Optical Coherence Tomography (OCT) is a non-invasive imaging test for diagnosing retinal diseases by providing cross-sectional images of the retina's layers. Developed since the early 1990s, OCT measures the thickness of these layers to aid in early detection and treatment planning for conditions like macular degeneration and diabetic eye disease. Limitations include difficulties with light passage due to dense cataracts and the need for patient cooperation during imaging.

1. OCT Basic For ALL
Gyanendra Lamichhane, MD
Phaco surgeon and Retina fellow,Japan
Lumbini Eye Institute
Bhairahawa,Nepal
yourgyanu@gmail.com
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2. • Non-invasive imaging test.
• OCT is a unique test as it allows to look at cross-sectional layers of
the retina.
( HISTOLOGY like)
• Each of the ten layers in the retina can be detected.
• OCT allows to measure the thickness of each layer to aid in the
early detection and diagnosis of retinal diseases and conditions.
• Reflected light is used instead of sound waves.
• Infrared ray of 830 nm with 78D internal lens. 2

3. HISTORY- OCT Timeline
• 1991–Concept of
OCT in
ophthalmology
• 1993 - First in vivo
retinal OCT images
• 1994-OCT prototype
• 1994-Anterior
segment/Cornea OCT
• 1995-The First
Clinical Retinal OCT
• 1995-The First
Glaucoma OCT
• 2002 – Time domain OCT (e.g. St r at us)
• 10 µm axial r esolut ion
• scan velocit y of 400 A-scans/ sec
• 2004 – Concept of spect ral domain OCT
int r oduced
• 2007 – Spectral domain OCT
• 1-15 µm axial r esolut ion
• up t o 52,000 A-scans/ sec

4. Theories and principle
• OCT images obt ained by measur ing
– echo time
– intensity of ref lect ed light
• Ef f ect ively ‘opt i cal
ul t ras ound’
• Opt ical proper t ies of ocular t issues, not a
t rue hist ological sect ion

5. • Laser out put f r om OCT is low, using a near-infra-red
br oadband light source
• Measures backscat t er ed or back-r ef lect ed
light
• Source of light : 830nm diode
laser

6. Principle

7. Light f r om Ref erence arm &
Sample arm combined
Division of t he signal by
wavelengt h
Analysis of signal
I nt er f er ence pat t ern
A-scan creat ed f or
each point
B-Scan creat ed
by combining A-scans

9. • Digit al pr ocessing aligns t he A-scan t o cor r ect
f or eye mot ion.
• Digit al smoot hing t echniques f urt her impr oves
t he signal t o noise r at io.
• The small f aint bluish dot s in t he pr e-r et inal
space is noise
This is an elect ronic aberrat ion
creat ed by increasing t he sensit ivit y of
t he inst rument t o bet t er visualize low

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15. RETI NA
OCT image display,
•Highest reflectivity - red
– nerve fiber layer
– retinal pigment
epithelium and
– choriocapillaris
•Minimal reflectivity appear blue
or black
– photoreceptor layer
– choroid
– vitreous fluid or blood

17. Ganglion Cell Complex
• Collect ive t er m
– RNFL
– Ganglion cell layer and
– I nner plexif orm layer
• GCC t hought t o be af f ect ed in ear ly
glaucoma

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19. Hyper ref lect ive scans
• RNFL
• I LM, RPE
• RPE-
chor iocapillar ies
complex
• PED
• Dr usen , ARMD
• CNVM lesions
• Ant erior f ace of
hemorrhage
• Discif orm scars
• Hard Exudat es
• Epiret inal
membrane

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57. • Optical coherence tomography (OCT) is a non-invasive imaging test that uses light
waves to take cross-section pictures of your retina,
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59. • With OCT, each of the retina’s distinctive layers can be seen to map and measure
their thickness. These measurements help with early detection, diagnosis and
treatment guidance for retinal diseases and conditions, including age-related macular
degeneration and, diabetic eye disease, among others.
•
Since OCT relies on light waves, it cannot be used successfully with any condition
that interferes with light passing through the eye, such as dense cataracts or
significant bleeding in the vitreous.
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60. • Optical coherence tomography (OCT) has been developed during the last 20
years. Applications include medical diagnostics.
• Now a days the resolution is approaching that of histology.
• Some of its advantages are that it can be used in situ, no excision of the tissue
investigated is needed and the method favours the use of endoscopes.
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61. The human eye
OCT in ophthalmology: Fercher and Fujimoto groups
(early 1990’s)
High resolution OCT: Fujimoto, Drexler (late 1990’s)

62. • Optical coherence tomography is aninterferometric technique, typically employing
near-infrared light.
• The use of relatively long wavelength light allows it to penetrate into the scattering
medium
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63. • Retina
• OCT showing both macular edema and subretinal fluid in a diabetic patient
• OCT is useful in the diagnosis of many retinal conditions, especially when the media is clear. In general, lesions in
the macula are easier to image than lesions in the mid and far periphery. OCT can be particularly helpful in
diagnosing:
macular hole
• macular pucker
• vitreomacular traction
• macular edema
• detachments of the neurosensory retina and retinal pigment epithelium (e.g. central serous retinopathy or age-
related macular degeneration)
• In some cases, OCT alone may yield the diagnosis (e.g. macular hole). Yet, in other disorders, especially retinal
vascular disorders, it may be helpful to order additional tests (e.g. fluorescein angiogram).
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64. • Optic neuropathies
• OCT is gaining increasing popularity when evaluating optic nerve
disorders such as glaucoma. OCT can accurately and reproducibly
evaluate the nerve fiber layer thickness.
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65. DIABETIC MACULAR EDEMA
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66. Macular hole
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67. Mild macular edema
good vision
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68. Macular edema improved after
lucentis
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69. Sub retina fluid
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71. • From its inception, OCT images were acquired in a time domain fashion. Time
domain systems acquire approximately 400 A-scans per second using 6 radial slices
oriented 30 degrees apart. Because the slices are 30 degrees apart, care must be
taken to avoid missing pathology between the slice
• Spectral domain technology, on the other hand, scans approximately 20,000-40,000
scans per second. This increased scan rate and number diminishes the likelihood of
motion artifact, enhances the resolution and decreases the chance of missing
lesions. Whereas most time domain OCTs are accurate to 10-15 microns, newer
spectral domain machines may approach 3 micron resolution. Whereas most time
domain OCTs image 6 radial slices, spectral domain systems continuously image a
6mm area. This diminishes the chance of inadvertently missing pathology.
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72. • Limitations
• Because OCT utilizes light waves (unlike ultrasound which uses sound waves) media
opacities can interfere with optimal imaging. As a result, the OCT will be limited the
setting of vitreous hemorrhage, dense cataract or corneal opacities.
• As with most diagnostic tests, patient cooperation is a necessity. Patient movement
can diminish the quality of the image. With newer machines (i.e. spectral domain ),
acquisition time is shorter which may result in fewer motion related artifacts
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73. Limitations contd
• The quality of the image is also dependant on the operator of the machine. Early
models of OCT relied on the operator to accurately place the image over the desired
pathology. When serial images were acquired over time (e.g. during treatment for
AMD with anti-VEGF therapy), later images could be taken that were off axis
compared to earlier images. Newer technologies, such as spectral domain acquisition
or eye tracking equipment, limit the likelihood of acquisition error.
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74. Please give your valuable feedback about this presentation
Contact
Dr Gyanendra Lamichhae
Vitreo retina Department
Lumbini Eye Instititue
yourgyanu@gmail.com
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