2. Presentation layout
1. Instrumentation
2. Different types of oct
3. Indication of oct
4. Procedures For Performing OCT
5. Interpretation of oct
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3. Introduction
Optical coherence tomography (OCT) is a 3-D imaging technique
that can provide high resolution (up to few micrometers) and
deep penetration(up to few millimeters) in a scattering media.
OCT technology is based on the principle of low coherence
interferometry.
The interference pattern are used to reconstruct an axial A-scan
and with compilation of A-scans, a two-dimensional cross section
image of the target tissue can be reconstructed and this is known
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4. OCT Introduction Cont’d
Typically OCT instruments use an infrared light centered at a
wavelength of about 840nm.
The latest commercial instruments typically have an axial
resolution of approximately 5 micrometer, while research
instrument have been built with a resolution as high as
approximately 2 micrometer.
The lateral resolution is limited by the diffraction caused by pupil
and it is normally 20 micrometer.
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5. Time-domain OCT
It uses low coherence light from a super luminescent diode.
The light is fed into a fine optics coupler that splits the light
beam into two arms (paths), one directed at the sample surface,
the other at a scanning reference mirrors.
The detector then capture the interference of light rays reflected
back these two arms.
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6. Time-domain OCT Cont’d…
Constructive interference is observed as an intensity
maximum when the optical paths of both arms are exactly
equal.
By scanning the length of the reference arm to bring forth
the appearance of interference signals, the detector
determines the precise position of the reflection point in the
sample.
Example-Stratus OCT, Carl Zeiss Meditec.
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7. Fourier Domain OCT
It uses light from a fast sweeping laser source instead of
super luminescent diode.
The reference mirror is fixed.
The detector capture the spectrum of the interference
pattern in time domain and then convert this spectrum to
time domain using Fourier transformation.
Other type include High-definition OCT.
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9. Advantage of Fourier OCT over Time-domain OCT
Scanning speed with SD-OCT instrument can exceed 100000
A-scan per second, about 200 times faster than TD-OCT.
With the recent development of high speed SD-OCT been
introduced based on acquiring three-dimensional datasets
and B-scan averaging.
Three-dimensional datasets are obtained using a dense two-
dimensional raster array over a relatively large retinal region.
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11. Advantage of Fourier OCT Over Time-domain
OCT cont’d…
The resulting datasets can be rendered as a volume image in
three dimensional and can be analyzed by showing two-
dimensions slices(i.e., sequence of parallel B-scans)
Three dimensional datasets give detailed information about
the retinal structure over the large area.
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12. Advantage of Fourier OCT Over Time-domain
OCT cont’d…
It is possible to generate en face fundus-like images directly
from the OCT datasets.
Exact correlation can be achieved between the retinal cross-
sectional geometry seen on the oct B-scan and retinal
landmarks seen on en face images, known as the OFI (OCT
fundus imaging).
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13. Commercially Available SD-0CT Instruments
Device
(manufacturer)
Axial resolution
(micrometre) ;
Scanning rate (KHz)
Special characteristics
3D-OCT 2000
(Topcon, Tokyo, Japan)
5; 27 Fundus camera
Bioptigen SD-OCT
(Bioptigen, Research Triangle park, NC)
4; 20 Designed for research application
Cirrus HD-OCT
(Carl Zeiss Meditec, Dublin, CA)
5; 27
RTVue-100
(Optopol, Zawiercie, Poland)
5; 26
SOCT Copernicus
(Optopol, Zawiercie, Poland)
6; 27
Spectral OCT SLO
(Opko, Miami, FL)
6; 27 Microperimetry
Spectarilis OCT
(Heidelberg engineering, Heidelberg Germany)
8; 40 Eye-tracking, FA, ICG angiography,
autofluorescence
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14. Indication Of OCT
1. To examine the retinal layer
2. Monitor progression
3. Treatment planning
4. Monitor response to therapy
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15. Interpretation Of Retinal Scan
COLOUR CODING
Highly reflective structure are shown in bright colours (white
and red).
Intermediate reflectivity is shown in green .
Low reflectivity is shown by dark colours( black and blue)
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31. Interpretation Of Imaging Data From Cirus HD-OCT
COLOUR CODE SCHEME IN CIRUS HD-OCT
COLOUR CODE A:
colour code A is used in RNFL thickness map(3) according to
the scale on the left side of the map(range: 0-350
micrometer, colour range: blue-white).
Cold colour(blue, green), represent thinner RNFL, and
Warm colour(yellow, red) represent region with thicker RNFL.
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32. COLOUR CODE SCHEME IN CIRUS HD-OCT Cont’d…
Color code B:
Color coded B is used in the key parameter table(2), RNFL
thickness TSNIT plot(4), RNFL deviation map(5), RNFL thickness
TSNIT plot(6),RNFL quadrant and clock hour graphs(7).
Measurements that are beyond the range of normative data
base are shaded grey.
Measurement that fall within the thickest 5% of the normal
measurement are displayed as white;
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33. COLOUR CODE SCHEME IN CIRUS HD-OCT Cont’d…
Those within 5-95% prediction limit are represented as
Green(normal);
Thickness measurement that fall between 1-5% of the prediction
limits of the normative database are considered borderline
abnormal and marked in yellow;
Measurement displayed in red are considered outside normal
limit and have thickness value below the thinnest 1% of
normative database measurement.
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34. COLOUR CODE SCHEME IN CIRUS HD-OCT Cont’d…
Color code C:
It is used in extracted horizontal and vertical ONH
tomograms(8) and the circular RNFL tomogram(9).
It is the false colour code scheme based on reflectance of
tissue layers.
The hot colour(red, yellow) represent layers with high
reflectance and the cold colour(blue-black) represents layer
with lower reflectivity.
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35. Section Of The Print Out
1. Patient Data And Signal Strength:
2. Key Parameter Table
3. RNFL Thickness Map
4. Neuro-retinal Rim Thickness Plot
5. RNFL Deviation Map
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36. Section Of The Print Out
6. RNFL Thickness TSNIT Plot
7. RNFL Quadrant And RNFL Clock-hour Thickness
Measurement
8. Extracted Vertical And Horizontal Tomograms
9. RNFL Circular Tomogram
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38. Sections of the printout
1. Patient Data And Signal Strength:
2. Thickness Map:
3. Deviation Map:
4. The Sector Map:
5. Thickness Table:
6. Horizontal Tomogram Of The Macula:
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44. References:
1. Page 2 through 13 (Optical Coherence Tomography-Carlos
Alexandre de Amorim Garcia Filho, Zohar Yehoshua,
Giovanni Gregori, Carmen A. Puliafito, Philip J. Rosenfeld)
2. Page 16, 22 and 23 ( A Handbook Of OCT)
3. Page 31 through 38 (Optical Coherence Tomography In
Glaucoma By Ahmet Akman)
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