Optical Coherence Tomography Guide for Retinal Imaging

Optical Coherence Tomography
Dr. Vivek B Wani MS, FRCSEd
Consultant, Vitreoretina
KLES DR. Prabhakar Kore Hospital &MRC ,KAHER
BELAGAVI
8th October 2022 OCT for KLE PGs I -DR WANI 1

VITREOMACULAR TRACTION VMT

OPTICAL COHERENCE TOMOGRAPHY(OCT)
OCT is a non invasive technique to
obtain cross sectional images of retina
with high resolution-’Optical biopsy’

WHAT IS THE RESOLUTION OF OCT VS MRI ?

OPTICAL COHERENCE TOMOGRAPHY
I) History
II) How does OCT work?
III) Techniques of OCT examination of Retina
IV) OCT in normal macula
V) What are abnormal findings in OCT
VI) OCT in common retinal disorders

OBJECTIVES of this talk are
• At the end of the class the participants should
know
1. Basics of OCT
2. Different generations or types of OCT
3. How is OCT performed
4. What are the OCT protocols
5. How to recognize normal layers of retina in the
OCT
6. What are abnormal findings in OCT?
7. How to interpret OCT in some retinal diseases

I) HISTORY
“Optical Coherence Tomography”
Huang, D et al Science;1991: 254: 1178–81

2012- SWEPT source OCT

OCT
Apart from ophthalmology OCT is also used in other
branches of medicine
 Dermatology
 Cardiology
 Gastroenterology
 Dentistry
 ENT
 Neurosurgery
 Others

II) How does OCT work?
• Principles of OCT are similar to USB scan
• In USB SCAN Ultrasound waves travel into the
globe and are reflected from various tissues
the eye
• We measure the following features of
reflected sound waves-echoes
 Amplitude and time delay
 Plot the structure and the distance of the
tissue
• ‘A scan’-point scan
• ‘B scan’ series of A scans in one plane

In OCT we use light waves
• Light enters the eye and is reflected from
retina or other structures
• Like USB WE need to measure
 Amplitude and time delay of the
reflected light from the eye to record the
structure and distance of the tissue
As speed of light is 299792km/sec it is
not easy to measure the time delay
directly

So we use an indirect method Low coherence
interferometry
• We use LASER light in OCT
• Super luminescent diode laser-SLD
• LASER light passes through an
optical beam splitter producing
two beams-
 Reference beam hits a reference
mirror at a known distance and
reflects back
 Measurement beam enters the
eye & is reflected from various
depths of the retinal tissue

OCT
• Reflected beams from reference
mirror and tissue are united to
produce an interference pattern
• When the distance of reference
mirror and the tissue are
equidistant from light the
interference pattern is constructive
• The interference patterns are
detected by a photodetector and
analyzed by computer &
• Amplitude and time delay of
reflected light from retina are
plotted

Time domain OCT-the original OCT
• The mirror moves constantly to
give different reference distances
to produce interference patterns
from various levels of tissue
• This limits the A scan rate to 400
per second
• This restricted the area that can
be scanned in time domain OCT

Serial A scans along a line –B scan
• B scan is obtained by
moving the OCT beam
in one direction (A
scans in a line)

OCT VS US
Character OCT Ultrasound
Type Non contact Contact
Time Quick Time consuming
Resolution 3-10 microns 150 microns(UBM-20-
50)
Pupil dilatation May need Not needed
Media Clear needed Not needed
Area studied Small, central Wide
Cost Expensive Less
Use Study retinal
microstructure
Study retinal/vitreous
integrity in non clear
media

VI)Advantages of OCT
 Non contact, painless and fast
 Instant optical ‘biopsy’ of retina WITH high
resolution
 Quantitative, objective and reproducible
 No dye needed like in contrast studies/FFA OR ICG
 No ionizing radiation so safe
 Excellent teaching tool for residents and patients too
 A great research tool

IV) New developments in OCT
A) Spectral domain OCT
B) SS(swept source) OCT
C) OCT with adaptive optics(AO)
D) OCT angiogram OCTA
E) Wide field OCT
F) Intra-operative OCT
G) OCT for infants and bedridden patients-hand
held
H) Doppler OCT

Spectral domain OCT
Four modifications to Time domain OCT
I- SD-OCT utilizes a SLD- diode laser light source 840 nm
with broad bandwidth of 150 nm V/S 820nm with
25nm bandwidth of TD OCT
II- The reference mirror in SD OCT is stationary
III-A charged coupled device (CCD) camera and
spectrometer with a diffraction grating are used in
place of the traditional photodetector
25th August 2018 KLE RETINA UPDATE 21

The fourth –Fourier transform
• Fourier transform is a
computational software
used by the
spectrometer
• It simultaneously
resolves the relative
amplitudes and phases
of the spectral
components
backscattered from all
depths of each A-scan

Fourier transform
• So it produces 2000 pixels at a single A scan
versus only one pixel by TD OCT in one A scan
• It performs 20000-70000 scans per second vs
400 of TD-OCT
• WE CAN SCAN LARGER AREA IN A SHORT TIME

Time domain OCT
Spectral domain OCT

Swept source -SS-OCT
• It uses a more complicated tuned dye laser-swept laser
(instead of a superluminescent diode laser)
• It emits different frequencies of light and that is rapidly
tuned over a bandwidth centered around 1050 nm
• It uses a high-speed complementary metal oxide
semiconductor (CMOS) camera and two parallel
photodetector
• Hence a very high speed -100,000-400,000 A-scans/second
• High 5.3-µm tissue axial resolution
• Penetrates choroid better –because of higher wave length

SS-OCT
SS-OCT offers several advantages over SD-OCT,
including
-less sensitivity variation with imaging depth
-deeper and longer imaging range
-higher detection efficiencies
-reduced fringe washout
-increased penetration into the choroid and optic nerve
head
- reduced sensitivity to ocular opacities and motion
artefacts

Differences between TD, SD OCT and
SS OCT
9th OCTOBER 2022 OCT FOR KLE PGS -DR WANI 28
Characteristic TD SD OCT SS OCT
Reference mirror moves stationary Stationary
Laser used SLD 820 NM SLD 840 NM Tunable dye laser 1050
BAND WIDTH 25 NM 150 NM 100 NM
SCAN rate 400/sec slow 25 k to 70 k per sec fast 100000-400000 very
fast
Depth of scan Less Up to choroid Choroid sclera
Axial resolution 8 to 10 mu 5 mu 5 MU
Light detector photodetector spectrometer & CCD COMS Camera and two
photodetectors
motion artefacts present less Very less
Area scanned Less-6MM More -9MM More 12MM
Hazy media Not useful May be done Can do better
Retinal thickness ILM to EZ or IS OS
junction
ILM TO interdigitation
zone
Or ILM to RPE OUTER
BOUNDARY
ILM TO interdigitation
zone
Or ILM to RPE OUTER
BOUNDARY

Bhende M et al Indian J Ophthalmol 2018;66:20-35

Comparison of different OCT machines ( modified from Walsh on
Heidelberg website)
Company Volume OCT AXIAL
resolution
MICRONS
Scanning speed Eye tracking Accessory imaging
Time Domain OCT No 10 400/sec Nil NO MORE USED
Zeiss cirrus Yes 5 27000 NO IR
C-SLO
Heidelberg Spectralis Yes 7 40000 YES C-SLO,FFA, ICG, AUTOFL
Topcon 3D 2000 Yes 6 50000 NO NEAR INFRA RED
COLOR FN
OPTOVIEW RT 100 Yes 5 26000 NO
C-SLO- CONFOCAL SCANNING LASER OPHTHALMOSCOPE

Indications for OCT
• For all macular diseases -vascular, inflammatory,
degenerative or hereditary
• VA and fundus status do not match
• To have objective data at baseline in AMD, DR,
vein occlusions, high myopes, macular
dystrophies, uveitis, chloroquine therapy,
multiple sclerosis, Alzheimer, Parkinson's
• Follow up data for above
• ONH evaluation in glaucoma, ONH swelling, optic
pit

Technique of OCT examination
Preparation
• Media clear- SS OCT is more useful in hazy media
• Pupil dilatation preferable
• Enter the data-Full name of the patient, file
number, physician name and working diagnosis to
enable retrieval of data later
• Also maintain data in a register with all details of
patients -including their diagnosis and phone
number

• Select the program you need for examination
• Macula or ONH or anterior segment?
• Macula- volume scan or raster scan
• OCT interface is extremely user friendly
• Patient is explained the procedure
• Patient comfortably places his/her chin on the chin rest and
fixes on the target in the view
• The eye can be centered by the examiner with the help of
interactive panel
• The scan is usually over in two minutes
• Internal fixation focus adjustment: -20D to +20D (diopters)
Technique of OCT examination

Posterior segment scan programs
• Macular (volume)scan covers 6x6 mm
square(now 9 mm) centered over fovea
• 128 horizontal line scans in 6x6 scan
• Each line has 512 A scans
• So 128x512=65536 A scans done in 36 sq mm
area!
• So the tissue is richly sampled
• Raster line scan 1 line or 5 line or cross

For ONH analysis
• 6x6 mm square centered on the
disc
• 200 lines are scanned
• Each line has 200 A scans

Raster scan
• Raster scans are line scans -one line or 5 lines
One HD line scan of 6 mm is scanned by 4098
A scan
5 line raster scan can be positioned on area of
interest -1028 A scans are done per line

RETINAL THICKNESS MAP-ETDRS subfields
• Three concentric circles
centered on fovea
• Central subfoveal field-
1 mm
• Inner circle 3 mm
diameter
• Outer circle has 6 mm
diameter

ETDRS fields
• Outer two circles are divided
by diagonal lines in to eight
subfields
• Inner superior
• Inner nasal
• Inner inferior
• Inner temporal
• Outer superior
• Outer nasal
• Outer inferior
• Outer temporal
• The OCT gives average
thickness of retina in each
subfield

NORMAL AVERAGE central subfoveal field
(diameter 1MM) in Adult population
• Stratus OCT –TIME DOMAIN----------- 212
± 19-250 mu- OBSOLETE
• Spectralis HRA OCT ------ 289 ± 16
• Cirrus HD-OCT ------------ 277 ±19
• SOCT Copernicus -------- 246 ± 23
• RTVue—100------- 245 ± 28
• Topcon 3d 1000- 231 ± 16- 263 mu
IOVS 2009

Slicing technique
• We can slice retina and view different layers in
an en face view
• We can measure thickness of different layers
too
• Especially helpful in OCT for diagnosis of
glaucoma to measure thickness of RNFL AND
Ganglion cell complex

SLICING

HOW DOES THE NORMAL RETINA
LOOK IN OCT?

Anatomy of the retina
• Inner limiting membrane -ILM
• Retinal nerve fiber layer
• Ganglion cell layer
• Inner plexiform layer
• Inner nuclear layer (nuclei of bipolar
cells)
• Outer plexiform layer
• Outer nuclear layer (nuclei of
photoreceptors)
• External limiting membrane –base of
the inner segments of the
photoreceptors -ELM
• Layer of photoreceptors (rods and
cones)
• Retinal pigment layer (RPE)

IN OCT
• We speak of hypo reflective or hyperreflective
• Layers is the term used for areas which have
no difference of opinions
• Zones-only two - for which there is no
concurrence
• 18 parts have been described in OCT by an
international nomenclature committee

Anatomy of photoreceptors
and four bands

Four OUTER RETINAL BANDS

Bhende M et al Indian J
Ophthalmol 2018;66:20-35

Bhende M et al Indian J Ophthalmol 2018;66:20-35

How do we interpret macular OCT
• Clinical data must be available
• Is the foveal contour +?
• Is PH face seen
• Is the retinal surface smooth
as expected
• All layers recognized and
normal?
• Are there hyperreflective or
hypo-reflective areas that are
not normal?
• Location of these areas
• Correlate these with color
photos

Posterior hyaloid

We will study role of OCT in some
common retinal diseases
• DME
• RVO
• Macular Hole
• ERM
• AMD
• Macular dystrophies

DIABETIC MACUAR EDEMA (DME)
• OCT has become the gold standard in
the care of pts with DME
• All the clinical trials of intravitreal drugs
used OCT to objectively assess the DME
• OCT criteria of Central subfoveal
thickness was used to treat DME and
assess effect of treatment in trials

OCT and DME –Its advantages
• Detects subclinical macular edema, cysts and SRF
• Quantifies DME and localizes it
• So helps in follow up
• Objectively assesses effect of treatment
• OCT detects tractional forces
• Prognostication –ELM and EZ, hyperreflective
spots, DRIL sign, subretinal fluid
• Great educational tool to motivate patients to
accept treatment and control their DM

Center involving DME- CI DME
• Whenever the central subfield thickness is
more than > 250mu(Stratus) it was defined as
CI DME in clinical trials of anti VEGF drugs
• The efficacy of treatment was decided by
improvement in VA and reduction of OCT
thickness from baseline
• The earlier definition of Clinically significant
macular edema(VSME) was not used in any
clinical trials of anti VEGF drugs

OCT IN DME
OCT classification of DME - four categories
• Diffuse or spongy edema
• Cystoid edema
• Subretinal fluid
• Tractional
Most of the cases of DME have combined
features

RE CSME-Diffuse n cystoid
Foveal contour lost
Hyporeflectivity in the fovea with increased thickness- spongy edema
Hyperreflective spots in temporal area in outer plexiform area with shadowing
ELM and EZ look intact

DME mainly cystoid
PRE AND POST IVA LE CSME
Note foveal contour lost
Large multiple Hyporeflective spaces
Mainly in fovea extending whole thickness
ELM AND EZ seem preserved

Subretinal fluid

Tractional maculopathy

JUNE 2010
SEPTEMBER 2011

April 2011 RE and Feb 2012 no follow
up

Characteristics of lesions
• Hard exudates, fibrovascular membranes
and hgs are hyper-reflective
• Intraretinal edema, cystoid spaces and
subretinal fluid are hypo-reflective
• Shadow effect –hard exudates, vessels
and hgs

DRIL SIGN-deranged retinal
inner layer sign
ERM
LOST ELM EZ over fovea, HRS

Note hyperreflective foci, ELM AND EZ loss in fovea,
cystoid changes and RPE changes too

Prognostic factors of OCT IN DME
• Disturbed ELM and Ellipsoid zone
• Cystoid spaces number and size
• Deranged Inner retinal layers or DRIL SIGN
• Retinal thickness a weak sign
• Hyperreflective foci or dots -solitary, small
(<30 µm), Reflectivity similar to RNFL
reflectivity

Central retinal vein occlusion/Branch
retinal vein occlusion (CRVO/BRVO)
• RVOs are second most common retinal vascular disorder after
DR
• Macular edema in RVOs leads to visual impairment, chronic
cystoid changes, PTMH OR FTMH
• In non ischemic CRVO or BRVO the ME can be effectively
treated with ranibizumab (CRUISE AND BRAVO studies
respectively)
• Dexamethasone depot inj or intravitreal aflibercept or
bevacizumab injections have also proved efficacious
• OCT is very helpful tool to diagnose and monitor the macular
status in venous occlusions

Venous occlusions and OCT
• In both CRVO and BRVO we aim to detect
Macular edema -diffuse or cystic and SRF
Quantify it –decide the central subfield thickness
Detect markers like hyperreflective foci in retina
Rarely –may get
Macular hole due to chronic edema
Macular thinning/atrophy due to chronic
edema/ischemia
Tractional changes by NVE or NVD

OCT OF ISCHEMIC CRVO

LE CRVO in a 43 YR OLD HT male-VA
20/150

LE CRVO DIFFUSE EDEMA, SRF,
CYSTOID changes

LE 11 mo later with 4 IVA inj

LE CRVO post 4 IVA

Hemi CRVO with no macular edema

LE BRVO 31/3/11 4 mo later after 3 IVA inj

What is this?

Idiopathic Macular Hole
• OCT has enhanced the knowledge about
idiopathic macular hole immensely
• It changed the concept of pathogenesis of
macular hole from Gass’s view of tangential
traction to anteroposterior traction

8th October 2022 OCT for KLE PGs I -DR WANI
Arch Ophthalmol. 1999;117(6):744-751.
doi:10.1001/archopht.117.6.744
Gass Am J Ophthalmol 1995;119:752-759
From: Macular Hole Formation: New Data Provided by Optical Coherence
Tomography
92

Stage 1A hole with cyst that is superficial –post hyaloid
attached to fovea (v/s foveal detachment)

STAGE 1b macular hole-intraretinal cyst that
extends deeper (v/s ring of xanthophyll)

Stage 2 -full thickness defect, intraretinal cysts, post
hyaloid still attached (St 2 hole<400 microns)

STAGE 3 HOLE with PVD from the macula with
operculum

STAGE IV hole
• PVD from macula and disc
• Weiss ring seen with FTMH

Role of OCT in Macular Hole
• Confirms the diagnosis and helps in classification
• Accurate measurement of the MH
• It accurately differentiates true hole from
pseudo-hole, Cyst, Lamellar hole
• Surgical decision and prognosis depending upon
size, changes in the RPE floor of hole as seen on
OCT
• OCT of operated eyes –VISUAL RECOVERY- OCT
• OCT of fellow eyes of MH patients n for follow up

A very small hole due to trauma

What is this?

Blunt trauma induced macular tear

PSEUDOHOLE

Lamellar macular hole

WHAT IS THIS?

SEVERAL indices which predict hole
closure –OCT based

Stage 3 MACULAR HOLE-with
prefoveal opacity LE VA 20/400

Macular hole post op PPV+ILM peeling
VA 20/50

ITO et al AJO 2012

This study concludes that
Restoration of ELM at 3 mo post
op will have better visual
prognosis
Ophthalmology 2010

Intraoperative OCT
• This facilitates identification of ERM, ILM flaps
during surgery

Epiretinal membrane (ERM)
OCT helps
• in its confirmation ERM is seen as hyper-
reflective layer over RETINA
• It helps to show the cystoid changes, SRF, saw
tooth appearance of retina
• Helps decide decision of surgery
• Will also show edge of the ERM/ pockets of
loose attachment to aid in surgery

RE ERM

RE OCT 20/50

Cataract+ ERM+DR- VA CF 1 MTR

Phaco/PPV/ILM peel 3 mo later 20/100

Age related macular degeneration
• OCT is now an important adjunct in the management of
AMD
• It helps in
 Detecting CNV membranes even before symptoms and
signs show up
 It can differentiate between types of CNV –type 1 or 2 OR
IPCV
 Activity of CNV membranes like subretinal fluid and
intraretinal fluid detected early
 PED characteristics are shown better –serous, hemorrhagic,
vascularized or avascular
 MUST FOR Follow up patients after anti VEGF treatment
shows persistent activity or recurrent activity or regression

Drusens
• Drusens are seen as hyperreflective bumps
under the RPE layer and make it appear wavy
if they are numerous
• May show overlying RPE atrophy
• EZ disruption over the DRUSEN may be seen
• A drusen program is available on some OCTs
and may help in follow up as to see if they are
increasing

AMD early stages
• Drusens

8th October 2022 120
OCT for KLE PGs I -DR WANI

AMD Geographic atrophy

Geographic atrophy

GEOGRAPHIC ATROPHY
8th October 2022
OCT for KLE PGs I -DR WANI
123
• Thin retina showing atrophy of outer retinal layers –outer nuclear layer, ELM line, EZ line and
RPE choriocapillaris layer
• Increased choroidal reflectivity due to atrophy of the RPE

AMD-wet or neovascular or exudative
• New vessels break Bruch’s membrane and
grow
Type 1- Grow under the RPE-OCCULT
Type 2- break the RPE and grow under
neurosensory retina-CLASSIC
• A combination of both types is common

CNV-type
I
Signs of CNV in OCT
• Fibrovascular PED
• Clinically seen as
irregularly elevated RPE
detachments
• FFA shows stippled
hyperflourescence in late
frames
• OCT
• Broad elevation of RPE
due to less fluid content
• Layers of solid material
separated by hypoecho
areas
Survey Ophthalmol 2012

Type I CNV

Serous PED
• Smooth dome shaped
elevation with uniformly
hyporeflective area
• Clinically seen as smooth
elevated lesion
• FFA shows uniform
leakage under the lesion
• The size of leakage
remains same but
intensity increases
• Bruchs membrane is
faintly seen

Serous RPE detachment
• In AMD they are classified in to vascularized
and non vascularized

Avascular serous PED
homogenously hyporeflective space
No intraretinal or subretinal fluid

Vascularized SEROUS PEDs
• Vascularized serous PEDs CNV is present under
the RPE
• The OCT appearance of such PEDs is often similar
to that of their avascular counterparts
• In some cases, however, small collections of solid
material (the apparent fibrovascular proliferation)
can be seen adherent to the outer surface of the
RPE
• Intraretinal fluid and subretinal fluid indicate CNV
• On FFA the vascularized PEDs usually show a
notch

Vascularised SEROUS PED

FFA of vascularized PED

Subretinal CNV-Type II
• CNV in sub neurosensory retinal space
• Amorphous lesion of medium to high
reflectivity above the RPE
• The lesion leaks and causes SRF, subretinal
blood and retinal edema
• In later stages the vascular component
decreases and fibrous component increases
leading to disciform scar

LE post phaco one yr ago
Disturbed vision -5 days LE 20/25

FFA LE

OCT signs of activity
• Intraretinal cyst
• Subretinal fluid
• RPE detachment
• Subretinal blood
• Subretinal tissue -hyperreflective material
SHREM

IPCV

AMD
LE 2011 APRIL

LE FFA

APRIL 2012

APRIL 2012 LE FFA

2012 OCTOBER after 3 IVAs

OCT and treatment of AMD
• OCT may be guide to start treatment but does
not replace FFA as confirmatory test
• But can be used in situations where FFA is not
possible
• OCT is very important in follow up of CNV
patients
• Persistence of fluid intraretinal, subretinal are
signs of activity and need to be treated

CONCLUSIONS
• OCT is useful device in diagnosis and
management of several important retinal
diseases

THANKS FOR YOUR ATTENTION

Optical Coherence Tomography Guide for Retinal Imaging

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