Optical coherence tomography (OCT) provides high-resolution cross-sectional images of the retina using infrared light. It has advanced from time domain OCT to spectral domain OCT, improving resolution and scan speed. OCT is used to qualitatively and quantitatively analyze retinal thickness, layers, and structures. It is useful for diagnosing and monitoring many retinal conditions like macular holes, edema, age-related macular degeneration, and more. Artifacts can occur but OCT provides crucial information with advantages of being non-invasive and having micron-level resolution.

1. Optical Coherence
Tomography
OCT---MACULA
PRESENTER:DR AKSHAY NAYAK

2. POINTS TO BE COVERED
 HISTORY
 INTRODUCTION
 PRINCIPLE
 TYPES OF OCT
 COLOUR CODES
 SCAN TYPES
 PROCEDURE OF OCT SCANNING
 NORMAL RETINA ON OCT
 INTERPRETATION
 ANOMALIES
 ARTIFACTS
 ADVANTAGES AND DISADVANTAGES
 NEWER OCTS

3. HISTORY OF OCT
• 1991 - first OCT paper - by Huang et al
• First in-vivo studies of human retina - 1993
• 2002 – Time domain OCT (e.g. Stratus)
• 10 µm axial resolution
• scan velocity of 400 A-scans/sec
• 2004 – Concept of spectral domain OCT introduced
• 2007 – Spectral domain OCT
• 1-15 µm axial resolution
• up to 52,000 A-scans/sec

4. INTRODUCTION
 Optical coherence tomography, or OCT is a non-
contact, noninvasive imaging technique used to
obtain high resolution 10micron cross sectional
images of the retina and anterior segment.
 Reflected light is used instead of sound waves.
 Laser output from OCT is low, using a near-infra-red
broadband light source
 Infrared ray of 830 nm with 78D internal lens.

5. non contact
non invasive
micron resolution
cross-sectional study of retina
correlates very well with the retinal
histology(Optical properties of ocular tissues,
not a true histological section)
IN SIMPLE WORDS…AN OCT
IS…

6. Qualitative analysis
description by location
description of form and structure
identification of anomalous structures
observation of the reflective qualities of the
retina
Quantitative analysis
retinal thickness and volume nerve fiber
layer thickness.
IT GIVES…

7. Basic Principle
• Combination of low-coherence interferometry
with a special broadband width light in near
infrared range ( 810 nm)

8. PHYSICS
• WAVELENGTH –The distance over which the
wave shape repeats
•

9. PHYSICS
• FREQUENCY – It is the number of occurrences
of a repeating event per unit time.
• Wavelength is inversely proportional to
frequency

10. INTERFERENCE
In physics , interference is a phenomenon in
which two waves superimpose to form a
resultant wave of greater or lower amplitude

11. • In physics two waves are coherent if they have
a constant phase difference and same
frequency and are non coherent if there is a
constant changing phase difference
COHERENCE

12. The process is similar to that of ultrasonography, except
that invisible light is used instead of sound waves.
Analog to
ultrasound

14. • Low-coherence infra-red light coupled to a fiber-optic travels
through a beam-splitter and is directed through the ocular
media to the retina and a reference mirror
• The distance between the beam-splitter and reference mirror
is continuously varied
• When the distance between light source & retinal tissue =
distance between light source & reference mirror, the
reflected light and the reference mirror interacts to produce
an interference pattern.

15. • The interference is measured by a photo detector
and processes in to a signal. A 2D image is built as
the light source moves along the retina , which
resembles a histology section.
The small faint bluish dots in the pre-retinal space is
noise

16. •When all of the A-scans are combined into one image, the
image has a resolving power of about 10 microns vertically
and 20 microns horizontally.
•Compare that to the resolution of a good ophthalmic
ultrasound at 100 microns, or 1/10th of a millimeter.
•

18. Lets see the OCTs
Initially, the time domain (TD) technology was
used (Stratus OCT, Carl Zeiss Meditec), which
employed a mobile reference arm mirror that
sequentially measured light echoes from time
delays with an acquisition speed of 400 A scans/
second and axial resolution of 810 μm.

20. • Time domain-OCT

22. Spectral Domain OCT

23. Types of OCT
TD – OCT ( time domain)
• Reference mirror moves
• Interference not detected
by special interferogram
• No Fourier transformation
• 1 pixel at a time
• Slow
• Motion artifacts present
• Less sharp images
FD - OCT / SD – OCT
( Fourier / spectral)
• Reference mirror stationary
• Interference detected by
special interferogram
• Interference pattern Fourier
transformed
• 2048 pixels at a time
• Rapid
• No motion artifacts
• Sharper and clear images

25. GENERATIONS OF OCT
• OCT 2 similar to OCT 1 but with an improved user interface.
OCT GENERATION TRANSVERSE
RESOLUTION
AXIAL
RESOLUTION
NO OF SCANS
OCT 1 FIRST (1995 ) 20 10 100
OCT 2 SECOND ( 2000) 20 10 100
OCT 3 THIRD ( 2002 ) 20 7-8 512

26.  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.

27. Scan Protocol Types
• Line
• Circle
• Radial Lines

28. The "line" scan simply scans in a single,
straight line. The length of the line can be
changed as well as the scan angle.

29. LINE SCAN…
• Acquire multiple line scans
• Default angle is 0 degree
• Scan line length is usually 5mm
But on increasing the
length the resolution
decreases

30. The "circle" scans in a circle instead of a line.

31. The "radial lines" scans 6 consecutive line scans
in a star pattern
Default number is 6 lines separated by
30degrees

32. The Fast Macular Thickness Scan
• The Fast Macular Thickness
Scan consists of 6 radial line
scans in a spoke pattern. It is a
low resolution scan that was
designed for quantitative
analysis (thickness and
volume)
• When scanning the macula,
the patient simply looks at the
fixation target.

33. Each of the 6 scans can be viewed individually
by clicking on the thumbnails on the left of
the scan selection screen

34. Other protocols
• Raster lines – multiple line scans in a rectangular
region to cover the areas of pathology – eg: CNVM
• Repeat scan – repeats previously saved scans
• 3D scan- 3D volumetric analysis

35. RASTER SCAN

36. Procedure
• Machine is activated
• Patients pupils are dilated
• Pt seated comfortably
• Asked to look into the target light in the ocular
lens
• Discouraged to blink
• Protocol selected as per case requirement

39. • Section 1: Patient related data, examination date, list and signal strength
• Section 2: Indicates whether the scan is related to macula with its pixel strength (as in
this
• picture) or optic disc cube (It also displays the laterality of the eye: OD
• (right eye), OS (left eye).
• Section 3: Fundus image with scan cube overlay. 3A: Color code for thickness overlays.
• Section 4: OCT fundus image in grey shade.
• Section 5: The circular map shows overall average thickness in nine sectors. It has three
• concentric circles representing diameters of 1 mm, 3 mm and 6 mm, and except for the
• central circle, is divided into superior, nasal, inferior and temporal quadrants. The
central
• circle has a radius of 500 micrometers.
• Section 6: Slice through cube front. Temporal – nasal (left to right).
• Section 7: Slice through cube side. Inferior – superior (left to right).
• Section 8: Thickness between Internal limiting membrane (ILM) to retinal pigment
• epithelium (RPE) thickness map. 8A: Anterior layer (ILM). 8B: Posterior layer (RPE). All
• these are 3-D surface maps.
• Section 9: Normative database uses color code to indicate normal distribution
percentiles.
• Section 10: Numerical average thickness and volume measurements.

40. PRINT OUT

41. Retinal Anatomy Compared to OCT
• The vitreous -
black space on the top of the image
• fovea –
normal depression
• Umbo-
central hyper reflective dot within foveola
• The nerve fiber layer (NFL) and the retinal pigment epithelium (RPE)
- highly reflective than the other layers of the retina ( red – yellow)
• RNFL –
thicker on nasal side of macula
• ONL –
thickest portion

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

44. Interpretation of an OCT
• 4 questions
1. How does the vitreo retinal interface appear ?
2. What is the foveal contour like ?
3. Is retinal architecture altered?
4. Whether the uniformity of RPE- CC layer is
disrupted?

45. Vitreo retinal interface
• Normal
• Membrane – single
- double
• Attachment- no attachment
- partial attachment
- total attachment

46. SINGLE MEMBRANE DOUBLE MEMBRANE

47. 1.TOTAL
ATTACHMENT
2. PARTIAL ATTACHMENT
3. NO ATTACHMENT

48. Foveal contour
• Normal
• Obliterated
pulling- due to overlying membrane
pushing – due to underlying fluid
• Widened – foveal thinning
• Hole – full thickness
- lamellar hole

50. Pulling mechanism Pushing mechanism

51. pseudohole Lamellar hole

52. Retinal architecture
• Normal
• Fluid- intra retinal – diffuse, cystoid
- subretinal
• Exudates
• schisis

53. Diffuse edema Cystoid edema

54. Rpe - choriocapillaris
• Normal
• Bumpy – drusen
• Fusiform thickening – CNVM
• Elevated- definite green line – serous PED
- Indefinite green line- fibrovascular
- no green line- haemorrhagic

55. drusen

56. Serous PED Haemorrhagic PED

57. Regions
For purposes of analysis, the OCT image of the
retina can be subdivided vertically into four
regions
• the pre-retina
• the epi-retina
• the intra-retina
• the sub-retina

58. The pre-retinal profile
• 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

59. Anomalous structures
• pre-retinal membrane
• epi-retinal membrane
• vitreo-retinal strands
• vitreo-retinal traction
• pre-retinal neovascular membrane

60. • A epi-retinal membrane with traction on the fovea
• These membranes may be associated with true or
pseudo macular holes Clearly seperable

61. The foveal profile
The normal foveal profile is a slight depression
in the surface of the retina

62. Deformations in the foveal profile
• macular pucker
• macular pseudo-hole
• macular lamellar hole
• macular cyst
• macular hole

64. Macular cyst

69. Deformations in the macular profile
• Serous retinal detachment (RD)
• Serous retinal pigment epithelial detachment
(PED)
• Hemorrhagic pigment epithelial detachment

70. Serous retinal pigment epithelial detachment

71. Hyper reflective lesions within NSR
• Hard exudates
• Cotton wool spots
• Micro aneurysms
• Hemorrhage
• Pigments
• Fibrin
• Erm
• Drusen
• Nevi
• Rpe hyperplasia

72. Hypo reflective lesions
• Asteroid hyalosis
• Vitreous haemorrhage
• Intraretinal fluid
• Intraretinal cysts
• PED

73. Choroidal neovascular membrane
Drusens
Hard exudates
Scar tissue
RPE tear

74. Drusen
of the
Retina

77. Sub-retinal fibrosis

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

79. Patterns of Diabetic macular edema in OCT:
 Sponge like thickening of retinal layers:
 Large cystoid spaces involving variable depth of the
retina with intervening septae
 Serous detachment under fovea
 Tractional detachment of fovea
 Posterior hyaloid traction

80. Diabetic macular edema in OCT:
 OCT CAN MAP RETINAL THICKNESS AND
CHARACTERISTICS OF VITREORETINAL ADHESIONS
 FOVEAL THICKENING IS SEEN
• VITREORETINAL TRACTION CAN EXPLAIN THE
REPORTS OF RESOLUTION OF DME WHEN
TRACTION IS SPONTANEOUSLY RELIEVED

81. IN MANAGEMENT OF DME
RETINAL OEDEMA EASILY PICKED
VITREO TRACTION –CAN CONSIDER SURGERY IF
NECESSARY AND IS EASILY MISSED ON CLINICAL
EXAMINATION OR FFA
MONITOR PRE AND POST OP COURSE

82. 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.

83. 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.
 Misidentification of outer retinal layers:
Commonly occurs in outer retinal diseases such as
central serous retinopathy ,AMD, CME and geographic
atrophy.

84. Out of register artifact:
 Out of register artifact is defined as a condition where
the scan is shifted superiorly or inferiorly such that some
of the retinal layers are not fully imaged.
 This is generally an artifact, which is operator
dependent and caused due to misalignment of the scan

85. OCT and Fluorescein Angiography in
retinal diagnosis
FAs provide excellent characterization of retinal
blood flow over time, as well as size and
extent information on the x and y axis (north-
south, east-west)
The OCT gives us information in the z (depth)
axis, telling us what layers of the retina are
affected

86. 1.Macular Hole
•confirmation of
diagnosis and
differentiates it from
lamellar hole, foveal
pseudo cyst.
•monitoring the
course of the disease
and the response to
surgical intervention.
Clinical applications of posterior segment scan

87. 2.Macular Edema
•: intraretinal areas of
decreased reflectivity
and retinal thickening.
•Round, optically clear
region within the
neurossensory retina
are noted in cystoid
macular edema.

88. 3. ARMD
Subretinal fluid,
intraretinal
thickening
•sometimes, choroidal
neovascularization in
exudative ARMD.
n

89. 4. Central serous retinopathy
• area of decreased reflectiv ity between two
hyper reflective areas

90. 5. Epiretinal membrane:
highly reflective diaphanous membrane over the surface of retina.

91. 6. Solar retinopathy
characterized by formation of an outer retinal hole.

92. 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
 Non-invasive
 Non-contact
 Minimal cooperation needed
 Resolution ~ 10 μm

93.  Penetration depth of OCT is limited
 Limited by media opacities
Densecataracts Vitreoushemorrhage
 Each scan must be taken in range and in focus
must be examined for blinksand motion artifacts
 Axial motion is corrected with computer
correlation software
LIMITATIONS OF OCT

94.  Unable to visualise
 neovascular network or analyse if a CNV is active
 fluorescein angiography still has a significantrole
 OCT images cannot be interpreted in isolation
 must be correlated with red-free OCT fundus image
and photography/ophthalmoscopy
Requires pupil diameter > 4 mm

95. Limited resolution due to infrared radiation
absorption by ocular structures, limited axial
and
lateral resolution due to image scattering from
ocular structures and restricted numerical
aperture of the optical system respectively, in
both TD and SD OCT, were the major
disadvantages that prompted
researchers to look for newer technologies

96. CURRENT,NEWER OCTs
Enhanced Depth Imaging
Spaide was the first to describe visualization of
the choroid after moving the zero delay line
deeper into the eye, focusing the OCT scanner
on the choroid instead of the retina. This is
known as EDI OCT.
This technique has enabled the visualization
of structures lying deeper in the eye.

97. En face OCT
‘En face’ OCT (eOCT) imaging is an imaging
technique
derived from SD OCT. It produces frontal
sections
of retinal layers, also called ‘C-scan OCT’.
Optical Coherence Tomography Retina Scan Duo
from NIDEK, Zeiss Swept Source OCT (prototype,
not yet FDA cleared) and deep range imaging

98. Intraoperative OCT
Microscope mounted OCT
The use of intraoperative SD OCT help surgeons to
better delineate tissue structures, reducing surgical
times and limiting the need for potentially toxic
stains and excessive illumination.
Handheld OCT
designed for handheld or microscope-mounted use

99. Swept source OCT
Swept source (SS) OCT utilizes a narrowband light
source with central wavelength of 1050 nm and
with a short cavity swept laser (instead of a super
luminescent diode laser as in previous OCTs) that
can emit different frequencies of light which are
then rapidly tuned over a broad bandwidth.
It uses a high-speed complementary metal oxide
semiconductor (CMOS) camera (instead of a
spectrometer in conventional SD OCT)
and two parallel photodetectors to achieve
100,000–400,000 A scan/second with 5.3-μm tissue
axial resolution over a 4-mm imaging range.

100. Swept source OCT scan of a normal retina
showing chorio-scleral interface clearly without
EDI.

101. Adaptive optics OCT
Adaptive optics corrects for higher-order ocular
aberrations during image acquisition, allowing
improved lateral resolution and a near-
cellularlevel
resolution.

102. Optical microangiography
Optical microangiography (OMAG) technology
utilizes an 840-nm wavelength with an A scan
rate of 27,000 Hz and an axial resolution of 8 μm
to image a 7.4 × 7.4 mm2 area of the posterior
segment, allowing volumetric map acquisition.
OMAG in combination with widefield OCT can
perform vascular perfusion mapping, down to
the capillary level comparable to fluorescein and
indocyanine green angiography

103. 12-mm OCT scan of proliferative diabetic retinopathy with vitreous hemorrhage done on (a)
Swept source OCT revealing peripheral retinal traction which is missed on (b) a regular Spectral
Domain OCT. Note the relative improvement in the visualization of the retinal surface on the
Swept
source OCT image even in the presence of media haze due to vitreous hemorrhage.

104. CONCLUSION
 OCT technology provides for enhancement of the
understanding, monitoring progression and response to
various treatment modalities employed in chorioretinal
diseases.
 Optical coherence tomography (OCT) has revolutionized the
clinical practice of ophthalmology.
 It is a noninvasive imaging technique that provides high-
resolution, cross-sectional images of the retina, retinal nerve
fiber layer and the optic nerve head.
 Further innovations in both hardware and software
technologies are expected to aid in the assessment of
chorioretinal diseases in more detail.