Accuracy and sensitivity of the dynamic ocular thermography and inter.docx

Accuracy and sensitivity of the dynamic ocular thermography and inter.docx

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Accuracyandsensitivityofthedynamicocularthermographyandinter

Accuracyandsensitivityofthedynamicocularthermographyandinter-subjectsocularsurfacetemperature（OST）inChineseyoungadults

LiliTana,,,Zhi-QiangCaibandNai-ShinLaic

aSingaporePolytechnicOptometryCentre,SchoolofChemicalandLifeSciences,500DoverRoad,139651Singapore

bSchoolofElectricalandElectronicEngineering,SingaporePolytechnic,Singapore

cMathematicsandScienceDepartment,SingaporePolytechnic,Singapore

Availableonline6February2009.

Abstract

Purpose

ToinvestigatetheaccuracyandsensitivityoftheThermo-TracerTH9100MV,NECSan-eiinmonitoringthetemperatureoftheanterioreyesurfaceandtoestablishaninter-subjectsocularsurfacetemperature（OST）norminChineseyoungadults.

Methods

Ablackbodywithfixedtemperaturewasusedtostudyaccuracyandsensitivityofthethermalcameraused（Thermo-TracerTH9100MV,NECSan-ei）.SixtyhealthyChineseyoungadultsaged17–21（meanage19）wererecruitedfromtheSingaporePolytechnicOptometryCentre.Aroomwithstandardroomtemperatureandhumiditywasused.Subjectswereadaptedtotheroomconditionsfor20 minbeforemeasurement.OSTwasthenmeasuredwithin4–5 safterablinkandwiththeirupperlidliftedbyacottonbud,usinginfraredthermo-camera,inanon-invasivemanner.

Results

AllfutureThermo-Tracerreadingscouldbeconvertedto‘true’temperatureviatheregressionequationderivedy = 1.0884x − 3.4026（r2 = 0.9985）,whereyisthe‘true’temperatureandxisreadingbyThermo-Tracer.Sensitivityofthemachineforall16temperaturesstudiedwasfoundtobe91.3%.MeanOSTforthepopulationstudiedwas34.70 ± 0.50 °C.MeanOSTatgeometricalcentrecornea（GCC）was34.39 ± 0.47 °Candinter-oculartemperaturedifferencewas0.20 ± 0.15 °C.BoththehorizontalandverticalOSTprofilewasestablished.Nosignificantdifferencesbetweenright/lefteyesandbetweengenderswerefoundat95%CI.

Conclusions

Findingsontheaccuracycanbeusedasareferencebyresearcherswhoareusingthesameinfraredthermalcamera.Itisproventhatthemachinehashighsensitivityindeterminingthetemperatureofanteriorocularsurface.Methodologyusedinthisstudycanalsobeappliedtothedeterminationoftheaccuracyandsensitivityofthedynamicrangeforotherinfraredthermalcameras.Inter-subjectsOSTnorminChineseyoungadultsaged17–21wasestablished.

Keywords:

Dynamicthermography;Ocularsurfacetemperature;Blackbody;Geometriccentreofthecornea;Infraredthermalcamera

ArticleOutline

1.Introduction

2.Methods

2.1.Accuracyandsensitivitystudy

2.2.Inter-subjectOSTnormofChineseyoungadults

2.2.1.Subjects

2.2.2.Procedures

2.2.3.Dataanalysis

3.Results

3.1.Accuracyandsensitivitystudy

3.2.Inter-subjectOSTnormofChineseyoungadults

4.Discussion

5.Conclusion

Acknowledgements

References

1.Introduction

Theinterestinthetemperatureoftheeyespansalmost130yearsandhasbeenanareaofresearchlargelydrivenbyprevailingtechnology[1].Currentinstrumentationoffersthepotentialtomeasuretheocularsurfacetemperature（OST）withmoreaccuracy,resolution,andspeedthanpreviouslypossibleandtheuseofdynamicocularthermographyoffersgreatopportunitiesformonitoringthetemperatureoftheanterioreye.ItisgenerallyagreedthattheapplicationsofOSTmeasurementcanincludedryeye,contactlenswear,cornealsensitivity,andrefractivesurgery[2].

Table1showshowthemeasurementsofocularsurfacetemperatureevolved,fromdirecttoindirecttechniques,fromplacementofamercurybulbatthecornealsurfacetominiaturizedthermisterbeadandeventuallyusinginfra-red[3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13],[14],[15]and[16].Thekeyfindingsarealsoshowninthetableincludingthecurrentstudy.

Table1.

Techniquesformeasuringhumanocularsurfacetemperatureandthekeyfindings.

Author

MeanTemp.（°C）

Range（°C）

Inter-oculartempdifference（°C）

Differenceb/wlimbusandcentralcornea（°C）

Technique

Dohnberg,1876a

36.50–36.70

Mercurybulb

Galezowski,1877a

36.40

Mercurybulb

Silex,1893a

35.55

Thermo-element

Giese,1894a

35.72

Thermo-element

Hertel,1900a

35.65

Mercurybulb

Kirisawa,1942a

34.50

Thermo-element

Kirisawa,1942a

36.34

Thermo-element

Holmberg,[3]

36.24

Thermo-electric

Hamanoetal.,[4]

34.00

Thermister

HillandLeighton,[5]

32.10 ± 0.90

Thermister

Mapstone,[6]

34.80 ± 0.30

33.20–34.80

Infra-red

Kolstrad,[7]

32.00

Thermister

KinnandTell,[8]

35.00–36.00

Liquidcrystal

RysäandSarvaranta,[9]

34.80 ± 0.50

Infra-red

Hørven,1975[10]

33.67

32.00–34.90

Contactprobe

Hamanoetal.,[11]

34.40

Infra-red

FattandChaston,[12]

33.00–36.00

Infra-red

AliòandPadron,[13]

32.90 ± 0.62

32.00–34.50

0.60

Infra-red

MartinandFatt,[14]

34.50 ± 1.00

Heatflow

Efronetal.,[15]

34.30

32.80–35.40

0.45

Infra-red

Morganetal.,[16]

0.60orless

0.37

Infra-red

Purslowetal.,[2]

35.00 ± 1.10

Infra-red

Currentstudy,2007

34.39 ± 0.47

32.70–35.40

0.20 ± 0.15

0.23–0.43

Infra-red

Full-sizetable

a CitedbyHolmberg[3].

ViewWithinArticle

BeforeMapstone[6]revolutionisedocularsurfacetemperaturemeasurementusinginfra-redtechnology,theearlyyearsoflabourssurroundingoculartemperaturemeasurementusedthecontacttechniques.Suchtechniquesrequiredtheuseofanaestheticandthefactthatitwasacontacttechniquesuggestedthattheresultswerenotasaccurateasheattransferredtotheavascularcorneabymeansofconductionfromtheprobetotheocularsurface.Itwasalsoclaimedthatthecontacttechniquesufferedfromrelativelypoorresolution[8].

Theapplicationofinfra-redthermometrywaspioneeredbyMapstone[6].Thistechniqueinvolvesmeasuringtheinfra-redenergyemittedbythecorneaandequatingthistotherelationshipbetweeninfra-redradianceandtemperatureforablackbody.Infra-redthermometryhasthemajoradvantageofbeingnon-contactandallowingvirtuallyinstantaneousmeasurementoftemperature.Wide-fieldinfra-redthermographyenablesthemappingoftemperatureacrossanextendedsurfaceandhasrecentlybeenappliedtothestudyofoculartemperature.However,precisedetailsofthevariationintemperatureacrosstheocularsurfacehavenotbeenpresented[6],[22],[23],[24],[25]and[26].

ItwasreportedbyEfronetal.[15]thatfollowingablink,thegeometriccentreofthecornea（GCC）hadameantemperatureof34.3 ± 0.7（32.8–35.4 °C）.Temperatureincreasedtowardstheperipheryofthecorneawiththelimbusbeing0.45 °CwarmerthantheGCC.Followingablink,theGCCcooledatameanof（±SD）rateof0.033 ± 0.024 °C/soverthefirst15 s.Subjectswhosecorneascooledmoreslowlyfollowingablinkdemonstratedagreatercapacitytoavoidblinkingforaprolongedperiod.Morganetal.[16]foundthat95%ofthenormalpopulationhaveaninteroculartemperaturedifference（temperatureofcentreofrightcorneaminustemperatureofcentreofleftcornea）of0.60 °Corlessbutnotstatisticallysignificant.Thereappearstobeagreaterdifferenceintemperaturebetweenthelimbusandthecentreofthecorneainpatientswithdryeyes.Analysisofatypicalthermogramrevealsthatthecoolestpartoftheocularsurfaceisthemiddleofthecornea（duetoitsavascularnature）slightlyinferiortothegeometricalcentre（duetocoveragetothesuperiorcorneabytheuppereyelid）.Theisothermsareellipticalinshapeduetothepositionofthelidmarginswhichisanimportantheatsource.

Inthestudyofoculartemperatureitisimportanttoconsiderallparameterswhichmightinfluencerecordedmeasurements.Examplesofsuchparametersincluderoomtemperature,timeofdayandageofsubject[17].AnegativecorrelationbetweenageandOSThasbeenreportedintheliteraturewithanaveragedecreaseof0.010 °Cperyear,althoughtherateofchangeincreasesaftermiddleage.

Thereisconflictingevidenceabouttheeffectofageonthetearfilm[27],butitisgenerallyagreedthatvolume,evaporationandlipidlayerthicknessareconstantinthehealthyeyewithincreasingage,despitechangesintearproductionandstability;thetearfilmbecomeslessstablewithage[28].NosignificanteffectofsexorraceonOSThasbeenobservedinpreviousstudies.

Astudyonalargesamplesize（124femalesand142males）foundthatcornealtemperaturecorrelateswithfingertemperatureevenafteradjustingforenvironmentalandtympanictemperaturesandfortheageandsexofparticipants.Apossiblecauseforthesefindingsissomeparallelismsinblood-flowregulationinthefingerandtheeye[29].ItisbelievedthattheOSTcouldvarythrough-outthedayastheoculartissuetemperaturehasproventobelinkedwithchoroidalblood-flow[30]whichchangesovertime.

IthasbeenshownthatOSTcanbeimportantindetectingearlyocularinflammationanddryeyes[16].ChangesinOSThasalsobeenobservedinpatientswithcarotidarterystenosis（CAS）[18],contactlenswearers[2]andpatientswhohadundergonephotorefractivekeratectomy[19]and[20].Assuch,ocularthermographycouldbeausefulclinicaltooltoidentifyearlychangesofocularpathologyaswellasotherocularconditionsthatmayoccurattheanterioreyebasedonthechangesofthetemperature.ItisthereforeimportanttostudytheaccuracyandsensitivityoftheThermo-TracerandtoestablishOSTnormforChineseyoungadultsbeforeaseriesofvalidstudiescanbeestablishedontheethnicgroup,particularly