Fourier Domain OCT: The RTVue

Michael J. Sinai, PhDDirector of Clinical Affairs

Optovue, Inc.

Rise of Structural Assessment with Scanning Lasers

• Scanning lasers provide objective and quantitative information for numerous ocular pathologies

• First appeared over 20 years ago as a research tool

• Today, structural assessment with retinal imaging devices has become an indispensable tool for clinicians

Role of imaging in clinical practice

• AAO preferred practice patterns recommends using scanning laser imaging in routine clinical exams

• In glaucoma, studies show imaging results can be as good as expert grading of high quality stereo-photographs1

• Pre-perimetric glaucoma is now commonly accepted• In OHTS, most converted based on structural assessment

only (not fields) 2

• OHTS has shown that imaging results have a high positive and negative predictive power for detecting glaucoma 3

1. Wollstein et al. Ophthalmology 2000 2. Kass et al. Arch Ophthalmol 2001 3. Zangwill LM, Weinreb RN, et al. Archives of Ophthalmol. 2005.

3 Imaging technologies have been shown to be effective in detecting and

managing ocular pathologies

• Scanning Laser Polarimetry (SLP)

• Confocal Scanning Laser Ophthalmoscopy (CSLO)

• Optical Coherence Tomography (OCT)

Retardation

Light Polarizer

Two polarized componentsBirefringent structure

(RNFL)

SLP – GDx VCCStrengths• Provides RNFL thickness• Large database• Easy to use/interpret (deviation map/automated classifier)• Progression

Weaknesses• Atypical Pattern Birefringence (RNFL artifact)1

• Converts retardation to thickness assuming uniform birefringence (not true) 2

• Only RNFL information (No Optic Disc info and no Retina info)• Data not backwards compatible

Normal Glaucoma Atypical

1. Bagga, Greenfield, Feuer. AJO, 2005: 139: 437.2. Huang, Bagga, Greenfield, Knighton IOVS, 2004: 45: 3037.

CSLO – HRT 3Strengths• Provides Optic Disc morphology• Sophisticated Progression Analysis• Large ethnic Specific Database comparisons• Automated classifier• Data backwards compatible• Some retinal capabilities• Cornea microscope attachment

Weaknesses• Only Optic Disc assessment (poor RNFL)• Manual Contour Line drawing• Reference plane based on surface height (can change)• Retina analysis confined to edema detection and sensitive to image quality• Cornea scans very difficult and impractical

OCT – Time Domain (Stratus from CZM and SLO/OCT from OTI)

Strengths• Provides Cross Sectional images• Useful to calculate RNFL thickness• Cross section scans useful for retinal pathologies• Database comparisons

Weaknesses• Slow scan speed (400 A scans / second)• Limited data for glaucoma, 768 pixel (A-scan) ring for RNFL• Limited data for retina, 6 radial lines with 128 A scans (pixels) each• Macula maps 97% interpolated• No progression analysis• Location of scan ring affects RNFL results• Prone to motion artifacts because of slow scan speed• Poor optic disc measurements

Time Domain OCT susceptible to eye movements

1. Koozekanani, Boyer and Roberts. “Tracking the Optic Nervehead in OCT Video Using Dual Eigenspaces and an Adaptive Vascular Distribution Model”; IEEE Transactions on Medical Imaging, Vol. 22, No. 12, 2003

• 768 pixels (A-scans) captured in 1.92 seconds is slower than eye movements

• Stabilizing the retina reveals true scan path (white circles)1

Scan location and eye movements affects results

T S N I T T S N I T T S N I T

Properly centered

Normal Double Hump

Poorly centered: too inferior Poorly centered: too superior

Inferior RNFL “Loss” Superior RNFL “Loss”

Time Domain OCT artifacts can be common

1. Sadda, Wu, et al. Ophthalmology 2006;113:285-2932. Ray, Stinnett, Jaffe . Am J Ophth 2005; 139:18-293. Bartsch, Gong, et al. Proc. of SPIE Vol. 5370; 2140-2151

The Future of OCT• RTVue Fourier Domain OCT overcomes limitations of

Time Domain OCT Devices– Better resolution (5 micron VS 10 micron)– Faster scan speeds (26,000 A scans / sec VS 400) – 3-D data sets (won’t miss pathology)– Large data maps (less interpolation)– Progression capabilities– Layer by layer assessment– Versatility (Anterior Chamber Imaging)

Retina Glaucoma Anterior Chamber

The Evolution of OCT Technology

Zeiss OCT 1 and 2, 1996

Zeiss Stratus 2002

RTVue

200626,000

400

100

16 10 5

Speed(A-scansper sec)

Depth Resolution (mm)

Fourier domain OCTTime domain OCT

• ~ 65 x faster• ~ 2 x resolution

7

40,000

20,000

Comparison of OCT Images

1996

2002

2006

OCT 1 / 2(Time Domain)

Stratus OCT(Time Domain)

RTVue(Fourier Domain)

Case 1: AMD

Stratus(Time Domain)

RTVue (Fourier Domain)

Drusen not visible in Stratus Time Domain OCT

Case 2: DME

Stratus(Time Domain)

RTVue (Fourier Domain)

Case 3: PED

Stratus(Time Domain)

RTVue (Fourier Domain)

Same eye, PED missed by Stratus

Case 4: Macula HoleStratus

(Time Domain)RTVue

(Fourier Domain)

Fourier Domain• Entire A scan generated at once based on Fourier transform of spectrometer analysis • Stationary reference mirror• 26,000 A scans per second• 5 micron depth resolution• B scan (1024 A-scans) in 0.04 sec• Faster than eye movements

Time Domain OCT vs Fourier Domain OCT

Time Domain

• A-scan generated sequentially one pixel at a time in depth • Moving reference mirror• 400 A scans per second• 10 micron depth resolution• B scan (512 A scans) in 1.28 sec• Slower than eye movements

Summary of Fourier Domain OCT Advantages

• High speed reduces eye motion artifacts present in time domain OCT

• High resolution provides precise detail, allows more structures to visualized

• Layer by layer assessment

• Larger scanning areas allow data rich maps & accurate registration for change analysis

• 3-D scanning improves clinical utility

RTVue Clinical Applications

GlaucomaRetina Anterior Chamber

Retina Analysis with the RTVue: Line ScansLine Scan

• Data Captured: 1024 A scans (pixels)• Time: 39 msec• Area covered: 6 mm line (adjustable 2-12 mm)

Provides •High resolution B scan•Image averaging increases S/N

• Data Captured: 2048 A scans (pixels)• Time: 78 msec• Area covered: 2 x 6 mm lines (adjustable 2-12 mm)

Provides • vertical and horizontal high resolution B scan•Image averaging increases S/N

Cross Line Scan

Courtesy: Michael Turano, CRAColumbia University.

Line Scan: Cystoid Macula Edema

Courtesy: Michael Turano, CRAColumbia University.

Retina Analysis with the RTVue: 3-D Scans

• Data Captured: 51,712 A scans (pixels)• Time: 2 seconds• Area covered: 4 x 4 X 2 mm (adjustable)• 101 B scans each 512 A scans

Provides•3 D map• Comprehensive assessment• Fly through review• C scan view• SLO OCT image simultaneously captured

3-D view reveals extent of damage over large area

Top Image: En face view of retinal surface from 3-D scanBottom Image: B scan from corresponding location (green line)

Full retinal thickness

• Layer specific thickness maps• Detailed B scans• ETDRS thickness grid

Outer retinal thickness

RPE/Choroid Elevation

• Data Captured: 19,496 A scans (pixels)• Time: 750 msec• Area covered: 5 mm x 5 mm (grid pattern)

Inner retinal thickness

ILM to RPE ILM to IPL IPL to RPE RPE height

Surface TopographyILM height

Provides:

Retina Analysis with the RTVue: Macula Maps (MM5)

Glaucoma Analysis with the RTVue: Nerve Head Map

Provides • Cup Area• Rim Area• RNFL Map

TSNIT graph

16 sector analysis compares sector values to normative database and color codes result based on probability values (p values)

Color shaded regions represent normative database ranges based on p-values

Glaucoma Analysis with the RTVue: Nerve Head Map Parameters

RNFL Parameters

All parameters color-coded based on comparison to normative database

Optic Disc Parameters

Glaucoma Analysis with the RTVue: Nerve Head MapNerve Head Map (NHM) Ganglion Cell Map (MM7) 3-D Optic Disc

• Data Captured: 9,510 A scans (pixels)• Time: 370 msec• Area covered: 4 mm diameter circle Provides

•Cup Area• Rim Area• RNFL Map

• Data Captured: 14,810 A scans (pixels)• Time: 570 msec• Area covered: 7 x 7 mm

Provides• Ganglion cell complex assessment in macula• Inner retina thickness is:

• NFL• Ganglion cell body• Dendrites

• Data Captured: 51,712 A scans (pixels)• Time: 2 seconds• Area covered: 4 x 4 X 2 mm

Provides•3 D map• Comprehensive assessment

TSNIT graph

The ganglion cell complex (ILM – IPL)

Inner retinal layers provide complete Ganglion cell assessment:• Nerve fiber layer (g-cell axons)• Ganglion cell layer (g-cell body)• Inner plexiform layer (g-cell dendrites)

Images courtesy of Dr. Ou Tan, USC

Normal vs Glaucoma

Normal Glaucoma

CupRim

RNFL

Ganglion cell assessment with inner retinal layer map

NHM4

GCC

Glaucoma Cases

Optovue, RTVue

Glaucoma Patient Case BK 64 year oldwhite male

24-2 white on white visual field Nerve Head Map on RTVue

Normal

Glaucoma Patient Case BK

10-2 white on white visual field

Macula Inner Retina Map on RTVue

Normal

RTVue Normative Database

34

• Age Adjusted comparisons for more accurate comparisons

• Age and Optic Disc adjusted comparisons for Nerve Head Map scans

• Over 300 eyes, ethnically mixed, collected at 8 clinical sites worldwide

• IRB approved study from independent agency

Nerve Head Map (NHM4)with Database comparisons

Patient Information

RNFL Thickness Map

RNFL Sector Analysis

Optic Disc Analysis

Parameter Tables

TSNIT graph

Asymmetry Analysis

Ganglion Cell Complex (GCC)with Database comparisons

Patient Information

GCC Thickness Map

Deviation Map

Parameter Table

Significance Map

Early Glaucoma

OS Normal

Borderline Sector results in Superior-temporal region

Abnormal parameters

TSNIT dips below normal

TSNIT shows significant Asymmetry

GCC Analysis may detect damage before RNFL

GCC and RNFL analysis will be correlated, however GCC analysis may be more sensitive

for detecting early damage

Glaucoma Progression Analysis(Nerve Head Map of stable eye)

Thickness Maps

Change in optic disc parameters

TSNIT graph comparisons

RNFL trend analysis

Change in RNFL

parameters

Glaucoma Progression Analysis(GCC of stable glaucomatous eye)

Thickness Maps

Deviation Maps

GCC parameter change analysis

Significance Maps

Versatility: Scanning the Anterior Chamber with the same device

Cornea Adapter Module

(CAM)

Higher resolution allows better visualization of LASIK flap

2 years after LASIK with mechanical microkeratomeImage enhanced by frame averaging

Post-LASIK interface fluid & epithelial ingrowth

100 200 300 400 500 600 700 800 900 1000

50

100

150

200

250

300

350

400

450

500

056-CP

Fibrosis

Epithelial ingrowthFluid

Higher resolution helps visualize pathogens

Acanthamoeba in 0.25% agar

Pachymetry Maps

Inferotemporal thinning

Normal Keratoconus

Angle Measurements

Normal Narrow

Narrow angle after peripheral iridotomy LD044, OS

Angle Opening Distance 500 m anterior to scleral spur

(AOD 500)Scleral spur

Limbus

Normal AngleMaTa, OD

Trabecular meshwork-Iris Space 750 m anterior to scleral spur

(TISA750)

Scleral spur

Limbus

Advantages of the RTVue• 5 micron resolution allows more structures and detail

to be visualized• High speed allows larger areas to be scanned• Layer by layer assessment• Data-rich maps• Volumetric analysis• Comprehensive glaucoma assessment (Cup, Rim, RNFL,

ganglion cell complex)• Normative Database• Progression Analysis• Anterior Chamber imaging

Thank You!