PDFlib PLOP: PDF Linearization, Optimization, Protection

Page inserted by evaluation versionwww.pdflib.com – sales@pdflib.com

bradycardias. One resolved with intravenous atropine, the otherproceeded to asystole, cyanosis and loss of consciousness requiringa brief period of CPR.2 All surgeries were completed without sys-temic or ocular morbidity. The common feature to all incidents wasprompt recognition and treatment by the attending anaesthetist. Ifgone unrecognized, it is likely that the patients who were in rapidatrial fibrillation would have gone on to present with either con-gestive heart failure or a thromboembolic event.

We also occasionally experience patients who suddenly becomeextremely anxious and therefore uncooperative intraoperatively. Itis often not feasible to abandon the procedure and commonly theonly way that these patients can be managed is with deep sedationusing intravenous propofol.

In all the cases described, these events could not have beenpredicted by preoperative screening.

We welcome Murray et al.’s suggestion that ophthalmologicdecisions should have well-developed evidence models.1 We feel,however, that one of his co-authors previous comments do not. Ina previous letter of correspondence, Haddad3 states that that thereis a ‘reluctance to move to topical anaesthesia’ as though it is thepreferred anaesthetic for cataract surgery. The superiority of topicalanaesthesia is not supported by evidence. We appreciate that somepractitioners use this anaesthetic method and obtain good resultswith it. The evidence, however, supports sub-Tenon’s anaesthesia asbeing the anaesthetic of choice. A recently conducted systematicreview4 has confirmed the superiority of sub-Tenon’s over topicalanaesthesia. This review of seven studies involving 742 eyes con-cluded that sub-Tenon’s anaesthesia provided better intraoperativeanalgesia, better patient satisfaction and was associated with a 50%reduction in posterior capsular tear/vitreous loss. Sub-Tenon’s ana-esthesia also provides better and more rapid pupillary dilatation.Haddad also claims that the eye is ‘quieter and settles down morequickly after topical anaesthesia’.3 We assume this means either lessinflammation or less conjunctival haemorrhage. This also has aweak evidence base. Postoperative conjunctival haemorrhage mayindeed be more common following sub-Tenon’s anaesthesia.4

However, when the block is performed by an experienced operatorand is combined with digital ocular pressure,5 the incidence of thisminor adverse effect is very low. Similarly, there is no evidence inthe literature supporting a reduction in postoperative inflammationwith topical anaesthesia.

Murray et al. describe one of their anaesthetic techniques as a‘limited sub-Tenon’s’.1 Based on the description of their method ofsedation, the sub-Tenon’s block is being performed on patients whohave received at most oral oxazepam. Our experience is in keepingwith the literature6 in that this block is associated with significantpatient discomfort unless patients are given sufficient short actingintravenous opioid. Further, without details of the criteria used forperforming a block in Murray et al.’s review, and the fact that smallvolumes were used (2.0 mL), we can only assume that the block wasbeing administered for intraoperative patient discomfort rather thanfor akinesia.

In conclusion, in our setting, skilled anaesthesia presence pre-vented not only serious ocular and cardiac morbidity, but alsopotential mortality. We can understand the ‘reluctance to move totopical anaesthesia’, but it is even clearer to us the greater ‘reluc-tance to dispense with the anaesthetist’.

Michael J Fredrickson FANZCA andNick M Mantell FRANZCO

Eye Institute, Auckland, New Zealand

REFERENCES

1. Murray P, Adams K, Haddad P, Murray N, O’Rourke M. Theroutine requirement for anaesthetists in local anaesthetic cata-ract surgery. Clin Experiment Ophthalmol 2007; 35: 195–6.

2. Hadden PW, Scott RC. Cardiac arrest during phacoemulsifica-tion using topical anesthesia in an unsedated patient. J CataractRefract Surg 2006; 32: 369.

3. Haddad PJ. Aeroplanes rarely crash nowadays, therefore theydon’t need pilots: anaesthesia, anaesthetists and cataract surgery.Clin Experiment Ophthalmol 2006; 34: 503–4; author reply 504.

4. Davison M, Padroni S, Bunce C, Ruschen H. Sub-Tenon’s ana-esthesia versus topical anaesthesia for cataract surgery. CochraneDatabase Syst Rev 2007; 4: CD006291.

5. Fredrickson M, Mantell M, Watson A, Vincent A. A simpletechnique to minimise conjunctival haemorrhage following sub-Tenon’s Bock. Clin Exp Ophthalmology 2007; 35: 685.

6. Briggs MC, Beck SA, Esakowitz L. Sub-Tenon’s versus peribulbaranaesthesia for cataract surgery. Eye 1997; 11 (Pt 5): 639–43.

A ‘reluctance to dispense with theanaesthetist’: for valid reasons:response

We note with interest the comments of Fredrickson et al.1 and appre-ciate the opportunity to specifically address those issues whichpertain to our letter.2

Recent systematic reviews emphasize that topical and subtenonsanaesthesia are both accepted and safe methods of providing ana-esthesia for cataract surgery.3,4 Topical anaesthesia is acceptedbecause it is a minimally invasive and low-cost option.4,5 Similar tothe limited subtenons anaesthesia described by us, it is efficaciousbecause anaesthesia, not akinesia, is the absolute requirement foroptimum operating comfort with minimal complications.3,4

We note Fredrickson et al.’s preference for subtenons anaesthesia.A systematic review reveals that when utilized, it can provide betterintraoperative pain relief than topical anaesthesia but questions theactual clinical significance, with the reported maximum differencein pain scores only 2.2 and all scores (topical and subtenons)skewed to the lower end of a 10-point visual analogue scale.3

It is of concern then to read that Fredrickson et al.’s experiencewith administering subtenons anaesthesia is such that ‘this block isassociated with significant patient discomfort unless patients aregiven sufficient short acting intravenous opioid’, in which circum-stances an anaesthetist would be required to monitor the patient. Theadministration of a subtenons block is more uncomfortable than atopical administration.3 However, the same review went on again tocomment that the clinical difference may not be significant, with amaximum difference of 1.1 and again the skewering of all scores atthe lower, less painful, end of the scale.3 This is more in keeping withour experience, and begs the question as to what is so different abouttheir subtenons administration. One suspects that if opioids arerequired then the aforementioned pain scale scores would beexpected to be skewed towards the upper, more painful end.

Notwithstanding any of the potential systemic consequences ofan intravenous opioid requiring subtenons anaesthesia administra-

Letters to the Editor 99

© 2007 The AuthorsJournal compilation © 2007 Royal Australian and New Zealand College of Ophthalmologists

tion, there is the ever present but thankfully – as Fredrickson et al.acknowledge from their own anecdotal survey of five anaesthetistsregularly performing local ocular anaesthesia – very low likelihoodof a serious medical complication occurring in the perioperativeperiod.3,4,6 They contend that an anaesthetist is mandatory not onlybecause of the apparently routine need for opioid but also becauseof life threatening risk. They go on to claim that our one reportedpatient (and suggest that there may have been others) who devel-oped an arrhythmia some hours after routine surgery might havehad earlier symptoms or signs of such an arrhythmia undetected byour perioperative regime.

We, on the other hand, stand by our finding, confirmed byothers, that the risk of a serious medical event occurring in acataract patient population group is very low.3,4,6 We contend thatcurrent evidence regarding the routine requirement of anaesthetistsfor topical or subtenons anaesthesia remains inconclusive. We echothe call of others for more studies with larger patient sample sizes tohelp determine the true levels of risk, and then allow for appropriateevidenced recommendations.3,6

Peter Murray and Neil Murray FRANZCOGosford Hospital, Gosford, New South Wales, Australia

REFERENCES

1. Fredrickson MJ, Mantell NM. A ‘reluctance to dispense with theanaesthetist’: for valid reasons. Clin Experiment Ophthalmol 2008;36: 98–9.

2. Murray P, Adams K, Haddad P, Murray N, O’Rourke M. Theroutine requirement for anaesthetists in local anaesthetic cata-ract surgery. Clin Experiment Ophthalmol 2007; 35: 195–6.

3. Davison M, Padroni S, Bunce CBM et al. Sub-Tenon’s anaesthesiaversus topical anaesthesia for cataract surgery. CochraneDatabase Syst Rev 2007; 3: CD006291. DOI: 10.1002/14651858.CD006291.pub2.

4. Ezra DG, Allan BD. Topical anaesthesia alone versus topicalanaesthesia with intracameral lidocaine for phacoemulsification.Cochrane Database Syst Rev 2007; 3: CD005276. DOI: 10.1002/14651858.CD005276.pub2.

5. Elder M, Leaming D, Hoy B. New Zealand cataract and refrac-tive surgery survey 2004. Clin Exp Ophthalmol 2006; 34: 401–10.

6. Kakrzewski P, Freil T, Fox G et al. Monitored Anaesthetic Careprovided by registered respiratory care practitioners during cata-ract surgery – a report of 1957 cases. Ophthalmology 2005; 112:272–7.

Scanning laser polarimetry: what couldwe measure?We read with interest the editorial by Dr Choplin1 in the July 2007issue of Clinical and Experimental Ophthalmology, and highly appreci-ated and agreed with the comments concerning the necessity ofunderstanding the underlying technologies of the different scan-ning laser imaging devices to interpret their results properly.

We would also like to add some complimentary remarks aboutthe subject.

In fact, the same target tissular structure can be measured differ-ently by two separate devices because they work distinctly, aspresented in the study referred by Dr Choplin in his Editorial.1 Inthis interesting work on the estimation of retinal nerve fibre layer(RFNL) thickness in eyes after the injection of colchicine (thatalters microtubules), the authors found changes in scanning laserpolarimetry (SLP) parameters, although optical coherence tomog-raphy (OCT) estimations remained unchanged.2

However, not only specific alterations in target tissular struc-tures, but also the same interfering structure (such as posteriorcapsular opacification, PCO) over one defined target tissular struc-ture (such as RNFL) may be interpreted in different ways by SLPand OCT. In this respect, our results suggest that SLP examinationwith GDx VCC overestimates RNFL retardation measurements inPCO-affected eyes owing to anterior segment birefringenceunderestimation.3,4 According to our recent study,5 however, nochange was observed after PCO removal in RNFL thickness param-eters of pseudophakic eyes with reliable examinations before cap-sulotomy as measured by OCT in a new series of patients (n = 32).

These aforementioned discords are due to the particular opticalproperties of target (or interfering) tissular structures and to thedifferent mechanism to perform SLP and OCT estimations. Indeed,OCT measures the echo time delay of a back-scattered laser lightby interferometry, and SLP quantifies the phase shift (retardation)of a polarized laser light passing through the naturally birefringenttissues of the eye.

Measuring the changes in the polarization state of light passingthrough the eye is very useful for investigating ocular media. Com-mercial SLP set-ups developed to date focus on the glaucoma diag-nosis where good sensitivity and specificity for separating normaleyes from glaucomatous ones is achieved.

But, could we use the special characteristics of SLP to performuseful measurements in the diagnosis and follow up of ocular patho-logic conditions other than glaucoma? We believe we could. One ofour recent studies showed that some SLP measurements were sig-nificantly associated with best-corrected visual acuity before capsu-lotomy, suggesting that this technology may be useful to quantifyPCO degree.4 In this particular sense, further investigation isnecessary.

Moreover, SLP technology can be useful for other clinical pur-poses: to localize the leakage point and area of fluid in central serouschorioretinopathy,6 to assess Henle fibre integrity in neovascularage-related macular degeneration,7 or to detect changes in progres-sive corioretinal atrophies such as choroideremia.8

Thus, we consider that SLP is a promising, emerging technologythat, once developed and applied to each specific pathologicalcondition, will provide ophthalmologists objective information inseveral ocular diseases in the near future. With a better understand-ing of SLP, clinicians will be able to make better use of thisinformation.

Jose Javier Garcia-Medina, MD PhD,1,2

Samuel Gonzalez-Ocampo MD,1,3

and Manuel Garcia-Medina MD PhD1,4

1Ophthalmology Research Unit ‘Santiago Grisolia’, Department ofOphthalmology, University Hospital Doctor Peset, Valencia,

2Department of Ophthalmology, Huercal-Overa Hospital SAS,Almería, 3Department of Ophthalmology, Albacete University

Hospital, Albacete, and 4Department of Ophthalmology, TorrecárdenasHospital SAS, Almería, Spain

100 Letters to the Editor

© 2007 The AuthorsJournal compilation © 2007 Royal Australian and New Zealand College of Ophthalmologists