the study protocol was approved by the institutional review board of kim 's eye hospital , seoul , korea .
all participants provided informed consent prior to enrollment and all procedures conformed to the guidelines of the declaration of helsinki . from june 2006 to july 2011 , 134 eyes from 132 patients who underwent agv implantation surgery at kim 's eye hospital were analyzed retrospectively .
each subject underwent a full ophthalmic examination , including visual acuity assessment , iop assessment with a goldmann applanation tonometer , anterior segment examination by slit - lamp biomicroscopy , fundus examination with a 90 diopter ( d ) lens , and 24 - 2 swedish interactive threshold algorithm standard automated visual fieldest ( humphrey visual field analyzer ; carl zeiss meditec , dublin , ca , usa ) before surgery as well as 1 day , 1 month , 2 - 3 months , 4 - 6 months , 11 - 16 months , and 17 - 24 months after surgery .
the study included any patient who underwent agv implantation surgery at kim 's eye hospital performed using the same technique by 1 of 2 glaucoma specialists ( yhs and hkk ) with a minimum of 6 months follow - up .
the exclusion criteria were : patients ' age less than 18 years or more than 80 years , agv implanted in inferior quadrants , previous seton surgery or trabeculectomy in the operated eye , inflammatory or ocular surface disease with severe conjunctival scarring , history of retinal detachment surgery with scleral buckle or vitrectomy in the operated eye , and history of endophthalmitis in the operated eye . among the 134 eyes from 132 patients , 44 eyes from 42 patients
before surgery included : 50 eyes had neovascular glaucoma , 36 eyes had secondary open angle glaucoma , and 4 eyes had primary open angle glaucoma .
the agv implantation selection was made by the surgeon based on conjunctival mobility and presence of previous surgical conjunctival scaring , limited subconjunctival space owing to previous ocular surgeries , scarred upper fornix , shallow fornix , and presence of small eyes .
eyes implanted with the fp7 and fp8 agvs were assigned to the fp7 group and fp8 group , respectively .
the procedures were performed in a similar manner in all subjects regardless of implant size .
the conjunctival incision was made 4 mm posterior to the limbus and , following dissection of the conjunctiva and tenon 's capsule toward the fornix and limbus , bipolar cautery was performed .
mitomycin - c ( 0.02% ) was applied with a large piece of soaked cellulose sponge under the conjunctival flap and over the episclera for 3 minutes followed by thorough irrigation of the area with a balanced salt solution .
the plate of the implant was then secured to the sclera 8 to 10 mm posterior to the surgical limbus using 2 interrupted 7 - 0 silk sutures .
the tube was trimmed to an appropriate length with the bevel facing anteriorly and , after injection of methyl cellulose into the anterior chamber via a clear cornea stab incision , the tube was inserted into the anterior chamber through a corneoscleral track created using a 23-gauge needle .
the tube was fixed to the episclera with a 10 - 0 nylon mattress suture .
a quadrangular donor scleral patch graft ( 4  7 mm ) was fashioned and secured over the exposed part of the tube using 10 - 0 nylon sutures .
the conjunctiva and tenon 's capsule were repaired using 8 - 0 vicryl suture material in a running fashion .
dexamethasone ( 4 mg ) and gentamycin ( 100 mg ) were injected subconjunctivally upon procedure conclusion .
the postoperative regimen included topical levofloxacin ( 0.5% ) eye drops 4 times per day for 1 week and topical fluorometholone ( 0.1% ) eye drops 4 times per day that was usually tapered over 6 to 8 weeks .
postoperative follow - up visits were scheduled for 1 day , 1 and 2 weeks , and 1 , 3 , 6 , and 12 months after the procedure and every 6 months thereafter .
surgical success was defined as iop maintained below 21 mmhg regardless of the number of iop medications used during the final follow - up observation .
the following observations made during follow - up were regarded as surgical failures : an iop greater than 22 mmhg at 2 or more consecutive follow - up visits , an iop less than 5 mmhg at 2 or more consecutive follow - up visits , additional glaucoma surgery was required , and loss of light perception .
independent t - tests and chi - squared tests were performed to compare ocular and demographic variables between the 2 groups . to compare the success rate of surgery between the 2 groups , a log - rank ( mantel - cox ) test was performed
the study protocol was approved by the institutional review board of kim 's eye hospital , seoul , korea .
all participants provided informed consent prior to enrollment and all procedures conformed to the guidelines of the declaration of helsinki . from june 2006 to july 2011 , 134 eyes from 132 patients who underwent agv implantation surgery at kim 's eye hospital were analyzed retrospectively .
each subject underwent a full ophthalmic examination , including visual acuity assessment , iop assessment with a goldmann applanation tonometer , anterior segment examination by slit - lamp biomicroscopy , fundus examination with a 90 diopter ( d ) lens , and 24 - 2 swedish interactive threshold algorithm standard automated visual fieldest ( humphrey visual field analyzer ; carl zeiss meditec , dublin , ca , usa ) before surgery as well as 1 day , 1 month , 2 - 3 months , 4 - 6 months , 11 - 16 months , and 17 - 24 months after surgery .
the study included any patient who underwent agv implantation surgery at kim 's eye hospital performed using the same technique by 1 of 2 glaucoma specialists ( yhs and hkk ) with a minimum of 6 months follow - up .
the exclusion criteria were : patients ' age less than 18 years or more than 80 years , agv implanted in inferior quadrants , previous seton surgery or trabeculectomy in the operated eye , inflammatory or ocular surface disease with severe conjunctival scarring , history of retinal detachment surgery with scleral buckle or vitrectomy in the operated eye , and history of endophthalmitis in the operated eye . among the 134 eyes from 132 patients , 44 eyes from 42 patients
before surgery included : 50 eyes had neovascular glaucoma , 36 eyes had secondary open angle glaucoma , and 4 eyes had primary open angle glaucoma .
the agv implantation selection was made by the surgeon based on conjunctival mobility and presence of previous surgical conjunctival scaring , limited subconjunctival space owing to previous ocular surgeries , scarred upper fornix , shallow fornix , and presence of small eyes .
eyes implanted with the fp7 and fp8 agvs were assigned to the fp7 group and fp8 group , respectively .
the procedures were performed in a similar manner in all subjects regardless of implant size . the conjunctival incision was made 4 mm posterior to the limbus and , following dissection of the conjunctiva and tenon 's capsule toward the fornix and limbus , bipolar cautery was performed .
mitomycin - c ( 0.02% ) was applied with a large piece of soaked cellulose sponge under the conjunctival flap and over the episclera for 3 minutes followed by thorough irrigation of the area with a balanced salt solution .
the plate of the implant was then secured to the sclera 8 to 10 mm posterior to the surgical limbus using 2 interrupted 7 - 0 silk sutures .
the tube was trimmed to an appropriate length with the bevel facing anteriorly and , after injection of methyl cellulose into the anterior chamber via a clear cornea stab incision , the tube was inserted into the anterior chamber through a corneoscleral track created using a 23-gauge needle .
the tube was fixed to the episclera with a 10 - 0 nylon mattress suture .
a quadrangular donor scleral patch graft ( 4  7 mm ) was fashioned and secured over the exposed part of the tube using 10 - 0 nylon sutures .
the conjunctiva and tenon 's capsule were repaired using 8 - 0 vicryl suture material in a running fashion .
dexamethasone ( 4 mg ) and gentamycin ( 100 mg ) were injected subconjunctivally upon procedure conclusion .
the postoperative regimen included topical levofloxacin ( 0.5% ) eye drops 4 times per day for 1 week and topical fluorometholone ( 0.1% ) eye drops 4 times per day that was usually tapered over 6 to 8 weeks .
postoperative follow - up visits were scheduled for 1 day , 1 and 2 weeks , and 1 , 3 , 6 , and 12 months after the procedure and every 6 months thereafter .
surgical success was defined as iop maintained below 21 mmhg regardless of the number of iop medications used during the final follow - up observation .
the following observations made during follow - up were regarded as surgical failures : an iop greater than 22 mmhg at 2 or more consecutive follow - up visits , an iop less than 5 mmhg at 2 or more consecutive follow - up visits , additional glaucoma surgery was required , and loss of light perception .
independent t - tests and chi - squared tests were performed to compare ocular and demographic variables between the 2 groups . to compare the success rate of surgery between the 2 groups , a log - rank ( mantel - cox ) test was performed
among them , 66 eyes underwent fp7 implant surgery , and 24 eyes underwent fp8 implant surgery .
table 1 summarizes the demographic and clinical characteristics of the study populations . the mean age was 57.6  11.4 years for the fp7 group and 61.0  9.9 years for the fp8 group ( p = 0.199 ) .
preoperative iop was 41.9  9.2 mmhg for the fp7 group and 39.0  6.6 mmhg for the fp8 group ( p = 0.105 ) .
there was no significant difference between the 2 groups in the following variables : sex , systemic disease distribution , glaucoma subtype , baseline visual acuity , number of preoperative antiglaucoma medications , previous ocular surgeries , laterality , and implantation site ( p > 0.05 ) ( table 1 ) .
the mean follow - up period was 17.2  9.1 months for the fp7 group and 20.3  4.4 months for the fp8 group ( p = 0.273 ) .
the postoperative visual acuity of the fp8 group was better than that in the fp7 group in some early postoperative periods ( 1 week , 2 to 3 months , and 7 to 10 months after the surgery ; p < 0.05 ) ; however , after 10 postoperative months , there were no significant differences in visual acuity between the 2 groups through the 3-year follow - up ( p > 0.05 ) ( table 2 ) .
postoperative iop was not significantly different between the 2 groups ( p > 0.05 ) except for the iop on postoperative day 1 ( 11.4  8.4 mmhg for the fp7 group and 7.4  3.9 mmhg for the fp8 group , p = 0.031 ) ( table 3 ) . there were no statistically significant differences between the groups in terms of the number of glaucoma medications after surgery ( table 4 ) . in this study , surgical success was considered as iop maintained at less than 21 mmhg regardless of the medication used , no additional glaucoma surgery required , non - occurrence of light sense loss , and no consecutive follow - up visits with low iop .
therefore , the cumulative success rate according to the log - rank test for kaplan - meier survival analysis was 79.2% for the fp8 group and 72.7% for the fp7 group at the 3-year follow - up ( p = 0.535 ) ( fig .
1 ) . the main reasons for failure were not significantly different between the 2 groups ( table 5 ) .
it has been hypothesized that glaucoma drainage implants with large plates produces an increased surface area of encapsulation and a higher degree of iop reduction . in a prospective randomized clinical trial comparing single - plate and double - plate molteno implants , heuer et al
.   found a higher success rate and greater iop reduction with the double - plate implants than with single - plate implants , presumably because of the large surface area of the double - plate implants . on the contrary , seah et al .   reported no significant difference in success rates , final iop , number of medications , and rates of complications between the 250 and 350 mm baerveldt glaucoma implants ( bgis ) . in another prospective study comparing the 350 and 500 mm bgis , lloyd et al .   reported that there was no difference in success rates and visual outcomes between the different implant sizes .
britt et al .   also reported that the 500 mm bgi was not superior to the 350 mm bgi for iop control .
these results are in agreement with the present study results : no differences were found in vision preservation , iop reduction , or decrease in number of glaucoma medications between the fp7 and fp8 agv implants in adult eyes with glaucoma .
thus far , this is the only study comparing the surgical outcomes between fp7 and fp8 agv implants in adult eyes .
similar surgical outcomes between the fp7 and fp8 groups imply that the plate area may not be the major factor in determining surgical success , and it is likely that there is a maximal surface area beyond which there is minimal improvement in iop control .
kang and kee   argued that there is an upper limit of the increase in the surface area at which the implants cease to have a beneficial effect on iop , and it is inferred that the effect of iop decrease does not depend on the area of filter cloth beyond a certain size .
this phenomenon may be at least partly responsible for the lack of superior iop reduction of the fp7 agv implants compared to the fp8 agv implants .
another possible explanation is the surgeon 's perceived a priori likelihood of failure or complications , because the choice of implant is to some extent influenced by the severity of the glaucoma .
it is difficult to compare surgical success rates from different studies because of differences in study design , populations studied , types of implants used , and lengths of follow - up periods .
variable success rates of agv implantation have been reported and range between 64.5% and 95.0% , with follow - up periods of 6 to 24 months .
with fp7 after a follow - up of 6 months and 78% was reported by coleman et al . , with fp7 after a follow - up of 12 months .
in addition , a success rate of 96% was obtained with the fp7 implant after a follow - up of 12 months .
these results are similar to the results ishida et al .   reported : a 94.2% success rate with fp7 implant at 12 months . in 40 eyes from 40 patients with different types of refractory glaucoma , a 92.5% success rate
was reported with both fp7 and fp8 after a follow - up period of 6 months .
unfortunately , this study did not report separate success rates between fp7 and fp8 groups .
although materials vary , a 53.8% success rate was reported with the 96 mm agv ( model s3 , new world medical inc . ) and a 92.3% success rate was reported with the 184 mm agv ( model s3 , new world medical inc . ) after a follow - up period of 10 months . in the present study ,
the success rates were 79.2% for the fp8 group and 72.7% for the fp7 group at the 3-year follow - up , which are comparable with the success rates of other studies . in adult eyes ,
however , in conditions with conjunctival scarring or limited subconjunctival space , fp7 agv implantation is challenging .
in addition , an oversized implant can result in various complications , including implant exposure , extrusion , discomfort , and motility defects .
given that fp7 and fp8 agv implants did not show differences in surgical outcomes , we suggest that fp8 implantation may be a useful surgical option for iop control in adult eyes with insufficient conjunctival or subconjunctival areas
. this option may be especially useful for special circumstances in asian eyes since small globes are common in this population . to compare surgical outcomes between fp7 and fp8 agv implants , randomization of subjects who underwent
however , in the present study , the type of agv was chosen per the surgeon 's clinical judgment without randomization .
other limitations include a relatively small sample size and limited follow - up period . long - term , prospective , randomized , patient- , and investigator - masked studies are needed to confirm the results of this study . in conclusion ,
fp7 and fp8 agv implants showed no difference in terms of preservation of vision , iop reduction , or decrease in the number of required glaucoma medications .
the fp8 agv implant appears to be a viable option for the management of refractory glaucoma in adult eyes with conjunctival scarring or limited subconjunctival space owing to the previous ocular surgeries , inflammatory ocular disorders , or small eyes .
 purposeto compare the success rates , complications , and visual outcomes between silicone ahmed glaucoma valve ( agv ) implantation with 96 mm2 ( fp8 ) or 184 mm2 ( fp7 ) surface areas.methodsthis study is a retrospective review of the records from 132 adult patients ( 134 eyes ) that underwent silicone agv implant surgery . among them , the outcomes of 24 eyes from 24 patients with refractory glaucoma who underwent fp8 agv implantation were compared with 76 eyes from 76 patients who underwent fp7 agv implantation . 
 preoperative and postoperative data , including intraocular pressure ( iop ) , visual acuity , number of medications , and complications were compared between the 2 groups.resultsthere were no significant differences in baseline characteristics between the 2 groups ( p > 0.05 ) . 
 the postoperative visual acuity of the patients in the fp8 group was better than that of the patients in the fp7 group in some early postoperative periods ( p < 0.05 ) ; however , after 10 postoperative months , visual acuity was not significantly different through the 3-year follow - up period ( p > 0.05 ) . 
 postoperative iop was not significantly different between the 2 groups ( p > 0.05 ) except for iop on postoperative day 1 ( 11.42 mmhg for the fp7 group and 7.42 mmhg for the fp8 group ; p = 0.031 ) . 
 there was no statistical difference in success rates , final iop , number of medications , or complication rates between the 2 groups ( p > 0.05).conclusionsthe fp7 and fp8 agv implants showed no difference in terms of vision preservation , iop reduction , and number of glaucoma medications required . 
Materials and Methods
Participants
Surgical procedures
Statistical analyses
Results
Discussion