Guide to Interpreting Spectral Domain Opitcal Coherence Tomography

98 Pages·2009·4.404 MB·English

by  Bruno Lumbroso, Marco Rispoli

B L M R
RUNO UMBROSO ARCO ISPOLI
Guide to Interpreting
Spectral Domain
Optical Coherence Tomography
©Copyright2009
BrunoLumbroso
ISBN978-88-86193-89-4
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USCKeckSchoolofMedicine
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Contents
PART ONE
CHAPTER1
OverviewofOpticalCoherenceTomography Page 7
CHAPTER2
GeneralPrinciplesforObtainingandInterpretingSpectralDomainOCTImages Page 9
CHAPTER3
InterpretationofthePathologicalCross-sectionalOCT Page 13
CHAPTER4
VisualizingOcularStructuresinThreeDimensions Page 37
CHAPTER5
RetinalTopographyWithSpectralDomainOCT Page 51
CHAPTER6
SD-OCTfortheStudyandManagementofGlaucoma Page 55
PART TWO
CLINICALREFERENCECASES
Introduction Page 59
VitreousandPathologiesoftheVitreoretinalInterface Page 61
MacularDegeneration Page 67
DiabeticRetinopathy Page 75
VascularOcclusionoftheRetina Page 80
RetinalEpitheliopathy Page 84
Cysticercosis Page 89
Vogt-Koyanagi-HaradaSyndrome Page 91
ComplexCases Page 93
3

PART ONE
Introduction
Opticalcoherencetomography(OCT)isanessentialtoolfordiagnosingand
managingretinaldiseasesandglaucoma.Inthishandbook,whichfeaturesde-
tailed schematic illustrations as well as actual OCT scans, we offer a step-by-
stepguideforinterpretingimagesanddataacquiredbytherevolutionaryand
novelspectraldomainOCTtechnology.
We believe this handbook is important because spectral domain technology
offerssignificantadvancesovertimedomaintechnology.Forexample,spectral
domainOCToffers:
1.Improvements to the sagittal OCT B-scan, which reveals previously un-
detected structures
2.Technical and clinical improvements in the study of glaucoma
3.Three-dimensional images that provide new information.(Although this
is a new way to view ocular structures, interpretation can be learned
quickly and easily,and these images enable more accurate diagnosis.)
AllreferencestospectraldomainOCTinthishandbookarebasedonourex-
periences with the spectral domain Cirrus™ HD-OCT manufactured by Carl
ZeissMeditec,Inc.,Dublin,Calif.(U.S.headquarters).Allimagesweregenerated
bytheCirrus™HD-OCT.
In these pages, we have ascribed great importance to explaining the mean-
ing of OCT images.In addition, we have tried to set forth a logical method for
interpretingophthalmicimages.Thefirstphaseofanalysissubdivideseachim-
age into its smallest components.The second phase combines these fine details
tosynthesizethedata,enablingustoarriveatanaccuratediagnosisandtode-
cideonappropriatetherapy.Wehopethishandbookhelpseyecarepractitioners
appreciatethenewpossibilitiesofferedbyspectraldomainOCT.
Bruno Lumbroso • Marco Rispoli
5

Chapter1
OVERVIEW OF OPTICAL
COHERENCE TOMOGRAPHY
Advances in technology usher in
a new era of expanded functionality
Optical coherence tomography (OCT) is an es- Time domain OCT,which was commercialized at
sentialtoolfornoninvasive in vivoanalysisofretinal the end of 1996 and improved with increased resolu-
tissue for diagnosis and management of retinal dis- tion in 2002,compares a reflected beam of light to a
ease and glaucoma.This technique is based on the beam of light from a reference mirror.Time delays be-
degreeofabsorptionordispersionoflighttraversing tweenthetwobeamscanthenbemeasured.Although
thetissue.Thelight,whichisdividedintoadetection thelowacquisitionrateexposestheimagestoaberra-
arm and a reference arm,is emitted by a superlumi- tionscausedbyeyemovement,increasingtheacquisi-
nescentdiodeatawavelengthofapproximately840 tion speed would degrade image resolution. At good
nm. resolution (1024 points in 6 mm of tissue),time do-
FIGURE1.
Cirrus™HD-OCTimageofahealthyretina.CourtesyofDavidS.Boyer,M.D.
7
Chapter1
mainOCTcanproduceoneB-scanevery1.6seconds the increased resolution,fine retinal detail is compa-
(400A-scanspersecond). rabletowhatisvisibleonahistologyslide.
The Cirrus™ HD-OCT combines image accuracy
and ease of use.The acquisition process is fully auto-
SPECTRALDOMAINOCT mated,including:
•Autofocus
Recently,we have seen the emergence of a new •Autooptimization
technologycalledFourierdomainorspectraldomain •Autopolarization.
OCT,which employs a different acquisition tech- Cycles follow one another in a few seconds,plac-
nique.Thistechniqueusesaspectrometeronthede- ing the retinal plane in the center of the screen.The
tector arm to measure the difference in wavelength operator need only position the scanner on the area
between the light from the fixed reference arm and of the retina to be studied.The instrument acquires
that returning from the tissue.The instrument uses imagesinhigh-resolutionorhigh-speedmode,taking
Fourier analysis to analyze the images according to into consideration the inverse proportions between
thelightwavelengthrecorded. thesevariables.
This type of OCT technology avoids moving the As mentioned previously,the wavelength of the
reference arm and instead analyzes the reflected lightsourceis840nm,andthesamplingfrequencyis
lightusingaspectrometer.Theimmediateadvantage about 27,000A-scans per second.The instrument ac-
of this technology is the high number of scans ac- quires 200 to 512 B-scans in rapid succession,from
quired per second – approximately 27,000 top to bottom,then constructs a 3-D retinal map by
A-scans per second – making true three-dimensional aligning the B-scans.Acquisition speed determines
(3-D) imaging possible and practical in a clinical en- the accuracy of the retinal map,so with spectral do-
vironment. maintechnology,itispossibletoobtainverydetailed
This sampling frequency has notable advantages. retinalmaps.
The possibility of artifacts due to eye movement is Theanalysisspeedforcalculationofaveragethick-
minimized because the operator can easily position nessandthedisplayofETDRSgridaveragesisalmost
and center the beam to control the image,especially the same.The higher density of data collected with
when working with pseudophakic or highly myopic spectral domain technology also allows for 3-D dis-
eyes,or when there is relevant media opacity.Given play.
8
Chapter2
GENERAL PRINCIPLES FOR OBTAINING AND
INTERPRETING SPECTRAL DOMAIN OCT IMAGES
Compared with time domain OCT, spectral domain OCT provides more detailed images and
moredatawithimprovedspeedandaccuracyforin-depthanalysis.
Spectral domain optical coherence tomography posed on fluorescein angiography,indocyanine
(SD-OCT) allows us to visualize cross-sectional,ante- green,andmicroperimetry.
rior segment,and three-dimensional (3-D) views of SpectraldomainOCTisareliableandsensitiveex-
the retina.This enables us to diagnose glaucoma and amination.Theimagesarereproducible.Scanacquisi-
retinal diseases and monitor treatment efficacy.The tion is rapid and simple,and does not require the ad-
data provided by SD-OCT are analogous to those ob- ministration of intravenous contrast media.In some
tained with ultrasound B examinations,but with cases,such as retinal edema follow-up,OCT may be
some notable advantages.For example,the resolu- preferabletofluoresceinangiography,whichisanin-
tion of ultrasound B is about 150 microns,while the vasivetestthatmayleadtocomplications.
resolution of time domain OCT is 10 microns,and
theresolutionofSD-OCTis5microns.
Retinal scans with SD-OCT are highly repro- OBTAININGOPTIMALOCTIMAGES
ducible.Afewtracepointsonthemarginoftheoptic
nerveortheretinalvasculatureallowtheregistration The most frequent impediments to acquiring
of one scan to another.In addition,the instrument is goodOCTimagesareocularmovement,mediaopaci-
easytooperate. ty, and an uncooperative patient.Images taken
Opticalcoherencetomographyallowsclinicalob- through miotic pupils are generally good.In rare cas-
servation, measurement,and identification of struc- es, dilation of the pupils is necessary.A normal
turesthatotherwisearenoteasilyvisible,suchasthe lacrimalfilmorgoodcornealhydrationwithartificial
external limiting membrane (ELM) and the junction tearsisnecessary.Althoughitispossibletoobtainim-
between the internal and external segment of the ages when early cataracts are present or when in-
photoreceptors (IS/OS junction).It also shows vari- traocularsiliconeoilispresent,theseconditionsmay
oustypesoflesionswithalteredmorphology,altered interfere with scan quality.The following tips may
reflectivity,and/or optically blank areas.OCT per- helpyouobtainoptimalOCTimages.
formsthefollowingfunctions:
•Measuresretinalthickness
•Measurestheretinalnervefiberlayer(RNFL) GENERAL
•Measuresthevolumeoftheretina
•Createsretinalthicknessmaps Corneal conditions can affect the clarity of an
•Isolatesandcreatesmapsoftheinternallimiting OCT image and,therefore,may interfere with accu-
membrane(ILM)andtheretinalpigmentepithe- rate interpretation.A dry eye,especially in the elder-
lium(RPE) ly, can lead to greatly compromised images.In these
•Measuresvariousparametersoftheopticdisc cases,it is best to instill artificial tears before the
•Displaysthree-dimensionalviews OCTexamination.
•Provides classic C-scan (en face) analyses,creat- Acquisitions with SD-OCT instruments can some-
inghorizontaltissuesections times produce artifacts.Artifacts are often caused by
•Offers an RPE-fit function,which provides a poor fixation or lack of cooperation by the patient,
viewofatissuesection. including excessive blinking.The patient should fix-
The images obtained can be analyzed,quantified, ateonthestimulus–acrossofgreensegmentssimi-
saved,compared with other results,and superim- lar to a star – in the interior of the instrument’s op-
9