BritishJournalofOphthalmology 1992; 76: 670-674

A new local anaesthesia technique for cataractextraction by one quadrant sub-Tenon's infiltration

J D Stevens

AbstractA new technique of local anaestheticadministration has been used for 50 patientsundergoing cataract extraction. The simpletechnique involves direct transconjunctivalinfiltration of local anaesthetic directly to thesub-Tenon's space, in the inferior-nasalquadrant, using a blunt 19-gauge Southamptoncannula. This method seeks to avoid the risksofretrobulbar haemorrhage, perforation oftheglobe, damage to the optic nerve, and injectioninto the subarachnoid space, whilst providingprolonged and reliable anaesthesia. Akinesia isachieved by the inferior-nasal placement ofsolution and if not sufficient, a top-up caneasily be given. Patients graded any discomfortor pain using a 10 cm visual analogue graphicalpain score chart with numerical and descriptiverating scale. The delivery of 50:50 mixture oflignocaine 2% and bupivacaine 0 5% anaes-thetic was evaluated by patients with a medianresponse of 'slight discomfort'. The operativeprocedure was graded with a median of 'nopain or discomfort', both for extracapsularcataract extraction and phakoemulsification.This is a new, modified, sub-Tenon tech-nique which is simple, reliable, and whichoffers excellent anaesthesia and akinesia andavoids a sharp instrument being passed intothe orbit.(BrJ Ophthalmol 1992; 76: 670674)

In 1884 Knapp reported successful cataractextraction by topical anaesthesia using frequentdrops of5% cocaine. He commented on the needfor more extensive anaesthesia if the iris is to beanaesthetised. Describing a technique forenucleation, he reported the successful use of aretrobulbar injection,' rotating the globe nasallyand introducing a needle through the musclecone temporally. In 1884 Turnbull also describeda local anaesthetic technique for enucleation,where topical 4% cocaine was applied to thecornea and conjunctiva, followed by the openingofTenon's fascia and cocaine being dropped intothe cut.2 Blunt pointed scissors which werecurved on the flat were introduced from the nasalside and drops instilled. This was reported assuccessful in causing anaesthesia andvasoconstriction.Today various methods oflocal anaesthesia are

in use for cataract extraction including retro-bulbar,3 peribulbar,4 subconjunctival,5 and sub-Tenon's6 application oflocal anaesthetic solution.

Moorfields Eye Hospital, The desire to find an alternative to retrobulbarCity Road, London EC1V anaesthesia has been caused by a variety of2PDJ D Stevens unusual but potentially severe complicationsAccepted for publication arising with this technique,78 including globe8 June 1992 perforation, retrobulbar haemorrhage, and

accidental injection of solution into a bloodvessel or the subarachnoid space.

Peribulbar anaesthesia has been advocated toreduce risk of respiratory arrest and othersystemic complications associated with retro-bulbar anaesthesia and since the muscle cone isnot entered, local anaesthetic solution is deliveredaway from the globe, so minimising risk to theeye. Anaesthesia is achieved by diffusion, oftenrequiring a greater volume of solution than fortrue intraconal retrobulbar anaesthesia. In spiteof an injection positioned away from the globe,peribulbar anaesthesia has been reported to beassociated with serious complications, includingglobe perforation.910

For both retrobulbar and peribulbartechniques a sharp, or relatively sharp, needle is'blindly' placed into the orbit to deliver theanaesthetic solution. To avoid injecting deepinto the orbit subconjunctival anaesthesia hasbeen advocated, involving a subconjunctivalinjection of anaesthetic at the 12 o'clockposition""'2; this technique also being termedlimbal subconjunctival injection.'3 In a co-operative patient able to maintain ocular position,topical and subconjunctival anaesthesia havebeen shown to be effective in providing anaes-thesia though more conjunctival chemosis occurswith subconjunctival than with retrobulbar orperibulbar anaesthesia.'4 Many ophthalmicsurgeons are reluctant to adopt a technique thatdoes not provide sufficient ocular akinesia and inpatients less able to understand the requirementsof the ophthalmologist, or who are anxious andunable to communicate properly, general anaes-thesia or a technique involving good akinesia isdesirable. Residual ocular muscle function notonly allows unexpected globe movement duringsurgery but may increase intraocular pressure.

Direct sub-Tenon's delivery of solution usinga blunt cannula offers an alternative method. Forretinal surgery'5 and for cataract extraction6 atechnique has been described where the conjunc-tiva is anaesthetised by subconjunctival injectionof local anaesthetic solution and then Tenon'sfascia is opened using blunt Westcott scissors. Ablunt 19 gauge cannula directly irrigates solutionposterior to the globe. In the case of retinalsurgery, solution is delivered to all fourquadrants5 and for cataract surgery6 the superiorquadrants have been used.A simple technique that produces excellent

anaesthesia and reliable akinesia, with minimalrisk of perforation of the globe, is the ideal. Thispaper describes a single quadrant inferior-nasalsub-Tenon's approach with a blunt cannulawhich is a modification of the original idea ofTurnbull,' the four quadrant method of Meinand Woodcock,'5 and the superior quadrantmethod ofHansen et al. 6 It has been developed to

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A new local anaesthesia techniquefor cataract extraction by one quadrant sub-Tenon's infiltration

be an effective and minimal risk anaesthetictechnique for cataract surgery.

MethodFifty patients who underwent cataract extractionwith posterior chamber lens implantation whowere scheduled for local anaesthesia, had ananaesthetic blockade by direct blunt cannulasub-Tenon's delivery. After informed consent,in the holding bay within the operating theatresuite, four drops of topical amethocaine 1% wereapplied to the cornea and conjunctiva followedby one drop ofadrenaline 0 1%. A blunt Westcott(spring) scissors was taken and a small 'nick'incision made in the conjunctiva in the inferior-nasal quadrant approximately 5 mm from thelimbus (Fig 1). A blunt 19 gauge Southamptoncurved cannula was used to deliver a small blebof local anaesthesia, using a 50:50 mixture oflignocaine 2% and bupivacaine 0 5% withoutadrenaline. This facilitates identification andelevation of Tenon's fascia and fine underlyingintermuscular septal fascia. The Wescott scissorsare then slid through the nick in the conjunctivaand used to create another 'nick' taking care tocreate a path in Tenon's capsule and the inter-muscular septal fascia. Moorfields forceps areused to grip the conjunctival edge where thesmall nick was made and the curved cannula isthen inserted onto bare sclera and glided along apath following the contour of the globe, untilposterior to the equator (Fig 2). It is veryimportant to pass through conjunctiva, Tenon'sfascia, and the intermuscular septum, to reachbare sclera and therefore into the Tenon's space,before sliding the cannula posteriorly. Often,after the cannula is passed back in the potentialspace between the intermuscular septum,Tenon's, and sclera, a resistance is felt owing tofascia adherent to sclera posterior to the equator.This tissue may be passed through by applicationof gentle pressure to the syringe and after a fewseconds a slight 'give' is felt, solution begins toflow, and the cannula may be further advanced.After delivery of approximately 1 ml, at thislevel, just posterior to the equator, the cannula isadvanced further to a total distance of approxi-mately 1X5 to 2X0 cm, depending upon globe size,

Figure I Ablunt Westcott(spring) scissors is taken anda small 'nick' incision madein the conjunctiva in theinferonasal quadrantapproximately 5 mmfromthe limbus. A blunt 19 gaugeSouthampton curvedcannula is used to deliver asmall bleb oflocalanaesthesta, so raisingTenon's capsule allowingbetter visualisation.

2 4 cm

41 17 cm

Figure 2 Schematic diagram ofthe path ofthe Southamptoncannula, following the contour ofthe globe, to deliveranaesthetic solution posterior to the equator.

and further solution delivered to a total volumeof 3 0 to 3 5 ml. At this stage a small degree ofproptosis of the globe is usually visible, thisproviding confirmation that the solution hasbeen delivered to the correct place. If care is nottaken to deliver solution to the posterior sub-Tenon potential space, then it is very easy todeliver anaesthetic solution as an anteriorsubconjunctival application. Immediate con-junctival chemosis then results and this may beextensive if the whole volume is given anteriorlyby mistake. It is important therefore for thevolume to be given slowly and in graded steps, soensuring that the site of delivery is that whichwas intended. With practice, the cannularposition, with respect to the fascial layers, can bejudged accurately by the operator and thetechnique becomes quicker and easier.

After giving the anaesthetic solution at least15 minutes was allowed for diffusion to occurbefore commencing surgery. Immediately priorto surgery, assessment of the amount of akinesia,presence and degree of ptosis, and eyelid tonewas made. Akinesia was assessed by a non-masked, four category, subjective scale graded ascomplete movement remaining, moderate move-ment, slight movement, no movement. If theeyelids were not flaccid immediately prior tosurgery, an additional Van Lint facial block wasgiven.Each patient was shown a 10 cm visual analogue

graphic pain score chart, on the first post-operative day, with numerical and descriptiverating scale, graded from 0 to 10 (Fig 3). Patientswere shown the chart and invited to score whereon the chart they could grade any discomfort orpain experienced. If patients were unable to seethe chart, or read the accompanying text (printedatN10 size), a verbal explanation and descriptionof the scoring chart was performed. Patientswere first requested to score verbally any pain ordiscomfort for the delivery of the anaesthetic andthen separately score the operation itself.

AnatomyConnecting the extraocular muscle capsules is asheet of condensed fascial tissue, the inter-

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6 7 8 9 10

muscular septum. As the extraocular musclespass forward they increase in separation fromeach other, but the intermuscular septumcontinues to connect them. External to theextraocular muscles is a fascial plane, the Tenon'scapsule.'6 Tenon's capsule is a relatively densefascial layer of elastic connective tissuesurrounding the globe and extraocular musclesextending from the limbus to the optic nerve. Allthe extraocular muscles penetrate Tenon'scapsule, the four recti penetrating posterior tothe equator. Tenon's capsule anterior to this hasbeen termed the anterior portion and extends tothe limbus. A posterior portion of Tenon'scapsule extends from the rectus penetrationsback to the optic nerve and is thinner. The innersurface of the posterior portion of Tenon'scapsule apposes sclera as there is no sub-Tenon'sintermuscular septum present. A potential spaceexists between sclera and Tenon's capsule, theTenon's or episcleral space, which does notnormally contain any fluid. The anteriorTenon's capsule and sclera are separated by theintermuscular septum which extends betweenthe extraocular muscle capsules in the same wayas between the muscles in the posterior orbit. Atabout 3 mm from the limbus the anteriorTenon's capsule and sub-Tenon's intermuscularseptum fuse to form a single fascial plane whichfurther fuses with conjunctiva 1 mm from thelimbus. Incision further back than 3 mm fromthe limbus must pass through all three layers.Incising conjunctiva closer than 3 mm from thelimbus allows one incision to pass throughconjunctiva, Tenon's capsule, and the inter-muscular septum simultaneously. This would bean advantage to easily reach bare sclera, but bycutting the conjunctiva further back at approxi-

mately 5 mm from the limbus, less of a curve isrequired for the path of the cannula as it followsthe contour of the globe. There is less trauma tothe conjunctiva with a direct posterior path, withless risk of conjunctival tearing.

Tenon's space delivery allows potentialdiffusion of the solution throughout thiscompartment, and solution may also diffuseback into the orbit, reaching the intraconalcentral region. Koorneef has stated that there isno clear cut compartmentalisation into central(retrobulbar) region and peripheral space outsidethe muscle cone, not finding a common musclesheath by serial section study. '7 Solution maythen diffuse extensively between compartmentsif sufficient time is allowed and may be facilitated

by use of hyaluronidase. I8 Hyaluronidase has notbeen used in this study owing to difficulties insupply during the period of the study, thoughwhen available it would be anticipated that itsuse may enhance the efficacy of the technique.To eliminate pain sensation for the globe, pain

fibres exiting from the eye must be blocked andto further achieve akinesia, the extraocularmuscle nerve supply should also be inhibited.Ocular pain sensation is mediated by the longsensory root of the ciliary ganglion. These fibrespass through the ganglion and provide sensationfrom the cornea, iris, and ciliary body.'8 Theciliary ganglion is situated posteriorly in the orbitapproximately 1 cm anterior to the optic foramenbetween the optic nerve and the lateral rectusmuscle within the muscle cone. It is separatedfrom the lateral rectus muscle by loose fat and isclose to the ophthalmic artery. Posterior diffusionof local anaesthetic solution may directly blockthe ganglion, or blockade of muscle functionmay occur by solution affecting nerves passingmore anteriorly. The differential temporaldecrease in muscle function, with those musclesclosest to the site of solution delivery, medial andinferior rectus being lost first, suggests that adirect block upon anterior nerve fibres may beoccurring.The extraocular muscles are supplied by

cranial nerves III, IV, and VI. To achieveakinesia, motor fibres within these nerves haveto be inhibited at some level in their path.Superior rectus is supplied by the superiordivision of the oculomotor nerve entering theinner surface of the muscle at the junction of itsmiddle and posterior thirds.'9 Inferior rectus,medial rectus, and inferior oblique are suppliedby the inferior division of the oculomotor nerve

entering the inner surface of the muscles at thejunction of the middle and posterior thirds.Lateral rectus is supplied on its inner aspect bythe abducens nerve just behind its middle. Onlysuperior oblique is supplied superiorly at itslateral border by the trochlear nerve, the mostanterior branch being at the junction of theposterior and middle thirds. All extraocularmuscles, except superior oblique, are thussupplied by nerves entering on the inner surface.The presence of superior oblique function aftereffective blockade of all other extraocular muscleactivity provides further evidence that a directaction upon nerve fibres in the retrobulbarcompartment is the mechanism of action. Towhat degree the anaesthetic solution affects theciliary ganglion is undetermined.

ResultsFifty consecutive patients who received localanaesthesia for cataract extraction had sub-Tenon's anaesthesia and none experienced a

problem of excessive discomfort on delivery ofthe block. Thirty four patients underwent extra-capsular cataract extraction and 16 phako-emulsification, all with posterior chamber lensimplantation. All local anaesthetic blocks were

performed by the author and no complicationoccurred which prevented surgery. No failuresin anaesthesia occurred which would havenecessitated supplemental anaesthesia using

0 1 2 4 5

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Figure 3 Visual analoguegraphic pain score chart. AIn *An;" eW rh"tt qov;thiu cm)pain scaLcarIt wiLznnumerical and descriptiverating scale.

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A nezv local anaesthesia techniquefor cataract extraction by one quadrant sub-Tenon's infiltration

FigureS Pain scoresrecordedfor the operativeprocedure. Forty one patientsrecorded no pain ordiscomfort, only onepatient describing significantpain with a score of 7.

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Visual analogue pain score

peribulbar infiltration. No patients who werescheduled for local anaesthesia were consideredunsuitable for the one quadrant sub-Tenon'sanaesthetic technique.

Pain scores assessed using the visual analoguescore chart produced a median score of 1 ('slightdiscomfort') and mean of 1-0 for the delivery ofthe sub-Tenon's block (Fig 4). Eighteen patientsgraded no pain or discomfort and 23 only slightdiscomfort, with no patient grading greater than5. Patients subjectively described the giving ofthe block most often as a feeling of 'slightpressure'.For the subsequent operative procedure the

median pain score was 0 ('no pain or discomfort')and the mean 0 3 (Fig 5); 41 patients scored 0indicating the effectiveness of local anaesthesiafelt during the operation. The one patient whogave a score of 7 ('severe pain') described theoperation as pain free and would have scored it as0 but felt sudden pain at the end of the operativeprocedure on giving subconjunctival injections.There was no difference of median pain scoresbetween those having extracapsular extractionand phakoemulsification (median score of 0).The anaesthetic block had no visible effect

on superior oblique muscle function whichremained for all 50 patients, though 27 patientsdeveloped otherwise complete akinesia. Thosepatients with incomplete akinesia most often hadpreserved lateral rectus muscle function. Inpatients where akinesia was not deemed sufficientby the surgeon (eight patients), a further 1-1 5ml of solution was delivered to the original sub-Tenon site. Excellent anaesthesia and goodakinesia was then achieved within 5 minutes ofdelivery of the top-up and the operativeprocedure then commenced.More conjunctival chemosis subjectively

occurred than usually seen with peribulbaror retrobulbar anaesthesia and subconjunctivalhaemorrhage extending to more than onequadrant, assessed at the commencement ofsurgery, occurred in 16 patients (32%). The useof adrenaline 0 1% immediately prior to the

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conjunctival incision is performed to attempt toreduce any subconjunctival haemorrhage byblanching conjunctival vessels. Complete ptosisoccurred in 18 patients and partial ptosis in 15.Twenty three patients had an additional VanLint facial block, subjectively based upon thepresence of remaining eyelid tone after the sub-Tenon block, immediately prior to surgery.

DiscussionThe delivery ofsub-Tenon's anaesthetic, directlyirrigating the immediate retrobulbar region, iseffective and reliable in providing both foranaesthesia and akinesia. Patients find not havingan injection through skin, simple and relativelypainless, except for those receiving a furtherfacial block.The method for sub-Tenon's irrigation

described in this paper differs from that ofHanson et al,6 in that anaesthetic is delivered tothe inferior-nasal quadrant and no' furtheropening of conjunctiva is performed. Hanson etal raise a conjunctival bleb by subconjunctivalinjection using a sharp needle, before incisingsuperior conjunctiva, and then delivering sub-Tenon solution. Iflimbal or scleral based cataractsection is employed, superior quadrantapplication provides a simple method of deliveryof solution peroperatively, though excess appli-cation of solution may result in a 'bulgy' eye ifapplied immediately prior to commencingintraocular surgery.

If solution is delivered to either of the superiorquadrants possible chemosis and subconjunctivalhaemorrhage may affect visualisation of theoperative section. Therefore it would bedesirable to deliver anaesthetic to an inferiorquadrant. The inferior temporal vortex veinemanates from the sclera 8 mm posterior to theinferior rectus muscle insertion at its temporalborder. It then loops on the inner surface ofTenon's capsule and it may be damaged if entryinto this quadrant is made without knowledge ofthe presence of the vein. The inferior-temporalquadrant is complicated by the presence of theinferior oblique muscle which passes up to rununder lateral rectus. The inferior nasal quadrantalso has a vortex vein but this is posteriorlysituated and does not loop in the same way as theinferior temporal vortex vein. Entering conjunc-tiva inferiorly also avoids damage to superiorconjunctiva, which is an important considerationif future glaucoma filtering surgery is to beperformed, or a filtering bleb is already present.The inferior nasal quadrant has thus been chosenas the best quadrant to site delivery ofanaesthesia, being the least likely to causecomplication.

After delivery of the local anaesthetic solutionsurgery was performed no earlier than 15minutes later, though anaesthesia has beendescribed as occurring after only a few minutesusing a different sub-Tenon's technique forpanretinal photocoagulation.20 The 15 minutedelay between delivery of block and commence-ment of surgery was to allow the solution time todiffuse, to achieve anaesthesia, akinesia, and toreduce any excess intraconal pressure on theglobe. On application of the one quadrant block

Figure 4 Pain scoresrecordedfor the delivery ofthe sub-Tenon localanaesthetic block. Eighteenpatients recorded no pain ordiscomfort and afurther 23only slight discomfort.

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some proptosis is usually seen and the spaceoccupying effect of the 3 ml delivered would beexpected to give some vis a tergo vitreous pressurewhich may give rise to a 'bulgy eye' if surgerywere to begin immediately.

Possible problems associated with thisinferior-nasal technique of anaesthesia includethe requirement for the patient to elevate orabduct the eye to expose the inferior-nasalquadrant and allow the cannula to pass back-ward, though no patients during this study hadany difficulty with this manoeuvre. Some per-operative chemosis is inherent with thistechnique and may be limited by ensuringposterior delivery of anaesthetic solution. Care-ful posterior delivery of anaesthetic not onlyprevents any chemosis extending to the region ofthe cataract section but also ensures that theblock is truly delivered to the posterior sub-Tenon's space and not inadvertently to theanterior subconjunctival space. An incision intoconjunctiva and underlying fascia is made and atheoretical risk of providing a route for infectionis possible, though any ocular surgery wouldnormally have antibiotic cover by topical treat-ment which would also provide cover for thissmall incision.

Subconjunctival haemorrhage is caused byfine vessels which are inevitably severed onmaking the conjunctival cut. Though a visiblehaemorrhage may occur, it was often small andextended over one quadrant, though the openingof a subconjunctival route for haemorrhage tospread is facilitated by anteriorly leaking anaes-thetic solution separating tissue planes. Thoughthe haemorrhage was able to spread, it was in athin layer and no patients had sufficient subcon-junctival haemorrhage to cause a problem.Patients using anticoagulant medication, how-ever, would require careful assessment beforeusing the sub-Tenon technique due to thepotential for haemorrhage from a severed con-junctival vessel. Use of the blunt cannulairrigation technique should, however, providemore safety, if local anaesthesia is used, than asharp needle local anaesthesia technique.One patient in this study had prior ocular

surgery for retinal detachment. No difficulty wasencountered with the delivery of the blockexcept some Tenon's dissection was required toachieve a satisfactory sub-Tenon avenue forsolution delivery. From the results of sub-Tenon's anaesthesia in vitreoretinal surgery, thepresence of scleral buckles, or previous surgeryresulting in adhesions ofTenon's fascia, does notappear to present a problem with this form ofblock other than that extra dissection may berequired.

Using a 50:50 mixture of lignocaine 2% andbupivacaine 0-5% the blocks have been found tohave a rapid onset within a few minutes and tolast a considerable length of time with somepatients taking many hours to recover full ocularmovements. The mean operative time for phako-emulsification was longer than for extracapsularextraction but the blocks remained effective for

the duration of both procedures. In view of theefficacy of the block and the presence of ptosis,no additional facial block was used in 27 patients.To prevent risk ofpostoperative corneal exposurea dressing using a pad and covering shield wereused routinely at the end of the procedure.

Anterior diffusion of solution to thesubconjunctival space occurs by anterior solutiondelivery on forming the initial bleb and forwardseepage of solution through the sub-Tenon pathcreated by the infusion cannula. This gives riseto the observed subconjunctival chemosis. Theconjunctival incision site provides a convenient,well-anaesthetised site to place a subconjunctivalinjection at the end of the operative procedure.With familiarity the technique is relatively

simple and quick to perform, offering excellentanaesthesia and akinesia, avoiding a sharpinstrument being passed into the orbit. Itprovides a technique where the risk of accidentalinjection of solution to the subarachnoid space,into a blood vessel or of globe perforation shouldbe practically eliminated, owing to use of theblunt cannula.

After over 100 years of sharp instrument localanaesthesia, a direct sub-Tenon irrigationapproach, such as described here, could beviewed as returning full-circle to a modificationof one of the first local anaesthetic techniquesever employed for ophthalmic surgery.2The author acknowledges the assistance of Mr A M P Hamilton,Mr A D McG Steele of Moorfields Eye Hospital.1 Knapp H. On cocaine and its use in ophthalmic surgery. Arch

Ophthalmol 1884; 13: 402-48.2 Turnbull CS. Editorial. Med SurgRep 1884; Nov 29: 628.3 Ellis PR. Retrobulbar injections. Surv Ophthalmol 1974; 18:

425-30.4 Bloomberg LB. Administration of periocular anaesthesia. J

CataractRefract Surg 1980; 12: 677-9.5 Smith R. Cataract extraction without retrobulbar anaesthetic

injection. BrJ Ophthalmol 1990; 74: 205-7.6 Hansen EA, Mein CE, Mazzoli R. Ocular anesthesia for

cataract surgery: a direct sub-tenon's approach. OphthalmicSurg 1990; 21: 696-9.

7 Morgan CM, Schatz H, Vine AK, Cantrill H, Davidorf FH,Gitter KA, et al. Ocular complications associated withretrobulbar injections. Ophthalmology 1988; 95: 660-5.

8 Smith JL. Retrobulbar bupivacaine can cause respiratoryarrest. Ann Ophthalmol 1982; 14: 1005-6.

9 Kimble JA, Morris RE, Witherspoon CD, Feist RM. Globeperforation from peribulbar injection. Arch Ophthalmol1987; 105: 749.

10 Hay A, Flynn HW Jr, Hoffman JI, Rivera AH. Needlepenetration of the globe during retrobulbar and peribulbarinjections. Ophthalmology 1991; 98: 1017-24.

11 Redmond RM, Dallas NL. Extracapsular cataract extractionunder local anaesthesia without retrobulbar injection. BrJOphthalmol 1990; 74: 203-4.

12 Petersen WC, Yanoff M. Subconjunctival anaesthesia: analternative to retrobulbar and peribulbar techniques.Ophthalmic Surg 1991; 22: 199-201.

13 Furuta M, Toriumi T, Kashiwagi K, Satoh S. Limbalanesthesia for cataract surgery. Ophthalmic Surg 1990; 21:22-5.

14 Khoo CY. Local anaesthesia without retrobulbar injection. BrJ Ophthalmol 1990; 74: 639.

15 Mein CE, Woodcock MG. Local anesthesia for vitreoretinalsurgery. Retina 1990; 10: 47-9.

16 Parks MM. Extraocular muscles. In: Duane TD, Jaeger EA,eds. Clinical ophthalmology. Philadelphia: Harper & Row,1987: Vol 1, Ch 1.

17 Koorneef L. New insights in the human orbital connectivetissue. Result of a new anatomical approach. Arch Ophthal-mol 1977; 95:1269-73.

18 Abelson MB, Mandel E, Paradis A, George M. The effect ofhyaluronidase on akinesia during cataract surgery. Ophthal-mic Surg 1989; 20: 325-6.

19 Eugene Wolffs anatomy of the eye and orbit. 7th ed revised byWarwick R, London: H K Lewis, 1976: 309-13.

20 Friedberg M, Palmer RM. A new technique of local anesthesiafor panretinal photocoagulation. Ophthalmic Surg 1991; 22:619-21.

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