fourier domain oct: the rtvue michael j. sinai, phd director of clinical affairs optovue, inc
TRANSCRIPT
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!