optical coherence tomography is a new tool that makes retinal diagnosis easier. the above ppt includes a detailed and precise notes on OCT and its interpretation.

1. Optical Coherence Tomography
OCT
G.M.Preethi

2. non contact
non invasive
micron resolution
cross-sectional study of retina
correlates very well with the retinal histology

3. HISTORY OF OCT
• 1991 - first OCT paper - by Huang et al
• First in-vivo studies of human retina - 1993

4. Qualitative analysis
description by location
description of form and structure
identification of anomalous structures
observation of the reflective qualities of the
retina

5. Quantitative analysis
retinal thickness and volume
nerve fiber layer thickness.

6. Basic Principle
• Combination of low-coherence interferometry
with a special broadband width light in near
infrared range ( 810 nm)

8. • Low-coherence infra-red light coupled to a fiber-optic travels
through a beam-splitter and is directed through the ocular
media to the retina and a reference mirror
• The distance between the beam-splitter and reference mirror
is continuously varied
• When the distance between light source & retinal tissue =
distance between light source & reference mirror, the
reflected light and the reference mirror interacts to produce
an interference pattern.
• Interference measured by a photo detector- produces a range
of time delays for comparison

10. Types of OCT
TD – OCT ( time domain)
• Reference mirror moves
• Interference not detected
by special interferogram
• No Fourier transformation
• 1 pixel at a time
• Slow
• Motion artifacts present
• Less sharp images
FD - OCT / SD – OCT
( Fourier / spectral)
• Reference mirror stationary
• Interference detected by
special interferogram
• Interference pattern Fourier
transformed
• 2048 pixels at a time
• Rapid
• No motion artifacts
• Sharper and clear images

11. TD - OCT FD - OCT

12. GENERATIONS OF OCT
• OCT 2 similar to OCT 1 but with an improved user interface.
OCT GENERATION TRANSVERSE
RESOLUTION
AXIAL
RESOLUTION
NO OF SCANS
OCT 1 FIRST (1995 ) 20 10 100
OCT 2 SECOND ( 2000) 20 10 100
OCT 3 THIRD ( 2002 ) 20 7-8 512

14. How does it work?
• 128 to 768 axial samples (A-scans) in a single
"scan pass“
• Each A-scan has 1024 data points and is 2mm
long (deep).

15. Resolution
• When all of the A-scans are combined into
one image, the image has a resolving power of
about 10 microns vertically and 20 microns
horizontally

16. Scan Protocol Types
• Line
• Circle
• Radial Lines

17. The "line" scan simply scans in a single,
straight line. The length of the line can be
changed as well as the scan angle.

18. The "circle" scans in a circle instead of a line.

19. The "radial lines" scans 6 consecutive line scans
in a star pattern

20. Other protocols
• The "fast" scan protocols - reduce the time needed
for multiple scans
• Raster lines – multiple line scans in a rectangular
region to cover the areas of pathology – eg: CNVM
• Repeat scan – repeats previously saved scans
• 3D scan- 3D volumetric analysis

21. RASTER SCAN

22. The OCT System
• Fundus viewing unit
• Interferometric unit
• Computer display
• Control Panel
• Color inkjet printer

23. Procedure
• Machine is activated
• Patients pupils are dilated
• Pt seated comfortably
• Asked to look into the target light in the ocular
lens
• Discouraged to blink
• Protocol selected as per case requirement

25. Production and display of image
• Z axis - 1024 points captured - 2 mm depth - resolution of
10 µ.
• On X-Y axis, tissue density profile is repeated up to 512
times every 5-60 µ to generate a cross sectional image.
• Image thus produced has an axial resolution of 10 µ and
a transverse resolution of 20 µ.
• Constructed tomogram displayed in either gray scale or
false scale on a high resolution computer screen.

26. PRINT OUT

27. • Section 1: Patient related data, examination date, list and signal strength
• Section 2: Indicates whether the scan is related to macula with its pixel strength (as in
this
• picture) or optic disc cube (It also displays the laterality of the eye: OD
• (right eye), OS (left eye).
• Section 3: Fundus image with scan cube overlay. 3A: Color code for thickness overlays.
• Section 4: OCT fundus image in grey shade.
• Section 5: The circular map shows overall average thickness in nine sectors. It has three
• concentric circles representing diameters of 1 mm, 3 mm and 6 mm, and except for the
• central circle, is divided into superior, nasal, inferior and temporal quadrants. The
central
• circle has a radius of 500 micrometers.
• Section 6: Slice through cube front. Temporal – nasal (left to right).
• Section 7: Slice through cube side. Inferior – superior (left to right).
• Section 8: Thickness between Internal limiting membrane (ILM) to retinal pigment
• epithelium (RPE) thickness map. 8A: Anterior layer (ILM). 8B: Posterior layer (RPE). All
• these are 3-D surface maps.
• Section 9: Normative database uses color code to indicate normal distribution
percentiles.
• Section 10: Numerical average thickness and volume measurements.

28. Retinal Anatomy Compared to OCT
• The vitreous - black space on the top of the image
• fovea - normal depression
• Umbo- central hyper reflective dot within foveola
• The nerve fiber layer (NFL) and the retinal pigment epithelium (RPE)
- highly reflective than the other layers of the retina ( red – yellow)
• RNFL – thicker on nasal side of macula
• Areas of minimal signals ( blue – black)
• ONL – thickest portion

30. TYPES OF MACHINE SCANS
• POSTERIOR SEGMENT SCAN
• MACULAR SCAN
• Optic disc scan
• GLAUCOMA RNFL THICKNESS ANALYSIS SCAN
• ANTERIOR SEGMENT SCAN

31. Regions
For purposes of analysis, the OCT image of the
retina can be subdivided vertically into four
regions
• the pre-retina
• the epi-retina
• the intra-retina
• the sub-retina

32. The pre-retinal profile
• A normal pre-retinal profile is black space
• Normal vitreous space is translucent
.

33. Anomalous structures
• pre-retinal membrane
• epi-retinal membrane
• vitreo-retinal strands
• vitreo-retinal traction
• pre-retinal neovascular membrane
• pre-papillary neovascular membrane

34. A pre-retinal membrane with traction on the fovea

35. The foveal profile
The normal foveal profile is a slight depression
in the surface of the retina

36. Deformations in the foveal profile
• macular pucker
• macular pseudo-hole
• macular lamellar hole
• macular cyst
• macular hole

37. Macular cyst

38. The macular profile
The macular profile can, and often
does, include the fovea as it's center

39. Deformations in the macular profile
• Serous retinal detachment (RD)
• Serous retinal pigment epithelial detachment
(PED)
• Hemorrhagic pigment epithelial detachment

40. Serous retinal pigment epithelial
detachment (PED)

41. Intra-retinal anomalies in the macular
profile
• Choroidal neovascular membrane
• Diffuse intra-retinal edema
• Cystoid macular edema
• Drusen
• Hard exudates
• Scar tissue
• Atrophic degeneration
• Sub-retinal fibrosis
• RPE tear

42. Hyper reflective lesions within NSR
• Hard exudates
• Cotton wool spots
• Micro aneurysms
• Hemorrhage
• Pigments
• Fibrin
• Erm
• Drusen
• Nevi
• Rpe hyperplasia

44. Hypo reflective lesions
• Asteroid hyalosis
• Vitreous haemorrhage
• Intraretinal fluid
• Intraretinal cysts
• PED

45. Sub-retinal fibrosis

46. OCT and Fluorescein Angiography in
retinal diagnosis
FAs provide excellent characterization of retinal
blood flow over time, as well as size and
extent information on the x and y axis (north-
south, east-west)
The OCT gives us information in the z (depth)
axis, telling us what layers of the retina are
affected

48. Optic disc scan
• OPTIC DISC- choriocapillaris terminates at the
lamina cribrosa
• Optic cup- NFL terminates
• Size of optic disc, cup
• C: D ratio
• Volume of cup
• RNFL thickness

49. The optic nerve scan can be analyzed with the
"optic nerve head analysis" protocol

50. RNFL thickness analysis scan
Protocols
• Circle scan
• Fast circle scan
• Proportional circles
• RNFL map
• Concentric 3 ring protocol

52. Clinical applications of posterior
segment scan
.

53. 1.Macular Hole
•confirmation of
diagnosis and
differentiates it from
lamellar hole, foveal
pseudo cyst.
• monitoring the
course of the disease
and the response to
surgical intervention.

54. 2.Macular Edema
•: intraretinal areas of
decreased reflectivity
and retinal thickening.
•Round, optically clear
regions within the
neurosensory retina
are noted in cystoid
macular edema.

55. 3. ARMD
•Morphological
changes in the non
exudative ARMD.
•Subretinal fluid,
intraretinal thickening
and
•sometimes, choroidal
neovascularization in
exudative ARMD.

56. 4. Central serous retinopathy
• area of decreased reflectiv ity between two
hyper reflective areas

57. 5. Epiretinal membrane:
highly reflective diaphanous membrane over the surface of retina.

58. 6. Solar retinopathy
characterized by formation of an outer retinal hole.

59. OCT IN GLAUCOMA
• Optic disc scan
• diagnosing and monitoring the glaucomatous change.
• evaluating the RNFL for early (pre- perimetric) glaucoma
detection.
• Detection, study and follow up of the macular changes in
hypotony induced maculopathy after glaucoma.
• Evaluation of cystoid macular edema after combined cataract
and glaucoma surgery.

60. ANTERIOR SEGMENT OCT
•corneal thickness and keratoconus evaluation
• LASIK flap and stromal bed thickness
•anterior chamber angle
•dimensions of the anterior chamber and assessing the fit of
intraocular lens implants
•results of corneal implants
•Imaging through corneal opacity to see internal eye
structures

64. NEWER OCT’s
• OCT- SLO
• 3D OCT
• OCT with HRA (FA and ICG)
• Increase in resolution to 5 microns
• OPMI LUMERA 700 and RESCAN 700 (
integrated intraoperative OCT)

65. • OCT – SLO
8 microns axial resolution
20 microns transverse resolution
Confocal SLO and OCT images simultaneously
Cross sectional and coronal sections
3 D view of pathology

68. LIMITATIONS OF OCT
• Minimal pupillary diameter of 4 mm
• Poor media clarity – limited application
• High astigmatism and decenterd iol-
compromised quality
• expensive

69. Interpretation of an OCT
• 4 questions
1. How does the vitreo retinal interface appear ?
2. What is the fovel contour like ?
3. Is retinal architecture altered?
4. Whether the uniformity of RPE- CC layer is
disrupted?

70. Vitreo retinal interface
• Normal
• Membrane – single
- double
• Attachment- no attachment
- partial attachment
- total attachment

72. SINGLE MEMBRANE DOUBLE MEMBRANE

73. 1.TOTAL
ATTACHMENT
2. PARTIAL ATTACHMENT
3. NO ATTACHMENT

74. Foveal contour
• Normal
• Obliterated
pulling- due to overlying membrane
pushing – due to underlying fluid
• Widened – foveal thinning
• Hole – full thickness
- lamellar hole – outer, inner

76. Pulling mechanism Pushing mechanism

77. pseudohole Lamellar hole

78. Retinal architecture
• Normal
• Fluid- intra retinal – diffuse, cystoid
- subretinal
• Exudates
• schisis

79. Diffuse edema Cystoid edema

80. 1.Subretinal fluid 2.exudates

81. Rpe - choriocapillaris
• Normal
• Bumpy – drusen
• Fusiform thickening – CNVM
• Elevated- definite green line – serous PED
- Indefinite green line- fibrovascular
- no green line- haemorrhagic

82. drusen cnvm

83. Serous PED Haemorrhagic PED

84. Thank you