OCT is used to non-invasively image the retina in cross-section with micrometer-level resolution. It works by measuring the interference of light reflected from retinal structures. OCT was developed in 1991 and uses near-infrared light wavelengths of 840nm and 1310nm. OCT provides high-resolution 2D images of the retina and can integrate data points over depth to form 3D representations. It is useful for diagnosing and monitoring many retinal diseases.

1. OCT

2. • OCT is a non contact, non invasive, micro resolution
cross-sectional study of retina which correlates very well
with the retinal histology.
• Histopathology without biopsy (Light is used instead of
knife)
• Developed by Huang and associates in 1991.

3. • Principle: Interferometry
- measures echo delay(time) and intensity of reflected
light from target structure.
• Wavelength used :
840 nm Posterior Segment
1310 nm Anterior segment

4. • Interference…?
addition of two waves mathematically.
Subtract from each other to
create a wave of lesser
amplitude than either one.
Destructive Interference
Add together to create a
wave of greater amplitude
than either one.
Constructive interference

5. • Coherence..?
– Correlation b/w physical quantities of a single wave, or
b/w several waves.
– High energy electrons return to low energy level and
emit radiation (in a waveform).
– The peaks and troughs of the waves correspond (no
interference) – constant phase (Coherence)
– Types : Spatial & Temporal

6. • Low Coherence infra red light coupled to a fibre optic travels
through a beam splitter directed through the ocular media to
the retina & a reference mirror

8. • Interference is measured by photo detector and
processed into a signal.
• Light source moves resembles a histology section
of retina.
• Forms 2 D image
– Axial resolution =<10 microns
– Transverse resolution is 20 microns
• Integrates data points over 2 mm depth

10. • Colour coding
– White & Red : highly reflective structures
– Black & blue : low reflective structures
– Green : intermediate reflective structures.

11. UBM
B scan
Abdo.USG

12. Two types
Time Domain
Fourier
Domain
Swept source
OCT
Spectral OCT

15. Types of OCT..

16. • The X, Y and Z planes…
• X plane is the horizontal B-scan as it is acquired. The anatomical
features as shown in the X plane are real since the eye movement is
Negligible.
• Y plane is the vertical reconstructed B-scan. The eye movement in the
reconstructed B-scan is quite noticeable.
• Z plane is a reconstructed en face image. It is also called the coronal
scan or C-scan.

17. • Many A-scans arranged in a line or circle and form high
definition B-scan (0.02 – 0.04 sec)
• Many B-scans compose 3D scan patterns.

18. Retinal scan patterns
• Line scan
• Cross hair scan
• High density scan (line/cross hair)
– 4096 A-scans(4 times) and no averaging
• Macular map scan
• Enhanced macular map scan and 3d reference scan
• Grid scan
• Raster scan
• Radial slicer scan & macular mapping 6 mm
• 3D macular scan

19. • Line scan
Length :6mm
Default fixation
target : fovea
High definition
Bscan – 1024 Ascans
Frame averaging (16)

20. • Cross hair scan
L: 6mm
0.63 sec
Default fixation :
foveal centre
Frame averaging
(8 Horizontal Bscan
8 Vertical Bscan)

21. • Macular map(MM5)
– 5*5 sq with 0.5mm
spacing
– Central 3mm sq with
0.25mm spacing
– 19,500 Ascans
– Takes 0.78 sec

22. • Enhanced macular map scan(EMM5) and
3d reference scan
– MM5 scan + extra raster scan in inferior macula (for
registration with 3D reference scan)
– 3D reference scan registered with EMM5 and create 7
mm sq of OCT SLO image
– To be done once for each patient

23. • Grid scan
– For cross hair scan, it is difficult to compare 2 visits
when the scan center has small shift due to movement
or poor vision.
– 5*5 lines
– Length of line is 8 mm
– Width of 5 lines is 2 mm

24. • Raster scan
– Used to give 3D view in
short time (0.34sec)
– 17 parallel lines
– Length of line is 6 mm
– Width of Scan : 4 mm

25. • Radial slicer scan
– 12 radial scans
• Macular Mapping scan
– Special radial slicer
scan
– Length is 6mm
– Provides analysis of
retinal thickness map.

26. Normal Anatomy
ILM, RNFL, OPL,IPL Hyper Reflective
GCL, INL,ONL Hypo Reflective
Retinal Vessels Circular hyper reflective

28. Pre retinal
• Pre retinal membrane
• Epi retinal membrane
• Vitreo retinal strands or traction
• NVE/NVD

29. Intra retinal
• Choroidal neovascularization
• Diffuse intra retinal edema
• CME
• Hard Exudates
• Scar

30. Sub retinal
• Choroidal neovascularization
• RPE detachment
• Drusens
• Sub retinal fibrosis
• Scar
• RPE atrophy

31. Systemic approach
Identify
RPE
Examine
anterior to
RPE
Examine
RPE
Examine
posterior to
RPE

32. Systemic approach
Identify
RPE
Examine
anterior to
RPE
Examine
RPE
Examine
posterior to
RPE

33. • Irregularity
• Fragmentation
• Rupture
• Interruption
• Depression
• Elevation
• Thinning
• Thickening

34. Systemic approach
Identify
RPE
Examine
anterior to
RPE
Examine
RPE
Examine
posterior to
RPE

35. • PED
• Bruch’s membrane
• Hyper reflectivity (fibrosis vs. RPE atrophy)

36. Systemic approach
Identify
RPE
Examine
anterior to
RPE
Examine
RPE
Examine
posterior to
RPE

37. • Vitreous
• Retinal thickness
• Foveal contour
• Sub retinal fluid
• ELM
• Intra retinal cysts
• Inner retinal layers

38. AMD
• Hard drusen
– discrete nodules of high reflectivity in RPE level.
– RPE showing discontinuity

39. • Soft drusen
– Elevations of RPE level
– Hyperreflective than Photorecepter layer and
hyporeflective than RPE layer.
– Confluent soft drusen have scattering deposits forming
‘dome like’ elevations.
– IS/OS and ELM can be absent above the large RPE
elevations-photoreceptor impairment

40. • Geographic atrophy
– Absence or thinning of overlying photoreceptors
– So bright areas of increase transmission (bright
shadowing) seen.

41. WET AMD
• CNVM
– Fusiform enlargement of RPE/Bruch’s membrane/
choriocapillaries reflective band.
Duplication with high
scattering material b/w 2
bands
Sub-retinal fluid seen as
optically empty space.

42. • Fibrovascular PED
– Elevation of pigment epithelial layer with irregular surface
– Space below RPE is filled with solid layers of medium reflectivity
separated by hypo-reflective clefts.
Sub retinal fluid

43. • Serous PED
– Elevation of RPE with flat top
– Homogenous hypo-reflective space under RPE.

44. • Haemorrhagic PED
– Blood under the RPE appears hyper-reflective,
attenuating the signal from deeper structures.
– Subretinal fluid can be observed as hyporeflective
spaces above the RPE (arrows).
SRF

45. RPE tear with rolled edge

46. • Application
– Retinal thickness
– Sub-retinal fluid
– Response to therapy

47. Central Serous Chorioretinopathy
• Elevated neurosensory retina + PED
• Posterior surface of detached retina is smooth
• Line corresponding IS/OS junction is not visible.

48. • After one month
– Decrease sub retinal fluid
– Small granules seen at posterior surface of detached retina
– Inferior shift of fluid must be visible in vertical scan

49. • After 3 month
– Thickness of photorecepter outer segment increase

50. • After the reattachment of retina
– The IS/OS line become visible

51. • OCT at leakage point
– PED (within or at margin of CSCR)
– Size of PED is independent to the size of CSCR
– Some eyes show residual PED even after the resolution
of CSCR

52. Epiretinal Membrane
Proliferation of glial cell or RPE cells over ILM and surrounded by
a newly-formed extra cellular matrix with PVD (partial/complete)
1. Macular cellophane
– Mild expression of disease
– Usually no symptoms
– Ophthalmoscope : nonhomogeneous enhanced reflex on the posterior pole
2. Macular pucker
– More severe form
– Decrease visual acuity, metamorphopsia
– Wrinkles on the retinal surface, distortion of retinal vessel coarse and
sometimes associated with CME
– ERM is thicker and adherent and contracted

53. • On OCT
– Hyper-reflective line upon the retinal surface

54. • Thickened the ERM = more the reflectivity = more traction
over retinal layers
• In long standing puckers, ERM can completely subvert the
retinal anatomy
• Eventually intraretinal small cystic spaces develops
• With progression, they grow in dimension and extend through
the retinal layers in the foveal region and form macular hole
(in the advance stages, ERM traction can rarely cause a
detachment of neuroretina)

56. Cystoid Macular Edema
• The shape, dimensions and extension of the cystic cavities depend on
the framework of retinal structures and layers in the macula that
influence the pattern.
• The Henle fibers are arranged radially in star shaped and centered on
the foveola.

57. • At the center of macula, muller cells binds photoreceptor cells
together without which, photoreceptor cell layer with its
horizontally radiating nerve fibers would be highly susceptible
to disruption at the umbo.
• Muller cells are arranged radially and not horizontally. That is
why on OCT imaging, cystic spaces are not confined to a single
layer
• The retina is divided in vertical and horizontal structures that
limit expansion of exudates, haemorrhages and edema.
– Vertical structures: muller cells unite the inner and outer
limiting membrane, chains formed by photoreceptor cell to
bipolar cells to ganglion cell
– Horizontal structures: inner limiting membrane, outer
limiting membrane, IPL,OPL

58. • Two mechanisms
– Breakdown of blood retinal barrier
– Vitreomacular traction

59. • Early cystoid edema
– One or more small rounded edema cells in
INL,ONL
– Later numerous, small cavities are formed
which are seperated by thick septa, mainly seen
in the ONL,INL and IPL

60. • Advanced cystoid edema
– Small cavities coalesce, cystoid cells merge, their dimensions
increase, the wall get thinner and form large, smooth, regular,
globular cysts.
• Largest cystic spaces are found centrally .
• Smaller cystic spaces are seen parafoveally and extra foveally.
• These aspects gives the major thickness to macular center.
• So, measurement of retinal thickness in the center reflects , the size of
a few or a single central cyst rather than that of the entire retina.

61. • Regressed cystoid edema
– Cavities decrease in dimension, triangular in shape with
sharp angles.
– Walls are less regular, thinner, makes bifurcations and
granulated.

62. • ERM : tractional CME
– ERM + increase retinal thickness+ irregular cystic spaces

63. • Vitreomacular traction and CME
– The tractional forces from the vitreous lead to edema formation.

64. • Macular hole with CME
– Full thickness macular hole with cysts of variable size.

65. Diabetic Retinopathy
• Why OCT?
– For subtle macular edema
– To classify macular edema
– To predict outcome of treatment in DME
• Irreversible damage is seen on oct

66. Classification
• OCT sensitivity to detect DME is very high (98.6 %) Evaluation of the
OCT scans demonstrated five distinct patterns of DME.
• Type 1: focal macular thickening.
• Type 2: Diffuse thickening without cysts(sponge like retinal thickening)
• Type 3: diffuse cystoid macular edema.
• Type 4: Tractional macular edema.
• Type 5: DME from one of the previous types associated to a macular
serous retinal detachment.

67. • Diffuse thickening without cysts (sponge like retinal thickening)
– Increase retinal thickening and reduce intra retinal reflectivity
– May be seen as an isolated or along with CME/ serous retinal
detachment.

68. • Cystoid macular edema
– May be isolated or along with other variety
– 2A: 1 / 2 cysts in IPL with central foveal thickness is > 325 micron
– 2B: patelloid pattern of intraretinal cysts; foveal thickness >485 micron
– 2C: chronic edema, major intraretinal damage with large cavities
resembling retinoschisis; foveal thickness >405 micron

69. • Tractional retinal edema
– Focal or diffuse traction by thickened and taut posterior hyaloid,
thickened ILM, or by epiretinal membrane
– Tangential or antero-posterior forces can be demonstrated by OCT
4A: posterior hyaloid traction
4B: epiretinal membrane
4C: both posterior hyaloid and epiretinal membrane

70. • Serous retinal detachment
– Empty space b/w RPE and outer layer of photoreceptor cell
– Difficult to diagnose clinically
– Presence of serous RD was initially thought to signal a severe stage of
DME. But recent OCT based studies suggest that prognosis is depend
on integrity of photoreceptor cell layer and thickness of retina above
serous RD.

71. Vitreomacular traction syndrome
• As a person ages, vitreous liquifies and detaches from the retina.
• Posteriorly, vitreous is bound with a thin membrane of condensed collagen,
termed the posterior hyaloid.
• Vitreous is most adherent to the vit base > optic disc > macula> blood vessels.
• In some cases, adhesions b /w vit and macula are abnormally firm and as the
vit begins to separate from retina, traction forces are generated in areas of
vitreomacular adhesions.
– Macular hole
– Tractional macular edema
– Subretinal fluid and/or macular edema
This entity is commonly referred to
as vitreomacular traction syndrome.

72. • On OCT, partially detached hyaloid appears as thin, moderately
reflective line anterior to neural retina.
• In some cases epiretinal membrane may be visualize as highly
reflective line just anterior to nerve fiber layer.

74. Macular Hole
• Why OCT is advisable in Macular hole?
– For clinically useful classification
– To determine if there is a concurrent ERM
– To examine IS/OS
– To evaluate post operative morphology of
fovea
– To differentiate it from other condition like
pseudohole, inner lamellar holes, cystoid
macular edema.

75. Classification
Stage 1: Loss of the foveal depression.
1A: Foveolar detachment characterized by a loss of
the foveal contour and a lipofuscin-colored spot.
1B: Foveal detachment characterized by a
lipofuscin-colored ring.
Stage 2: A full thickness break < 400µm in size. It might
be eccentric with an inner layer “roof.” In most cases, the
posterior hyaloid has been confirmed to be still attached
to the fovea on OCT analysis.
Stage 3: A hole ≥400 µm in size. The posterior hyaloid
is noted to be detached over the macula with or without
an overlying operculum.
Stage 4: MH is characterized by a stage 3 MH with a
complete posterior vitreous detachment and Weiss ring.

76. Lamellar hole
A partial thickness. macular hole, where the inner layers of the macula are involved with
traction and detached from the underlying layers.

77. • Pre operative evaluation
1. Pre-op size of hole is inversely correlated to success rate
2. It is good to know extent of ERM on OCT before OT.
• Post operative evaluation
1. IS/OS junction indicates normal alignment which is necessary
for good visual outcome
2. To classify healing pattern
Other classification
3. CME and ERM in post op OCT are useful findings to predict the
risk of reopening
Type 1: closed without foveal neurosensory retinal defect
Type 2: closed with foveal neurosensory retinal defect
U – Normal foveal contour
V- Steep foveal countour
W – foveal defect of neurosensory retina

78. Type I
Type II

79. V type
U type

80. Hole form factor

81. Macular hole index
MHI > 0.475 :
good visual
prognosis after
surgery

82. Tractional Hole Index
• THI = H
M
• THI > 0.973 – good
visual prognosis after
suregery.