Optical Coherence Tomography Too Good To Be True?

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5/25/2018Optical Coherence TomographyToo good to be true? Caroline B. Pate, OD, FAAO Associate ProfessorUAB School of OptometryBirmingham, AlabamaHistory of Optical Coherence Tomography20152003SD OCT gainspopularity inclinical practice1993First in vivoOCT imagesof humanretina arepublished20062002Publicationshows SpectralDomain OCT1997has advantagesFirst commercial over Timeuse of OCT in Domain OCTOphthalmologyOptoVueRTVueavailable with65x speed and2x resolutionthan StratusOCTTime Domain vs. Spectral (Fourier) Domain OCT First commerciallyavailable OCT-Aintroduced in theUnited States2018Pubmed search showsover 35,000publications on OCT2015 Review ofOptometry’s annualdiagnostic technologysurvey lists OCT as the#1 most desired pieceof equipmentNon-contactNon-invasivePainlessNo radiationFastReliableDetection of pathology that cannot be seenophthalmoscopicallySensitive .micrometer resolution! Slower than eyemovements ( 1secimage acquisitionspeed)Sequential – 1 pixel ata time Faster than eyemovements(milliseconds)Simultaneous – 2048pixels at a timeHigher resolution1991OCT isintroducedD. Huang, USCLots of options - Spectral Domain OCTModelCirrus HD(Manufacturer) OCT 5000(Carl ZeissMeditec)3D OCT – 1Maestro(TopconMedicalSystems)Spectralis SDOCT(HeidelbergEngineering)Avanti RTVueXR (Optovue)Scanning27,000Speed (A-scans 68,000per second)50,00040,00070,000Axial5Resolution (µmin tissue)5-63.95Minimum Pupil 2Diameter (mm)2.5How does OCT work? Uses light rather than sound or radio frequency Faster Layers2.5speed higher resolutionUses principle of low-coherence interferometry tomeasure optical reflectivity of tissuesThe interferometer integrates data points toconstruct a tomogram of retinal structuresof different optical densities2.5Adapted from: Mazzarella & Cole. Review of Optometry Sept 2015.1

5/25/2018Limitations Mydriasis may be necessaryCataracts and poor tear film can degrade theimageAccuracy is limited by high refractive error andaxial lengthLimited to posterior poleCaution comparing measurements from one brandof OCT to anotherIndications Diagnosis and detection of pathologyMonitoring for progressionEvaluation for need for laser or surgical interventionQuantification – evaluation of thickness, volume,surface areaMonitoring for changes due to medicationsEvaluation of postoperative progressObtaining a scanRunning an OCT Numerous scanning protocols Anteriorsegment and Posterior segment Grid, raster, volume scans, single line, etc Adjustable parameters Patient fixates on target inside the instrumentOperator aligns instrument via a camera whichallows visualization of the fundus and the scanbeamRecommended minimum pupil size 3mm, howeverdilation improves the signal strength and imagequalityWhat can we see with the OCT?Results Imagesdisplayed on monitor representing reflectivedifferences between structures Operator may choose to save image or repeat scan Often compared to normative database2

5/25/2018Know the anatomy!VitreousRoss MH, Kaye GI, Pawlina W: Histology, a Text and Atlas. 4th ed. Philadelphia: Lippincott Williams & Wilkins, 2003Gabaeff SC. WestJEM 16(7): 2010.Anatomy of a retinal OCT image Reflectiveinterfaces betweenstructuresLarge reflectionsare warm colors(red, yellow)Mild reflections arecool colors (green,blue)Absence ofreflection is black3D imaging of ocular structuresOphthalmology Volume 121, Number 8, August2014 X, Y, and Z axisFigure 1. Nomenclature for normal anatomiclandmarks seen on spectral domain opticalcoherence tomography (OCT) images proposedand adopted by the International Nomenclaturefor Optical Coherence Tomography Panel.Healthy retina imaged using HeidelbergSpectralis. RPE ¼ retinal pigmentepithelium.3

5/25/2018OCT-Angiography Allows for betterassessment of retinaland choroidal vasculardisease and bloodflowUseful in diseases suchas maculardegeneration, diabeticretinopathy, and veinocclusionsOCT-A systems: AngioPlex (CarlZeiss Meditec) AngioVue (OptoVue)Retinal examinationReview of Optometry, 2017Clinical applications 1. Macular disorders – especially helpful inconfirming those that are not evident clinically2. Macular hole – allows for confirmation ofdiagnosis and staging and monitoring throughtreatment3. Macular edema – characterized by areas ofincreased thickening and decreased reflectivity diabetes,vein occlusion, uveitis, post cataract surgerymeasurements allow for monitoring forprogression/resolution 4. Macular degeneration Detectionof RPE changes and disruption in dry AMDof subretinal fluid and choroidalneovascularization in wet AMD Detection 5. Medications Response Sideto treatmenteffects of systemic medications QuantitativeVitreous detachment vs. Vitreomacular TractionMacular hole4

5/25/2018Epiretinal membrane20/80 BCVA, noticed vision worsening over past few months26 yo AA F, 34 weeks pregnant Type 1 DMPre-eclampsia20/40020/10068 yo AA M, sudden vision loss OS5

5/25/201876 yo WM, being followed for AMD20/6020/40Recommendations for patients onPlaquenil Risk of toxicity increases sharply towards 7.5% after 5-7 yrs ofuse, or cumulative dose of 1000 g HCQInitial baseline exam with DFE, then annual screenings after 5yearsScreening: Regular exams with DFE 10-2 SS (white stimulus) 24-2 SS or 30-2 SS (white stimulus)for Asian patients SD OCT*, FAF or mfERG *most objective, lowest variabilityNo longer recommending Amsler Grid“Flying Saucer Sign”Disruption to the ellipsoid zone line/parafovealthinning Optic nerve evaluationDisruption to the ellipsoid zone (EZ) lineChen E, et al. Clinical Ophthalmology 2010.6

5/25/2018Optic disc scan Traditional methods of evaluating apatient for glaucomaHigh resolution imaging with OCTallows for an accurate assessmentof: Theone riskfactor that canbe controlled Sizeof the optic cuparea C/D ratio Volume of the cup RNFL thickness Disc Measuring IOP Serial measurements are useful tomonitor for glaucomatouschangesStereoscopicoptic nerveevaluationVisual fieldtesting Patientmustcooperate foraccurate resultsRNFL ThicknessMap shows thepatterns andthickness of thenerve fiber layerThe RNFL Deviation Mapis overlaid on the OCTfundus image to illustrateprecisely where the RNFLthickness deviates fromnormal.Also can see boundariesdrawn for cup and disc,along with the RNFLcalculation circle.TSNIT curvecompares patientto normativedatabaseImportance of scan placement 2 scans of same eye1st scan is well centered; 2nd scan is not centered-7

5/25/2018Function vs. StructureGuided progression analysisPapilledema vs. ONH drusenImages courtesy of Frannie Davis, ODImages courtesy of Frannie Davis, ODAnterior Segment OCTAnterior Segment Imaging Tear heightPachymetryLASIKCorneal diseaseCustom design andevaluation of specialtycontact lensesIOL/implant imagingAnterior chamber depth,angles GlaucomaImage from: Baldwin, MoyerReview of Cornea & ContactLenses 20128

5/25/2018CASE EXAMPLE 23 year old Optometry StudentOcular history: Suspectedlatent hyperopea headache after dilation Gets dilated 1-2 times per week !! Reports VH angles— 1:1/8 or lessIOP-16/17Cirrus operator manualTemporal Angle-Gonio: Ant TMOCT: SSSchwalbe’s LineScleral SpurCase Example #2 29 WF, lab techPHx: Turner Syndrome (X)FHx: Father melanomaHyperopeSteady increase in IOPs over last 6 years—11 to 13to 18 to 21mmHgNarrow angles with vH (1:1/4 to 1/8)Longstanding Hx large choroidal nevusSchwalbe’s LineScleral Spur9

5/25/2018Angle to Angle ViewingTemporal Angle-Gonio: SLOCT: Ant TMSchwalbe’s LineScleral SpurIris Melanoma 56 YO Caucasian FemaleRoutine eye examPupil distortion(-)iris transilluminationIOP: 17/163-Mirror angle and retinalexam: clearTips and Tricks Signal strength score is not the same as a scan qualityscore Artifacts watch for the unusual Make sure image is centered with no missing or weak signalareasKnow your targets to help you better direct the patientDilation greatly improves the quality of the scanGood idea to have artificial tears nearby in case dryeye is contributing to a poor quality scanRemind patient to keep eyes open wide between blinksIn cases of poor central vision in the eye being tested,the external fixation wand can be used for the othereye Anomalies in the scan that are not actual physicalstructures, but instead due to an external agent oractionExamples:Patient blinked during scan acquisition10

5/25/2018Shadows“Waves” in retinal contour eye movementblood vessels casting a shadowWhat if the scan isn’t “perfect”? DecentrationMedia opacitiesLower signal strength/lower quality imageBlinks/shifts in gazeArtifactsInsurance/Billing Anterior9213292133 Retina 92134 ONH .THESCAN MAY STILL BE USEFUL!!Bilateral codes Generally cannot perform same day as fundusphotography or as each otherCheck with local carrier for frequencyWide variety ICD-10 codes acceptedHelpful Resources11

5/25/2018Thank you!12

History of Optical Coherence Tomography 1991 OCT is introduced 1993 First in vivo OCT images of human retina are published 1997 First commercial use of OCT in Ophthalmology 2002 Publication shows Spectral Domain OCT . Clinical applications

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