1. Dr Rajvin Samuel PonrajDr Rajvin Samuel Ponraj
MS ophthalmologyMS ophthalmology
Optical Coherence
Tomography (OCT)

2. Optical coherence tomographyOptical coherence tomography
 Optical Coherence Tomography, or OCT, is aOptical Coherence Tomography, or OCT, is a
noncontact, noninvasive imaging technique used tononcontact, noninvasive imaging technique used to
obtain high resolution 10 um cross-sectional imagesobtain high resolution 10 um cross-sectional images
of the retina and anterior segment.of the retina and anterior segment.
 Reflected light is used to create image instead ofReflected light is used to create image instead of
sound wavessound waves
 Infrared ray of 830 nm with 78 D internal lens.Infrared ray of 830 nm with 78 D internal lens.
 Based on interferometryBased on interferometry
– involves interference between reflected light andinvolves interference between reflected light and
a reference beam.a reference beam.

3. Types:
Time domain Spectral domain

6. Physics:
 Cross sectional images are generated by
scanning the optical beam in a transverse
direction thus yielding a two dimensional
data set that can be displayed as a false
colour or gray scale image.

7. Normal appearance
 Plexiform [inner & outer] Red/yellow /bright
 Nerve fibre layer
green
 Inner & outer nuclear layer blue/black

8. Indications:
 Macular pathology
 Analysis of optic nerve head & RNFL
thickness
 In glaucoma to monitor progression &
response to disease

9. Scan Protocol Types
 Line
 Circle
 Radial Lines

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

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

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

13. INTRODUCTIONINTRODUCTION
 OCT of the retina -> vertical biopsy section ofOCT of the retina -> vertical biopsy section of
the retina.the retina.
 Instead of a knife, light is used.Instead of a knife, light is used.
 Instead of viewing a stained section under aInstead of viewing a stained section under a
microscope, we are presented with a "false-microscope, we are presented with a "false-
color" view with micron level resolution.color" view with micron level resolution.

14. Optical coherence tomography-Optical coherence tomography-The processThe process
is similar to that of ultrasonography, except that light is used insteadis similar to that of ultrasonography, except that light is used instead
of sound waves.of sound waves.
Analog to
ultrasound

15. single reflection site

16. Transverse Scanning
Backscatter Intensity
Axial
Scan
(Depth)
Construction of tomographicConstruction of tomographic
imageimage

17. •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.
•Compare that to the resolution of a good ophthalmic ultrasound at 100
microns, or 1/10th of a millimeter.

18. Difficulties and limitationsDifficulties and limitations
Limited by intraocular mediaLimited by intraocular media
opacities , which attenuateopacities , which attenuate
measurement beam andmeasurement beam and
reflected lightreflected light

19. OCT Image of Normal FoveaOCT Image of Normal Fovea

20. Qualitative and Quantitative AnalysisQualitative and Quantitative Analysis
 The OCT allows both qualitative and quantitativeThe OCT allows both qualitative and quantitative
analysis of the retina.analysis of the retina.
 Qualitative analysis involves describing or identifyingQualitative analysis involves describing or identifying
morphological changes and anomalous structures inmorphological changes and anomalous structures in
the retina. Morphology is the study of forms andthe retina. Morphology is the study of forms and
structures of organisms.structures of organisms.
 Quantitative analysis is possible because the OCTQuantitative analysis is possible because the OCT
software is able to identify and "trace" two key layerssoftware is able to identify and "trace" two key layers
of the retina, the NFL and RPE. The software canof the retina, the NFL and RPE. The software can
then measure the distance between these twothen measure the distance between these two
layers, which represents retinal thickness.layers, which represents retinal thickness.

21. RegionsRegions
For purposes of analysis, the OCT image of the retina can beFor purposes of analysis, the OCT image of the retina can be
subdivided vertically into four regions:subdivided vertically into four regions:
 the pre-retinathe pre-retina
 the epi-retinathe epi-retina
 the intra-retinathe intra-retina
 and the sub-retinaand the sub-retina

22. ProfilesProfiles
OCT retinal morphology (form and structure)OCT retinal morphology (form and structure)
can be subdivided into four "profiles": Eachcan be subdivided into four "profiles": Each
profile has it's own set of deformations andprofile has it's own set of deformations and
anomalous structures.anomalous structures.
 1. pre-retinal profile1. pre-retinal profile
 2. overall retinal profile2. overall retinal profile
 3. foveal profile3. foveal profile
 4. macular profile4. macular profile

23. The pre-retinal profileThe pre-retinal profile
 A normal pre-retinal profile is black space, as pictured below,A normal pre-retinal profile is black space, as pictured below,
because the normal vitreous space is translucent, meaning it hasbecause the normal vitreous space is translucent, meaning it has
minimal reflective properties. The small, faint, bluish dots in the pre-minimal reflective properties. The small, faint, bluish dots in the pre-
 retinal space is "noise". This is an electronic aberration created byretinal space is "noise". This is an electronic aberration created by
increasing the sensitivity of the instrument to better visualize lowincreasing the sensitivity of the instrument to better visualize low
reflective structures.reflective structures.

24. Anomalous structures that have been observed in the pre-retinal profile
include the following:
1. pre-retinal membrane
2. epi-retinal membrane
3. vitreo-retinal strands
4. vitreo-retinal traction
5. pre-retinal neovascular membrane
6. pre-papillary neovascular membrane

25. The over-all retinal profileThe over-all retinal profile
A slightly concave curvature that you would expect from observing the
surface of a globe. Abnormal profiles would include exaggerated
concavity and convexity. Retinal folds would also result in an abnormal
over-all profile.

26. Pigment epithelial detachment is causing the convexity.

27. Abnormal concavity -the retinal detachment suggesting the
long eye of a significant myope.

28. The foveal profileThe foveal profile
The normal foveal profile is a slight depression in retina surface

30. macular cystmacular cyst

34. The macular profileThe macular profile
The macular profile can, and often does, include the fovea as
it's center. Therefore, a common OCT scan length of 6 mm
would include 3 mm of the macula on each side of the fovea.

35. Deformations that have been observed in the macular profile include
the following:
1. serous retinal detachment (RD)
2. serous retinal pigment epithelial detachment (PED)
3. hemorrhagic pigment epithelial detachment
A serous PED is pictured below. We know that it is a PED because
the fluid (black space around the arrow) is pushing up underneath
the retinal pigment epithelium, identified by the relatively highly
reflective (red and orange) line (arrow).

36. Intra-retinal anomalies that have been
identified in the macular profile
include:
1. choroidal neovascular membrane
2. diffuse intra-retinal edema
3. cystoid macular edema
4. drusen
5. hard exudates
6. scar tissue
7. atrophic degeneration
8. sub-retinal fibrosis
9. RPE tear

37. Cystoid Macular Edema
OCT is capable of detecting small, fluid-filled,
cystic spaces within the macula.

38. Central Serous Chorioretinopathy
Central serous chorioretinopathy is characterized by the
presence of fluid between the RPE and neurosensory
retina.

39. Diabetic Retinopathy
Exudates appear as accumulation of dense material
within the neurosensory retina.

40. ArtifactsArtifacts
 Artifacts in the OCT scan are anomalies in the scan that are not accurateArtifacts in the OCT scan are anomalies in the scan that are not accurate
images of actual physical structures, but are rather the result of an externalimages of actual physical structures, but are rather the result of an external
agent or action.agent or action.
 Notice the large gap in the middle of the scan below. This is an artifactNotice the large gap in the middle of the scan below. This is an artifact
caused by a blink during scan acquisition. The was a high resolution scan,caused by a blink during scan acquisition. The was a high resolution scan,
which takes about a second for the scan pass, which is plenty of time towhich takes about a second for the scan pass, which is plenty of time to
record a blink.record a blink.

41. The scan below has waves in the retinal contour. These are
not retinal folds, but rather movement of the eye during the
scan pass.

42. Anterior segment optical coherence
tomography (OCT)•
•High-speed anterior segment optical coherence
tomography (OCT) offers a non-contact method for
high resolution cross-sectional and three-
dimensional imaging of the cornea and the anterior
segment of the eye.•Anterior Segment Optical Coherence Tomography
enhances surgical planning and postoperative care for
a variety of anterior segment applications by expertly
explaining how abnormalities in the anterior chamber
angle, cornea, iris, and lens can be identified and
evaluated

43. On the leading edge of anteriorOn the leading edge of anterior
segment imaging:segment imaging:
 Mapping of corneal thickness and keratoconusMapping of corneal thickness and keratoconus
evaluationevaluation
 Measurement of LASIK flap and stromal bedMeasurement of LASIK flap and stromal bed
thicknessthickness
 Visualization and measurement of anterior chamberVisualization and measurement of anterior chamber
angle and diagnosis of narrow angle glaucomaangle and diagnosis of narrow angle glaucoma
 Measuring the dimensions of the anterior chamberMeasuring the dimensions of the anterior chamber
and assessing the fit of intraocular lens implantsand assessing the fit of intraocular lens implants
 Visualizing and measuring the results of cornealVisualizing and measuring the results of corneal
implants and lamellar proceduresimplants and lamellar procedures
 Imaging through corneal opacity to see internal eyeImaging through corneal opacity to see internal eye
structuresstructures

44. Image shows an anterior-chamber angle as viewedImage shows an anterior-chamber angle as viewed
with gonioscopy and the OCTwith gonioscopy and the OCT
The latter replaces subjective evaluation with objective
measurement.

45. Anterior Segment Optical Coherence
Tomography is a must-have for anterior
segment, refractive, cornea, and glaucoma
surgeons.

46. THANK YOU