General OCT working principle Introduction to Macular Disorders 1. CME 2. CSR 3. PED 4. Druscen 5. CNV 6.ARMD Recent advances OCT-Angiography

1. Dr. Sajjan Sangai
Dept. Of Ophthalmology
MGM Medical College and Hospital, Aurangabad

2.  Retina is a multi layered tissue with each
layer having a different reflectance pattern
thus by this principleOCT permits
recognition of multiple retinal layers in vivo.

3. Optical
Related to
light and
optics
Coherence
Two light
beams of
the same
wavelength
in phase
Tomography
Sectioning
/Cutting

6. Horizontal
Structures
• Inner and Outer
Plexiform layer
• Inner and Outer
Limiting Membrane
• Pigment epithelium
Vertical
Structures
• Müllers fibres
• Cell chains
containing of
photoreceptor to
bipolar and ganglion
cells

8.  Imaging with OCT is based on Michelson's
Interferometer and includes complex analysis
of reflections of LOW COHERENCE LIGHT
from the ocular tissue ( low coherence
interferometry)

9. Low coherence
infrared light
840 nm
Reflected by
different retinal
tissue layers

11. The
reflected
light from
the retinal
tissue and
reference
mirror
interacts
to form an
Step 3
Distance
between
the light
source
and
reference
mirror
Step 2
Distance
between
the light
source
and retinal
tissue
Step 1
INTERFERENCE PATTERN
This interference pattern is processed into a signal

12.  The signal is analogous to that obtained with
A Scan Ultrasonography.
 A 2D image is built as the light source is
moved across the retina and then the series
of stacked and aligned A scans produce a
2dimensional cross sectional image
resembling a HISTOLOGIC SECTION

13. Transverse scanning at multiple
sequential points (A-Scans)
2 Dimensional data collection
Generation of Cross sectional map
Display in pseudo colours

14.  The infrared image has a field of 30˚ .
 OCT operates like a fundus camera but
resolves like a USG machine .
USG OCT
Source Sound waves Infrared light
waves
Resolution 150µ 10µ
Patient Contact Needed Non- Invasive

15. Macular hole
Macular edema
Central serous retinopathy
Epiretinal membranes
Diabetic retinopathy
Age-related macular degeneration
Scars, Foveal burns
http://www.aao.org/eye-health/treatments/what-does-optical-coherence-tomography-diagnose

16. Non
contact
Non
invasive
High
Resolution
Real time
Imaging

17. Corneal
Opacities,
Cataract
Poor patient
cooperation
Asteroid
hyalosis,
Vitreous
Haemorrhage
Intraocular Gas
(SF6 ,C2F6,C3F8 )

18.  Time domain OCT
 Spectral domain OCT

20.  Time-domain devices can provide 400 A
scans per second with a maximal axial
resolution of 8-10µm
 High quality images require longer time to
create.Therefore time is the major limitation
of this technique.

21.  Absence of movable mirror speeds up the
image acquisition up to 50 times.This
technique enables to obtain large numbers of
A-scans that allows creating high resolution
images.
 SD devices can provide 20.000-52.000 A-scan
per second with a 5-7µm resolution
 Such a speed reduces the eye movement
artefacts.

23. TIME DOMAIN OCT SPECTRAL DOMAIN OCT
RESOLUTION : 10µ 5-7µm
2 Dimensional images 2 D and 3 D
Low coherence Interferometry Low coherence interferometry
Uses fixed wavelength Broad wavelength spectrum
Lower speed 400-512 A scan/sec High speed : 52000 A scans/ sec

26. Scan Utility
Line Multiple line scans can be obtained
without returning to main window
Radial Lines Determines entire macular thickness/
volume
Raster lines Entire area of pathology can be scanned
Repeat scan Monitoring change during follow-up
Macular thickness Determines entire macular thickness/
volume
Fast macular thickness Allows comparative thickness/ volume
analysis

27. Qualitative
• Morphological changes
• Reflectivity
• Shadowing
• Structure
microstructure
segmentation-
alteration/ deformation/
loss of structure.
Quantitative
• Retinal Map
• RetinalThickness
• RetinalVolume

28. Retinal edema-
1.CME
2.Vitreoretinal
traction leading
to edema
Retinal atrophy
secondary to
1.Laser
2.Trauma
3.Inflammations
IncreasedThickness
DecreasedThickness

29.  High Reflectivity:
(Red andYellow):
 Superficial:
1. Epiretinal/ vitreal membranes
2. Sub hyaloid / Sub ILM haemorrhage
3. CottonWool Spot’s
4. Myelinated nerve fibres.

30.  Intraretinal:
1. Hard exudates,
2. Intraretinal haemorrhages
3. fibrosis and scarring

31.  Deep:
1. Drusen
2. RPE Hyperplasia
3. Scarring , atrophy
4. Sub retinal neovascular membrane
5. Deep pigmented lesion e.g. Nevus

32.  Low reflectivity: ( Black and Blue)
1. Gross separation of cellular elements and
fluid present either in form of cystoid spaces
2. Neurosensory detachment
3. RPE detachment
results in decreased reflectivity

33. Shadowing:
 Dense highly reflective elements produce a
kind of blockage of light waves by
attenuation
 This appears a shadow that conceals the
element lying behind it
 E.g. Haemorrhage's, Hard exudates, cotton
wool spots, dense pigmented lesion or scar,
retained foreign body.

34.  Age related Macular Degeneration
a) Dry / non-neovascularAMD: Drusen
b) Wet / neovascularAMD: CNV and PED
 Epiretinal Membrane
 FullThickness Macular Hole
 Central Serous Chorioretinopathy
 Cystoid Macular Edema

35.  Degenerative disorder affecting macula
 Clinical classification of AMD:
Category Definition, based on lesion ( within 2DD of fovea)
No apparent
ageing change
No drusen
No AMD pigmentary abnormalities
Normal ageing
changes
Only druplets
No AMD pigmentary abnormalities
Early AMD Medium drusen (>63 µm - < 125 µm)
No AMD pigmentary abnormalities
Intermediate AMD Large drusen (>125µm)
Any AMD pigmentary abnormalities
Late AMD Neovascular AMD and/or any geographic atrophy

36.  Extracellular deposits located at the interface
between the RPE and Brusch membrane.
 Derived from immune mediated and metabolic
processes in RPE.
 On OCT:
Medium sized and large drusen are seen as hyper
reflective irregular nodules beneath the RPE

37. • Small drusen/ Hard drusen
• Well defined , whitish yellow lesion
• < 63 µm
• Fairly well defined yellow white focal
deposits
• Measuring between 63 µm - 125 µm
Intermediate
Drusen
• Large drusen/ Soft drusen
• Less well delineated yellow white deep
retinal lesion
• >125µm

38.  Causes:
Degenerative Inflammatory
Traumatic Neoplastic
Brusch memb./ RPE
Compromised by

39.  Types: Classified according to Macular
Photocoagulation Study (MPS): Based on FA
 Classic CNV (20%): well defined lacy pattern
during early transit of dye subsequently
leaking to sub retinal space.
 Occult CNV (80%): Limits cannot be fully
defined on FA
 Predominantly / Minimally classic CNV:
Classic element is grater or less than 50 % of
total lesion

40.  On OCT:
CNV is shown as
1. thickening and fragmentation of RPE and
Choriocapillaries
2. Sub retinal, Sub-RPE fluid,
3. Blood and scarring
are demonstrated.

42.  Thickened and dysfunctional Brusch
membrane impending movement of fluid
from RPE towards the choroid PED.
 On OCT :
PED shows
Separation of RPE from the Brusch membrane
by an optically empty area
Clinically:Orange dome shaped
lesion
FA:Well demarcated Hyperfluroscent
pooling
ICGA: Hypofluroscence
OCT: Optically empty area below
RPE

43.  Sheet like fibro cellular structure that
develops over surface of retina.
 Proliferation of cellular component and
contraction of membrane leads to visual
symptoms.
 On OCT-
o Highly reflective surface layer associated
with retinal thickening.
o Useful to exclude significantVMT .

45.  Pathogenesis:
The vitreofoveal traction is central to
development of a full thickness macular hole.
 Gass: Proposed that contraction of
prefoveolar cortical vitreous results in
tangential traction

46.  Classification:
1. Gass classification scheme on
Biomicroscopy,
2. New OCT based classification- IVTS-
(InternationalVitreomacularTraction Study)

51.  Differential Diagnosis
1. Lamellar hole
2. Pseudo hole
3. ERM
4. CME
5. CSR with central yellow spot

52.  Idiopathic
 Characterised by local serous detachment of
the sensory retina at the macula secondary to
leakage from choriocapillaries through one or
more hyper permeable RPE sites
 Affects young , middle aged men
 Risk factors: Steroid administration,Cushing
syndrome, H. Pylori infection, pregnancy,
psychological stress, sleep apnoea.

53.  On OCT:
Optically empty neurosensory elevation,
Other findings – one or more smaller RPE
detachments , precipitates on posterior surface
of detached retina , thickened choroid.
 On FA:
Hyperfluroscent spot that enlarges- Ink Blot
Vertical column- Smoke stack

55.  Accumulation of fluid in outer plexiform layer
and inner layers of retina with formation of
tiny cyst like cavities.
 Fluids may initially accumulate intracellularly
in Müller cells with subsequent rupture.

56. 1. Ocular Surgery and Laser.
2. RetinalVascular Disease: Diabetic
retinopathy, RetinalVein occlusions.
3. Inflammation: Intermediate Uveitis
4. Drug induced: topical prostaglandin
derivatives.
5. Retinal dystrophies: Retinitis pigmentosa
6. Conditions havingVMT: ERM
7. CNV
8. Tumours: Retinal capillary haemangioma
9. Systemic diseases : CRF

57.  On OCT:
Retinal thickening with cystic hypo reflective
spaces, and loss of foveal depression.
Lamellar holes may be demonstrated in
advanced cases.
 On FA:
A petalloid pattern is seen due to dye
accumulation in microcytic spaces in outer
plexiform layer

59.  Various newer OCT systems are:
1. Ultra high resolution OCT
2. Doppler OCT
3. CAS OCT-Visante OCT
4. Combined FFA and en-faceOCT
5. IntraoperativeOCT

60.  Axial resolution of 3 µm
 Transverse resolution of 15-20 µm
 Useful for visualization of
a) External limiting membrane
b) Ganglion cell layer
c) Photoreceptor layer

61.  Technique that combines laser doppler
velocimetry and OCT for imaging the depth ,
diameter flow rate, retinal haemodynamic
characteristic
 Only possible in larger vessels
 Not well suited for angiography of retinal and
choroidal microvasculature, where vessels
are nearly perpendicular to the OCT beam.

62.  Surgical microscope integrated with OCT to
perform simultaneous imaging and en face
visualization
 Uses are:
Macular hole surgery,
ERM peeling,
Sub retinal surgery
Zeiss OPMI LUMERA® 700 and RESCAN™ 700

63.  Doppler OCT uses the Doppler phase shift to
quantify blood flow in larger vessels and
measure total retinal blood flow
 OCTA is more concerned about separating
moving scatters from static background
tissue to create angiograms.

68.  Principles and Practices of Ophthalmology,Vol. 2 ,
Third edition, Albert and Jacobiec’s.
 RETINA,Vol.1 , Fifth edition, Ryan.S.J.
 Kanski’s Clinical Ophthalmology, 8th edition,
Bowling B.
 Practical Handbook of OCT , Lumbroso.B, Rispoli M.
 Step by Step Optical CoherenceTomography.