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What’s New in Optic Nerve What’s New in Optic Nerve ImagingImaging

H. George Tanaka, MD

Glaucoma Progression:Glaucoma Progression:Structure vs. FunctionStructure vs. Function

normal

pathological

time

optic nerve

visual field

pre-perimetric

“glaucoma suspect”

perimetric

“glaucoma”

ocular hypertension

normal

abnormal

borderline

time

normal

abnormal

optic nerve

A

Make Definitive Diagnosis at AMake Definitive Diagnosis at A

“Doctor, do I have glaucoma?”

time

B

ORORDocument Progression at BDocument Progression at B

normal

abnormal

optic nerve

A

Make Definitive Diagnosis at AMake Definitive Diagnosis at A

CHANGE = A - B

“Doctor, am I getting worse?”

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What’s OLD in Optic nerve imagingWhat’s OLD in Optic nerve imaging

Scanning Laser Tomography (HRT)Scanning Laser Tomography (HRT)(Heidelberg Engineering, Heidelberg, Germany)(Heidelberg Engineering, Heidelberg, Germany)

Scanning Laser Scanning Laser PolarimetryPolarimetry ((GDxGDx®))((Carl Carl ZeissZeiss MeditecMeditec , Jena, Germany, Jena, Germany ))

TimeTime --DomainDomainOptical Coherence Tomography (OCT)Optical Coherence Tomography (OCT)((Carl Carl ZeissZeiss MeditecMeditec , Jena, Germany, Jena, Germany ))

Cross sectional imaging

Optical Coherence Tomography

Source

Reference Mirror

BeamSplitter

Detector

Sample

Time Domain OCT (OCT3)

Axial (Z)Scanning

Lateral (X-Y)Scanning

OCT Signal

Optic Nerve Head Analysis

Topography (interpolated)

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Green = Within normal limits

Yellow = Borderline

Red = Outside normal limits

Nerve Fiber LayerThickness Normative Database

OCT RNFL scan circle misalignment

Inferior NFL increased Scan circle too HIGH

Vizzeri et. al., Journal of Glaucoma 2008; 17:341-349

Progression plot WhatWhat ’’s New in Optic Nerve Imaging:s New in Optic Nerve Imaging:

Spectral Domain OCTSpectral Domain OCT

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time

ampl

itude

Time DomainTime DomainSignal amplitude varies with timeSignal amplitude varies with time

time

ampl

itude

Time Time DomainDomain

frequency

ampl

itude

Frequency A = 1/t

A

Frequency Frequency DomainDomain

t

time

ampl

itude

frequency

ampl

itude

Frequency A

A

Frequency B

B

Time Time DomainDomain

Frequency Frequency DomainDomain

time

ampl

itude

frequency

ampl

itude

AB CD

Frequency AFrequency BFrequency CFrequency D

Time Time DomainDomain

Frequency Frequency DomainDomain

5

time

ampl

itude

frequencyAB CD

Time Time DomainDomain

Frequency Frequency DomainDomain

FourierFourierTransformTransform

Source

Reference Mirror

BeamSplitter Sample

(Fourier transform)

Spectrometer

Spectral Domain OCT

OCT Signal

Spectral Domain OCT Advantages of Spectral Domain OCTAdvantages of Spectral Domain OCT

• More scans in less time– 20,000 to 40,000 A-scans per second

• Better resolution– 5 micron

• Less motion artifact – Blinking, saccades, fixation losses

• 3D scans = cube of data

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Comparison of ModelsModel Scanning speed

(A scans/sec)Axial Resolution

3-DBscan

Fundusimaging, misc

Cirrus 27,000 5 microns Yes SLO

Optovue 26,000 5 microns Yes Near IRnon-mydAS OCT

Spectralis 40,000 7 microns Yes SLO,FA, ICG, autofluo, IR

Stratus OCT3

400 10 microns No No

Stratus OCT

Cirrus HD -OCT

OCT 2

Glaucomatous damage occurs at 3 levels in the posterior segment

Ganglion cells

(Cell body)

Highest concentration

in the macula

Retinal nerve fiber layer (Axon)

Optic nerve head(Axon + connective

tissue)

Ganglion cell complex (GCC) scan Nerve fiber layer + Ganglion Cell layer + inner plexiform layer

RTVue

SD OCT allows us to scan the macula for glaucoma

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Cirrus™ HD-OCTCarl-Zeiss Meditec (Dublin, CA)

www.meditec.zeiss.com

• Scan type – Optic disc cube 200 x 200 scan

– 200 line scans each consisting of 200 A scans each

– Covers 6 mm2 area

RNFL analysis with SDOCT

• TSNIT graph based on circle scan 3.45 in diameter centered on optic disc – Unlike TDOCT, centration of

TSNIT circle can be performed post-scan acquisition with SDOCT

• RNFL maps with comparison to normative database

CirrusNormal ODEarly glaucoma OS

CirrusNormal ODEarly glaucoma OS

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CirrusAdvanced glaucoma OS

StratusAdvanced glaucoma OS

Optovue RTVue™(Fremont, CA)

www.optovue.com

• Scan types– 3D Disk (covers 4mm2 area)– ONH (Grid pattern with circular

and radial scans)

– GCC (Ganglion cell complex scan, covers 7mm2 area

Glaucoma suspectDisc and cups areasymmetricalNormal NFL and GCC

OD shows superiorNFL loss

OS normal

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OD and OS bothShow severe NFLloss

High myopeWith tilted discsUnable to analyzeoptic disc OD but GCC normal

SpectralisHeidelberg Engineering (Heidelberg, Germany)

www.heidelbergengineering.com

• Unique features– Eye tracking technology– Image noise reduction– Can add capability for FA, ICGA, red

free & infrared imaging, autofluorescence

Stratus 3 Spectralis

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RNFL Circle Scan / RNFL Progression Normal Images and Thickness Map

RNFL fibers canbe seen following the blood vessel arcades on the infrared image.

The OCT scan shows a normal

distribution of RNFL thickness around

the ONH

Posterior Pole thickness map shows thicker areas (white and

red) along the blood vessel arcades and around the macula.

(The ganglion cell complex (GCC) is

typically thicker around the macula.)

Case 1 – Loss visible on multiple tests

Fundus photo has a clearly defined wedge of RNFL loss

Both the RNFL - OCT and the visual field confirm this RNFL loss superior to the ONH

Retinal thickness map correlates with other tests showing a wedge shaped thickness loss

Case 2 – Thinning beyond circle scan

The wedge defect is not very wide at the circle scan location and is not easily seen in the RNFL – OCT thickness graph

The infrared image shows a darker wedge defect in the inferior temporal area

The posterior pole thickness map shows asymmetrical thinning in this inferior temporal area

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Case 3 – Thickness Map Confirmation

The RNFL - OCT shows thinning in the inferior temporal area on the thickness graph but the defect is not significant enough to trigger the sector classification

The posterior pole thickness map shows a clearly defined area of thinning in this inferior temporal area and thinning around the macula is not picked up by the other tests.

The infrared image shows a hint of discoloration, but does not clearly indicate thinning.

New Reports – RNFL & Post. Pole

New reports – Asymmetry OU

Yes

Yes

Yes

Normative database

YesNoNoYesSpectralis

YesYesYesYesOptovue

YesNoNoYesCirrus

ProgressionOptic disc

Macular Inner Retinal Layer

RNFL(TSNIT/Map)

Glaucoma analysis

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Conclusions•• HighHigh --tech imaging enhances tech imaging enhances but does not replacebut does not replace

good clinical skills in diagnosing glaucomagood clinical skills in diagnosing glaucoma•• Potentially useful in following optic nerve Potentially useful in following optic nerve

progression in early glaucomaprogression in early glaucoma•• AIGS (Advanced Imaging in Glaucoma Study)AIGS (Advanced Imaging in Glaucoma Study)

•• HRT2, HRT2, GDxGDx, OCT3, , OCT3, OptovueOptovue•• www.AIGStudy.netwww.AIGStudy.net

Conclusions

• Do not base treatment decisions on a single imaging study

• Interpret imaging data in a clinical context

• Reliable criteria for progression are lacking

• Prospective validation is needed

Technology progresses faster than most optic nerves.

Has Optic Nerve Imaging Made Has Optic Nerve Imaging Made Stereo Disc Photography Stereo Disc Photography

Obsolete?Obsolete?

Not yet.