cataract surgery is one of the most common ophthalmic surgical procedures currently performed and has become one of the most prevalent surgeries because of the growth of the elderly population ( 1 , 2 ) . postoperative endophthalmitis is one the most serious complications of cataract surgery that always presents a poor visual prognosis ( 1 - 8 ) . despite the low incidence rate of endophthalmitis ( 0.03 - 0.015 ) , large numbers of cataract surgeries contribute to this low rate and thus preventive measures are important ( 3 , 6 , 8 , 9 ) . several studies have shown that the eyelids and conjunctiva are the source and the origin of endophthalmitis following cataract surgery ( 3 , 4 , 6 - 8 ) . phacoemulsification using topical anesthesia is at present the most common cataract surgery technique ( 10 - 13 ) . in this method , the small incision may not be completely closed by stromal hydration and a potential space may remain between anterior the chamber and cul - de - sac for hours after surgery ( 9 - 13 ) . consequently , the elimination or reduction of microorganisms contained in the surgical field requires deliberate attention . the belief that the organism responsible for endophthalmitis may enter the eye , during surgery ( 10 - 13 ) , has led to the use of antibiotics as infusion or injection within the anterior chamber ( ac ) ( 1 , 14 - 18 ) , although minute variation error in antibiotics concentration may induce endothelial cell decompensation and irreversible corneal edema ( 4 , 15 ) . increasing injection of antibiotics within the ac following cataract surgery , especially after the european society cataract and refractive surgery ( escrs ) study , has led to decreased postoperative endophthalmitis by about five folds compared to the control group ( 1 , 14 , 16 ) . however , the use of topical levofloxacin and third and fourth generation fluoroquinolones ( 1 , 15 ) for up to one week after surgery , may still allow the transmission of the organism from the conjunctiva and eyelid , especially during the first post - operative day , which means there remains a strong possibility for endophthalmitis ( 7 , 9 , 11 ) . at present , among different methods of preoperative prophylaxis , applying 10% povidone - iodine to prepare the skin of the eyelid and use a 5% povidone - iodine with or without third and fourth generation fluoroquinolones , are the most acceptable methods that reduce cul - de - sac microbial colonies and possibility of endophthalmitis ( 2 , 5 - 8 , 10 , 12 , 14 , 16 , 17 ) . thus , in this study we assessed the effect of subconjunctival injection of cefazolin and placing one drop of 10% povidone - iodine in the conjunctival sac on the bacterial colony forming units at completion of surgery until the first day post - surgery . this double - blinded , randomized clinical trial was conducted on 122 patients , who had undergone cataract surgery at imam khomeini hospital since october 2011 . this study was approved by ahvaz jundishapur university of medical sciences ethics committee and an informed consent was obtained from all patients . povidone - iodine ( 5% and 10% ) was purchased from iran najo pharmaceutical co. , tehran , iran . subjects who were using topical or systemic antibiotics , had a history of sensitivity to iodine , a history of previous eye surgery , pregnant women and those who refused to participate were excluded . patients were randomly divided in to two groups , including group 1 ( cefazolin injection under the conjunctiva at the end of surgery ) and group 2 ( povidone - iodine recipients at the end of surgery ) . in both groups , before the preparation of the operation filed , two samples from each eyelid , conjunctiva , and the fornix were collected using sterile swabs impregnated with sterile distilled water . the samples were then aseptically inoculated using the linear method to blood and chocolate agar media to determine bacterial colony counts . after preparing the patient 's skin , their cheeks and forehead were washed using povidone - iodine 10% , their eyelids and eye lashes were covered with a sterile adhesive , and next to where the speculum was placed , the edge of the eyelids were washed using swabs emulsified in povidone - iodine 10% and all patients received povidone iodine 5% in the conjunctival cul - de - sac for 3 minutes before the operation . all cataract surgeries were performed according to standard methods of phacoemulsification , through the temporal clear corneal incision by two surgeons , also operating at the imam khomeini hospital . after finishing the surgery , another sampling of the conjunctiva and the fornix was performed , using the above mentioned method . in group 1 , 50 mg of cefazolin ( 0.5 cc of 100 mg / ml ) was injected under the conjunctiva and in group 2 , a drop of povidone - iodine 10% was applied on the conjunctival sac . the patient 's eye was covered by a bandage patched and protected by a plastic shield and the collected samples were sent to the laboratory incubator .   the day after the surgery ( with a time interval of 14  2 hours from termination of surgery ) after removing the bandage , two samples were collected from the eyelid and conjunctival sac and inoculated in the aforementioned manner and sent to the laboratory . besides , the blood agar plate was incubated at 37 c under anaerobic conditions and the chocolate agar plate was incubated in 5% co2 at 37 c ; all plates were incubated for 24 to 48 hours . the colony counts have performed at each time point according to the colony - forming units ( cfu ) . following two days of incubation , each specimen was analyzed by the laboratory scientist , and when colonies were present , basic bacteriology identification tests were performed to identify the present bacteria . in this , study antibiotic drops were not administrated for the days before and at the end of the surgery . data were analyzed using the spss 15.0 software . due to the highly abnormal distribution of data , the wilcoxon test was used to compare the observed count in each group and the mann - whitney test was used to compare colony count between the two groups . to determine the effect of povidone - iodine 10% solution and antibiotics at the end of the cataract surgery , conjunctival colony count and confidence limits of 95% , test power of 80% and sample size for p  0.05 , this double - blinded , randomized clinical trial was conducted on 122 patients , who had undergone cataract surgery at imam khomeini hospital since october 2011 . this study was approved by ahvaz jundishapur university of medical sciences ethics committee and an informed consent was obtained from all patients . povidone - iodine ( 5% and 10% ) was purchased from iran najo pharmaceutical co. , tehran , iran . subjects who were using topical or systemic antibiotics , had a history of sensitivity to iodine , a history of previous eye surgery , pregnant women and those who refused to participate were excluded . patients were randomly divided in to two groups , including group 1 ( cefazolin injection under the conjunctiva at the end of surgery ) and group 2 ( povidone - iodine recipients at the end of surgery ) . in both groups , before the preparation of the operation filed , two samples from each eyelid , conjunctiva , and the fornix were collected using sterile swabs impregnated with sterile distilled water . the samples were then aseptically inoculated using the linear method to blood and chocolate agar media to determine bacterial colony counts . after preparing the patient 's skin , their cheeks and forehead were washed using povidone - iodine 10% , their eyelids and eye lashes were covered with a sterile adhesive , and next to where the speculum was placed , the edge of the eyelids were washed using swabs emulsified in povidone - iodine 10% and all patients received povidone iodine 5% in the conjunctival cul - de - sac for 3 minutes before the operation . all cataract surgeries were performed according to standard methods of phacoemulsification , through the temporal clear corneal incision by two surgeons , also operating at the imam khomeini hospital . after finishing the surgery , another sampling of the conjunctiva and the fornix was performed , using the above mentioned method . in group 1 , 50 mg of cefazolin ( 0.5 cc of 100 mg / ml ) was injected under the conjunctiva and in group 2 , a drop of povidone - iodine 10% was applied on the conjunctival sac . the patient 's eye was covered by a bandage patched and protected by a plastic shield and the collected samples were sent to the laboratory incubator .   the day after the surgery ( with a time interval of 14  2 hours from termination of surgery ) after removing the bandage , two samples were collected from the eyelid and conjunctival sac and inoculated in the aforementioned manner and sent to the laboratory . besides , the blood agar plate was incubated at 37 c under anaerobic conditions and the chocolate agar plate was incubated in 5% co2 at 37 c ; all plates were incubated for 24 to 48 hours . the colony counts have performed at each time point according to the colony - forming units ( cfu ) . following two days of incubation , each specimen was analyzed by the laboratory scientist , and when colonies were present , basic bacteriology identification tests were performed to identify the present bacteria . in this , study antibiotic drops were not administrated for the days before and at the end of the surgery . data were analyzed using the spss 15.0 software . due to the highly abnormal distribution of data , the wilcoxon test was used to compare the observed count in each group and the mann - whitney test was used to compare colony count between the two groups . to determine the effect of povidone - iodine 10% solution and antibiotics at the end of the cataract surgery , conjunctival colony count and confidence limits of 95% , test power of 80% and sample size for p  0.05 , during this project , data were collected from 122 eyes of 122 patients with cataract . in group 1 ( 61 recipients of subconjunctival cefazolin ) , there were 34 ( 55.7% ) males and 27 ( 43.3% ) females , and in group 2 ( 61 recipients of povidone - iodine ) , there were 33 ( 54.1% ) males and 28 ( 45.9% ) females . the age range of patients in group 1 was 34 - 84 years , with a mean of 68.1 years , and in group 2 the range was 35 - 84 years with a mean of 67.2 years ( p < 0.05 ) . the mean rank of colony count of eyelid samples on blood and chocolate agars on the day after surgery in groups 1 showed 52% and 56% reduction and in second group reduction was 58% and 50% respectively ( p < 0.05 ) compared to the day before surgery ( table 1 ) . in group 1 the median blood and chocolate agar colony counts changed from 100,000 preoperatively to 100 during the postoperative day , indicating a 99.9% reduction . in group 2 the median blood agar colony count decreased from 100,000 preoperatively to 290 during the postoperative day indicating a 99.7% reduction . these values regarding chocolate agar colony counts changed from 50,000 to 100 , which indicates a reduction of about 99.8% . comparing the colony counts of conjunctiva samples during the pre - operative and first postoperative days , in group 1 the mean rank of colony count blood and chocolate agars showed 48% and 45% reduction and in group 2 a 44% and 40% reduction was indicated , respectively ; these results indicate a significant decline in colony counts on the first postoperative day compared to the preoperative day , for both groups ( p < 0.05 ) ( table 1 ) . however , the difference between the two groups was not significant ( p > 0.1 ) ( table 3 ) . between group comparisons of the colony counts of conjunctiva samples pre - surgery and at the end of surgery , the mean rank of colony count blood and chocolate agars were 57% and 56% , and in group 2 these values were , 51% and 52% , respectively , showing a significant reduction , in colony counts of conjunctiva samples at the end of surgery compared to preoperative samples , in both groups ( p < 0.05 ) ( table 2 ) mann - whitney tests proved that this difference in the two groups is not statistically significant ( p > 0.1 ) ( table 3 ) . by comparing the colony counts of conjunctiva samples at the end of the surgery and the day after surgery , it was determined that in group 1 the mean rank of both blood and chocolate agars showed 27% and in group 2 these showed 20% and 21% increase , respectively , which reflects the proliferation of bacteria in the conjunctival crypts at the interval between the day after surgery compared to the end of surgery in both group ( p < 0.05 ) ( table 2 ) . however , these differences between the two groups were not statistically significant ( p > 0.1 ) ( table 3 ) .   a , cefazolin group , b , betadine group ; l , lid ; ba , blood agar ; ch , chocolate agar ; p , post.op ; b , before , c , conjunctiva ; pos , positive ; neg , negative .   a , cefazolin group ; b , betadine group ; c , conjunctiva ; ba , blood agar ; ch , chocolate agar ; e , at the end of surgery ; b , before ; neg , negative ; pos , positive .   at the end of surgery abbreviations : c , conjunctiva ; l , lid ; ba , blood agar ; ch , chocolate agar ; diff , difference . the primary source of postoperative endophthalmitis , are bacteria present in the eyelids and conjunctiva . thus eliminating or reducing these microorganisms can decrease the risk of endophthalmitis ( 3 ) . numerous reports have indicated ( 9 - 13 ) that even through completely sealed incisions , bacteria available in tears and the conjunctiva sac may possibly enter the eye in the early postoperative hours , which can lead to increased frequency of postoperative bacterial endophthalmitis ( 9 - 13 ) . taban and colleagues ( 9 ) showed that as india ink can cross the seemingly closed incision of the clear cornea and enter the anterior chamber , bacteria can also get into the eye . light micrographs that were obtained from the clear corneal incision without suture , revealed that india ink could penetrate across the incision . this phenomenon indicates that before any process of wound healing , tears and microorganisms can enter into the anterior chamber in the early stages after surgery , so the integrity of surgical incision is a crucial factor in postoperative bacterial endophthalmitis prevention . many reports have demonstrated ( 9 - 12 ) the relationship between corneal incision diffects without suture and increasing frequency of postoperative bacterial endophthalmitis ( 9 - 12 ) . in most cases the end of surgery incision is self - sealed or completely water tight after stromal hydration ( 9 - 12 ) , however wound integrity is influenced by changes in intra - ocular pressure ( iop ) . a report showed ( 9 ) that 21% of eyes following phacoemulsification surgery from the clear corneal incision had iop of 5 mmhg or less , which is a temporary hypotony in the first 24 hours and may allow the conjunctival microorganisms access the anterior chamber of the eye through the incision .   in vitro studies showed that tears and cul - de - sac content can enter the anterior chamber via single or two planed clear corneal incision ( 9 - 13 ) . eye movements and eyelid squeezing in the immediate period after surgery with local anesthesia changes the iop and transient wound gap , which facilitates bacterial entrance into the eye ( 8 - 11 ) . fluoroquinolones drops are prophylactic agents for the ocular condition before intraocular surgeries . the purpose of prophylactic use of antibiotics before cataract surgery is reducing pathogenic microorganisms in the eyelids and conjunctiva , and obtaining proper concentrations of antibiotics in the cornea and aqueous humor ( 19 , 20 ) . thus , for the antibiotic to be effective it must not only have high tissue penetration but it should also be capable of eliminating conjugative bacteria ( 19 ) . bucci and colleagues ( 21 ) evaluated the ocular surface and aqueous antimicrobial effects of gatifloxacin and moxifloxacin administered in two dosing regimens on the normal florabacteria of patients undergoing phacoemulsification . the authors claimed that these two antibiotics equally reduced the chances of getting a positive culture of the organism from the aqueous liquid . conducted a prospective randomized triple - masked trial , including two parts , in which one part evaluated the aqueous concentration of moxifloxacin following two dosing regimens of topically administered moxifloxacin hydrochloride ophthalmic solution 0.5% ( vigamox ) ( 19 ) ; while the second part determined whether a regimen of vigamox administered on the day of cataract surgery reduces conjunctival bacterial flora . they claimed that both regimens produced substantially higher aqueous concentrations ; topical moxifloxacin administered two hours before surgery achieved significantly higher aqueous concentrations . other studies ( 1 , 2 , 17 ) were conducted on the efficacy of levofloxacin and showed that topical application of this antibiotic accompanied by washes with povidone - iodine , results a more effective reduction in bacterial ocular surface . another factor that effects endophthalmitis after phacoemulsification is incision diffect , taban and colleagues showed ( 9 ) that 80% of postoperative bacterial endophthalmitis were related to incision diffects such as a wound gape and malposition . simultaneous suture handling of corneal incision with application of povidone - iodine at closure , and initiation of antibiotic eye drops within the first 24 hours of surgery can reduce the risk of endophthalmitis ( 10 ) . thus far , there has not been the possibility to create a sterile conjunctivitis ( 5 ) . the effect of 5% povidone - iodine as a broad spectrum antibiotic to reduce microbial flora of the conjunctiva and eyelids and decrease the incidence of endophthalmitis has been proven by many studies ( 1 , 2 , 5 - 10 , 14 - 17 , 19 , 20 ) . although , the use of topical antibiotics one hour before or during the day of the surgery reduces the microbial flora of the conjunctiva and eyelids , yet it does not eliminate the bacteria from the surgical field . thus , the growth of organisms during the first hours after the surgery and the possibility of getting into the anterior chamber via surgical incision remains a potential risk for endophthalmitis ( 7 , 8) . we tried using subconjunctival injection of cefazolin and povidone - iodine 10% to control microorganism replication during the early hours after surgery . this study assessed the effect of post - cataract surgery conjunctival injection of cefazolin and 10% povidone - iodine on bacterial colony count at end of the surgery until the first post - surgery day , and showed no statistical difference between usage of povidone - iodine and antibiotics . subconjunctival injection of antibiotics at the end of cataract surgery is one of the oldest prophylactic measures to prevent endophthalmitis ( 6 ) . but later studies showed that subconjunctival injection was not effective in prevention of endophthalmitis ( 7 ) . the effect of povidone - iodine as a broad spectrum antiseptic to reduce the incidence of endophthalmitis in the preoperative preparation period , has been reported by many studies ( 5 - 8 , 10 - 12 , 14 , 16 , 17 ) , which showed the use of povidone - iodine 5% in the fornix before the surgery , significantly decreases conjunctival colonies . feghhi and colleagues approved the efficacy of povidone - iodine on corneal ulcers compared with standard antibiotics in animals ( 22 ) . thus , the most acceptable method for preparation of the eyelid and conjunctiva , is the use of povidone - iodine , however the preferred method for the end of the surgery still depends on the surgeon s opinion ( 14 - 16 , 18 - 20 , 23 ) .   in this study we showed that the use of povidone - iodine before surgery is very effective in reducing conjunctival bacteria counts during the operation ; eyelid mean colony counts on blood and chocolate agar decreased from 100,000 on the preoperative day to 100 on the postoperative day indicating about a 99.9% reduction rate . these values in the group that received subconjunctival antibiotics at the end of the surgery ( group a ) , decreased from 100,000 on the preoperative day to 290 on the days after the surgery showing about a 99.7% reduction ( p > 0.1 ) . however , the colony count of days after the surgery was significantly higher than that of the end of the surgery , in both study groups . comparison of colony counts of the conjunctiva at the end of the surgery and on the first day after the operation for group 1 , showed an increase of 27% and group 2 , showed 20% and 21% increase ; although in terms of numeric values , use of povidone - iodine , at the end of surgery was associated with less bacterial colony replication on the first day after the surgery , yet statistical comparisons showed no significant differences between the two groups ( p > 0.1 ) . this implies that the use of subconjunctival cefazolin and povidone - iodine at the end of the surgery , will continue reducing bacterial counts from the time of preparation before the surgery until the day after the operation . the reason is that despite all arrangements and preparations , a completely sterile conjunctiva in the fornices is probably unreachable , because this area has deep crypts , which despite using povidone - iodine preoperatively , complete sterility among these crypts is not possible ( 5 ) . therefore , these residual values can grow in the interval between end of the surgery and the next day , and if no antiseptic agents are used at the end of the surgery , they may grow more and make further colonies that finally increase the risk of endophthalmitis . it is important to mention that in none of the 122 patients , acute or chronic postoperative bacterial endophthalmitis was observed , and those patients , who were exposed to povidone - iodine 10% , tolerated this treatment well and no complications and adverse effects such as corneal edema or epithelial diffects , and sensitivity to povidone - iodine , were detected . in conclusion , due to the ease and cost efficiency of povidone - iodine 10% and patients good tolerance of this treatment , when the surgeon does not intended to use injected intracameral antibiotic at the end of the cataract surgery , pouring a drop of povidone - iodine 10% seems to be a simple and acceptable method to reduce the growth of microorganisms of the conjunctiva .
background : postoperative endophthalmitis is one the most serious complications of cataract surgery . 
 the majority of causative organisms in this destructive infection come from the patient s own periocular flora . 
 efforts have been made to reduce the virulence of organisms in the eyelid and conjunctiva with perioperative topical antibiotics , preparation of surgical field , covering eyelids and conjunctival surface with 5% povidone  iodine solution and intracameral antibiotics at the time of surgery to minimize the risk of endophthalmitis.objectives:we assessed the effect of subconjunctival injection of cefazolin and pouring povidone - iodine on the conjunctiva bacterial colony forming units ( cfu ) in phacoemulsification cataract surgery.patients and methods : in this prospective , randomized , double - blind clinical trial , 122 patients having phacoemulsification cataract surgery with clear corneal incision and topical anesthesia were randomized into two groups including group 1 ( subconjunctival injection of cefazolin ) and group 2 ( recipients of a drop of povidone - iodine ) . 
 cultures were collected from the bulbar conjunctiva at the injection site and from the corresponding location in the patient s eye , three different times.results:the mean of eyelid samples on blood and chocolate agars , on the day after compared to the day before the surgery in group 1 showed a 52% and 56% reduction . 
 these values were 58% and 50% in group 2 ( p < 0.05 ) . 
 the mean cfu of conjunctiva before and at the end of surgery on blood and chocolate agars showed 57% and 56% reduction in group one and 51% and 52% reduction in group 2 ( p < 0.05 ) . while comparing mean cfu of conjunctiva at the end and one day post - surgery ( interval of 14  2 hours ) showed 27% and 27% increase in group 1 and 20% and 21% increase in group 2 ( p < 0.05 ) , which reflects conjunctival flora proliferation during the early postoperative period.conclusions:due to the good tolerance of patients towards topical anesthesia , pouring a drop of povidone - iodine 10% seems to be a simple and acceptable method to reduce the growth of microorganisms of the conjunctiva .