OCT ANGIOGRAPHY

1. OCT ANGIOGRAPHY
BY SAPNA MOHAN

2. DEFINITION
 Study of histology of vascular structures of the retina in vivo
without using any dye.
Non invasive imaging technique that provides 3- dimensional
visualization of retinal and choroidal vasculature.
It provides layer specific microvascular details from both
retina and choroid.

3. PRINCIPLE
 SSADA – Split spectrum amplitude decorrelation angiography.
In contrast to standard structural OCT, it not only detects the
intensity of reflected light but temporal changes in reflection by
moving particles.
Erythrocytes flowing through the vessels.
These changes are detected by repeatedly capturing B scan at each
point on retina.
This allows for creation of image contrast between static
surrounding tissues and perfused vessels.

4. Technique
OCTA produces 3D data that requires segmentation in to different tissue layers
(Slabs) by reference planes.
Reference planes
1. Internal limiting membrane (ILM)
2.Outer boundary of inner plexiform layer (IPL)
3.Outer boundary of outer plexiform layer (OPL)
4. RPE
5. Bruch membrane
Automated algorithms are commonly used in identifying these layers but in
deformed retina manual correction of the reference planes / slab boundaries
may be required.

5. Cross sectional OCT Angiograms combine flow information superimposed on
gray scale reflectance signal.
 Blood flow and retinal structural information is presented together.
This provides detailed information regarding the depth of abnormality.
En face projection process compresses the 3D angiogram to several 2D images
that can be easily interpreted.
Each En face projection summarizes only the vascular flow information with in
the depth range of that slab.

6. The following Default slabs can be visualized in separate En face
1. vitreous
2. Superficial Vascular Complex (SVC)
3. Deep Vascular Complex (DVC)
4. Outer retina
5. Choriocapillaries
6. Deeper Choroid

7. 1. Vitreoretinal interface
Healthy eye – the Vitreous slab is taken
above the ILM and is normally avascular
Normal
Neovascularization

8. 2. Superficial Vascular Complex
Multiple large linear vessels converging
towards the fovea- originating from upper and
lower vascular arcade.
Reference plane ( ILM to outer border of IPL)
1. Nerve fibre
layer vascular
plexus (NFLVP)
2. Superficial
Vascular Plexus
(SVP)

9. 3. Deep Vascular Complex
Small capillary vessels are arranged in an orderly pattern ,
with interwoven horizontal and radial connections.
Pattern is concentric around FAZ
Reference plane (outer border of IPL to outer border of
OPL)
Intermediate
Capillary Plexus
(ICP)
Deep Capillary
Plexus
(DCP)

10. 4.Outer Retina
Normally avascular
Reference plane (outer boundary of OPL to RPE)
Flow projection artifact from superficial layers can
be seen due to the highly reflective nature of RPE
layer.

11. 5. Chorio capillaries
This layer is seen as confluent lobular structures arranged
densely within macula and appears coarser outside the
macula.
Reference plane (10-20 µm below the BM)

12. 6. Deeper Choroid
Reference plane (20 µm beyond the BM )
Deeper choroidal vessels typically appear as dark vessels in
relief to surrounding bright stroma in En face.
This is mainly due to OCT signal attenuation by RPE layer and
Fringe washout artifact.

13. Terminologies
1.Segmentation
• Separation at key reference anatomic layers like ILM, outer
boundary of OPL etc
•Rapid interpretation and identification of pathological vascular
structures.
•Automated algorithms may not always produce accurate
segmentations in conditions of grossly disorganized retinal layers.
•In such cases manual offsetting of automated segmentation is
the alternative

14. 2.Slabs/ Slices
•These are 3D sections of volumetric data
•They are delimited anteriorly and posteriorly by Retina or
choroid boundaries.
3. En face image
• Transverse slab orientation
• Resulting image will give an impression of looking on to
the retina.

15. 4. Flow projection artifact
•Fluctuating shadows cast by flowing blood in a superficial
vascular bed over a deeper layer like the highly reflective
layer – RPE
•Software provides a “Remove artifact “ check box to avoid it.
•It digitally substract the overlying vessel pattern from the
RPE.

16. 5.Motion Correction Technology (MCT)
•Some patients will have involuntary saccades during
the acquisition window.
•They show up on the OCTA as narrow straight lines
across the image.
•After each scan, MCT software will perform the
necessary calculations and remove the remaining
saccades and display the image.
•The operator should examine the displayed OCTA
image for evidence of artifacts and if present should
necessitate a re – scan.

17. 6. Avascular area
•These are areas devoid of flow signal on En face
angiogram.
•E.g. Macula – FAZ ( normal avascular area)
7. Non perfusion area
•Areas that should be normally vascular but appear
avascular in the OCTA
•E.g. Macula – any avascular area outside the FAZ
7.Neovascularizaion area

18. 8.Neovascularizaion area
•Sum of pixel areas in a pathological neovascular net
identified in En-face OCT angiogram
•PDR – area of vessel growth is above the ILM.
•ARMD – area of vessel growth is in outer retina

19. SCAN PROTOCOLS
HR 10 HR 20

20. HR 10 PROGRAM
• 10°×10° field
• Area of 2.9mm × 2.9mm
• Lateral resolution of 5.7µm
• High resolution is needed to
visualize the smallest capillaries.

21. HR 20 PROGRAM
• 20 °× 20° Field
• Large vascular abnormalities that may
extend beyond the central macula
• Lateral resolution of 11µm
• Used to study capillary dropout in
Diabetic retinopathy and Vascular
occlusions

22. MAIN ADVANTAGES OR DIFFERENCES OF OCTA COMPARED TO
FFA OR ICG ?

23. Do not need intravenous injection
Can be acquired in a few seconds
Do not cause nausea, vomiting or anaphylaxis
Follow up scans can be conducted more frequently
It cannot evaluate leakage, it detects abnormalities by methods
based on
1. Depth
2. Vascular pattern

24. Since there is no dye leakage or late staining it helps to precisely
measure boundaries of
1. Capillary dropout
2. Neovascularization
The visualization of IRF and SRF in the structural OCT provides
additional information analogous to leakage.
3 dimensional nature of OCT angiography helps in separate
evaluation of retinal and choroidal circulations.

25. DIABETIC RETINOPATHY
OCTA is the only available imaging modality that can visualize the early subclinical changes seen
in the deep vascular plexus.
FFA cannot visualize the deep vascular plexus
1. Intraretinal Depth
2. Small size of the blood vessels
• Increase in the FAZ
• Small areas of ischaemia that
grow and merge with central
FAZ.
• Vascular fan is irregular
• Presence of microaneurysms,
vascular loops etc
Deep vascular plexus

26. Superficial vascular plexus
• Enlargement of FAZ
• Increased capillary tortosity
• Narrowing of capillary
lumens
• Dilatation of its terminals
adjacent to FAZ
Normal eyes
Diabetic Retinopathy eyes

27. FEATURES
1. Enlargement of FAZ
2. Areas of capillary non- perfusion
3. Increased perifoveal inter capillary areas
4. Retinal capillary tortosity and dilatation
5. Microaneurysms
6. Neovascularization of Disc
7. Neovascularization Elsewhere

28. FAZ and perifoveal inter
capillary areas
Normal eyes
Diabetic Retinopathy eyes
• FAZ of normal nondiabetic eye
measures 0.16mm(yellow)
• Peri foveal intercapillary areas
are areas of non perfusion at
least 0.15mm that are
continuous with the FAZ(white)
• Together the measure of FAZ and
perifoveal intercapillary areas
extending beyond 0.35mm is
considered abnormal.

29. MICROANEURYSMS AND AREAS OF CAPILLARY
NON PERFUSION
Microaneurysms
Capillary non perfusion
areas
• Microaneurysms are seen as
focal dilatation or areas of
capillary non perfusion on
OCTA.
• Compared to FFA, octa can
detect most but not all
microaneurysms.
• This is because some of the
microanerysms have slower
flow, lesser than the sensitivity
threshold of OCTA

30. Neovascularization Else where
• The neovascularization is
seen as abnormal vessels
growing in to the vitreous or
in to the pre retinal space.
• Neovascularization is seen as
irregular masses on En face.
• A breach in ILM is a requisite Small neovascular complexes on the en-face
angiogram breaching the ILM and with positive
flow signal in the structural B-scan (within
dashed lines), in accordance with active NVEs.

31. Neovascularization
Disc
NVDs consisted on thick tissue
protruding from the disc that
grew axially along the posterior
hyaloid and extended into the
peri-papillary ILM surface

32. RETINAL VEIN OCCLUSION
In OCTA, vascular network with evident non-perfusion
corresponding to non perfusion visible in FFA.
In OCTA it is clearly visualized as there is no masking by leakage.
• Capillaries in the non perfused areas are
truncated with abrupt interruptions.
• Areas of retinal oedma is seen as
widening and distortion of the mesh of
capillary network.
• Non perfusion areas are seen as greyish
granulated areas with absence of
capillary net.
SUPERFICIAL VASCULAR PLEXUS

33. • Irregular distribution
with vessels frequently
changing direction in the
affected area.
• Increased shunts seen
between superficial and
deep plexus.
DEEP VASCULAR PLEXUS

34. RETINAL ARTERY OCCLUSIONS
SUPERFICIAL VASCULAR
PLEXUS
Superficial vessels in the
occluded area loose some of
the collaterals.
DEEP VASCULAR PLEXUS
Large areas of capillary
dropout and sparse mesh

35. MACULAR TELANGECTASIA ( MAC TEL)
STAGE 1
Superficial Retinal Slab- no change
Deep Retinal slab – Telangiectatic capillary in temporal perifoveal area.

36. STAGE 2
Superficial Retinal Slab – Dilated feeder arteriole and draining venule.
Deep Retinal Slab – Perifoveal Telangiectatic capillaries

37. STAGE 3
Superficial Retinal Slab – Right angled draining vessel at 3 o clock,
capillary drop out and disruption of perifoveal capillary net.
Deep Retinal Slab – Telangiectatic vessels in the temporal and nasal
side.
Outer Retina Slab – Telangiectatic vessels reaching the RPE.

38. STAGE 4
Superficial and Deep Retinal Slab- Vascular ingrowth to the FAZ with irregular shape of FAZ,
multiple dilated feeder and drainage vessels.
Outer Retina Slab and Choriocapillary Slab – Sub retinal Neovascular membrane (SRNV)

39. STAGE 5
Superficial and Deep Retinal Slab- Vascular ingrowth to the central fovea with
patchy loss of foveal tree.
Outer Retina Slab and Choriocapillary Slab – Neovascular membrane connected to
dilator outer retinal vessels.

40. DRY ARMD
Early/ intermediate AMD
Generalised reduction of choriocapillary density with
focal areas of loss.
Dark patches is accompanied by displacement of large
choroidal vessels in to choriocapillary layer.
Late AMD
Geographic atrophy- areas of large choriocapillary loss
with displacement of choroidal vessels in to their space.
These displaced vessels appear as large bright vessels.

41. CNVM
Abnormal dilated tortous vessels detected in
1) Avascular complex ( Outer retina)
2) Under the RPE
USES
1. Allows to assess the extend and morphology of Neovascular network without the problem
of dye leakage.
2. Follow up of CNVM lesions treated with anti- VEGF injections- This produces regression
and pruning in small abnormal capillaries without any change in large trunks.

42. CNVM- PATTERNS
SEA FAN MEDUSA ILL DEFINED DEAD TREE PATTERN

43. EXUDATIVE CNVM
Classification of Neovascularization in Exudative ARMD
TYPE 1 CHOROIDAL NEOVASCULARIZATION ( OCCULT)
TYPE 2 CHOROIDAL NEOVASCULARIZATION (CLASSIC)
MIXED TYPE 1 and 2 CHOROIDAL NEOVASCULARIZATION
TYPE 3 NEOVASCULARIZATION : RETINAL ANGIOMATOUS PROLIFERATION (RAP)
POLYPOIDAL CHOROIDAL VASCULOPATHY (PCV)

44. TYPE 1 CNVM
• Outer retinal slab and
superficial vascular plexus-
no abnormal vessels
• Chorio capillaries slab shows
blood flow in a neovascular
net.

45. TYPE 2 CNVM
• Superficial retinal slab- no
abnormal vascular flow
• Outer retina slab and
Chorio capillaries slab
shows small CNV vascular
net.

46. TYPE 3 CNVM (RAP)
Deep Retinal slab – enlarged
proliferative intraretinal capillary
bed corresponding to capillary
location on structural OCT

47. POLIPOYIDAL CHOROIDAL VASCULOPATHY
(PCV)
•Manual segmentation line near the apex – Polyp
•Segmentation line near the base – BVN
•Curved segmentation line- Polyp and BVN

48. PRE TREATMENT AFTER TREATMENT

49. PATHOLOGICAL MYOPIA
DEFINITION
• Axial length > 26mm
• Refractory error - 6D
1. Peripapillary myopic cresent
2. Tessellated fundus
3. Dome shaped macula
4. Focal patchy atrophy
5. Lacquer cracks
6. Myopic schisis with macular hole
7. Myopic CNVM

50. PATCHY MACULAR ATROPHY CHOROIDAL SLAB- Glomerular
CNVM with thin feeder vessels.
Macular Hemorrhage with
lacquer crack

51. THANK YOU