small - gauge pars plana vitrectomy ( ppv ) systems have gained wide acceptance in vitreoretinal surgery due to their potential for reduced inflammation and rapid visual recovery.1 recently , valved cannulas have been added to the vitreoretinal surgery armamentarium . they alleviate the need for cannula plugs during instrument exchange and minimize egress of fluid through cannulas during surgery . these advantages allow stable intraocular fluidics and improved dynamic control of intraocular pressure ( iop ) . proliferative vitreoretinopathy ( pvr ) is the most common etiology for recurrent retinal detachment ( rd).2 the pathophysiology leading to pvr formation is not fully understood but thought to be at least partially inflammation mediated in a process analogous to excessive wound healing , driven by migrating and proliferating retinal pigment epithelium ( rpe ) , glial cells , and bone marrow - derived inflammatory cells.3,4 clinically , pvr is currently classified into grades a  c , with grade c being the most severe form manifested by preretinal and/or subretinal membranes.5 rd complicated by grade c pvr poses a significant surgical challenge . the optimal surgical approach for grade c pvr , such as use of an adjuvant scleral buckle ( sb ) , inferior retinectomy , choice of tamponade , and vitrectomy gauge , remains controversial.2,6 limited studies demonstrate encouraging surgical success rates when small - gauge vitrectomy systems are employed in the repair of rd with grade c pvr.710 to our knowledge , no studies in the literature have specifically evaluated the use of valved cannulas for rd repair complicated by pvr . it is possible that there is decreased washout of debris and inflammatory products in eyes operated with valved cannulas that may lead to an increased rate of pvr and surgical failures . alternatively , the diminished intraocular fluid currents associated with valved cannula use may cause decreased liberation of rpe cells , resulting in lower rates of induced pvr and improved surgical outcomes . in this study , we retrospectively reviewed outcomes and complication rates of valved vs nonvalved cannula ppv for rd repair complicated by grade c pvr at a single academic institution and found comparable functional and anatomic results as well as complication rates . the study protocol was approved by the institutional review board of the duke university school of medicine . we performed a retrospective chart review of eyes that underwent small - gauge ( 23 or 25 gauge ) ppv with valved vs nonvalved cannulas for rd repair complicated by grade c pvr . the clinical database tool duke enterprise data unified content explorer was used to search for current procedural terminology codes 67108 and 67113 , which are associated with vitrectomy for repair of rd.11 the duke vitreoretinal service transitioned to valved cannulas in may 2012 and started exclusive use of valved cannulas in july 2012 . the valved group consisted of valved cannula ppv between july 1 , 2012 and january 31 , 2013 ; the nonvalved group consisted of nonvalved cannula ppv between july 1 , 2011 and january 31 , 2012 . charts were reviewed to identify eyes with rds complicated by documented grade c pvr that were repaired with small - gauge ppv and use of temporary perfluorocarbon liquid ( perfluoro - n - octane [ pfo ] ) . the exclusion criteria included use of 20-gauge vitrectomy , no ppv ( eg , sb only ) , diagnosis other than rd ( vitreous hemorrhage , epiretinal membrane [ erm ] , etc ) , traumatic rd or open globe , no use of pfo during ppv , abortion of the surgery from anesthesia - related complications , and postoperative follow - up <3 weeks . multiple surgeons performed standard three - port ppv using valved or nonvalved cannulas with an alcon constellation vitrectomy system ( alcon laboratories , inc . , forth pfo was used temporarily to flatten and stabilize the retina during pvr membrane peeling and/or to drain subretinal fluid . based on individual discretion of the surgeon , adjuvant sb was placed , relaxing retinectomy was performed , and silicone oil , octafluoropropane gas ( c3f8 ) , or sulfur hexafluoride gas ( sf6 ) tamponade was utilized . for silicone oil fill , automated viscous fluid control injection was utilized in both valved and nonvalved cannula cases . for valved cannulas , either a chimney or a second instrument to displace one of the valve leaflets was used to vent the system , whereas for nonvalved cases , the cannula was left open to vent the system . pfo injection was performed slowly with a single bore cannula , and injection was temporarily halted in the case of optic nerve compromise until reperfusion was noted in both valved and nonvalved cannulas ; the infusion line allowed retrograde fluid flow to alleviate the increased pressure induced by pfo injection . charts were analyzed for baseline demographics and preoperative characteristics ( lens status , macula on vs off rd , recurrent rd [ ie , unsuccessful prior rd repair ] in the presenting eye , previous placement of sb ) and type of surgery ( gauge , adjuvant sb , relaxing retinectomy , and tamponade ) . the primary outcomes included best - corrected visual acuity ( bcva ) change as well as rate of anatomic reattachment including single surgery success ( retina attached at the final follow - up after single operation ) and final anatomic success ( retina attached at the final follow - up ) . secondary outcomes included complication rates , including pfo - related complications , postoperative day 1 hypotony , hypertony , and rate of anterior chamber fibrin formation as well as rate of subsequent erm peel after rd repair . visual acuity was converted to logarithm of the minimum angle of resolution ( logmar ) . to facilitate clinical interpretation of results , visual improvement was converted to approximate early treatment diabetes retinopathy study ( etdrs ) letter improvement scores.12 statistical differences were assessed by either the fisher s exact test or wilcoxon rank sum test . visual acuity was converted to logarithm of the minimum angle of resolution ( logmar ) . to facilitate clinical interpretation of results , visual improvement was converted to approximate early treatment diabetes retinopathy study ( etdrs ) letter improvement scores.12 statistical differences were assessed by either the fisher s exact test or wilcoxon rank sum test . we reviewed 364 charts ( 196 in the valved group and 168 in the nonvalved group ) , of which 201 eyes were excluded based on prespecified criteria ( valved cannula group : no pfo [ n=38 ] , insufficient follow - up [ n=26 ] , diagnosis other than rd [ n=20 ] , 20-gauge ppv [ n=5 ] , and traumatic rd [ n=3 ] ; nonvalved cannula group : 20-gauge ppv [ n=34 ] , no pfo [ n=29 ] , insufficient follow - up [ n=23 ] , diagnosis other than rd [ n=18 ] , no ppv [ n=4 ] , and surgery aborted because of anesthesia complications [ n=1 ] ) . of the remaining 163 eyes , 67 eyes were documented to have preoperative grade c pvr . there were 36 eyes in the valved group and 31 eyes in the nonvalved group . no significant demographic or preoperative characteristic differences existed between the groups . in the majority of eyes , the rd was macula off ( 83% in valved eyes vs 81% in nonvalved eyes , p=1.000 ) and recurrent ( 67% in valved eyes vs 71% in nonvalved eyes , p=0.795 ) . the mean preoperative bcva was 1.83 logmar ( snellen equivalent = 20/1,352 ) in the valved group vs 2.06 logmar ( snellen equivalent = 20/2,296 ) in the nonvalved group ( p=0.127 ) . the majority of eyes underwent 23-gauge ppv ( 86% in the valved group vs 94% in the non - valved group , p=0.437 ) , and the remaining minority eyes underwent 25-gauge ppv . adjuvant sb was placed in 61% of the valved eyes vs 58% of the nonvalved eyes ( p=0.809 ) . relaxing retinectomy was performed in 50% vs 39% in the valved and nonvalved groups , respectively ( p=0.461 ) . all eyes received temporary pfo to drain subretinal fluid and/or flatten and stabilize the retina during pvr membrane peeling as per the study inclusion criteria . in both groups , the most common tamponade was silicone oil ( 72% in valved eyes vs 68% in nonvalved eyes , p=1.000 ) followed by c3f8 ( 28% in valved eyes vs 32% in nonvalved eyes , p=0.791 ) . sf6 was not used for tamponade in any of these grade c pvr rd repairs . the final mean bcva in the valved group was 1.47 logmar ( snellen equivalent 20/590 ) vs 1.74 logmar ( snellen equivalent 20/1,099 ) in the nonvalved group ( p=0.124 ) . compared to baseline preoperative bcva , the mean logmar improvement at the final follow - up visit was 0.36 in the valved group and 0.33 in the nonvalved group ( p=0.824 ) . the corresponding approximate etdrs letter improvement score was + 17 in the valved group vs + 16 in the nonvalved group . no statistically significant differences between the valved and nonvalved groups were found in anatomic outcomes ( table 3 ) . the single surgery success was 83% vs 77% ( p=0.555 ) and the final anatomic success was 94% vs 87% ( p=0.404 ) in the valved vs nonvalved groups , respectively . the decision to observe and not to operate on detached retinas was due to poor visual prognosis ( n=1 in the valved group , n=3 in the nonvalved group ) and patient preference ( n=1 in the valved group , n=1 in the nonvalved group ) . pvr was the most common etiology for recurrent rd in both groups ( 83% in the valved eyes vs 71% in the nonvalved eyes , p=1.000 ) . alternative etiologies were recurrent rd without documented hole , break , or pvr under silicone oil ( n=1 , valved group ; n=1 , nonvalved group ) and recurrent rd without documented hole , break , or pvr 1 month following silicone oil removal ( n=1 , nonvalved group ) . intraocular retained pfo was reported in 6% vs 10% of the valved and nonvalved groups ( p=0.656 ) , which was removed surgically in 100% ( n=3 ) of the valved group and 0% of the nonvalved group ( p=0.100 ) . subretinal retained pfo was detected in 11% of the valved group and 3% of the nonvalved group ( p=0.363 ) and was observed without surgical removal in all cases . there were no significant differences in postoperative day 1 anterior chamber fibrin reaction , postoperative day 1 hypotony or hypertony , as well as subsequent erm peeling between the groups . no cases of iatrogenic retinal breaks due to retinal incarceration at the cannula site were reported in either group . we reviewed 364 charts ( 196 in the valved group and 168 in the nonvalved group ) , of which 201 eyes were excluded based on prespecified criteria ( valved cannula group : no pfo [ n=38 ] , insufficient follow - up [ n=26 ] , diagnosis other than rd [ n=20 ] , 20-gauge ppv [ n=5 ] , and traumatic rd [ n=3 ] ; nonvalved cannula group : 20-gauge ppv [ n=34 ] , no pfo [ n=29 ] , insufficient follow - up [ n=23 ] , diagnosis other than rd [ n=18 ] , no ppv [ n=4 ] , and surgery aborted because of anesthesia complications [ n=1 ] ) . of the remaining 163 eyes , 67 eyes were documented to have preoperative grade c pvr . there were 36 eyes in the valved group and 31 eyes in the nonvalved group . no significant demographic or preoperative characteristic differences existed between the groups . in the majority of eyes , the rd was macula off ( 83% in valved eyes vs 81% in nonvalved eyes , p=1.000 ) and recurrent ( 67% in valved eyes vs 71% in nonvalved eyes , p=0.795 ) . the mean preoperative bcva was 1.83 logmar ( snellen equivalent = 20/1,352 ) in the valved group vs 2.06 logmar ( snellen equivalent = 20/2,296 ) in the nonvalved group ( p=0.127 ) . the majority of eyes underwent 23-gauge ppv ( 86% in the valved group vs 94% in the non - valved group , p=0.437 ) , and the remaining minority eyes underwent 25-gauge ppv . adjuvant sb was placed in 61% of the valved eyes vs 58% of the nonvalved eyes ( p=0.809 ) . relaxing retinectomy was performed in 50% vs 39% in the valved and nonvalved groups , respectively ( p=0.461 ) . all eyes received temporary pfo to drain subretinal fluid and/or flatten and stabilize the retina during pvr membrane peeling as per the study inclusion criteria . in both groups , the most common tamponade was silicone oil ( 72% in valved eyes vs 68% in nonvalved eyes , p=1.000 ) followed by c3f8 ( 28% in valved eyes vs 32% in nonvalved eyes , p=0.791 ) . sf6 was not used for tamponade in any of these grade c pvr rd repairs . the final mean bcva in the valved group was 1.47 logmar ( snellen equivalent 20/590 ) vs 1.74 logmar ( snellen equivalent 20/1,099 ) in the nonvalved group ( p=0.124 ) . compared to baseline preoperative bcva , the mean logmar improvement at the final follow - up visit was 0.36 in the valved group and 0.33 in the nonvalved group ( p=0.824 ) . the corresponding approximate etdrs letter improvement score was + 17 in the valved group vs + 16 in the nonvalved group . no statistically significant differences between the valved and nonvalved groups were found in anatomic outcomes ( table 3 ) . the single surgery success was 83% vs 77% ( p=0.555 ) and the final anatomic success was 94% vs 87% ( p=0.404 ) in the valved vs nonvalved groups , respectively . the decision to observe and not to operate on detached retinas was due to poor visual prognosis ( n=1 in the valved group , n=3 in the nonvalved group ) and patient preference ( n=1 in the valved group , n=1 in the nonvalved group ) . pvr was the most common etiology for recurrent rd in both groups ( 83% in the valved eyes vs 71% in the nonvalved eyes , p=1.000 ) . alternative etiologies were recurrent rd without documented hole , break , or pvr under silicone oil ( n=1 , valved group ; n=1 , nonvalved group ) and recurrent rd without documented hole , break , or pvr 1 month following silicone oil removal ( n=1 , nonvalved group ) . intraocular retained pfo was reported in 6% vs 10% of the valved and nonvalved groups ( p=0.656 ) , which was removed surgically in 100% ( n=3 ) of the valved group and 0% of the nonvalved group ( p=0.100 ) . subretinal retained pfo was detected in 11% of the valved group and 3% of the nonvalved group ( p=0.363 ) and was observed without surgical removal in all cases . there were no significant differences in postoperative day 1 anterior chamber fibrin reaction , postoperative day 1 hypotony or hypertony , as well as subsequent erm peeling between the groups . no cases of iatrogenic retinal breaks due to retinal incarceration at the cannula site were reported in either group . while small - gauge systems have been increasingly adopted in the management of a variety of vitreoretinal conditions , only limited knowledge exists regarding their impact on outcomes and complications of complex pathologic conditions such as grade c pvr - associated rd . to our knowledge , the present study is the only series specifically investigating valved cannulas for the repair of rd complicated by grade c pvr . we show statistically equivalent visual improvement , single surgery success , final anatomic success , as well as complication rates with valved vs nonvalved ppv . the study population consists of eyes with complex rd associated with grade c pvr presenting to a tertiary referral center . there is a correspondingly high proportion of recurrent rds and macula off detachments associated with poor preoperative vision and poor anatomic and functional prognosis . in this series , repair with valved cannulas was performed 1 calendar year following nonvalved cannulas , but both groups had comparable baseline demographics and preoperative characteristics . anatomic outcomes of this study , with single surgery success of 83% vs 77% and final anatomic success of 94% vs 83% in valved vs nonvalved eyes , respectively , compare favorably to the literature of traditional 20-gauge ppv as well as the available data on small - gauge ppv for grade c pvr - associated rd repair.7,10,1316 despite anatomic success and overall visual improvement in both groups , functional data demonstrate less encouraging results . sixty - six percent of the valved eyes and 84% of the nonvalved eyes remained with 20/200 or worse bcva at the final follow - up , which is consistent with the previously reported studies on eyes with pvr - associated rd.13,15 in a previous study , we did not identify differences in outcomes or complications with valved versus nonvalved cannulas for a heterogeneous rd population of simple and complex detachments.17 however , we hypothesized that altered intraocular fluidics associated with valved cannulas may modulate the outcome of pvr - associated complex rd repair . decreased intraocular fluid currents with valved cannulas may result in reduced rpe seeding and less recurrent pvr . alternatively , the reduced egress of fluid through valved cannulas may hinder washout of inflammatory proteins , debris , and cells , resulting in higher rates of recurrent pvr . however , for both functional and anatomic outcomes , the study found no measurable difference between valved and nonvalved cannulas . there were trends toward improved outcomes with valved cannulas in this study , and it is possible that this study was not adequately powered to detect this difference . iatrogenic retinal breaks may be a complication of vitrectomy , and reported incidences range from 1.6% to 6.2%.1820 one etiology for iatrogenic retinal breaks is vitreous incarceration , which can occur due to vitreous attraction to open cannulas.2123 the stable fluidics of valved cannulas offers a potential for decreased attraction of vitreous incarceration into the cannulas , which has been shown experimentally in the eyes of rabbit.24 in our series , no case of vitreous incarceration at the cannula site was reported in either group , but it is possible that a larger series will elucidate a difference . the improved stability of intraocular fluidics with valved cannulas requires adjustments to certain surgical approaches . owing to the closed system fluidics of valved cannulas , venting must be performed when injecting additional volume such as silicone oil or pfo . a chimney or a second instrument to displace one of the valve leaflets was used to vent the eye when inserting silicone oil with valved cannulas , whereas with nonvalved cannulas , a cannula was simply left open . typically , slow injection of pfo is sufficient to avoid significant iop rise with both valved and nonvalved cannulas , as the infusion line can allow retrograde flow of fluid ( but not air ) , but if optic nerve perfusion was compromised , temporary pausing of the injection was performed . dual - bore injection cannulas may also be used to avoid iop rise secondary to pfo injection,25 but were not used during the time of this study . while the methods of administration of these agents were similar between valved and nonvalved cannula groups , differences in fluidics may result in important differences in outcomes or complications that were undetected by this study . this is a retrospective study whose data are limited by what was recorded in the medical record . there was a significantly longer follow - up time in the nonvalved group , whose study period was 1 year prior to the valved group , which may bias the nonvalved group toward worse anatomic outcomes . the study times of the two groups were temporally distinct , and although the baseline characteristics and surgical approaches of the two groups were not different , there may have been differences in variables that were not analyzed . on the other hand , these distinct study periods may also reduce selection bias from surgeon preference or based on preoperative characteristics , as choice of valved vs nonvalved cannula use was not at the surgeon s discretion but rather a result of an institutional shift from the use of nonvalved to valved cannulas . this is the first series that specifically evaluated valved vs nonvalved ppv for grade c pvr - associated rd . no differences in functional or anatomic outcomes as well as complication rates were identified between the ppv of valved and nonvalved cannulas . in our opinion , advantages of valved cannulas , including minimal egress of fluid during instrument exchange and associated stable intraocular fluidics , translate into easier and more controlled surgery with equivalent anatomic outcomes in complex grade c pvr rd without measurable increase in complication rates . future studies should focus on improving functional visual results in grade c pvr - associated rd .