This document provides a brief history and overview of optical coherence tomography (OCT). It discusses that OCT was first used to image the retina in 1991 with a resolution of 17 μm. Commercially available OCT systems emerged in 1996 and provided cross-sectional retinal images with 10 μm resolution. The document then outlines the development and advantages of newer spectral domain OCT technology, which offers higher resolution, faster scanning speeds, and 3D imaging capabilities compared to earlier time domain OCT. A variety of clinical applications of OCT are also reviewed.

1. A brief history of OCT
Nawat Watanachai
Sir Charles Gairdner Hospital
October 2007

3. OCT : Optical Coherence Tomography
1st OCT image of the retina
Resolution: 17 μm
depth ~1.5 mm into the
tissue
• Huang, Hee, Fujimoto, Puliafito 1991
• 1st in vivo retinal images at the MIT in 1993
• Commercially available in 1996
• Optical B-scans (Cross-sections)
• Resolution ~ 10 microns

4. BASIC OCT

5. Clinical Applications
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Visualization of vitreoretinal interface
Cross-sectional visualization retinal pathology
Nerve fiber layer analysis for glaucoma
Optic nerve head analysis for glaucoma
Other jobs eg. Anterior segment

6. Does OCT make a difference?
 Clinical Diagnosis/
Decision Making
 Medical Record/
Documentation
 Patient Education/
Satisfaction

7. Medical Proof
 OCT provides objective evidence for treatment
decisions, both to treat or not to treat, and of
response to treatment
 Examples:
CNV and AMD
 cystoid macular oedema
Macular hole
 retinal vein occlusion
PMF
 diabetic maculopathy
 Others eg fleck diseases

8. Time domain OCT
 Current clinical OCT devices utilize time domain
technology ---> limit in signal acquisition time
 700-900 nm*
Samples tissue with 1024 data points
over 2mm depth
 Z Dimension:

Takes a sample every 5-60 microns
apart, 128-512 scans
X-Y Dimension:

9. Time domain OCT : problems
 1 detector, Each A-scan requires the movement of
several mechanical parts
 Excellent image quality…if device and patient are
not moving

10. Time domain OCT : problems
 ~400 A-scan per sec
 take time to catch the image
 Can give poor image resolution
 No image registration --> not easily reproduce
 Error in both quantitative and qualitative
measurement in some situations

11. So, what are we looking for in the newer OCTs?
•
•
•
•
Higher resolution
Higher imaging speed
Image registration
Quantitative information
extraction

12. Newer OCTs
1. Spectral domain OCT -- available
2. Other OCTs
2.1 Ultrahigh resolution OCT
2.2 Adaptive optic OCT
2.3 Hybrid machines eg OCT/SLO, HRA/OCT
3. OCT for anterior segment

13. 1. Spectral domain OCT

14. 1. Spectral domain OCT
 High speed high resolution OCT
 Frequency swept light source at around 850-1040 nm
 Improved axial image resolutions (<6 microns axial
resolution appears possible)

15. 1. Spectral domain OCT
 The output is measured with
the use of a spectrometer
(may be > 2,000 detector
elements), doesn’t need
moving part during scanning
16,000-75,000 scan/sec
(TD-OCT ~400)

16. 1. Spectral domain OCT
 Real time display and data streaming capabilities
enable video-rate imaging at more than 30fps
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17. 1. Spectral domain OCT
 Can produce 3-D projection image which can be aligned
with the actual fundus image to provide pixel-to-pixel
registration
 3-D imaging produces layers of information
 Isolation of retinal layers makes image analysis possible
in a broad fashion
 3-D thickness map
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18. 1. Spectral domain OCT
 Pixel-to-pixel registration
 Precise scan location
 Image reproducibility
 Some machines can
generate fundus imaging
and register the spatial
location of each OCT
section image
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19. 1. Spectral domain OCT
 Pros
 Higher resolution/ 3D imaging
 Enhanced imaging speed
 Pinpoint registration
 Cons
 Signal strength and depth resolution is dependent on the
path difference between the retina and the reference mirror
--> the greater the distance (myopic eye), the weaker the
signal and the lower the resolution
 Yes………it’s price!

20. 2. Other OCTs
2.1 Ultrahigh resolution OCT
2.2 Adaptive optic OCT
2.3 Hybrid machines eg OCT/SLO,
HRA/OCT

21. 2.1 Ultra-high Resolution OCT
 First described by Drexler and Fujimoto in 2001
 Broad bandwidth, 150nm femtosecond Ti-sapphire
laser source (TD-OCT 10-25 nm)
 1-3 microns axial resolution
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22. 2.1 Ultra-high Resolution OCT
 Video-rate with up to 25-50 B-scans/sec
3,000 axial pixels and 600 transverse pixels (OCT-3
1,024 and 512 pixels)
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23. 2.1 Ultra-high Resolution OCT

24. 2.1 Ultra-high Resolution OCT
 Pros
 Enhanced anatomic
detail
 Enhanced
visualization of the
subretinal CNV
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25. 2.1 Ultra-high Resolution OCT
 Cons
 Slow acquisition time of 4-5 sec (OCT-3 can do
the job in 1.3 sec)
 Require significant technical support for day-today operation
 Limited ability to localize scans in relation to
precise fundus landmarks
 Alignment of serial scans dependent on fixation is
inaccurate

26. 2.2 Adaptive optic OCT
 Use electromagnetic deformable mirror (adaptive
optic) to improve the spatial resolution
 Correct chromatic aberration of the eye to get
better light pathway

27. 2.2 Adaptive Optic OCT
 Pixel resolution of 3µm x 3µm
 Very fine image : able to Imaging the retinal cells

28. 2.2 Adaptive optic OCT
 3D video
 Voxel resolution of 3µm x 3µm x 3 µm
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29. 2.3 OCT/SLO : multimodal imaging
 Introduced by
Podoleanu and Jackson
in 1998
 Employs OCT scan
simultaneous with
confocal SLO images
 SLO = surface detail
 OCT = internal detail

30. 2.3 OCT/SLO : multimodal imaging
 Single illumination source with parallel detector
systems ensures pixel-to-pixel correlation between
views
 Overlay capability permits view of internal anatomy
beneath surface landmarks
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Cinepak decompressor
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31. 2.3 OCT/SLO : multimodal imaging
 Coronal OCT scans capture details often lost in
fixation-driven B scanning
 SLO channel facilitates integration of functional
testing such as angiography, microperimetry, and
mfERG

32. 2.3 OCT/SLO
TD-OCT
OCT/SLO

33. Matching C-Scan Images
Provide Linear Reference

34. 2.3 OCT/HRA
 OCT + laser angiography
 Image registration --> precisely define the scan
location -->good for repeat measurement
 Record fundus image in the same time

35. 2.3 other multimodaling machines
 Ultra-high Resolution OCT/SLO
 Combined Spectral Domain/ Time Domain HighResolution OCT/SLO

36. Will you own this machine?
 Keeps in mind
 OCT has become gold standard for some diseases
eg. PMF, MH
 Non invasive
 limitation
 OCT does NOT provide dynamic information (FA
does)
 Depend on operator techniques
 Degraded in the presence of media opacity
 Computer can do wrong things

37. Which OCT is ‘the one’ for you?
devices
B-scan/ 3D
Axial
resolution
Scanning
speed
Non-OCT
imaging
(TD-OCT)
Yes/no
10
400
Near IR
Heidelberg
Spectralis
HRA/OCT
Yes/yes
7
40,000
SLO, ICG, autoF
Optopol Copernicus
2
Yes/yes
6
25,000
Near IR
Optovue RTVue1001
Yes/yes
5
26,000
Near IR
OTI OCT/SLO1
Yes/yes
5
28,000
SLO, ICG,
microperimetry
Topcon 3D-OCT10002
Yes/yes
6
18,000
Near IR/ color
Carl Zeiss Meditec
Cirrus1
Yes/yes
5
27,000
LSLO

38. Which OCT is ‘the one’ for you?
 Time domain OCT (~60,000+ AUD)
 Spectral domain OCT (>100,000 AUD)
 Researchers
 Retinal specialists who can use this
images to help with decision making in
selected difficult cases

39. Thank you