DTIC ADA627820: Changes in Intraocular Pressure due to Surgical Positioning Studying Potential Risk for Postoperative Vision Loss

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by  Defense Technical Information Center

SPINEVolume32,Number23,pp2591–2595
©2007,LippincottWilliams&Wilkins,Inc.
Changes in Intraocular Pressure due to
Surgical Positioning
Studying Potential Risk for Postoperative Vision Loss
Kristina S. Walick, MD,* John E. Kragh, Jr, MD,† John A. Ward, PhD,‡
and John J. Crawford, MD*
Visionlossafterspinesurgeryoccursinapproximately1
StudyDesign.Parallelgroupdesign. in500to1in1000procedures,or1caseper100spine
Objective.Comparetheintraocularpressureresponses surgeons per year.1–5 Until recently, authors attributed
intheproneflatversusproneTrendelenburg’sposition.
vision loss to increased intraocular pressure (IOP) sec-
Summary of Background Data. Postoperative vision
ondarytoinadvertentorbitalcompressionoranillfitting
loss(PVL)complicatesapproximately0.05%ofspinesur-
geries. Prone positioning is considered a risk factor be- headrest during surgery.6–12 The contribution of poor
cause it increases intraocular pressure, which may de- headpositioningwaschallengedbyevidencefromcases
crease perfusion pressure to the optic nerve (perfusion whereexternalcompressionoftheorbitswasclearlynot
pressure(cid:1)meanarterialpressure(cid:2)intraocularpressure a factor.13–15 Recent studies now state that risk factors
[IOP]).TheproneTrendelenburg’spositionisoftenused
maybehypotension,anemia,obesity,peripheralvascu-
during spine surgery; however, its effect on optic nerve
perfusion is unknown. The purpose of this study is to lar disease, and middle-aged men.1,3,4,12,16–25 Yet there
comparetheIOPresponsesintheproneflatversusprone arecaseswherenoneoftheseriskfactorswaspresent.12,14
Trendelenburg’s positions to determine if prone Tren- The one risk factor present in every case is prone posi-
delenburg’spositionalsorisksPVL.
tion. Prone positioning is considered a risk factor be-
Methods.Twentysubjectsrandomizedinto2groups.
cause it increases IOP, which decreases perfusion pres-
Group1layintheproneflatposition(0°).Group2layin
the prone Trendelenburg’s position ((cid:2)7°). IOPs were sure to the optic nerve. This occurs because perfusion
measuredwithahand-heldapplanationtonometerwhile pressure equals mean arterial pressure minus IOP.26
seated, 1 minute after assuming the group’s position Prone Trendelenburg’s position (or head-down tilt) is
(Time0),andat10-minuteintervalsfor60minutes.
occasionallyusedduringspinesurgerywhilerepairinga
Results.ThedifferencesinmeanIOPswithrespectto
positions and time were significant (P (cid:1) 0.0001, P (cid:1) duraltearortoenhanceexposure.However,theeffectof
0.000).Therewasasignificantdifferencebetweensitting this surgical position on IOP and perfusion to the optic
andallothertimesforbothgroups.InGroup1,therewas nerve during spine surgery is not known. Moreover,
a significant difference in IOP between Time 0 and all most surgeons and anesthesiologists do not record the
othertimesproneflat(P(cid:3)0.05).InGroup2,therewasa
degreeoftabletiltusedduringsurgerynordotheymon-
significant difference in IOP between Time 0 all other
timesproneTrendelenburg(P(cid:3)0.05). itorthedurationinposition.Wechosetostudythetim-
Conclusion. IOP increases in the prone Trendelen- ingandmagnitudeofIOPintheproneTrendelenburg’s
burg’s position, and when combined with other factors, position to determine if this position contributes to de-
may be a risk factor for PVL. The pathophysiology is creasedperfusionpressureandpossiblyriskspostopera-
discussedandsuggestionsforcliniciansaremade.
tivevisionloss.Thepurposeofourstudyistodetermine
Key words: intraocular pressure, prone Trendelen-
if normal volunteers have increased IOP in the prone
burg,postoperativevisionloss.Spine2007;32:2591–2595
Trendelenburg’s position compared with the prone flat
positionovera1-hourstudytime.
Materials and Methods
From the *Department of Orthopaedics and Rehabilitation, Brooke
ArmyMedicalCenter,†UnitedStatesArmyInstituteofSurgicalRe- Ourtargetpopulationincludedhealthymenandwomenvol-
search,and‡DepartmentofClinicalInvestigation,FortSamHouston, unteers older than age 18 years. Volunteers were included if
TX. theyhadnohistoryofglaucoma,eyetrauma,injuryorsurgeryto
Acknowledgmentdate:August25,2006.Firstrevisiondate:March24,
either eye, including Laser-Assisted in Situ Keratomileusis and
2007.Acceptancedate:April30,2007.
Themanuscriptsubmitteddoesnotcontaininformationaboutmedical photorefractivekeratectomy.Patientswithoneoftheabovecon-
device(s)/drug(s). ditionsorallergytotopicalanestheticswereexcluded.
Nofundswerereceivedinsupportofthiswork.Nobenefitsinany AfterapprovalbyourInstitutionalReviewBoard,informed
formhavebeenorwillbereceivedfromacommercialpartyrelated
consent was obtained from 20 healthy volunteers 25 to 40
directlyorindirectlytothesubjectofthismanuscript.
years of age. Subjects were randomly divided into 2 groups
Theopinionsorassertionscontainedhereinaretheprivateviewsofthe
authorsandarenottobeconstruedasofficialorreflectingtheviewsof designatedtolayeitherproneflatorproneTrendelenburg.The
theDepartmentofDefenseorUSGovernment.Theauthorsareem- eyes were anesthetized with 0.05% tetracaine topical anes-
ployeesoftheUSgovernment.Thisworkwaspreparedaspartoftheir thetic while subjects were seated and reanesthetized intermit-
officialdutiesand,assuchthereisnocopyrighttobetransferred.
tentlyasneededforcomfort.Bothgroupswereseatedforan
Address correspondence and reprint requests to Kristina S. Walick,
MD,134LamontAve,SanAntonio,TX78209;E-mail:Kristina.walick@ initialbaselinemeasurementofIOPrecordinginordertode-
amedd.army.mil termine the similarity of IOP in the 2 groups before position
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4. TITLE AND SUBTITLE 5a. CONTRACT NUMBER
Changes in intraocular pressure due to surgical positioning: studying
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potential risk for postoperative vision loss
5c. PROGRAM ELEMENT NUMBER
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Walick K. S., Kragh Jr. J. E., Ward J. A., Crawford J. J.,
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2592 Spine•Volume32•Number23•2007
Table 1. Descriptive Statistics for Intraocular Pressure Measurements
Group Position Time(min) MeanIOP(mmHg) 95%CI
Proneflat(N(cid:1)10) Seated 0 19.3(cid:5)2.9 13.6–25.0
Proneflat(0°) 0 25.8(cid:5)4.4 17.2–34.4
10 29.7(cid:5)4.1 21.6–37.8
20 29.6(cid:5)6.3 17.2–42.0
30 32.0(cid:5)5.0 22.2–41.8
40 30.0(cid:5)4.8 20.6–39.4
50 30.8(cid:5)4.1 22.8–38.7
60 31.1(cid:5)3.4 24.4–37.7
ProneTrendelenburg(N(cid:1)10) Seated 0 21.4(cid:5)4.5 12.5–30.2
ProneTrendelenburg((cid:2)7°) 0 31.1(cid:5)2.8 25.6–36.6
10 36.2(cid:5)4.0 28.3–44.1
20 36.9(cid:5)4.9 27.2–46.6
30 36.8(cid:5)6.2 24.7–48.9
40 36.4(cid:5)2.6 31.4–41.4
50 35.6(cid:5)5.3 25.1–46.0
60 37.5(cid:5)4.6 28.4–46.5
TherewasasignificantdifferencebetweenmeanIOPinthesittingpositionandallothermeanIOPsfrom0to60min(P(cid:3)0.001,S-N-Ktest).Therewasa
significantdifferencebetweenmeanIOPat0minintheproneorproneTrendelenburg’spositionandallothermeanIOPsfrom10to60min(P(cid:3)0.001,S-N-K
test).TherewasnosignificantdifferencebetweenIOPsfrom10through60min(P(cid:1)1.000,S-N-Ktest).
IOPindicatesintraocularpressure;CI,confidenceinterval.
change.Allmeasurementsweremadewithahand-heldappla- ments within the 5% confidence interval were obtained and
nationtonometerbyanophthalmologist(Tonopen,Medtronic thenaveragedforeachindividual.
Solan,Jacksonville,FL)inthelefteye.27Next,thesubjectslay Our statistical analysis was done with Sigma Stat version
proneintheirdesignatedtestpositionsonawell-paddedoper- 3.11(SystatSoftware,Inc.,PointRichmond,CA)usinga2-fac-
atingroombedwithoutbolters.Allfaceswerecarefullyplaced toranalysisofvariance(position,time)withrepeatedmeasures
in a horseshoe headrest (Quantum 3080 SP, Steris Corp., on one factor (time) to determine if there was a difference in
Montgomery,LA)topreventextraocularpressure.Thissetup mean IOP with respect to position and time between groups.
waschosentofacilitateexposuretotheeyessothatIOPmea- Next,weusedaStudent-Newman-Keuls(S-N-K)posthoctest
surementscouldbemadewithoutmovingthehead.Neckflex- to determine the difference in mean IOP with respect to time
ion and extension were minimized such that the head was in within each group. P levels less than 0.05 were considered
linewiththethorax. statisticallysignificant.
Theproneflatgrouplaidproneonatablewith0°inclineso
thattheeyeswereattheleveloftheheart.TheproneTrendelen-
Results
burggrouplaidintheproneTrendelenburg’spositionwiththe
headofthetableinclinedto(cid:2)7°sothattheeyeswerebelowthe Therewasnosignificantdifferencebetweengroupmean
leveloftheheart.Theinclineanglewasmeasuredwithagoniom- IOPswhileseated(P(cid:4)0.312,S-N-Ktest,Table1).The
eter. IOP was measured within 1 minute of assuming the test
differences in mean IOPs with respect to both position
positionsinbothgroups(designatedasTime0inposition).Mea- and time were significant (P (cid:1) 0.001 and P (cid:3) 0.001,
surementswerethenmadeat10minuteintervals,for60minutes.
respectively, Figure 1). There was a statistically signifi-
Thehand-heldapplanationtonometerhasbeenshowntobe
areproducibleandreliablemethodtomeasureIOP.27,28After cant difference in mean IOP in the sitting position be-
itcontactsthecorneaonetime,theunitdisplaystheaverageof tween all other mean IOPs from 0 to 60 minutes (P (cid:3)
4independentreadingsalongwiththestandarddeviationand 0.001, S-N-K test). There was a statistically significant
confidence interval. A minimum of 2 contacts with measure- differenceinmeanIOPbetweenTime0intheproneflat
Figure 1. The difference be-
tween group means is statisti-
callysignificantateverytime.
IntraocularPressureandSurgicalPositioning•Walicketal 2593
Figure 2. Intraocular pressures
are greater than 40 mm Hg at
every time measured after 10
minutesinpositionandmeasure-
mentsareashighas51mmHg.
Pressure measured while sitting
isdesignatedastime(cid:2)10.
positionandallothertimesproneflat(P(cid:3)0.05).Inthe andisknowntooccurinarterialhypertension,diabetes,
proneTrendelenburggroup,therewasastatisticallysig- atherosclerosis, hypercholesterolemia, aging, and other
nificantdifferenceinmeanIOPbetweenTime0inprone unknowncauses.26Therefore,inselectpatients,asmall
Trendelenburg’spositionandallothertimesproneTren- elevationofIOPaboveacriticallevelmaytipthescale.
delenburg (P (cid:3) 0.05). There was no significant interac- Our1-hourstudyresultssuggestinthesepatientslonger
tion between position and time (P (cid:1) 0.351), meaning timeinproneTrendelenburgmaybeharmful.
that the pressure trends maintain the same difference The increase of IOP with time in position advances
throughoutthestudytimeperiod. and confirms prior similar findings (Figure 3). Similar
The5.4mmHgdifferenceinmeanIOPbetweenprone sustainedincreasesinIOPovertimehavebeenreported
Trendelenburgandproneflatpositionswasstatistically inanimalstudiesaswellashumansandhavebeenshown
significant (P (cid:1) 0.001). The mean IOP difference be- to have negative effects.27,29,32–35 Draeger and Hanke
tween groups at Time 0 (5.3 mm Hg, P (cid:1) 0.005) was foundthatIOPinsupineTrendelenburgsubjectsreacheda
statisticallysignificantandremainedstatisticallysignifi- maximumat15minutesandthenreachedaplateauafter
cantatTime60minutes(6.4mmHg,P(cid:1)0.002). 45minutes.36Chengetalfoundincreasedtimeintheprone
position in anesthetized patients correlated with the in-
Discussion
creasedIOPmeasuredattheendofthecase.37,38
The idea of IOP being associated with increases in the TheeffectsofpronepositioningandTrendelenburgpo-
pronepositionisnotnew,butthecurrentstudyisorig- sitioning are additive.39 Turning a patient from supine to
inalinthatitisthefirsttocompareIOPsofsubjectsinthe prone,abdominalcompression,andtiltingtheheadbelow
prone flat versus Trendelenburg position for the ex- the heart each increases IOP independently.4,36,39,40–43
tendeddurationof1hour.Themainfindingofthisstudy ProneTrendelenburgcombinesthese,givingthehigherIOP
is that surgical positions and time in surgical positions measurementsrecordedinourstudy.
elevateIOPtolevelsthathavebeenthoughttoriskisch- SubjectsinproneTrendelenburghadmorefacialdis-
emicopticneuropathy26,29(Figure2). comfortoverthedurationoftheexperimentthanthose
ThemeandifferenceIOPbetweenbothgroupsmaybe prone flat. These findings support prior clinical find-
clinicallyrelevant(Figure1).Thebloodflowintheoptic ings.29,34,35,42ThesubjectsinproneTrendelenburgcom-
nerveheadremainsrelativelyconstantdespitechangesin plained more of headache, nasal congestion, and a sen-
IOP due to an increase in mean arterial pressure as a sation of pressure behind the eyes, which steadily
result of autoregulation in the vascular system.29,30 worsenedthroughthetesting.
However, beyond a certain point, autoregulation has Thereareseveralweaknessesofourstudy.Wetested
been shown to fail. Recent data in human volunteers normal volunteers, not the patients who undergo spine
indicate that blood flow in the optic nerve head is con- surgery. Patients are more likely to have one or more
stantuntilocularpressuresreach40mmHg.30Inmon- identifiableriskfactorsofischemicopticneuropathyal-
keys,sustainedIOPs(cid:4)50mmHgfor180minuteshave ready. We did not conduct the study during surgery, so
induced optic neuropathy.31–33 Additionally, vascular patients were not anesthetized. General anesthesia has
endothelial dysfunction interferes with autoregulation beenshowntodecreaseIOP.44Whiletestingsubjectswe
2594 Spine•Volume32•Number23•2007
Figure 3. The data are repre-
sented as median (dark line)
within 25th and 75th percentiles
(boxes). The flags represent the
largest and smallest observed
valuesthatarenotoutliers.Out-
liers are values more than 1.5
boxlengthsfromthequartileand
arerepresentedascircles.Mean
IOP differences between seated
andallothertimesisstatistically
significant (P (cid:3) 0.001). IOP dif-
ference between Time 0 in the
prone flat versus all other times
in the prone flat is statistically
significant at every time (P (cid:3)
0.05). IOP difference between
Time 0 in prone Trendelenburg
and all other times prone Tren-
delenburg is statistically signifi-
cantateverytime(P(cid:3)0.05).
did not use bolters nor did we use a Jackson table, so Based on our study, clinicians may want to consider
abdominal compression was not minimized in either thefollowingrecommendations:
group. The effect of tetracaine topical anesthetic may
1. Avoidusingheaddowntiltwhenpossible.
havealteredtheIOPpressuremeasurements.Finally,we
2. If Trendelenburg positioning is needed at some
used an applanation tonopen. The most accurate mea-
point during surgery, be vigilant to return to less
surementofIOPisinvasivemonitoring,butthiswasnot
riskypositionswhenappropriate.
ethicalinawakesubjects.
3. Consider anesthesiologists recording the duration
There are known risk factors for ischemic optic neu-
and degree of Trendelenburg used during surgery
ropathy, yet determining who will end up with postop-
so that future studies can evaluate complications
erative vision loss is still poorly understood. Practitio-
associatedwithahead-downposition.
ners should be aware of risk factors, such as diabetes,
4. Askpatientsaboutvisiononawakeningfromsur-
aging,chronichypertension,arteriosclerosis,atheroscle-
gery, and early ophthalmology referral is war-
rosis,andischemia.26,45–48Theymaycauseapathologic
rantedifanyabnormalityexists.45,51Salvagemay
change in mean arterial pressure, thereby lowering the
bepossibleifunderlyingcausessuchasanemiaor
IOPneededtodecreaseperfusion.(perfusionpressure(cid:1)
hypotensionarecorrectedimmediately.
meanarterialpressure(cid:2)IOP).20,26
On the other hand, there are unidentifiable risk fac- Thecurrentstudymayhelpincreaseawarenessofthe
tors that predispose young healthy patients to ischemic mechanism of IOP elevation with surgical positioning
optic neuropathy, such as anatomic variations, water- andtimebyfillingaspecificphysiologicknowledgegap.
shedzones,andabnormalautoregulation.26,34,49 We hope it will stimulate further study of patients in
Precipitatingfactorsinbothhealthyandsickpatients ordertobetterunderstandrisksofIOPelevation.Future
include hypotension, anemia, and increased IOP.26 studiesshouldlookattheeffectofproneTrendelenburg
Combinedwithpredisposingriskfactors,thesemayact on anesthetized patients undergoing surgery.52 The
asthefinalinjuryandresultinopticnerveischemia. amount of amelioration obtained with elevation of the
ThedatahereinestablishedIOPincreasesintheprone head in reverse Trendelenburg should be included in
Trendelenburg’s position, and when combined with comparisonstudies.50
other factors, may be a risk factor for postoperative vi-
sion loss. Additionally, pressures elevate over time. Al-
though we did not study the reverse Trendelenburg’s Key Points
position, use of a head-up tilt position to decrease IOP
● Pronepositioningmayriskpostoperativevision
has been suggested. Ozcan et al discovered that the in-
loss because it increases intraocular pressure
creaseinIOPinproneflatisamelioratedbyreverseTren-
which,whencombinedwithotherfactors,mayde-
delenburg.50 Similarly, a 15° head-up tilt has been rec-
creaseperfusionpressuretotheopticnerve.
ommendedforeyeproceduresbyophthalmologists.45
IntraocularPressureandSurgicalPositioning•Walicketal 2595
25. KatzDM,TrobeJD,CornblathWT,etal.Ischemicopticneuropathyafter
lumbarspinesurgery.ArchOphthalmol1994;112:925–31.
● Intraocular pressures are higher in prone Tren- 26. HayrehS.Anteriorischemicopticneuropathy.ClinNeurosci1997;4:251–63.
delenburg’s position than prone flat; therefore, 27. SetogawaA,KawaiY.Measurementofintraocularpressurebybothinvasive
and noninvasive techniques in rabbits exposed to head down tilt. Jpn
proneTrendelenburghashigherrisk.
JPhysiol1998;48:25–31.
● Longer time in position increases intraocular
28. ReitsamerH,KielJ,HarrisonJ,etal.TonopenmeasurementofIOPinmice.
pressures,increasingrisk. ExpEyeRes2004;78:799–804.
29. MaderT,TaylorG,HunterN,etal.Intraocularpressure,retinalvascular,
Acknowledgment andvisualacuitychangesduring48hoursof10degreesheaddowntilt.Aviat
SpaceEnvironMed1990;61:810–3.
The authors thank Dr. Jason E. Karo, Brooke Army 30. PillunatL,AndersonD,KnightonR,etal.Autoregulationofhumanoptic
nerveheadcirculationinresponsetoincreasedintraocularpressure.ExpEye
MedicalCenter,DepartmentofOphthalmology,forhis
Res1997;64:737–44.
assistancewiththisproject.
31. HargadenM,GoldbergS,CunninghamD,etal.Opticneuropathyfollowing
stimulationoforbitalhemorrhageinthenonhumanprimate.Ophthalmic
PlastReconstrSurg1996;12:264–72.
References
32. HayrehS,WeingeistT.Experimentalocclusionofthecentralarteryofthe
retina:retinaltolerancetoacuteischemia.BrJOphthalmol1980;64:896–
1. MyersM,HamiltonS,Bogosian,A,etal.Visuallossasacomplicationof
spinesurgery:areviewof37cases.Spine1997;22:1325–9. 912.
2. RothS,BarachP.Postoperativevisionloss:stillnoanswersyet.Anesthesi- 33. HargadenM,GoldbergS,CunninghamD,etal.Opticneuropathyfollowing
ology2001;95:575–7. stimulationoforbitalhemorrhageinthenonhumanprimate.Ophthalmic
3. RothS,ThistedR,EricksonJ,etal.Eyeinjuriesafternonocularsurgery. PlastReconstrSurg12:264–72.
Anesthesiology1996;85:1020–7. 34. DouthwaiteWA.Doesthechangeofanteriorchamberdepthor/andepis-
4. ChengM,SigurdsonW,TempelhoffR,etal.Visuallossafterspinesurgery: cleralvenouspressurecauseintraocularpressurechangesinposturalvaria-
asurvey.Neurosurgery2000;46:625–31. tion?OptomVisSci1997;74:664–7.
5. WarnerME,WarnerMA,GarrityJA,etal.Thefrequencyofperioperative 35. FribergT,SanbornG,WeinrebR.Intraocularandepiscleralvenouspressure
visionloss.AnesthAnalg2001;93:1417–21. increaseduringinvertedposture.AmJOphthalmol1987;103:523–6.
6. ManfediniM,FerranteR,GildoneA,etal.Unilateralblindnessasacompli- 36. DraegerJ,HankeK.Posturalvariationofintraocularpressure:preflight
cationofintraoperativepositioningforcervicalspinesurgery.JSpinalDis- experimentsfortheD1mission.OphthalmicRes1986;18:55–60.
ord2000;13:271–2. 37. ChengM,TodorovA,TempelhoffR,etal.Theeffectofpronepositioningon
7. WolfeS,LospinusoM,BurkeS.Unilateralblindnessasacomplicationof intraocularpressureintheanesthetizedpatient.Anesthesiology2001;95:
patientpositioningforspinalsurgery.Spine1992;17:600–5. 1351–5.
8. HoskiJ,EismontF,GreenB.Blindnessasacomplicationofintraoperative 38. HuntK,BajekalR,CalderI,etal.Changesinintraocularpressureinanes-
positioning:acasereport.JBoneJointSurgAm1993;75:1231–2. thetizedpronepatients.JNeurosurgAnesthesiol2004;16:287–90.
9. BenumofJ,MazzeiW.Multifactorialetiologyofpostoperativevisionloss. 39. LamA,DouthwaiteW.Doesthechangeofanteriorchamberdepthor/and
Anesthesiology2002;96:1531–2. episcleralvenouspressurecauseintraocularpressurechangesinpostural
10. BekarA,TureyenK,AksoyK.Unilateralblindnessduetopatientpositioning variation?OptomVisSci1997;74:664–7.
duringcervicalsyringomyeliasurgery:unilateralblindnessafterproneposi- 40. MansourA,FeghaliJ,JaroudiN.Increasedintraocularpressurewithhead
tion.JNeurosurgAnesthesiol1996;8:227–9. downposition.AmJOphthalmol1984;98:114–5.
11. GrossmanW,WardT.Centralretinalarteryocclusionafterscoliosissurgery 41. CookJ,FribergT.Effectofinvertedbodypositiononintraocularpressure.
withahorseshoeheadrest.Spine1993;18:1226–8. AmJOphthalmol1984;98:784–7.
12. LocastroA,NovakK,BiglanA.Centralretinalarteryocclusioninachild 42. FribergT,WeinrebR.Ocularmanifestationsofgravityinversion.JAMA
aftergeneralanesthesia.AmJOphthalmol1991;112:91–92.
1985;253:1755–7.
13. AbrahamM,NavinS,SinhaS,etal.Unilateralvisuallossaftercervicalspine
43. LeMarrJ,GoldingL,AdlerJ.Intraocularpressureresponsetoinversion.
surgery.JNeurosurgAnesthesiol15:319–22.
AmJOptometryPhysiolOptics1984;61:679–82.
14. RothS,NunezR,SchreiderB.Unexplainedvisuallossafterlumbarspinal
44. TsamparlakisJ,CaseyT,HowellW,etal.Dependenceofintraocularpres-
fusion.JNeurosurgAnesthesiol1997;9:346–8.
sureoninducedhypotensionandpostureduringsurgicalanesthesia.Trans
15. LeeL,LamA.Unilateralblindnessafterpronelumbarspinesurgery.Anes-
OphthalmolSocUK1980;100:521–6.
thesiology2001;95:793–5.
45. WilliamsE.Postoperativeblindness.AnesthesiolClinNorthAm2002;20:
16. DilgerJ,TetzlaffJ,BellG,etal.Ischaemicopticneuropathyafterspine
605–22.
fusion.CanJAnesthesiol1998;45:63–6.
46. Connolly S, Gordon K, Horton J. Salvage of vision after hypotension-
17. KatzmanS,MoschonaC,DziobaR.Amaurosissecondarytomassiveblood
inducedischemicopticneuropathy.AmJOphthalmol1994;117:235–42.
lossafterlumbarspinesurgery.Spine1994;19:468–9.
47. Haeflinger I, Meyer P, Flammer J, et al. The vascular endothelium as a
18. BrownR,SchaubleJ,MillerN.Anemiaandhypotensionascontributorsto
regulatoroftheocularcirculation:anewconceptinophthalmology?Surv
perioperativelossofvision.Anesthesiology1994;80:222–6.
19. StevensW,GlazerP,KelleyS,etal.Ophthalmiccomplicationsafterspinal Ophthalmol1994;39:123–32.
surgery.Spine1997;22:1319–24. 48. HayrehS,PodhajskyP,ZimmermanB.Nonarteriticanteriorischemicoptic
20. DunkerS,HsuH,SebagJ,etal.Perioperativeriskfactorsforposterior neuropathy:timeofonsetofvisualloss.AmJOphthalmol1997;124:641–7.
ischemicopticneuropathy.JAmCollSurgeons2002;194:705–10. 49. HayrehS.Invivochoroidalcirculationanditswatershedzones.Eye1990;
21. LeeA.Ischemicopticneuropathyfollowinglumbarspinesurgery.JNeuro- 4:273–89.
surg1995;83:348–9. 50. OzcanM,PraetelC,BhattiT,etal.Theeffectofbodyinclinationduring
22. MurphyM.Bilateralposteriorischemicopticneuropathyafterlumbarspine pronepositioningonintraocularpressureinawakevolunteers:acomparison
surgery.Ophthalmology2003;110:1445–57. oftwooperatingtables.AnesthAnalg2004;99:1152–8.
23. LeeLA.ASAPostoperativeVisionalLossRegistry:preliminaryanalysisof 51. WilliamsE.Postoperativeischemicopticneuropathy.AnesthAnalg1995;
factorsassociatedwithspineoperations.ASANewsletter2003;67:7–8. 80:1018–29.
24. HoVT,NewmanNJ,SongS,etal.Ischemicopticneuropathyfollowing 52. JantzenJ,HennesH,Rochels,R.etal.Deliberatearterialhypotensiondoes
spinesurgery.JNeurosurgAnesthesiol2005;17:38–44. notreduceintraocularpressureinpigs.Anesthesiology1992;77:536–40.