***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: OBJECTIVES To evaluate and compare levels of patient discomfort and perioperative complications during phacoemulsification and implantation of a foldable intraocular lens under topical lidocaine hydrochloride and retrobulbar anesthesia in patients with cataract who also had exfoliation syndrome , uveitis , posterior synechia , phacodonesis , or previous intraocular surgery . DESIGN A prospect i ve , r and omized , controlled trial was carried out at 2 institutions . PARTICIPANTS A total of 476 eyes of 476 patients with various well-established risk factors fulfilled the inclusion criteria . In 238 eyes , phacoemulsification was performed under retrobulbar anesthesia , while the other 238 eyes received topical anesthesia . INTERVENTIONS All patients underwent temporal clear corneal phacoemulsification and implantation of a foldable intraocular lens .  Patients under retrobulbar anesthesia received a single injection ( 3 . 5 - 5.5 mL ) of a combination of 0.75 % bupivacaine hydrochloride , 2 % lidocaine , and hyaluronidase into the retrobulbar space . Patients in the topical anesthesia group received a minimum of 5 doses ( approximately 40 microL per dose ) of 2 % topical lidocaine . No intracameral injection of any anesthetic was given . MAIN OUTCOME MEASURES The number of complications and adverse events . The intraoperative conditions were judged by the surgeon ( P.C.J. or F.K. J. ) , and a 10-point visual analog scale was used immediately after surgery to assess each patient 's overall severity of intraoperative pain . RESULTS The overall intraoperative complication rate was 1.9 % for capsular tear , 3.8 % for zonular tear , 1.5 % for vitreous loss , and 1.0 % for iris prolapse . Apart from the incidence of vitreous loss , which was significantly ( P = .041 ) lower in the topical anesthesia group , no statistically significant differences in intraoperative and early postoperative complications were found between the groups . A supplemental posterior sub-Tenon space injection was required in 1.3 % of the topical anesthesia group and in 0.8 % of the retrobulbar anesthesia group . Chemosis ( 2.5 % ) , subconjunctival hemorrhage ( 1.7 % ) , and periorbital hematoma ( 0.8 % ) were seen only in the retrobulbar anesthesia group . The mean + SE pain scores estimated by the patients were 0.84 + 1.30 in the topical anesthesia group and 0.73 + 1.50 in the retrobulbar anesthesia group ( P = .41 ) . Patient preference for topical anesthesia ( 91 % ) appeared to be significantly ( P = .01 ) higher than for retrobulbar anesthesia ( 62 % ) . The surgeons found anesthesia-related intraoperative difficulty to be slightly lower in the retrobulbar anesthesia group ( 8 % ) than in the topical anesthesia group ( 14 % ) . CONCLUSIONS Surgery-related complications and patient discomfort were similar for the 2 methods of anesthesia . Topical anesthesia is justified as a means of improving safety without causing discomfort to the patient even in complicated cases of cataract surgery . Arch Ophthalmol . 2000;118:1037 - AIMS The effect of local anaesthetics on optic nerve function can be investigated by quantifying the relative afferent pupillary defect ( RAPD ) . METHODS The study compared the depth of induced RAPD following posterior sub-Tenon 's , retrobulbar , and peribulbar local anaesthetics using crossed polarising filters before cataract surgery ( time 1 = 5 minutes ) , immediately after surgery ( time 2 = 42 minutes ( av ) ) , and once again on the ward ( time 3 = 107 minutes ( av ) ) . RESULTS All patients developed a RAPD .  There was no significant difference in the depth of RAPD between the groups at any one time period . The peribulbar group had a significantly steeper decay in RAPD from time 1 to time 2 ( p = 0.014 ) . This effect was reduced when the shorter operation time for this group was entered as a cofactor ( p = 0.063 ) . By time 3 the RAPDs for all groups had decayed similarly so that no differences could be detected . CONCLUSION All three anaesthetic methods caused a similar level of disruption to optic nerve conduction immediately following administration and at the time of day case discharge BACKGROUND AND OBJECTIVE To evaluate the response of intraocular pressure ( IOP ) to retrobulbar and peribulbar anesthesia . PATIENTS AND METHODS Patients were prospect ively masked and r and omized to receive either 4 cc of retrobulbar anesthesia  ( X = 29 )  or 6 cc of peribulbar anesthesia ( X  = 30 )  , each consisting of a 50:50 mixture of 2 % xylocaine and 0.75 % bupivacaine with 150 units of hyaluronidase .  IOPs were measured pre-anesthesia and 1 , 2 , and 5 minutes post-anesthesia in nonglaucoma patients undergoing cataract extraction and intraocular lens implantation . RESULTS Mean IOPs in the retrobulbar group as determined with a tonometer were 18.24 , 18.66 , 19.14 , and 17.86 mm Hg pre-anesthesia and 1 , 2 , and 5 minutes post-anesthesia , respectively . In the peribulbar group , the mean IOPs were 18.53 , 21.20 , 20.40 , and 19.20 mm Hg , respectively . The 1-minute pressures in the two groups were statistically different ( P = .023 ) . Within the peribulbar group , the 1- and 2-minute pressures were statistically different from the pre-anesthesia IOP ( P = .001 and P = .018 , respectively ) . CONCLUSION Peribulbar anesthesia , with its higher volume of anesthetic ( 6 vs 4 cc ) , results in a higher initial IOP . This difference was slight and short lived , and occurred in the absence of any external ocular compression . This study may have application in avoiding elevation of IOP in select patients undergoing a local procedure ABSTRACT One hundred patients having elective cataract surgery were evaluated in a prospect i ve , r and omized , double‐blinded study comparing retrobulbar and peribulbar anesthesia . Patients were divided into two study groups and evaluated on three criteria felt to be critical to intraocular surgery . Results showed that the efficacy of the oneinjection‐site peribulbar block was similar to that of the retrobulbar block for all three criteria . Because the one‐injection‐site anesthetic is administered outside the muscle cone , the potential for optic nerve and central nervous system complications should be minimized Abstract Although usually safe , retrobulbar anesthesia and peribulbar anesthesia have potentially sight‐ and life‐threatening complications . Although it has been suggested that peribulbar anesthesia is as effective and safer than retrobulbar anesthesia , no large study has addressed the true rate of complications . To determine the efficacy and safety of peribulbar anesthesia , this study prospect ively examined 16,224 consecutive peribulbar blocks . Twelve centers in the United States , Germany , and Chile participated in the study . After a peribulbar block was administered , the degree of akinesia , amaurosis , percentage of supplemental blocks required , and side effects and complications occurring after the block and for six weeks were recorded . Perioperative and late optic nerve complications were included . To approximate a real‐life situation , ophthalmologists , anesthesiologists , and certified registered nurse anesthetists performed the blocks . Ninety‐five percent of patients achieved a 95 % or greater degree of akinesia . The incidence of complications in the consecutive cases was low . Orbital hemorrhage occurred in 12 cases ( 0.74 % ) . There was one globe perforation ( 0.006 % ) , two expulsive hemorrhages ( 0.013 % ) , one gr and mal seizure ( 0.006 % ) , and no cases of cardiac or respiratory depression or deaths . Peribulbar is as effective as retrobulbar anesthesia and appears to lead to fewer sight‐ and life‐threatening complications , even when slightly different peribulbar techniques are used . This is especially true when the anesthetic is administered with a 1 1/4‐inch or shorter needle with the eye in the primary position , followed by ten to 15 minutes of ocular compression Complications of retrobulbar anesthesia are rare but significant . Periocular anesthesia has been advocated as an alternative to retrobulbar injections . In a prospect i ve , r and omized , masked study of 79 consecutive cataract extraction s with intraocular lens implantations , 40 patients received retrobulbar injections  and 39 patients received periocular injections .  In every instance , the volume of the injection was 5 mL. No significant difference in surgeon 's assessment of akinesia and anesthesia was found . Supplemental anesthesia was required in eight ( 21 % ) of the patients who received retrobulbar injections and in 11 ( 28 % ) of the patients who received periocular injections . A significant increase in chemosis was found with periocular injections . There was one complication with retrobulbar anesthesia and none with periocular anesthesia . No significant difference in patient assessment of comfort was found . The efficacy of periocular anesthesia appears to be comparable to that of retrobulbar anesthesia Two methods of periocular anaesthesia ( PI and PII ) were compared with the traditional retrobulbar block in a prospect i ve study of 450 patients undergoing elective cataract extraction and intraocular lens implantation . A solution of local anaesthetic containing equal amounts of 2 % lignocaine and 0.5 % bupivacaine was used in all the groups . Hyaluronidase ( 75 IU/10 ml of local anaesthetic solution ) was added . Three groups of patients were studied , with 150 patients in each group . The retrobulbar injection ( group R ) was performed with 4 ml of the anaesthetic solution through the lower eyelid inferotemporally and a further 6 ml was injected for seventh cranial nerve block . In the first periocular technique ( group PI ) the local anaesthetic was injected inferotemporally ( 5 ml ) through the lower lid and superonasally ( 5 ml ) through the upper lid . In the second periocular technique ( PII ) the injections were performed inferotemporally ( 5 ml ) and into the medial compartment ( 2 ml ) of the orbit at the medial canthus . Satisfactory anaesthesia could be achieved with all of these methods . Additional block because of insufficient akinesia of the muscles was required in 12 % ( 18/150 ) in group R , in 19 % ( 28/150 ) in group PI , and in 11 % ( 16/150 ) in PII . The medial compartment technique ( PII ) was associated with the highest percentage of total akinesia of the muscles and lowest reblock rate . All three methods produced sufficient analgesia during surgery and there were no differences in the requirements for additional analgesic drugs during surgery . It is concluded that the medial compartment technique represents a good alternative to retrobulbar block A prospect i ve trial was conducted on 142 patients who underwent cataract surgery  , to compare the efficacy of a single point , low volume peribulbar with that of retrobulbar anaesthesia . It was found that peribulbar anaesthesia is as efficacious as retrobulbar anaesthesia without the associated complications . It also avoids the facial block used by most ophthalmologists to supplement a retrobulbar block , thus markedly reducing the post-operative patient discomfort as well as the total volume of anaesthetic used Purpose : To assess the effects of retrobulbar and peribulbar anesthesia on nerve function as detected by visual‐evoked potentials ( VEPs ) . Setting : University hospital in southern Brazil . Methods : In a prospect i ve study , 7 patients had peribulbar anesthesia and 9 had retrobulbar anesthesia for extracapsular cataract extraction . Visual‐evoked potentials with pattern reversal and flash stimulation were performed at least 1 month before and 1 month after surgery . Study participants did not have ocular pathology other than cataract . The Lens Classification System III was used to grade the opacities before surgery . Results : No significant difference was found between preoperative and postoperative evaluations in VEP flash and pattern‐reversal amplitude and latency in either group ( P > .05 ) . Postoperative amplitude and latency was not significantly different between the peribulbar and retrobulbar groups . Two cases in the peribulbar group had altered wave morphology without clinical manifestation postoperatively . All patients had a final best spectacle‐corrected visual acuity of 20/20 . Conclusion : Block anesthetic procedures were safely used in cataract surgery , with no clinical sequelae to the optic nerve Peribulbar anaesthesia is now established as an alternative to retrobulbar anaesthesia for cataract surgery . However , the larger volume of anaesthetic solution in the extraconal 
    Output:
    
Three of the six trials had adequate sequence generation while all the trials had unclear allocation concealment There was no evidence of any difference in pain perception during surgery with either retrobulbar or peribulbar anaesthesia .
Both were largely effective .
There was no evidence of any difference in complete akinesia or the need for further injections of local anaesthetic .
There is little to choose between peribulbar and retrobulbar block in terms of anaesthesia and akinesia during surgery measuring acceptability to patients , need for additional injections and development of severe complications .
Severe local or systemic complications were rare for both types of block