About optical coherence tomography

1. OCT
Dr David Khiangte
S4 Jr 2
23/9/2020

2. OCT
OPTICAL : relating or involving light and optics
Coherence : constant phase difference in 2 or more waves overtime
Tomography : Imaging by sectioning or slicing.

3. The advantage of OCT is that it is giving us diagnostic capability at
cellular level

4. It also gives us a lot of histological details of Retina and Choroid

6. • Quick
• Non Invasive
• Reproducible

7. Todays talk :
• PRINCPLE OF OCT
• EVOLUTION OF OCT
• COMMON PROTOCOLS FOR IMAGING
• HOW TO READ AN OCT SCAN
• COMMON RETINAL CONDITIONS
• GALUCOMA
• PAPILLEDEMA VS PSEUDOPAPILLEDEMA

8. Principle of OCT : Interferometry
• Like an Optical analogue of ultrasound
• Uses low coherence light source to produce cross sectional images of
Retina

9. PRINCIPLE
• It is based on the principle of optical
reflectometry(interferometry), which involves the
measurement of intensity and echo time delay of light back-
scattering through transparent or semi-transparent media
such as biological tissues
• Light from a broadband light source is broken into two arms, a
reference arm and a sample arm that is reflected back from
structures at various depths within the posterior pole of the
eye. The echo time delay of the light reflected from various
layers of retina is compared with echo time delay of light
relected from reference mirror

10. TD OCT SD OCT SS OCT
EVOLUTION OF OCT

12. Time domain(TD) vs Spectral (SD) vs Swept source(SS) OCT

14. • Fundus viewing unit
• Interferometry unit
• Computer display
• Control panel
• Colour printer

15. Scan Acquisition Protocol : Each commercially available OCT device has
unique scan patterns that are programmed into the machine

16. Scanning Protocols
line scans are a single B-scan composed of generally a
higher number of A-scans than the cube scans. This
higher sampling density allows higher resolution
scans of the retinal tissue to be acquired
Line Scan

17. Raster scan
• Series of parallel line scans that can be obtained in any angle
• Higher resolution (resolution of 5-line or 7 line raster scans provides an excellent image for viewing macular
pathologies in the retinal layers)

18. Radial scan
6-12 line arranged in equal angles with a common axis
When the axis coincides with the fovea, the relationship of the lesion to the fovea is documented
It gives relationship of the lesion with respect to the fovea

19. 3D SCAN
A number of horizontal line scans co mposing a 6x6 mm or 7x7 mm or 12X9 mm rectangular box
3D view – implementation of advanced , complex analysis – topographic maps and cystic volume
These types of scans, however, are more prone to artefact caused by eye movement

20. Steps :
• Machines is activated
• Patients pupils are dilated (3mm minimum)
• Patient is seated comfortably
• Asked to look into target light in the ocular lens
• Discouraged to blink
• Protocol selected as per case requirement – A protocol is simply a pre-
determined procedure or method
• OCT image – upright and straight and the reference scan pattern
should center on the fovea or area of interest

21. Enter Patients details

22. Select appropriate scan

24. How to read an OCT Scan

25. CHECK LIST

29. Direction line of scan

30. For purposes of analysis , the OCT
image of the retina can be
subdivided vertically into four
regions
Pre retina
Epi retina
Intra retina
sub retina

31. NORMAL OCT

32. OCT MACULA

33. Reflectivity

34. HYPERREFLECTIVE
• Hard
Exudates
• Hemorrhage
• Drusen, PED
• Epiretinal
Membrane
• CNVM Lesion
• Disciform
scars

35. HYPOREFLECTIVE
Intraretinal/
Subretinal
fluid

36. HYPER REFLECTIVE HYPOREFLECTIVE
ILM
RNFL
IPL,OPL,ELM,EZ
RPE
RPE – CHORIOCAPILLARIS COMPLEX
GANGLION CELL LAYER
INNER NUCLEAR LAYER
OUTER NUCLEAR LAYER
DRUSEN, PED
EPIRETINAL MEMBRANE
CNVM
DISCIFORM SCARS
HARD EXUDATES
HEMORRHAGE
INTRARETINAL/SUBRETINAL FLUID

37. QUALITATIVE ANALYSIS OF OCT
• Description by location
• Description of form and structure
• Identification of anomalous structure
• Observation of the reflective qualities – Hypo/Hyper reflective

38. QUANTITATIVE ANALYSIS
• Thickness
• Volume
• Shadow areas

39. Quantitative Analysis

40. COMMON RETINAL DISEASES

41. Retinal layers absent causing light to pass easily and choroid gets
highlighted
Lesion on top of retina not allowing light to pass through
Choroidal lesion not allowing light to pass through

42. Retinal vascular disorders
Role of OCT :
Retinal thickness assessment
Patterns of DME
Deciding Rx protocol in DME
Quantification of CME in vein occlusion
Monitoring response to treatment in DME, RVO
Prognostic indicators

43. Diabetic Macular Edema
Key OCT Features
• Sub- and intra-retinal fluid accumulation are the
key features
• There is decreased reflectivity of outer retinal
layers on OCT due to increased foveal thickness.
• Exudates can be seen as hyper-reflective spots
within the retina.

44. Spongy macular edema
cystoid macular edema
Posterior hyaloidal traction without TRD
Serous retinal detachment
Posterior hyaloidal traction with TRD
Types of DME (OCT Classification)

45. Vein occlusions
Role of OCT
• CME , SRD
• Prognostic aid
• Great follow up tool
• Complications – ERM, Lamellar hole , RPE changes

46. Key OCT Features
• Macular edema
• Visual acuity inversely correlates with macular
thickening measured with OCT.
• After treatment of macular edema, discontinuity
of the photo- receptors (especially the ellipsoid
zone) and retinal architecture correlate with
worse visual acuity.
CRVO

47. Key OCT Findings
• OCT is key to diagnosing associated macular edema, deter-
mining if the fovea is involved, and determining response to
therapy.
• OCT findings include cystoid macular edema, intraretinal
hyperreflectivity from hemorrhages, shadowing from edema
and hemorrhages, and subretinal fluid
• Even with resolution of cystoid macular edema, disruption of
the foveal photoreceptor layer, specifically the ellipsoid layer
and external limiting membrane, have been associated with a
poorer visual prognosis.
BRVO

48. CRAO
Acute phase
Chronic phase
Key OCT Findings
• OCT in acute CRAO
demonstrates inner retinal
thickening, and the RPE,
photoreceptors, and outer
nuclear layer appear relatively
unaffected
• Chronic CRAO demonstrates
inner retinal atrophy and loss
of the foveal depression

49. BRAO
Oct shows one half normal
Key OCT Findings
• structural damage to the inner retina
• Increased hyperreflectivity in the affected inner
retinal layers and retinal thickening where the
occlusion occurred.
• In chronic BRAO, OCT reveals atrophy in the nerve
fiber layer and inner retina, while the outer
nuclear layer and adjacent photoreceptor/RPE
layers retain their physiologic thickness

50. Non Exudative/Dry AMD
Extent of disease
Monitoring of disease progression
Staging and prognosis
OCT – Drusens, loss of RPE and morphological alterations, increased hyperreflectivity
Outer retinal tubulations

51. Geographic atrophy
Key OCT Points
• GA is characterized on OCT by loss of
the hyperreflective external band
(attenuation of the RPE layer) and/or
by the hypertransmission effect
secondary to loss of outer retinal
layers, RPE and choriocapillaries
• Nascent GA is a recently described
entity, based on specific OCT features
that precede manifestations on
clinical examination or other imaging
modalities
RPE affected/loss with hypertransmission in geographic atrophy

52. Exudative AMD
CNVM lesion type/location/extent
FFA/ICG correlation
Subretinal / Intraretinal fluid
PEDs – types
Response to anti VEGFs

53. Exudative AMD
If choroid thickened – more likely PCV
If choroid not thickened - typical AMD
Choroid extremely thin – Myopic CNVM
Key OCT Points
• Type 1 CNV is classified based on its anatomic location, being
present above Bruch’s membrane but below the RPE.
• Type 2 CNV refers to vessels expanding into the subretinal
space between the neurosensory retina and the RPE
On OCT type 1 CNV manifests as PED and commonly multi-
lobulated with variable internal reflectivity.
OCT CNVM

54. Central Serous Chorioretinopathy
Extend , nature of SRF
PED
Follow up
Response to treatment
Complications
Acute/chronic CSCR
Prognostic aid
Role of OCT

55. CSR
Subretinal fluid with elevations in RPE in a patient with CSR
OCT Key Features
• Serous macular detachment along with
retinal pigment epithelium detachment
• Choroidal thickening
• Outer retinal granulations

56. Myopia
• Staphylomas
• Haemorrhages and scars
• Myopic CNVMs
• Myopic foveoschisis
• Macular and lamellar holes
• ERMs
Above image showing alteration of contour of eye in Myopia
Key OCT Features
• Myopic CNVMs appears as a highly reflective, well-
circumscribed, round complex on OCT
• Typically, minimal associated exudation such as
cystoid macular edema or subretinal fluid is
present.
Role of OCT

57. Retinoschisis type
Foveal detachment
Macular hole type
Key OCT Features
• Schisis may occur in multiple layers of the macula;
however, the outer layers are most commonly affected
leaving a thicker inner retina and thinner outer retina.
• Perpendicular strands stretching within the schisis cavity
are thought to be Müller cells.
• Other associated features of myopia may be noted on
OCT, such as staphyloma, RPE atrophy, and vitreomacular
interface abnormalities

58. Ocular trauma
• Macular hole
• Outer retinal changes
• Choroidal ruptures
• Prognostic aid
• Descision making

59. Retinitis Pigmentosa
Diffuse loss of outer retinal layer

60. COMMON RETINAL DISORDERS
VITREO MACULAR DISORDERS
• Asymptomatic
• Metamorphosia/DV
• Altered fovea
• CME/SRD
• Surgical treatment/observation

61. VMA
Vitreomacular adhesion
key OCT features
• Vitreomacular adhesion is a benign physiologic finding that
should be distinguished from similar, often pathologic states of
the vitreomacular interface.
• In a patient with a history of full-thickness macular hole in one
eye, if vitreomacular adhesion is present in the fellow eye,
there is a risk for future full-thickness macular hole (FTMH)
formation in that eye

62. VMT
VMT Key OCT Features
• VMT is due to an abnormally strong focal adhesion of the posterior
hyaloid to the macula. VMT is distinguished on OCT by disruption of
the normal macular contour at a focal point with overlying vitreous
insertion.
• VMT may resolve spontaneously or progress to visually impact- ful
sequela, including lamellar macular hole and FTMH.

63. Macular hole
• Provides confirmation of clinical findings
• Further anatomic characterization
• Means of educating patient
• Improved staging of MH
Role of OCT

64. Stage 0 – vitreomacular adhesion
Stage 1a – impending macular hole
With underlying yellow spot
Stage 1b – occult macular hole
Stage 2 – small full thickness macular hole
(<400 micrometer in diameter)
Stage 3 – full thickness macular hole ( > 400
micrometer in diameter)
Stage 4 – full size macular hole with
complete PVD.

66. Lamellar hole
Key OCT Features
• Irregular foveal contour
• Defect of inner fovea
• Separation of the inner and outer retinal layers
• Lack of a full-thickness retinal defect
Lamellar macular holes typically remain stable over time,
and surgical treatment is rarely required.

67. Lamellar macular hole
• Intra retinal split with separation of the inner and
outer foveal retinal layers
Pseudo hole
• An appearance of the retina due to contraction (or
pulling) from the ERM

68. Epiretinal membrane
Group 1 – Fovea involving
1A – with outer retinal thickening and minimal inner retinal
change
1B – with outer retinal inward projection and inner retinal
thickening
1C - with prominent thickening of the inner retinal layer
Group 2 – Fovea sparing
2A – with formation of a pseudohole
2B – with schisis like intraretinal splitting

69. Key OCT Features
• ERM appears as a hyperreflective, thickened membrane on the
inner surface of the macula.
• An ERM may take on a corrugated or undulating contour in cross
section.
• In the presence of ERM, the macular contour may appear normal or
become highly disorganized on OCT.

70. VKH
septa inside the sub retinal fluid, denotes
inflammatory pathology eg VKH
Loss of choroid architecture in uveitic condition eg : VKH

72. GLAUCOMA
• Structural damage precedes functional
loss
• 50% RNFL loss before VF defect
• RNFL thinning can be detected in 60%
cases up to 6 years before appearance of
VF defect
• Visual fields have poor repeatability (85.9% of abnormal
and reliable fields not confirmed on retest in OHTS
• 3 or more consecutive fields required to reliably confirm
diagnosis
OCT
- DIAGNOSE AND FOLLOW UP PRE PERIMETRIC GLAUCOMA
- HELPS TO CONFIRM WHETHER VF DEFECTS IS REAL OR ARTEFACT
- MONITOR PROGRESSION

73. Glaucoma affects 3 areas in the posterior
segment of eye

74. RNFL Analysis
White , Green , Yellow, Red compared to normative data base
RNFL axon bundles are thickest superiorly and inferiorly
Most significant in IT and ST quadrant

75. Macular Analysis – uses 6mm radial line scans centered on
fovea
RFNL Analysis – uses 3.4 mm circular scan centered on the
optic disc
Optic Nerve Head Analysis - uses six 4mm radial scans around
optic disc

76. Optic Nerve Head (ONH) evaluation
Outlines
• Optic Nerve Head
• Optic cup and Disc borders
Objectively measures
• Optic Disc area
• Cup volume
• Cup:disc ratios
• Average
• Vertical
• Horizontal

77. Oct Macula

81. There are three important parameters that can affect the interpretation of a scan. They are signal
strength, centration, and scan alignment

82. Complications that can decrease signal strength :
1. Poor Fixation or disease that can prevent fixation
2. Lack of patient cooperation
3. Dry Eye
4. Corneal opacity
5. Cataract
6. Vitreous opacities i.e., silicone oil, blood, floaters, and asteroid hyalosis.
7. Blinking
Signal Strength

83. Signal strength
• Signal strengths of ten are most desirable.
• A strength of six or higher are acceptable.
• If the signal strength is less than ten, you should save and then repeat the scan as
the one you saved may be the best scan of all future scan
Problem?

84. Alignment
• Not only does the eye have to be aligned on the visual axis, but the depth of the scan has to be
correct
• Ask your patient to look directly at the center of the green cross or star, where the lines come
together in the middle, will help with this alignment
Problem?

85. Scan centration The scan circle should be centered around the optic nerve
Problem?
This is an error that you won’t pick up by looking at the scan quality and
signal strength
* Newer oct have auto-tracking feature to maintain scan centration

86. Decentration

89. Papilledema vs Pseudopapilliedema

93. Favouring pseudopapilledema
• RNFL thickness normal in all 4 quadrans
• Direct Optic Nerve Head Drusen visualization in OCT (buried drusen)
• Nasal RNFL thickness has the highest diagnostic ability to differentiate TP from pseudopapilledema

94. Spectral domain optical coherence tomography can differentiate between papilledema,
pseudopapilledema, and a normal disc
(a) If the RNFL thickness is normal in all four quadrants, it is more in favour of pseudopapilledema as
none (0%) of the patients with TP had a normal RNFL thickness in all four quadrants. Similarly,
increased RNFL thickness in all four quadrants is more suggestive of papilledema.
(b) The direct visualization of the ONHD is the most important feature on SD-OCT to differentiate
between pseudopapilledema and papilledema as the ONHD could be visualized on OCT in all (100%)
eyes with buried drusen.
c).

95. Advantages of OCT
• Non contact , non invasive, real time
• Histological images in vivo
• High resolution images
• Uses harmless radiation
• Children can tolerate it
• Very helpful for quantitative information about
macular thickness
• Valuable teaching tool for ophthalmologist and
patients

96. Disadvantages of OCT
• Media opacity
• Scan quality depends on skill of OCT operator
• Not possible with uncooperative patients
• Measurement of foveal thickness not accurate if scan not through center of fovea