The document discusses optical coherence tomography (OCT) and its role in ophthalmology. It provides details on: - The history and development of OCT, how it works using interferometry and low coherence light, and its advantages over ultrasound. - How OCT allows high-resolution, non-invasive cross-sectional imaging of the retina and other ocular structures. - How OCT is used to detect and monitor various retinal pathologies like age-related macular degeneration, diabetic retinopathy, macular edema and more. Abnormal findings on OCT like fluid, exudates and neovascularization are summarized. - The principles of different OCT technologies over time including time domain, spectral domain

1. Role of OCT in
ophthalmology
Dr Shyam Kumar Sah
Final Year PG Scholar
SDM College of Ayurveda & Hospital
Hassan, Karnataka
E-mail: drsksah99@gmail.com

2. INTRODUCTION
 OCT was first developed in 1990 by Naohiro Tanno and introduced in 1991 by
a professor Huang et. al. at Yamagata University, in Prof. James
Fujimoto laboratory at Massachusetts Institute of Technology
 Optical Coherence Tomography (OCT) is a non-invasive diagnostic technique
that performs an in vivo cross sectional view of the biological tissue.
 OCT utilizes a concept known as interferometry to create a cross-sectional
map of the retina that is accurate to within at least 10-15 microns.
 It utilizes light waves of <10 micrometer axial resolution
 The operation is similar to USG B-scan or RADAR except instead of acoustic
or radio waves , it utilizes low coherence light.
 OCT is especially designed to study a cross sectional image of the anterior and
posterior segment of the eye with a high resolution, similar to histological section.
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3. Retinal
morphology
Retinal
thickness
Retinal
volume
RNFL
ONH
Anterior
segment OCT 5/25/2019
3
OCT
OCT allows detection & management of :

4. PRINCIPLE
OCT utilizes the interferometry and low coherence
light in near infrared range.
Michelson Interferometer
A beam of light passes through semitransparent
mirror that splits the beam into two.
These two beams are then thrown on two equidistant
mirrors; reflected light from these mirrors is then
picked up and summed up by a detector.
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5. These mirrors reflect the light wave in same phase
so that one beam strikes the a fixed mirror and the
other a movable mirror.
The reflected beams are brought back together and
these waves combine in a way that will give a
meaningful property i.e. diagnostic of the original
state of the waves.
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6. 5/25/2019
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7. OCT operates like a Fundus camera but resolves like a
USG machine
 The images formed by A-scans, a 2D crossectional image
of the target tissue reconstructed which is known as B-scan
USG & OCT differences
USG OCT
Source sound waves Infrared light
Resolution 150μ 10μ
Patient contact Needed Non-invasive
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8. TYPES OF OCT
Time Domain OCT (TD-OCT)
Spectral/Frequency Domain OCT (SD-OCT)
Specially encoded frequency domain OCT (SEFD-
OCT)
Time encoded frequency domain OCT (TEFD-OCT)
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9.  TD OCT, Depth information of the retina are obtained after a longitudinal translation in time
of a reference arm. This system acquire approximately 400 A-scans per second using 6
radial slices oriented 30 degrees apart. Because the slices are 30 degrees apart, hence
chances of missing pathology between the slices are high.
 SD OCT device include a spectrometer in the receiver that analyze the spectrum of light on
the retina and transforms it into information about depth of the structures. It scans
approximately 20,000-40,000 scans per second. This increased scan rate and number
diminishes the likelihood of motion artefact, enhances the resolution and decreases the
chance of missing lesions.
 Most of the TD OCTs are accurate to 10-15 microns. While newer SD OCTs may approach
3 micron resolution.
 TD OCTs image 6 radial slices while SD spectral domain systems continuously image a
6mm area. This diminishes the chance of inadvertently missing pathology.
 The TD representation gives the amplitude of the signal while in SD both amplitude and
phase values are used.
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10. Diagnosis by OCT
Macular hole
Macular pucker
Macular edema, CSME
ARMD & its progression
CSR, CSCR
Diabetic retinopathy
Vitreo-macular adhesions
& Traction (PVD)
Vitreo-retinal Interface
Syndrome
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•ERM
•PED
•CNV, CNVM
•Choroidal thickness measurements
•Glaucoma and its progression
•CRVO
•BRVO
•Anterior segment :Corneal
pathology, Uveitis, Trabecular
meshwork (IC angle), ant.segment
neoplasms.

11. Currently using OCT devices
 ZEISS Angioplex™ OCT angiographic imaging on the CIRRUS™ HD-OCT platform,
with a scanning rate up to 68,000 A-scans per second and an improved tracking
software known as FastTrac™. A three-dimensional image is obtained depicting
erythrocyte flow as well as the microvasculature of the superficial, deep, and avascular
layers of the retina.
 Optovue AngioVue® (Optovue, Inc., Freemont, CA), which uses split-spectrum
amplitude-decorrelation angiography algorithm, which minimizes motion noise. This
system also allows quantitative analysis, since it provides numerical data about flow
area and flow density maps.
 Topcon® uses a different algorithm, OCTA Ratio Analysis, which benefits from being
paired with SD-OCT, and improves detection sensitivity of low blood flow and reduced
motion artifacts without compromising axial resolution.
 Heidelberg engineering® uses the active eye-tracking system (TruTrack™) that
assesses simultaneously fundus and OCT images acquisition in order to achieve a
better signal-to-noise ratio. 5/25/2019
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12. OCT Artefacts or Noise depends on
 Dry Eye
 Corneal opacity
 Small pupil
 Cataract
 Vitreous densities
 Not proper fixation
 Not good technician
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13. Macular OCT (Some important points)
 The small, faint, bluish dots in the pre retinal space is
NOISE (Artefacts)
 It is intraretinal cross sectional anatomy with Axial
resolution ≤ 10 μ and Transverse resolution of 20 μ.
 Highly reflective structures: Bright colour (White &
Red)
 Low reflective structures: Dark colour (Black & Blue)
 Intermediate reflective structures: Green colour
 It is real time Tomogram with FALSE colours
 Pupil size should be 3 mm
 Red -Yellow colour: maximum optical reflection
 Blue-black colour minimal signals
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OCT Scan Pattern
Vitreous
Retina
Choroid
Scan & Analysis Points
•Cross sectional image of each 6 scans
•Mean & SD data
•Retinal thickness measurement in 9
regions of macula
•Surface map display
•Retinal volume

14. OCT study
 2 modes- objective & subjective by
combining both
 OCT reading done in 2 stages-
i. Qualitative and Quantitative analysis
ii. Deduction and synthesis
 Qualitative study:
i. Morphology:
Change in retinal outline, retinal structure in
layers
Anomaly in Pre/Epi/Intra/Sub Retinal region
ii. Reflective: Hyper/Hypo/Shadow areas
 Quantitative study: Thickness, Volume
and Shadow areas
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non reflective area seen as Dark space
• Vitreo-retinal interface : well defined due to contrast
between non reflective vitreous & the back scattering
retina.
• Retinal Layers:
i. Anterior boundary is highly reflective RNFL is seen
as RED layer due to bright scattering
ii. Posterior boundary also seen RED layer of highly
reflective RPE & Chorio-capillaries
iii. Outer segment of Photoreceptors is minimal
reflective seen as DARK layer just ant. To RPE-
Choreo-capillaries complex (Bruch’s complex)
iv. Different intermediate layers of neuro-sensory retina
black & white the dark layers of photoreceptors &
RED layer of RNFL are seen alternating layers of
moderate & low reflectivity
Retinal thickness high in: CME, DME, ARMD,
Macular hole, ERM

15. Colours in OCT
Hyper reflective
 Neovascularisation
 Hard exudates
 Microaneurysms
 Fibrous tissue
 Astroid hyalosis
 Cotton wool spots
 Congenital hypertrophy of RPE
 Nevus
Hypo reflective
 Fluid collection area
 Cyst
 Intraretinal cavities
 Diffuse intraretinal edema
 Exudative detachments
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16. Macular scan
How to examine OCT
1. Identify RPE
2. Examine RPE
3. Examine posterior to RPE
4. Examine anterior to RPE
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Identify RPE
1. Irregularity
2. Fragmentation
3. Rupture
4. Interruption
5. Depression
6. Elevation
7. Thinning
8. Thickening
Posterior to RPE
1. Bruch’s membrane
(Hyper reflectivity- atrophy
of RPE vs Fibrosis))
2. Hypo reflectivity (screen
effect)
Anterior to RPE
1. SRF
2. Ellipsoid zone: (Photoreceptor IS/OS zone)-
hyper reflective spots, dense area
3. ELM
4. ONL
5. Inner retinal layers
6. Intraretinal cyst
7. Retinal thickness
8. Foveal depression
9. Vitreous
 From inner to outer
1. Pre retina ( close to vitreous)
2. Epi retina ( close to ILM)
3. Intra retina (Neuro sensory retina)
4. Outer retina Between RPE to Photo
receptor layers)
5. Sub retinal (Outside RPE)

17. OCT study
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1. Patient name, age, sex
and other geographical
data
2. Signal strength: the
higher the number better
the quality
3. Fundal image
4. Retinal thickness
map/Red free
5. Shadow gram
6. Measurement box
7. ETDRS
8. Tomogram(V+H)
9. ILM-OS/RPE Map &
OS/RPE surface
1
2
4
3
5
6
8
7
9

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Macula & optic nerve.
RNFL,
GCL,
IPL,
INL,
OPL,
ONL,
OLM,
IS,
IS/OS junction;
OS,
RPE,
A healthy retinal OCT B-scan showing the macula

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(A) The red arrows show
the location of blood vessels, which block the infrared signal
and cause shadows to fall underneath them. (B) The red
arrow shows the area of photoreceptor outer segment
elongation which is seen under the foveola zone

21. Shadowgram
 The shadowgram is a surface image of
all of the aligned B-scans.
 Anything that blocks light in an OCT
scan will appear as a shadow, while the
deeper the light penetrates, the brighter
the area will appear.
 it offers a quick way to determine scan
quality
over the whole scan area.
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A. An ideal shadowgram, showing
capture of good quality B-scans
across the whole scan area.
B. The black arrow points to a
horizontal black line which
indicates missing B-scan data,
caused by a patient blink.
C. The black arrow points to a
shadow, which in this case is likely
to indicate blocking of the OCT
signal by a vitreous floater

22. Temperature/Retinal thickness plot
 The temperature thickness
plot gives a representation of
the retinal thickness over the
scan area, with thicker areas
appearing as warmer
colours, and thinner areas as
cooler colours.
 It provides a quick method for
establishing whether the
retinal architecture is normal
over the macular region,
 Hence, abnormality can be
determined by observing the
B-scans.
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A. A retinal thickness plot showing the normal retinal
architecture
B. A retinal thickness plot showing multiple ‘pits’,
characteristic of drusen.
C. A retinal thickness plot showing severe retinal
thickening nasally with wet AMD as the most likely
cause

23. ETDRS Thickness Grid- 9 segment
 It is real-time quantitative evaluation of
retinal thickness (ILM-RPE)
 Average retinal thickness: 222±16μm
to 260±12.2μm for the central area of
the ETDRS grid.
 Thinnest in the centre and Temporal
area is thinner than nasal area.
 Thickness vary inversely with age & axial
length and also with ethnicity & Gender
(Africans & Women have thinner
macula).
 ETDRS grid: retinal thickness is
compared to that of a normative
database and classified as ‘within
normal limits’, ‘borderline’ or ‘outside
normal limits depending upon colour of
the grid.
 Color indicates normality percentage
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A. Retinal thickness falls within the middle 90 per cent of the
normative population for all areas of the ETDRS grid.
B. Retinal thickness is considered outside normal limits in the
pink areas, as it falls within the top 1% of the normative
population.
C. Retinal thickness is considered borderline in the central area of
the ETDRS grid where it appears yellow, falling within the bottom
5 per cent of the normal population, whereas the red area is
considered outside normal limits, falling within the bottom 1
per cent of the normative population
Zone I: central 1mm foea
Zone II: 3mm parafovea
Zone III: 6mm perifovea

24. Retinal Thickness Measurement Box
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25. 5/25/2019
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RETINAL PATHOLOGY
OCT

26. AMD
 Dry AMD: Drusen in the macular region
appears as focal hyper-reflective elevations
of the RPE, disrupting the typically straight
and smooth RPE (A)
 Wet AMD: CNV is hallmark of wet AMD &
also in DME & seen as increased reflectivity
of the RPE, often associated with irregular
RPE elevation.(B). Leakage of these new
vessels produce dark space (FLUID) which
may be Intra-retinal (above
photoreceptors) or Sub retinal (between
photoreceptor & RPE) or sub RPE (below
RPE).
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(A) drusen (red
arrow);
(B) wet AMD with
subretinal
oedema;
(C) vitreomacular
traction
(D) cystoid macula
oedema
secondary to
BRVO
(E) sub-retinal
oedema in CSR
(F) exudates (red
arrows) in
diabetic
Maculopathy
Exudates: are usually located in or adjacent to the outer
plexiform layer because they are lipid residues that originate from
damaged capillaries found in the inner retina whereas drusens are
deposits located between the retinal pigment epithelium (RPE) and
Bruch's membrane because the RPE is not functioning correctly

27.  Vitreomacular traction: seen as a
thin, moderately reflective band
which is pulling on the retina in an
incomplete v-shaped PVD. (C)
 CME: Associated with DM & BRVO
 Intra-retinal fluid forms characteristic
cystic spaces (D)
 Central Serous retinopathy or
chorioretinopathy: occurs due to
Serous Neurosensory Retinal
Detachment, TRD. Small elevated
dark space (FLUID) in subretinal
spaces. (E)
 Diabetic maculopathy: hyper
freflective lesions (Hard exudates)
below macula in outer layer of
retina. (F) 5/25/2019
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(A) drusen (red
arrow);
(B) wet AMD with
subretinal
oedema;
(C) vitreomacular
traction
(D) cystoid macula
oedema-DM &
secondary to
BRVO
(E) sub-retinal
oedema in CSR
(F) exudates (red
arrows) in
diabetic
Maculopathy

28. Neovascularisation
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29. Pigment Epithelial Detachments (PEDs)
 Serous PED: sharply
demarcated dome shaped
serous elevation of the RPE
from Bruch’s membrane
due to accumulation of fluid
under RPE.(WET AMD).
May or may not associated
with CNV.
 Drusenoid PED: due to
large drusen in DRY AMD
causes dome shaped
elevation of RPE from
Bruch’s membrane.
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30. CRVO/BRVO
 Seen as in macular edema,
retinal haemorrhages, and cotton
wool spots.
 Optic disc edema is a common
feature in CRVO
 Accumulation of fluid in outer
retina as hypo reflective lesion.
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31. CRAO/BRAO
 Diffuse thickening of the
neurosensory retina
 Increased reflectivity in the inner
retinal layers
 decreased reflectivity of the
photoreceptor layers and the RPE
secondary to the shadowing effect.
 Cystoid changes in the macular area
with loss of the macular contour.
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SCI: superficial capillaries ischaemia
DCI: deep capillaries ischaemia
PAMM: paracentral acute middle maculopathy

32. EPIRETINAL
MEMBRANE
 ERMs are seen as a highly reflective
layer on the inner retinal surface
 ERMs can be classified as idiopathic
or secondary
 Idiopathic ERMs -fibroglial
proliferation on the inner surface of
the retina, secondary to a break in
ILM, during posterior vitreous
detachment.
 Secondary ERMs result from an
already-existing ocular pathology
such as central or branch retinal vein
occlusion, diabetic retinopathy, uveitis
and retinal breaks with or without
detachment
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33. MACULAR HOLE
 Macular hole is partial or full thickness dissolution of
retinal tissue at the foveal region.
 It may occur following blunt trauma, longstanding
macular edema or as an idiopathic condition.
 Stage 1a: Foveolar detachment with yellow spot. OCT
shows a cystoid space occupying the inner part of the
foveal tissue.
 Stage 1b: Foveolar detachment with yellow halo. OCT
shows impending hole with extension of cystoid space
Posteriorly, disrupting the outer retinal layers.
 Stage 2: Formation of minute eccentric holes. OCT
shows eccentric opening of the roof of the hole with
presence of an operculum
 Stage 3: Full thickness macular hole with or without
operculum. OCT shows a central full thickness macular
hole with detached posterior vitreous.
 Stage 4: Full thickness macular hole with posterior
vitreous detachment. OCT shows a central full thickness
macular hole with a cuff of sub retinal fluid and
completely detached posterior vitreous.
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1a
2
3
4
1b
4

34. Geographical atrophy
 Geographic atrophy - large area of irregular, well-
defined chorioretinal atrophy involving the macula.
 Exudative form-CNVM and its sequel like
Serous detachment
Hemorrhagic detachment
Exudation and distortion of the retinal
photoreceptors.
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35. Choroidal Thickness Measurements
 Choroidal thickness is
measured from the posterior
edge of RPE to the
Choroid/sclera junction.
 Normal = 272- 448 μ and
below macula about 250 μ.
 Thin choroid seen in high
Myopia, Choreo-retinal
Degeneration, RP, DR,
Glaucoma etc.
 Thin choroid causes
Neovascularisation.
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Retinal Thickness
Choroidal Thickness

36. Optic Nerve Head & Retinal Nerve Fibre Layer
(ONH & RNFL) OCT
It is done to study the stage of glaucoma and its
progression
Identification of glaucoma in primary eye care relies
upon the following classic triad:
i. Optic disc assessment,
ii. Measurement of IOP and
iii. Visual field evaluation
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37. How to read an OCT
1. Patient name, age, sex and
other geographical data
2. Signal strength: the higher the
number better the quality
3. Thickness map
4. Deviation map
5. ONH & RNFL parameters
6. NRR & RNFL thickness
7. Clock hour & Quadrant data
8. Tomogram 5/25/2019
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1 2
3
4
5
6
6
7
8

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39. Signal strength
10, 9, 8: good
7, 6: not optimal
but can be
interpreted with
caution
≤ 5 : not reliable
i.e. Not acceptable
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Blue area:
Thinnest
Red & white:
thickest
Thickness map RNFL Deviation
Abnormal: flat
Colour:
Yellow, Red
ONH & RNFL
Parameters
• Normal eye has good
RNFL symmetry
• In glaucoma RNFL
symmetry go down
Graphs
• Normal graph: Double or
Triple hump
• In glaucoma: looses its
double or triple hump
pattern
• Reduces into Yellow &
Red area

40. Optic Disc Scan
A. Normal anatomical disc (defined by
the opening in Bruch’s membrane),
along with the size and depth of the
cup.
B. A cross-sectional view of the disc
allows observation of optic disc
swelling, which may be associated
with:
 optic disc Drusen
 Crowded optic nerve heads
 Raised intracranial pressure
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A. Healthy optic nerve head the structures identified
B. A raised optic nerve head scan
Bruch’s membrane Lamina cribrosa
opening
Blood vessel
Raised Optic disc
A
B

41. Shadowgram
 In a reliable scan, the
Shadowgram will appear sharp
(indicating high scan quality) and
will show no signs of fixation
errors or blinks.
 Fixation errors, blinks and poor
scan quality will all result in
reduced diagnostic accuracy
Therefore the scan should be
repeated.
 Poor scan quality can be caused
by media opacities, incorrect
focus, or even dry eye.
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A. Shadowgram showing high scan quality, but a fixation error (black
arrow).
B. Shadowgram showing no fixation errors but poorer scan quality, shown
by the less distinct blood vessels
Disc Shadowgram

42. Temperature thickness plot
 It gives a representation of the RNFL
thickness across the scan area
 Thicker areas appears as warmer colours,
and thinner areas as cooler colours.
 RNFL thickness is calculated between the
inner plexiform layer and the outer edge of
the RNFL
 RNFL thickness measures should not be
relied upon if scan quality is low. Hence a
high quality scan needed.
 Around the major blood vessels, the RNFL
thickness appears thin due to high
reflectance of blood vessels can cause the
automated segmentation to miscalculate
RNFL.
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RNFL temperature thickness plots for 3 different right eyes.
A. A healthy RNFL, with RNFL thickest temporally and
symmetrical across the horizontal raphe.
B. A ‘cooler’ plot, showing diffuse RNFL loss.
C. Inferior temporal RNFL loss, showing asymmetry across the
horizontal raphe

43. Normative comparison
 All the OCT machines come preloaded with an
internal normative database.
 It enables practitioners to classify a patient’s
RNFL thickness as ‘normal’, ‘borderline (within
1-5 per cent of the normal distribution)’ or
‘outside normal limits (within the bottom 1 per
cent of the normal distribution)’.
 Normative comparison is often shown in three
different ways; on a TSNIT chart, on a 3.4mm
ring, and on a significance grid
 Normality percentage:
Green zone: 95% normal
Yellow zone: <5% normal
Red zone: <1% normal(outside normal limits)
 Interpretation should be very cautious. An area of
red does not automatically mean the patient has
glaucoma, and likewise, a completely green plot
does not mean the patient definitely does not
have glaucoma.
 High myopia have thinner RNFL, so others
investigations should perform to confirm
glaucoma: CCT, Dilated stereoscopic disc
examination, Visual fields Test, Applanation
tonometry.
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Normative comparisons for a healthy (A-C) and a glaucomatous (D-F) eye.
A. TSNIT graph showing RNFL thickness is within (green) or above (white) normal limits.
B. 3.4mm diameter circle showing RNFL thickness is within or above normal limits.
C. Significance plot showing that RNFL thickness is borderline(yellow) at a few grid locations
near the disc, but within normal limits (clear) for all other locations.
D. TSNIT graph showing RNFL thickness is outside normal limits (red) across the superior
temporal (ST) to superior nasal (SN) quadrants.
E. 3.4mm circle showing RNFL thickness is borderline or outside normal limits.
F. Significance grid showing the RNFL is borderline or outside normal limits in the superior
nasal quadrant, highlighting a possible RNFL arcuate defect

44. Disc topography
 Evaluation of the optic nerve head or
OD size is crucial in the detection and
monitoring of glaucoma, its risk &
progression
 Average disc area= 2.8 ± 0.5mm2
 In both eye asymmetry of C:D ratio of
0.2 or more suggests open-angle
glaucoma.
 Vertical CDR is more significant than
horizontal.
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Automatic disc topography parameters
The disc rim is identified by the opening in Bruch’s membrane (blue
rim), while the cup (pink rim) is identified at a reference height of
120μm above the RPE

45. Trend analysis
 Helps to early access
glaucoma by monitoring the
structural changes over
time, rather than waiting for
a visual field defect to
present.
 It detects progression by
evaluating the slope of
RNFL thickness over time
 Hence glaucoma
progression can be
identified.
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Glaucoma trend analysis function including optic nerve photographs which can be
overlaid with temperature thickness plots or normative data, normative TSNIT graphs
and linear regression trend analysis graphs

46. Ganglion cell layer
 The 3D disc scan automatically detects and
measures the RNFL thickness but not the
ganglion cell layer (GCL).
 As glaucoma results from ganglion cell
apoptosis, the GCL should also be quantified.
 GCL thickness is best measured over the
macular region, where more than 50% of the
retina’s ganglion cells reside.
 While the diagnostic capabilities of measuring
the GCL thickness have been found to be
comparable to those of the RNFL.
 In myopic patient, the retinal thinning is more
around the disc leading to false positive results
when compared to the normative population.
 Hence, macular ganglion cell scan is preferred
in myopic patients.
 The retinal GCL shows the greatest
glaucomatous thinning in the inferior retina
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Macular ganglion cell analysis for a left eye
A. Temperature thickness plot showing thinning inferiorly.
B. Significance graph showing areas of ganglion cell thickness that are ‘borderline’ or
‘outside normal limits’ in a wedge pattern.
C. Asymmetry plot showing that the ganglion cell layer is thinner inferiorly relative to
the superior retina

47. 47
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Thanks