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1. OPTICAL COHERENCE
TOMOGRAPHY
Group:48
Solanki Ujjval

2. PRESENTATION
LAYOUT
Introduction
Principles
Types
Interpretation
Clinical Applications
Limitations & Advantages
Latest Developments

3. INTRODUCTION
Optical coherence tomography, or OCT is a non-
contact, noninvasive imaging technique used to
obtain high resolution 10 micro cross sectional images
of the retina and anterior segment.
Reflected light is used instead of sound waves.
Infrared ray of 830 nm with 78D internal lens.

4. OPTICAL COHERENCE
TOMOGRAPHY
Optical Coherence Tomography, or OCT, is a
noncontact, noninvasive imaging technique used to
obtain high resolution cross-sectional images of the
retina and anterior segment.
Three-dimensional imaging technique with ultrahigh
spatial resolution
Measures reflected light from tissue discontinuities
Based on interferometry
.

5. Analog to
ultrasound

6. PRINCIPLE
OCT images obtained by measuring
 echo time
 intensity of reflected light
Effectively ‘optical ultrasound’
Optical properties of ocular tissues, not a true
histological section

7. Laser output from OCT is low, using a near-infra-red
broadband light source
Measures backscattered or back-reflected light
Source of light: 830nm diode laser
1310 nm : AS-OCT

9. Light from Reference arm &
Sample arm combined
Division of the signal by
wavelength
Analysis of signal
Interference pattern
A-scan created for
each point
B-Scan created
by combining A-scans

11. Digital processing aligns the A-scan to correct for eye
motion.
 Digital smoothing techniques further improves the signal
to noise ratio.
The small faint bluish dots in the pre-retinal space is noise
This is an electronic aberration created by increasing the sensitivity
of the instrument to better visualize low reflective structures

12. COLOR CODING IN OCT
 Highly reflective structures are shown in bright colures (white and red) .
 Those with low reflectivity are represented by dark colours (black and blue).
 Intermediate reflectivity is shown Green.

13. Advantages
 Non-invasive
Non-contact
 Minimal cooperation
needed
 Resolution ~ 10 μm
 Pick up earliest signs
of disease
 Quantitatively monitor
disease/staging
Disadvantages
 Best for optically
transparent tissues
 Diminished
penetration through
 Retinal/subretinal
hemorrhage
 Requires pupil
diameter > 4 mm
OCT

14. RESOLUTION OF AN
OCT
 Axial resolution
-Wavelength and
-Bandwidth of the light source
Long wavelength - visualisation of choroid,
laminar pores, etc
 Transverse resolution
•Based on spacing of A-scans
•Limited by optics of eye and
media opacity

15. Speed of acquisition
Faster acquisition speed in the newer generation OCT
 Increased signal-noise ratio
 Reduced motion artifacts
Spectral domain OCT :1-15 µm axial resolution &
Up to 52,000 A-scans/sec

16. 1. Time domain-
OCT
Types of
OCT

17. 2.
Spectral Domain
OCT

18. Spectral-domain OCTs: –
Spectralis (Heidelberg)
Cirrus (Zeiss)
RTVue (Optovue)
Optovue and Cirrus : Anterior eye imaging
capabilities in addition to posterior eye
Spectralis : Require special lens and anterior segment
module for anterior eye imaging

19. SCANNING TIPS
1. Communicate with the doctor regarding the size and
location of the pathology of interest.
2. Refer to other images of the pathology, e.g. color
photos and FA.
3. Review past OCT exams and repeat scan types used
before.
4. Dilate the eye well.
5. The patient must keep the forehead against the bar
and the chin in the chinrest, with teeth together. Use
the marker on the headrest to align the patient
vertically. The outer canthus should be even with the
line.

20. 6.Use the two buttons near the joystick for freezing and
saving scans. This saves you from having to juggle the
joystick and the mouse.
7.Minimize patient fatigue by keeping scan time to
a minimum. Never scan an eye for more than
10 minutes (FDA regulation).
8.Keep the cornea lubricated. Use artificial tears
and have the patient blink when you are not
saving a scan pass.
9.Move the instrument on the x and y axis (using
the joystick) to work around opacities.

21. INTERPRETATION &
CLINICAL APPLICATIONS
1. SPECTRALIS-Anterior Segment
Module
2. OCT – Posterior Segment Module

22. SPECTRALIS-ANTERIOR SEGMENT
MODULE
New dimension to anterior segment imaging
Cornea
Angle structure
Iris details
Consists of Add-on lens and dedicated software
Compatible with all SPECTRALIS SD-OCT models

23. A study comparing AS-OCT with Goniscopy
 AS-OCT detected more closed angles than gonioscopy
Disparity to attributed
 Possible distortion of the anterior segment by contact
gonioscopy
 Differences in illumination

24. ANTERIOR SEGMENT
OPTICAL COHERENCE
TOMOGRAPHY (OCT)
•High-speed anterior segment optical
coherence tomography (OCT) offers a non-
contact method for high resolution cross-
sectional and three-dimensional imaging of the
cornea and the anterior segment of the eye.
•Anterior Segment Optical Coherence Tomography
enhances surgical planning and postoperative care for a
variety of anterior segment applications by expertly
explaining how abnormalities in the anterior chamber
angle, cornea, iris, and lens can be identified and
evaluated

25. ON THE LEADING EDGE OF
ANTERIOR SEGMENT
IMAGING:
 Mapping of corneal thickness and keratoconus
evaluation
 Measurement of LASIK flap and stromal bed thickness
 Visualization and measurement of anterior chamber
angle and diagnosis of narrow angle glaucoma
 Measuring the dimensions of the anterior chamber and
assessing the fit of intraocular lens implants
 Visualizing and measuring the results of corneal
implants and lamellar procedures
 Imaging through corneal opacity to see internal eye
structures

26. IMAGE SHOWS AN ANTERIOR-
CHAMBER ANGLE AS VIEWED WITH
GONIOSCOPY AND THE OCT
The latter replaces subjective evaluation with
objective measurement.

27. A NARROW ANGLE IS APPARENT WITH OCT
IMAGING, IN THIS CASE 9.5°.

28. With the increase in popularity of anterior
chamber imaging, and anterior segment OCT
proving to be the best tool for high resolution
biometry, Anterior Segment Optical
Coherence Tomography is a must-have for
anterior segment, refractive, cornea, and
glaucoma surgeons.

29. OCT – POSTERIOR SEGMENT
MODULE
Glaucoma
ONH analysis
Retina
Choroid

30. GLAUCOMA
Diagnosis of glaucoma difficult in early stage
 Infrequency of episodes of rise in the IOP
 Visual field tests not being sensitive enough
Glaucoma diagnosis traditionally performed by
examining
 optic nerve cupping
 width of the neuroretinal rim

31. Limitations of Visual Field Tests:
Visual field loss late clinical findings
Detected only after significant loss of retinal nerve
fibers
Difficult to differentiate early glaucoma from normal

32. POSTERIOR POLE ASYMMETRY ANALYSIS
 Combines mapping of the posterior pole retinal
thickness with asymmetry analysis
 Both eyes
 Hemispheres of each eye

33. RETINA
OCT image display,
 Highest reflectivity - red
 nerve fiber layer
 retinal pigment epithelium
and
 choriocapillaris
 Minimal reflectivity appear blue
or black
 photoreceptor layer
 choroid
 vitreous fluid or blood

35. GANGLION CELL COMPLEX
Collective term
 RNFL
 Ganglion cell layer and
 Inner plexiform layer
GCC thought to be affected in early glaucoma

36. HYPER REFLECTIVE SCANS
RNFL
ILM, RPE
RPE-
choriocapillaries
complex
PED
Drusen , ARMD
CNVM lesions
Anterior face of
hemorrhage
Disciform scars
Hard Exudates
Epiretinal
membrane

37. PED

38. Drusen of the
Retina

40. DISCIFORM SCAR

41. HYPO REFLECTIVE SCANS
Retinal atrophy
Intraretinal/subretinal fluid

43. Regions:
The Pre-retina
The Epi-retina
The Intra-retina
The Sub-retina

44. A normal pre-retinal profile is black space
Normal vitreous space is translucent
The small, faint bluish dots in the pre retinal space is
noise
This is an electronic alteration created by increasing the
sensitivity of the instrument to better visualize low
reflection structures

45. Anomalous structures in Pre-retinal area:
Pre-retinal membrane
Epi-retinal membrane
Vitreo-macular traction

47. DEFORMATIONS IN THE FOVEAL
PROFILE
 Macular pucker
 Macular lamellar hole
 Macular hole, stage 1( no depression, cyst present)
 Macular hole, stage 2 (partial rupture of retina, incraesed
thickness)
 Macular hole stage 3 (hole extends to RPE, increased thickness,
some fluid)
 Macular hole, stage 4 (complete hole, edema at margins,
complete PVD)

49. LAMELLAR MACULAR HOLE

50. FULL THICKNESS MACULAR HOLE
WITHOUT PVD

51. DEFORMATIONS IN THE MACULAR
PROFILE
Serous retinal detachment

52. DEFORMATIONS IN THE MACULAR
PROFILE
Serous retinal pigment epithelial detachment

53. MACULAR CYST

57. INTRA-RETINAL ANOMALIES IN THE
MACULAR PROFILE
Choroidal neovascular membrane
Drusens
Hard exudates
Scar tissue
RPE tear

58. OCT deformations:
Concavity
 myopia
Convexity
 PED
 Subretinal cysts
 Subretinal tumors
Disappearance of foveal
depression

59. CSR

60. Patterns of Diabetic macular edema in OCT:
 Sponge like thickening of retinal layers:
Mostly confined to the outer retinal layers due to backscattering from
intraretinal fluid accumulation
 Large cystoid spaces involving variable depth of the
retna with intervening septae
Initially confined to outer retina mostly
 Serous detachment under fovea
 Tractiional detachment of fovea
 Taut posterior hyaloid membrane

61. FOVEA
Loss of foveal photoreceptors can be assessed with
OCT, as occurs with
full-thickness macular holes
 central scarring or fibrosis
Steepening of the foveal contour
 epiretinal membranes and
 macular pseudoholes or lamellar holes .
 Loss or flattening of the foveal contour
impending macular holes
 foveal edema or foveal neurosensory detachments.

62. OCT: ARTIFACTS
Artifacts in the OCT scan are anomalies in the scan
that are not accurate the image of actual physical
structures, but are rather the result of an external
agent or source
Misidentification of inner retinal layer:
Occurs due to software breakdown, mostly in
eyes with epiretinal membrane vitreomacular
traction or macular hole.

63. Mirror artifact/inverted artifact:
Noted only in spectral domain OCT machines.
Subjects with higher myopic spherical equivalent, less
visual acuity and a longer axial length had a greater
chance of mirror artifacts.

64.  Misidentification of outer retinal layers: Commonly occurs in
outer retinal diseases such as central serous retinopathy ,AMD, CME and
geographic atrophy.

65. OCT ARTIFACT AND WHAT TO DO?
OCT artifact Remedial measure
Inner layer misidentification Manual correction
Outer layer misidentification Manual correction
Mirror artifact Retake the scan in the area
of interest
Degraded image Repeat scan after proper
positioning
Out of register scan Repeat the scan after
realigning the area of interest
Cut edge artifact Ignore the first scan
Off center artifact Retake the scan/manually
plot the fovea
Motion artifact Retake the scan
Blink artifact Retake the scan

66. NEW SPECTRALIS OCT FEATURES
Imaging of deeper tissue structures
Difficult due to :
 Pigment from the Retinal Pigment Epithelium (RPE)
 Light scattering from the dense vascular structure of the choroid
 Enhanced Depth Imaging (EDI) :
 New imaging modality on the Spectralis OCT
 Provides an enhanced visualisation of the deeper structures, like choroid
 Particularly useful for imaging pigmented lesions in the choroid such as
naevi and melanomas

67. LIMITATIONS OF OCT
 Penetration depth of OCT is limited
 Limited by media opacities
 Dense cataracts
 Vitreous hemorrhage
 Lead to errors in RNFL and retinal layer segmentation
 Each scan much be taken in range and in focus
 must be examined for blinks and motion artifacts
 Axial motion is corrected with computer
correlation software
 transverse motion cannot be corrected

68. CONTD
Unable to visualise
 neovascular network or analyse if a CNV is active
 fluorescein angiography still has a significant role
OCT images cannot be interpreted in isolation
 must be correlated with red-free OCT fundus image and
photography/ophthalmoscopy
Aligning the scanning circle around the optic disc
may be difficult in patients with abnormal disc
contours

69. Some major limitations in the normative databases
Long term data on monitoring disease progression
with SD OCT unknown
Depends on operator skill

70. ADVANTAGES OF OCT
Best axial resolution available so far
Scans various ocular structures
Tissue sections comparable to histopathology
sections
Easy to operate
Short scanning time

71. REF
 Internet
 books
>optical coherence tomography- Carmen puliafito and
michael Hee
>optical coherence tomography- Gangjun liu
Important links:
http://www.intechopen.com/books/optical-coherence-
tomography