Anterior and Posterior OCT Principle & Instrumentation Clinical Procedure & Interpretation Glaucoma imaging & newer developments https://www.youtube.com/watch?v=j-u3IEgcTiQ (from 2:35-4:00)

1. Optical Coherence
Tomography
Rajeswari K
M.Optom

2. R K o p t o A s O C T
OCT
OCT is a non- contact, noninvasive imaging technique
used to obtain high resolution 10 cross sectional images
of the retina and anterior segment.
Re
fl
ected light is used instead of sound waves.
Infrared ray of 830 nm with 78D internal lens.
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3. R K o p t o A s O C T
Basics
Principle of OCT is based on Michaelson’s
interferometer.
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5. R K o p t o A s O C T
Theory
Scattering is a fundamental property of a heterogeneous
medium, and occurs because of variations in the
refractive index within tissue
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6. R K o p t o A s O C T
Principle
Interferometry is the technique of superimposing
(interfering) two or more waves, to detect differences
between them.
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7. Principle
Interferometry works because
Two waves with the same
frequency that have the
same phase will add each
other (constructive)
Two waves that have
opposite phase will
subtract.(destructive)

8. R K o p t o A s O C T
Instrumentation
Light from a source is directed onto a partially re
fl
ecting
mirror and is split into a reference and a measurement
beam.
The measurement beam re
fl
ected from the specimen
with different time delays according to its internal
microstructure.
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9. R K o p t o A s O C T
Working
The light in the reference beam is re
fl
ected from a
reference mirror at a variable distance which produces a
variable time delay.
The light from the specimen, consisting of multiple
echoes, and the light from the reference mirror,
consisting of a single echo at a known delay are
combined and detected.
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11. R K o p t o A s O C T
Types
Anterior segment OCT
Posterior segment OCT
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ANTERIOR SEGMENT
OCT

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Overview
Because anatomy plays a large role in chronic angle closure, evaluating the
angle anatomy is a critical
fi
rst step in treat ing this disease.
Using a combination of various AS imaging technique examiner will get a
clear picture of the angle anatomy and help to make appropriate treatment
decisions.
Gonioscopy is the current gold standard, but imaging techniques such as
anterior segment optical coherence tomography (AS-OCT) provide
additional valuable information.
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History
First described using the same wavelength of
light as retina l OCT
, namely 830nm.
OCT imaging of t he anterior segment with a
longer wavelength of 1310nm was developed
later on and had t he advantages of better
penetration through sclera
Rapid, non contact method that maybe
performed by a technician with patient sitting
Upright.

15. R K o p t o A s O C T
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Obtains a high-resolution cross-section of the anterior
segment without touching the eye.
Enables visualisation of the form, site & position of AC
components.
De
fi
nes & measures the distances between them.
Machine automatically eliminates distortion induced by
optical transmission factors.

16. R K o p t o A s O C T
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Re
fl
ex Saturation Beam indicates
perpendicularity of the eye to
minimal tilting of the image.
The scan dimensions are 16 x 6 mm and 4 image frames are
averaged.
Resolution is 2-20microns which makes it suita ble for
measurement of
fi
ner eye structures.

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Qualitative Assessment
An important landmark to identify in ASOCT images is the scleraI spur.
This is visible as an inward projection of the sclera at the junction
between the inner sclera and cornea
Apposition between the iris & inner corneo-scleral wall has been used
as a qualitative method of detecting angle closure

18. R K o p t o A s O C T
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Quantitative Assessment
Quantitative measurement of the AC angle is possible with
in-built software & requires identi
fi
cation of the sclera l spur.
The commonly used quantitative parameters
Angle opening distance(AODSOO/AOD750}
Angle recess area(ARASOO/ARA750}
Trabecular space area(TISASOO/T ISA750)

19. R K o p t o A s O C T
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Angle opening distance(mm): Perpendicular distance between a
point anterior to the scleral spur and the opposing iris. (500µm)
Angle recess area(mm2): The triangular area bounded by the
anterior iris surface and the inner corneo-scleral wall
Trabecular Iris space area(mm2): the perpendicular distance
between the scleral spur and the opposing iris.

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Newer Modalities
A new swept source FD-OCT device can rapidly obtain
high-resolution scans with 3D reconstruction of the
anterior segment.
Casia SS-1000
Tomey Corporation

22. R K o p t o A s O C T
Clinical Uses
An adjunct to gonioscopy as well as a substitute when gonioscopy is not feasible.
Useful as a patient education tool, especially when laser peripheral iridotomy is being
recommended.
Photo-therapeutic keratectomy to assess the depth of corneal opacity.
LASIK for CCT & to measure
fl
ap thickness.
Keratoconus & INTACS
Cysts of anterior segment to diagnose etiology.
Biometry for phakic IOL.
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Glaucoma Imaging &
Newer Developments

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BLEB

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26. R K o p t o A s O C T
Useful tool for evaluating
fi
ltering bleb or GDD in post-
op period.
Clinical description of bleb & Visualising intra-bleb
morphology with AS-OCT may enhance our
understanding of different surgical outcomes.
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27. R K o p t o A s O C T
Newer Uses of OCT
Measuring the tear
fi
lm :Although this work is still
mostly showing value in research situations
Measuring contact Lens
fi
t: Scleral CL
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28. R K o p t o A s O C T
ADVANTAGES
Non contact.
More physiological.
Shorter imaging time.
Less learning curve for operator.
Target may be used to induce accommodation in eye imaged.
Less inter operator variability.
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LIMITATION
No penetration of pigmented iris epit helium.
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Completely reduced anterior chamber (A).
The same eye after treatment, now with an open angle (B).
Malignant
Glaucoma

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Decedent’s Membrane Detachment

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Granular Dystrophy

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POSTERIOR SEGMENT
OCT

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Types
1. Time domain
2. Fortier domin
3. Spectral domin
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36. R K o p t o A s O C T
Time Domin
The Michelson interferometer splits the light from the broadband
source into two paths, the reference and sample arms.
The interference signal between the re
fl
ected reference wave
and the backscattered sample wave is then recorded.
In order to measure the time delays of light echoes coming from
different structures within the eye, the position of the reference
mirror is changed so that the time delay of the reference light
pulse is adjusted accordingly
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37. R K o p t o A s O C T
Fortier Domin
In FD-OCT ,the detector arm of the Michelson
interferometer uses a spectrometer instead a single
detector.
The spectrometer measures spectral modulations
produced by interference between the sample and
reference re
fl
ections.
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38. R K o p t o A s O C T
TD vs FD
No physical scanning of the reference mirror is required;
thus, FD-OCT can be much faster than TDOCT.
The simultaneous detection of re
fl
ections from a broad
range of depths is much more ef
fi
cient than TD-OCT, in
which signals from various depths are scanned sequentially.
FD-OCT is also fast enough for sequential image frames to
track the pulsation of blood vessels during the cardiac cycle.
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41. R K o p t o A s O C T
Limitation - SLO
Limitation of OCT technology was dif
fi
culty in accurately
localising the cross-sectional images and correlating
them with a conventional en face view of the fundus.
To localise and visually interpret the images, a scanning
laser ophthalmoscopy (SLO) was needed.
This was initiated by OTI technologies (Toronto, Canada)
to develop the Spectral OCT/SLO.
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42. R K o p t o A s O C T
Spectral Domin
The Spectral OCT/SLO is a computerized optical scanner device
providing high-resolution, high-de
fi
nition images of the fundus
anatomy.
It integrats SLO’s confocal imaging principles with OCT.
The system simultaneously produces SLO and OCT images that are
created through the same optical path,
It produces a new image format with high resolution tomographic
images.
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43. R K o p t o A s O C T
Clinical Uses
Oct is used for diagnosis, monitoring, quantitative and
qualitative assessment of macular pathology
It is used in most of the Vitreo-retinal conditions
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44. R K o p t o A s O C T
7. Epiretinal Membrane in
Diabetic Retinopathy.
8. Central Serous Retinopathy.
9. Foveal thining in Retinitis
Pigmentosa and in Myopic
Degeneration.
10.Age Related Macular
Degeneration.
11.Post Retinal Detachment
Surgery.
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1. PosteriorVitreous Detachment
(PVD)
2. Vitreo-MacularTraction Syndrome
(VMT)
3. Asteriod Hyalosis
4. Intra-retinal Hemorrhage.
5. Macular Edema ( CME, CSME)
6. Macular Holes and cysts.
U
S
E
S

45. R K o p t o A s O C T
Interpretation
Following things need to observed in OCT:
A. Vitro-retinal interface.
B. RetinalThickness:
(I) Increases: Edema,Traction.
(II) Decreases: Foveal atrophy.
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46. R K o p t o A s O C T
C. Re
fl
ectivity:
(I) Hyper-re
fl
ective lesions: Hard Exudates, Blood, Scars.
(II) Hypo-re
fl
ective lesions: Serous Fluid, Hypo-pigmented
lesions of Retinal Pigment Epithelium, Media Hazy.
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47. R K o p t o A s O C T
Normal
Highly re
fl
ective structures are shown in bright colures (white and red).
Those with low re
fl
ectivity are represented by dark colors (black and blue).
Intermediate re
fl
ectivity is shown Green.
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48. R K o p t o A s O C T
Diabetic Macular Edema
Sponge like retinal thickness.
Macular edema and Cystoid Macular Edema.
Serous Retinal Detachment.
Epi-retinal Membrane.
Vitro-macular traction.
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RD

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ERM

54. R K o p t o A s O C T
ARMD
Focal elevation of Retinal Pigment Epithelium.
Large drusen shows irregular elevation of Retinal
Pigment Epithelium with shadow from underlying
choroid.
Large drusen carry high risk of Choroidal Neo-Vascular
Membrane.
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55. R K o p t o A s O C T
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56. R K o p t o A s O C T
MACULAR HOLE
Three are three type of macular hole we can see:
1. Impending Macular Hole.
2. Lamellar Macular Hole.
3. FullThickness Macular Hole.
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60. R K o p t o A s O C T
Disadvantage
Clear ocular media is needed for better performance
Minimum pupillary size of 4mm is required.
It is a costly apparatus.
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