative hypotony.5 it is used in refractory glaucoma cases both as a primary surgical choice and after the failure of conventional filtering surgery .
several reports exist on success rate of agv in different situations and races.46789 however , reports are rare on long - term outcomes of the device from the middle east . in the current study
, we evaluated the outcomes of agv implantation in refractory glaucoma cases in a major tertiary eye hospital in iran .
this retrospective cohort study evaluated the medical records of patients with refractory glaucoma who underwent agv implantation at farabi eye hospital , tehran , iran .
the chart review included all consecutive cases with refractory glaucoma , unresponsive to medical and conventional surgical intervention , who underwent agv implantation by one surgeon ( prof .
we selected this period to evaluate the long - term result of the cases that is the fate of the procedure over a 10-year period .
patients with previous drainage device implantation were excluded from the study . as the hospital serves both primary and referral patients , some of the operated patients are followed - up by the referring physician and have follow - up data were missing after the 1 postoperative week .
preoperative data were collected on patient age , gender , intraocular pressure ( iop ) measured by a calibrated goldmann applanation tonometer , number of anti - glaucoma medications , best - corrected visual acuity using a tumbling e - chart , and cup - to - disk ratio .
surgical data were collected including any intraoperative complications along with other intraoperative findings and site of agv implantation .
all surgical and clinic records in the hospital were hard copies and were reviewed case by case for this study .
complete success was defined as iop < 22 mmhg , without anti - glaucoma medications or need for additional surgery .
iop < 22 mmhg regardless of the number of anti - glaucoma medications was classified as qualified success .
iop 22 mmhg with maximal , tolerable medications , iop 5 mmhg , need for additional surgical intervention , loss of light perception , or phthisis bulbi was considered a surgical failure
briefly , under monitored anesthetic care along with topical and subconjunctival anesthesia for adult patients and general anesthesia for pediatric subjects ; a clear corneal traction suture was placed parallel to limbus and a limbal based superotemporal or superonasal peritomy was performed .
the agv was primed with balanced salt solution , and its plate was fixed to sclera at least 10 mm posterior to the surgical limbus with two nylon 8 - 0 sutures .
the tube was trimmed and inserted into the anterior chamber in a plane parallel to iris and as far from corneal endothelium as possible .
a scleral patch graft from banked donor sclera was placed over the tube , and water tight closure of tenon 's and conjunctiva was performed with running vicryl 8 - 0 sutures . at the conclusion of surgery , subconjunctival cefazoline , and betamethasone were administered .
kaplan - meier survival analysis was performed to evaluate success rate over the study period .
furthermore , repeated measure analysis of variance ( anova ) along with bonferroni adjustment was performed to evaluate iop and medication changes over time .
briefly , under monitored anesthetic care along with topical and subconjunctival anesthesia for adult patients and general anesthesia for pediatric subjects ; a clear corneal traction suture was placed parallel to limbus and a limbal based superotemporal or superonasal peritomy was performed .
the agv was primed with balanced salt solution , and its plate was fixed to sclera at least 10 mm posterior to the surgical limbus with two nylon 8 - 0 sutures .
the tube was trimmed and inserted into the anterior chamber in a plane parallel to iris and as far from corneal endothelium as possible .
a scleral patch graft from banked donor sclera was placed over the tube , and water tight closure of tenon 's and conjunctiva was performed with running vicryl 8 - 0 sutures . at the conclusion of surgery , subconjunctival cefazoline , and betamethasone were administered .
kaplan - meier survival analysis was performed to evaluate success rate over the study period .
furthermore , repeated measure analysis of variance ( anova ) along with bonferroni adjustment was performed to evaluate iop and medication changes over time .
the mean age was 44.3  22.3 years ( median : 44.00 years ; range : 775 years ) .
fifteen patients were male ( 53.5% ) , and all included patients were caucasians and iranians .
the mean follow - up time was 48.2  31.7 months ( median : 40.5 ; range : 3124 months ) ; 92.8% had at least 12 months follow - up and 78.5% of participants had 24 months follow - up .
pseudophakic glaucoma was the most common type of glaucoma ( 13 eyes ; 46.4% ) .
demographic data and preoperative characteristics of eyes that underwent ahmed glaucoma valve implantation in this study mean preoperative iop was 30.8  5.6 mmhg ( range : 23.050.0 mmhg ) with 3.7  0.4 medications ( range : 34 medications ) .
mean postoperative iop decreased to 20.0  6.4 mmhg ( range : 15.035.0 mmhg ) with a mean of 2.5  1.1 ( range : 04 ) medications .
the iop , differed statistically significantly at different times when analyzed with anova using bonferroni adjustment .
however , using tukey 's post - hoc test , a statistically significant difference was observed only for comparison between preoperative and postoperative iops at different times ( p < 0.0001 ) , and there was no statistically significant difference between iop measurements comparing different postoperative visits .
intraocular pressure and number of medications preoperatively and postoperatively in life - table survival analysis and based on the predefined success criteria , qualified success was achieved in 69% of subjects at the end of 120 months of follow - up .
the mean  standard error of mean time to failure according to complete and qualified success criteria was 51.6  6.8 months and 92.3  9.4 months , respectively [ figure 1 ] .
survival curve of complete success following ahmed glaucoma valve implantation in 28 eyes with refractory glaucoma ( a ) complete success , ( b ) qualified success on average , visual acuity decreased by one snellen line at the last postoperative visit .
mean preoperative visual acuity was 0.62  0.43 logarithm of the minimum angle of resolution units and statistically significantly decreased to 0.76  0.49 at last follow - up visit ( p = 0.007 ) .
the visual acuity remained unchanged in 12 ( 42.9% ) eyes , improved in 6 ( 21.4% ) eyes , and decreased in 10 ( 35.7% ) eyes ( p < 0.0001 ) .
the most common complication was focal endothelial corneal decompensation due to tube - cornea touch in 3 ( 10.7% ) eyes .
two aphakic eyes had vitreous incarceration in the tube orifice and were managed with neodymium - doped / yttrium aluminum garnet vitreolysis .
agv tube was extruded in two cases , which were managed with scleral patch graft and conjunctival advancement .
postoperative surgical complications following ahmed glaucoma valve implantation in 28 iranian eyes with refractory glaucoma qualified success was achieved in 77.8% , 69.2% , and 66.7% of phakic , pseudophakic and aphakic eyes , respectively ( p = 0.871 ) .
table 4 compares the results of the current study with the results of previously published articles .
summary of previous published study on surgical outcome of glaucoma drainage devices along with the result of current study
in the current study , we retrospectively reviewed the results of agv implantation in iranian patients with refractory glaucoma . in this series of 28 patients with a median follow - up time of 40.5 months ,
69% of eyes achieved qualified success . however , various complications were encountered in almost 57% of cases during follow - up .
surgical success rates for glaucoma shunting procedures vary in published studies from 20%32 to 98%.20 however , because of differences in the study population , type of implants , and the duration of follow - up , the results are not directly comparable to our study . hence , it is tenous at best to make a globally valid conclusion about the efficacy of the procedure for the refractory glaucoma cases .
the majority of the current body of literature regarding the success of drainage devices is from the developed countries , whereas refractory glaucoma seems to be more prevalent and disabling in developing and undeveloped countries.33 the current study focused on the long - term success of agv shunting procedure in refractory glaucoma cases in iran .
table 4 presents the outcomes of previous studies on tube shunt implantation including our study .
the differences on types of races of the study population could explain the variations in success rate between studies .
interestingly , a large multicenter study by gedde et al.17 ( tube vs. trabeculectomy study [ tvt ] ) had compared outcomes of primary shunting procedure , using 350 mm baerveldt glaucoma implant in 107 eyes , and trabeculectomy with mitomycin c in 105 eyes .
the cumulative probability of failure for tube shunt ( vs. trabeculectomy ) during 1 year , first 3 years , and first 5 years of follow - up was , 3.9% ( vs. 13.5% ) , 15.1% ( vs. 30.7% ) , and 29.8% ( vs. 46.9% ) , respectively.23435 they17 concluded that tube shunts had a higher success rate than trabeculectomy in their cohort of patients .
the cumulative probability of failure in the current study at 1-year , 3-year , and 5-year follow - up was 14% , 31% , and 31% , respectively .
these rates are higher than the tvt study.17 syed et al.26 reported similar surgical outcomes for the ahmed and baerveldt implants , and we believed that the observed differences are because we included eyes with failed previous incisional surgeries in our study .
souza et al.6 retrospectively evaluated 78 eyes with agv implant and proposed that prior glaucoma surgery could increase the risk of failure of agv implantation by more than three - fold . in the current study ,
we implanted silicon type agv ( agv fp7 ) in our patients that may be associated with a higher complication rate.36 however , there was no major tube - related visual loss in our patients , and our complication rate is comparable to previous studies [ table 4 ]
. limitations of this study include the retrospective design and the small sample - size .
another drawback was our inclusion of only subjects with previously failed incisional surgeries and refractory glaucoma in the study . additionally , the study population was heterogeneous in terms of the type of glaucoma and duration of follow - up .
farabi eye hospital is the largest referral eye hospital in iran , and many patients went for further management to the referring ophthalmologist after a few postoperative visits .
. however , our study has the largest follow - up of agv implantation in the region .
we believed that agv implantation could have an acceptable success rate in patients with refractory glaucoma and failed previous incisional glaucoma surgery in patients in the middle east .
however , to achieve adequate iop control , topical anti - glaucoma medications should be continued postoperatively in most subjects .
a further implication of the current study is the need for periodic , long - term follow - up for proper management of failures or complications .
after the 1 postoperative month , we suggest follow - up visits every 3 months in the 1 year , then every 6 months over the next 4 years , and annually thereafter . however , this recommendation should be further validated and should be tailored according to clinical judgments on many factors including but not limited to the severity of glaucomatous damage , level of iop , general health of patients , and life expectancy .
 purpose : to describe long - term outcomes and complications of ahmed glaucoma valve ( agv ) implantation in subjects with refractory glaucoma at farabi eye hospital , tehran , iran.materials and methods : this retrospective cohort study evaluated patient records of all subjects with refractory glaucoma who had undergone agv implantation up to january 2013 . 
 the main outcome measure was the surgical success rate . 
 complete success was defined as intraocular pressure ( iop ) < 22 mmhg , without anti - glaucoma medications or additional surgery . 
 qualified success was iop < 22 mmhg regardless of number of anti - glaucoma medications . in all cases , 
 loss of vision ( no light perception ) was considered an independent indicator of failure . 
 data were also collected on intraoperative and postoperative complications.results:twenty-eight eyes were included in the study . with a mean follow - up of 48.2  31.7 months ( median : 40.50 months ; range : 3124 months ) , 
 the iop decreased from a mean preoperative value of 30.8  5.6 mmhg to 20.0  6.4 mmhg at last visit . 
 the number of medications decreased from 3.7  0.4 preoperatively to 2.5  1.1 postoperatively . 
 cumulative qualified success was achieved in 69% of eyes . 
 mean time to failure according to qualified success criteria was 92.3  9.4 months . 
 postoperative complications were recorded in 16 ( 57.1% ) eyes . 
 the most common complication was focal endothelial corneal decompensation at the site of tube - cornea touch.conclusion:agv implantation with adjunctive topical anti - glaucoma drops controlled iop in approximately 70% of eyes with refractory glaucoma with a median of 40.5 months of follow - up . however , complication rates were higher . 
INTRODUCTION
MATERIALS AND METHODS
Surgical technique
Statistical analysis
RESULTS
DISCUSSION
CONCLUSIONS
Financial support and sponsorship
Conflicts of interest