Optical coherence tomography (OCT) is a non-invasive imaging technique that uses light to generate high-resolution cross-sectional images of the retina and optic nerve. It provides detailed visualization of retinal structures on a microscopic scale. OCT is useful for diagnosing and monitoring various posterior segment diseases. It allows differentiation between stages of macular hole, detection of epiretinal membranes, and identification of fluid associated with neovascular age-related macular degeneration. Advances in spectral domain OCT technology have improved imaging speed and resolution, enabling clearer visualization of small retinal structures and layers.

1. OPTICAL COHERENCE TOMOGRAPHY
IN POSTERIOR SEGMENT DISEASES

2. DEFINITION
 Optical Coherence Tomography, or OCT, is a
noncontact, noninvasive imaging technique
based on the principle of optical reflectometry
light which enables precise anatomic
examination of ocular structures.

3. FEATURES
 High resolution evaluation of tissue pathology at the
cellular level, achieving axial resolution of 2-3 um.
 Direct correspondence to the histologic appearance
of retina, cornea and optic nerve in health and
disease
 Critical tool in diagnosis and monitoring of ocular
disease involving the retina, choroid, optic nerve
and anterior segment

4. INTRODUCTION
 Non-invasive imaging technique for the examination
of ocular structures
 Similar to ultrasound except that the reflected and
backscattered light is used to create the image.
 Infrared light at approximately 830 nm is scanned
across the tissue and focussed with an internal
lens.

5.  A second beam internal to the OCT unit is used as a
reference beam and a signal is formed by measuring
the amount the reference beam is altered to match
the reflected beam from the retina.
 Based on low coherence interferometry
 The use of light allows for high resolution. OCT
permits evaluation of tissue pathology at cellular
level, achieving resolution of 2-3 um.
 OCT can image through various media opacities
including vitreous haemmorhage, cataract and
silicone oil.

6. THE PROCESS IS SIMILAR TO THAT OF
ULTRASONOGRAPHY, EXCEPT THAT LIGHT IS USED
INSTEAD OF SOUND WAVES.
Analog to
ultrasound

7. OCT Ultrasound

8. HISTORY
• Invented by Fujimoto, Puliafito and coworkers in 1991
• Commercialized by Humphrey Zeiss
• A broad based tool for comprehensive
ophthalmologists

9. OCT TECHNOLOGY PLATFORMS

10. Commercial OCT Systems
OCT1 (1996)
Zeiss Humphrey Ophthalmic
Systems
OCT2 (2000)
OCT3 (2002)

11.  1996 OCT1 debuted at 100 axial scans per
second
 2002 The Stratus OCT was introduced and
quadrupled the speed 400 axial scans per
second
 Stratus became the standard for the diagnosis of
many retinal diseases and glaucoma
 Utilizes time domain technology

12. SPECTRAL DOMAIN OCT
 Carl Zeiss: Cirrus
 OptiVue: Rtvue
 Heidelberg: Spectralis
 Topcon

13. RETINAL OCT FROM CARL ZEISS MEDITEC
Stratus OCT™
Cirrus™HD-OCT

15.  The light beam is split into 2 beams by a semi-
reflecting mirror (beam splitter): a reference beam
is received then reflected by a reference mirror that
can be mechanically mobilized.
 The other sample beam continues along the same
path and is reflected by the fundus.
 The 2 reflected beams are simultaneously directed
onto the photo detector.
 The combination of the wave front of each of these
2 beams results in the formation of interferences
received by the detector and whose amplitude is
measured to acquire the image.

16.  The time necessary for this scanning and for
acquisition of these sections is the essential
determinant of the quality of the signal, hence the
name of Time-Domain given to conventional OCT
or TD-OCT.
 Main limitations in the clinical use of TD OCT are
limited resolution and slow acquisition.
 With each successive axial scan, patient axial eye
motion becomes an increasingly important factor in
image quality and accuracy.

17.  Image acquisition speed also limits the total number
of cross-sectional images that can be acquired in
succession.
 Eye motion, drying tear film, and blinks may all
contribute to poor-quality images with increased
image acquisition time.
 As a result, time-domain OCT coverage of the
retina is limited.

19. The light beam is split into 2 beams by a beam
splitter: the reference and sample beams are
acquired simultaneously by a spectrometer
(which does not need to be mobilized). Signal
analysis is based on Fast Fourier Transform.
 Thereby the information of the full depth scan
can be acquired within a single exposure.
Improved sensitivity and image acquisition
speed as compared to TD OCT.
Shift from 2D to 3D images of ocular anatomy.

20.  The high resolution of SD-OCT images allows a
better discrimination of retinal and subretinal layers.
 SD-OCT imaging allows a reduction of movement
artifacts, which cause distortion of the surface and
the retina-RPE junction.
 This more rapid image acquisition allows the
creation of 3D images and more precise
quantitative measurements (total volume) of
macular changes (fluids, drusen, CNV, edema),
allowing follow-up after treatment.

21. HIGH SPEED, ULTRA HIGH
RESOLUTION OCT(HSUHR-OCT)
 This system uses spectral or fourier domain
detection, allowing for a dramatic improvement in
the cross sectional image resolution and acquisition
speed.
 The system allows for axial resolution of
approximately 3.5um compared with 10um
resolution in standard OCT, and it also allows for
imaging speeds that are approximately 75 times
faster than standard OCT.
 Superior visualisation of retinal morphology.

22. PROCEDURE
 The patient is positioned at the OCT and asked to
place their chin and forehead in the machine
much like a slit lamp.
 Adjustments can be made to ensure proper
height and comfort for the patient
 Mydriasis is preferred but is not absolutely
necessary.

23.  An infrared image of the patient’s fundus can be
seen on the screen and a pointer is used to focus
the image and move the fixation target so the area
of interest can be properly scanned.
 Multiple scanning sequences and programs can
be used but the majority involve the acquisition of
multiple radial scans.

24. OCT INTERPRETATION
 The OCT images correspond to the histologic
appearance of the retina
 High reflectivity structures are depicted as red,
intermediate as green-yellow and low reflectivity as
blue-black.
 The superior reflection on an OCT scan
corresponds to the nerve fiber layer and is red
representing high reflectivity.

25.  An external red line on the bottom of the OCT scan
represents RPE, Bruch’s membrane, and the
choriocapillaris.
 Between these, a thin red line marks the junction of
the inner and outer segments.
 Inner cellular layers have lower reflectivity and are
yellow, green, and blue. Nuclear layers are
hyporeflective and plexiform layers are
hyperreflective.
 The vitreous is typically black as it is not reflective,
although the posterior hyaloid face can sometimes
be seen

26.  High resolution OCT has the ability to identify fine
retinal structures such as the external limiting
membrane and ganglion cell layer which are not
visualized as clearly with standard resolution.
 Detailed quantitative information on retinal
thickness can be displayed numerically and in a
false-colour topographical map
 Software programs allow for measurement of retinal
thickness.

27.  A line is drawn at the anterior extent of the internal
reflective band and at the posterior extent of the
posterior reflective band.
 By taking multiple radial scans through the macula
a topographic graph of the posterior pole can be
created with thickness estimates for nine segments
within the macula.
 It is important to review the accuracy of the line
placement as erroneous readings can be given if
the OCT does not recognize the true anterior and
posterior extent of the retina

28. LAYERS OF RETINA

29. OCT IMAGE OF NORMAL
RETINA:CONVENTIONAL OCT
Standard resolution of a normal macula in which most of the major
retinal layers can be visualized
INL = inner nuclear layer; IPL = inner plexiform layer; IS/OS =
photoreceptor inner and outer segment junction; NFL = nerve fibre
layer; ONL = outer nuclear layer; OPL = outer plexiform layer; RPE
= retinal pigment epithelium

30. SPECTRAL DOMAIN(SD) OCT
high-resolution improves visualization of smaller structures such as the
external limiting membrane (ELM) and ganglion cell layer (GCL)

31. IMAGE OPTIMISATION
 OCT measures the intensity of a backscattered
optical signal, which represnts the optical properties
or reflectivity of the target tissue.
 The tissue reflectivity varies among different
structures , allowing for measurements that can be
displayed as false colors or gray scale images.
 The gray scale runs continously from high
signal(white) to no signal (black), and images can
contain upto 256 shades of gray corresponding to
the optical reflectivity of various tissue artifacts.

32.  The standard color scale uses a modified continous
rainbow spectrum in which darker colors such as
blue and black represent regions of minimal or no
optical reflectivity, and lighter colors such as red
and white represent a relatively high reflectivity.
 Studies have shown that the gray scale images are
easier to interpret and are more informative than
the color ones due to their improved ability to
visualise subtle retinal structures such as
photoreceptor inner and outer segment
junction[IS/OS] and subtle pathologies such as thin
epiretinal membranes.

34. PATTERN OF OCT IN MACULAR
DISEASES
 MACULAR HOLE
OCT has become gold standard in diagnosing and
monitoring macular holes.
STAGE 1 MACULAR HOLE
In a stage 1 macular hole, no true neural retinal
defect is present, the photoreceptor layer is
believed to be intact, and no vitreofoveal separation
has occurred.
 Oblique vitreous traction on the fovea is
hypothesized to be the inciting event and can
typically be observed on OCT.

35. 1- Stage 1a- impending macular hole
Signs: flattening of the foveal depression with
an underlying yellow spot
Pathology: inner retinal layers (‘Müller cell
cone’) detach from the underlying photoreceptor
layer, with the formation of a schisis cavity.
In a stage 1a macular hole, a small central yellow
spot is seen on ophthalmoscopy.
The fovea may be thickened along with a loss of the
normal foveal contour.

36.  Gass suggests that the yellow spot of a stage 1a
macular hole results from a small foveal
detachment.
 OCT studies conclude that a stage 1a macular hole
actually represents a cystic change within the
fovea, rather than a true photoreceptor detachment
from the retinal pigment epithelium.

37.  2- Stage 1b: Occult macular hole
Signs: a yellow ring that may be associated with
metamorphopsia or a mild decrease in
visual acuity.
Pathology: loss of structural support causes the
photoreceptor layer to undergo centrifugal
displacement
In a stage 1b macular hole, a yellow ring is visible in
the foveal area.
In a stage 1b macular hole, the cyst-like space is
accompanied by a foveal detachment that
coalesces to a point just short of actual dehiscence.

38. STAGE 1B MACULAR HOLE
stage 1b shows attachment of the posterior hyaloid to the
fovea, separation of a small portion of the sensory retina from
the RPE in the foveolar region and intraretinal cystic changes

39. STAGE 1B MACULAR HOLE

40.  Stage 2: Small full-thickness hole
 Partial break in the retinal surface with small full
thickness loss of retinal tissue with cystic spaces
in the retina
 Stage 2a: <400um FTMH with posterior hyaloid
face remaining attached to roof of pseudocyst
 Stage 2b: <400um FTMH with operculum

41.  The visual acuity typically is diminished and a
pseudo-operculum, which represents condensed
vitreous, may overlie the hole.
 It is believed that once a stage 2 hole occurs, it
nearly always progresses to stage 3, with little hope
for spontaneous visual improvement.

42. STAGE 2 MACULAR HOLE
eccentric stage 2 shows attachment of the vitreous to the
lid of the hole and cystic changes

43. STAGE 2 MACULAR HOLE
As the pseudo-operculum lifts, the hole goes to stage 2 and
becomes apparent on clinical examination

44.  Stage 3: Full-size macular hole
 A fully developed hole with or without operculum

45. STAGE 3 MACULAR HOLE
stage 3 shows a full-thickness hole with intraretinal
cystic spaces at its border

46. STAGE 3 MACULAR HOLE
The pseudo-operculum is now separated from the retina in
this stage 3 macular hole

47.  Stage 4: Full-size macular hole with complete PVD
 Signs: same as stage 3
 Pathology: the posterior vitreous is completely
detached, often suggested (but not confirmed) by
the presence of a Weiss ring.
 Complete posterior separation of the vitreous from
the fovea.

48. STAGE 4 MACULAR HOLE
stage 4 shows a full-thickness macular hole with intraretinal
cystic spaces and an overlying pseudooperculum

49. STAGE 4 MACULAR HOLE
The macular hole is stage 4 when the posterior vitreous
detaches

50. STAGE 4 AFTER SURGICAL CLOSURE

51. PRE-RETINAL MEMBRANE
 An epiretinal membrane is a result of proliferation
of abnormal tissue on the surface of the retina.
 It is semi translucent and proliferates on the
surface of the internal limiting membrane.
 OCT has emerged as a useful, noninvasive tool for
the evaluation of epiretinal membranes.
 On OCT epiretinal membrane appear as a highly
reflective thick membrane on the surface of the
retina.

52.  The strength of signal can differentiate from
posterior hyaloid, which appears as a minimally
reflective signal.
 The majority of epiretinal membranes are globally
adherent to the retinal surface, however, some
appear to have focal adhesions.
 These focal adhesions may be more common in
eyes with secondary epiretinal membranes and
may reflect differences in pathogenesis

53.  OCT is useful in the differentiation of macular
pseudoholes from lamellar and full-thickness
macular holes.
 Macular pseudohole is a result of anterior and
central displacement of the perifoveolar retina
during contraction of epiretinal membrane
 OCT image show an intact photoreceptors layer in
contrast to a full macular hole.
 Pseudoholes typically have a visible gap in the
hyper-reflective epiretinal membrane.

54.  The foveal thickness is near normal while the
parafoveal retina is thickened.
 OCT is also useful for detecting or confirming the
presence of vitreomacular traction .

55. Epiretinal membrane(ERM)

56. Optical coherence tomography of an epiretinal membrane with a
central pseudohole

57. PRERETINAL MACULAR FIBROSIS
Contraction of
preretinal
membrane
(arrows) caused
retinal thickening
with fluid
accumulation in
the outer layer of
the retina

58. PRERETINAL MACULAR FIBROSIS
WITH PSEUDOHOLE
The foveal
structure showed sharp
columnar depression
(arrows)
surrounded by thickened
perifoveal retina

59. AGE RELATED MACULAR
DEGENERATION
 OCT is useful in any AMD patient with visual acuity
complaints.
 OCT allows the physician to distinguish between
causes of visual acuity loss that may not be directly
associated with AMD such as a subtle epiretinal
membrane or vitreomacular traction.
 OCT also permits a detailed evaluation of the RPE
and photoreceptor layer to help identify anatomic
causes of metamorphopsia and visual acuity loss
due to disruption of the photoreceptors and the
presence of PEDs.

60.  OCT can also identify the earliest manifestations of
neovascularization that may appear as subretinal
fluid and increased retinal thickness often with
intraretinal cystic spaces.

61. ARMD
OCT shows separation of the RPE from
Bruch membrane

62. Spectral/Fourier domain cross-sectional scan of a patient with nonneovascular
AMD and multiple drusen (yellow arrows). The ELM follows the contour of the
raised RPE overlying drusen. Bruch’s membrane (BM) is visible as a fine,
backscattering line underneath drusen.

63. PIGMENT EPITHELIAL DETACHMENT
 A retinal pigment epithelial detatchment (PED) is
formed by the seperation of the RPE from Bruch’s
membrane due to the presence of sub-RPE fluid,
blood, fibrovascular membrane, or dreusenoid
material.
 Important predictor of vision loss in AMD patients.

64. Optical coherent tomography demonstrates a bilobed retinal
pigment epithelial detachment (arrowheads). In contrast,
observe a shallow localized elevation of external
hyperreflective retinal pigment epithelium-choriocapillaries
complex band associated with drusen (arrow).

65. Optical coherence tomography (OCT) demonstrates serous
pigment epithelial detachment (PED) as a localized, dome-
shaped elevation of the external hyperreflective retinal pigment
epithelium-choriocapillaris complex band that appear optically
empty with sharp margins.

66. (A) Fundus photograph shows a hemorrhagic pigment epithelial
detachment (arrow). (B) Optical coherence tomography shows
an elevation of both the neurosensory retina and a reflective red band,
which corresponds to the retinal pigment epithelium (RPE). Moderate
reflections can be observed directly beneath the detached RPE, which
correspond to the region of hemorrhage (arrows).

67. VIREOMACULAR TRACTION
SYNDROME
 The vitreomacular traction is a complication of
anamolous partial PVD where the vitreous is
seperated from the retina throughout the peripheral
fundus, but remains adherent in a broad region
encompassing the macula and/or optic nerve.
 OCT has probably become the principal ancillary
test for confirming the diagnosis of pathognomonic
vitreoretinal attachment .

68. Optical coherence tomography (OCT) of a patient. Demonstrating
the insertion of vitreous into the posterior pole and prominent
epiretinal membrane. (A) Preoperative OCT appearance of a 79-
year-old female with epiretinal membrane

69. B)Postoperative OCT shows normalization of the fovea. The
visual acuity has improved to 20/40, 3.5 months
postoperatively.

70. OCT in vitreomacular traction shows incomplete posterior
vitreous separation with persistent attachment at the fovea

71. HIGH MYOPIA
 Optical coherence tomography (OCT) can identify
peripapillary detachment, also termed peripapillary
intrachoroidal cavitation.
 OCT also reveals foveal retinoschisis, inner retinal
breaks, and full-thickness macular holes in some
eyes with degenerative myopia.

72. Highly myopic eye. Fundus photograph (top) and OCT3 (bottom). The
fundus has retinochoroidal atrophy within the staphyloma. OCT3 shows
a localized retinal detachment (*) and perifoveal retinoschisis (Δ)

73. DIABETIC RETINOPATHY

74.  Some eyes have more than one pathologic change.
 Retinal swelling is more pronounced in the outer
than in the inner retinal layers.
 Cystoid macular edema is located mainly in the
outer retinal layers.
 In eyes with long-standing cystoid macular edema,
cystoid spaces fuse, resulting in a large cystoid
cavity involving almost the entire retinal layer.

75.  Hard exudates are seen as highly reflective areas
that cause a shadowing effect of the underlying
retinal layers.
 Retinal exudates are most commonly seen in outer
plexiform layer.
 In eyes with a serous retinal detachment, hard
exudates tend to deposit not only in the retina but
also in the subretinal space.

76. DIABETIC MACULAR OEDEMA
Diabetic macular edema
with hard exudates.
Fundus photograph (top)
and OCT3 (bottom). In
OCT3 image, hard
exudates are seen as
highly reflective areas
located in the outer retinal
layers (arrows)

77. Diabetic retinopathy with
cystoid macular
edema. Fluorescein
angiography (top) and OCT3
(bottom).
In the late phase of angiogram,
hyperfluorescent cystoid
spaces occupy most of the
macula. OCT3 shows round
cysts mainly in the outer retina
that caused the fovea
to protrude

78. Diabetic retinopathy
with serous retinal
detachment. Fundus
photograph (top) and
OCT3 (bottom). OCT3
reveals a serous retinal
detachment at the fovea
(arrows)

79. CENTRAL SEROUS
CHORIORETINOPATHY
 Optical coherence tomography is a noninvasive
technique that can demonstrate the presence of
subretinal fluid .
 OCT shows an optically empty neurosensory
elevation
 A RPE detachment or a deficit in the RPE may also
be seen.
 In cases of CSC, optical coherence tomography is
also used to quantify and follow the amount and
extent of subretinal fluid and to demonstrate
thickening of the neurosensory retina.

80. Optical coherence
tomography of central
serous
chorioretinopathy
showing subretinal
fluid. A RPE detachment
or a deficit in the RPE
may also be seen.

81. Central serous
chorioretinopathy.
Fundus
photograph (top) and
OCT (bottom). A fundus
photograph
shows a serous retinal
detachment. In OCT
image through
the fovea, the detached
retina is swollen, with
intraretinal
areas of low reflectivity

82. RETINAL DETACHMENT
 Optical coherence tomography can be helpful, in
differentiating retinoschisis from retinal detachment.
 OCT images of retinal detachment show separation
of full-thickness neurosensory retina from the retinal
pigment epithelium, while retinoschisis shows the
splitting within the neurosensory retina .

83. Rhegmatogenous retinal
detachment.
Fundus photograph (top) and OCT
(bottom) show the
detached retina with intraretinal
separation (arrows)

84. RETINOSCHISIS
 Juvenile retinoschisis is characterized by bilateral
maculopathy, with associated peripheral
retinoschisis in 50% of patients.
 The basic defect is in the Müller cells, causing
splitting of the retinal nerve fibre layer from the rest
of the sensory retina.
 This differs from acquired (senile) retinoschisis in
which splitting occurs at the outer plexiform layer.

85.  The retina is split into two layers in the central
fovea which extended into the perifoveal area.
 The inner retina contains two highly reflective
zones corresponding to the nerve fiber and inner
plexiform layers.
 Columnar-shaped structures, presumably Müeller
cells, bridge the separated two layers.
 Scanning laser ophthalmoscope shows elevation
of the Henle’s fiber layer.

86. JUVENILE RETINOSCHISIS
OCT3 shows columnar-shaped structures bridging the
separated two layers

87. VITELLIFORM MACULAR DYSTROPHY
 Absence of subretinal fluid differentiates adult
vitelliform dystrophy from Best’s disease.
 Eyes at the vitelliform stage showed a highly
reflective fusiform thickening of the layer at the level
of the retinal pigment epithelium (RPE) and
choriocapillaris.
 A flat dome-shaped space was present between the
level of the RPE and the choriocapillaris

88. Vitelliform macular
dystrophy (Vitelliform
stage). Fundus photograph
(top) and OCT (bottom):
OCT
shows a highly reflective
fusiform thickening of the
layer
(white arrows) at the level
of retinal pigment
epithelium and
choriocapillaris

89. JUVENILE BEST MACULAR
DYSTROPHY
 Best (vitelliform) macular dystrophy is the second
most common macular dystrophy.
 OCT shows material within the RPE.

90. JUVENILE BEST MACULAR
DYSTROPHY
OCT shows material within the RPE

91. OCT IN CHOROIDAL PATHOLOGY
 CHOROIDAL NEOVASCULARISATION(CNV)
Type 1 CNV-- occult CNV- lesion found in sub-
RPE space –RPE detachments on OCT
Type 2 CNV– classic CNV– vessels are found in
sub retinal space– serous RD and retinal
thickening
Type 3 CNV– retinal angiomatous proliferation
(RAP)– abnormal vessels originate from both
retinal and choroidal circulation.

92. TYPE 2 CNV- Optical coherence tomography imaging reveals a
fusiform enlargement of the retinal pigment epithelium
(RPE)/choriocapillaris reflective band with defined borders (arrow). The
highly reflective band appears disrupted, irregular, and duplicated, with
high backscattering material between the two bands. Occasionally, it
may be possible to image the membrane above the RPE .

93. CHOROIDAL NEOVASCULAR
MEMBRANE
a classic well-defined choroidal neovascular membrane.

94. OCT IN GLAUCOMA
 Glaucomatous cupping consists of loss of axons,
blood vessels and glial cells.
 The axons of retinal ganglion cells(RGC) whose cell
bodies lie in the GCL form the NFL.
 OCT provides important qualitative and quantitative
information on the morphology and the
morphometry of optic disc, RGC and NFL.

95.  Recently, SDOCT has been used to assess the
thickness of the inner three retinal layers, known as
macular Ganglion cell complex (GCC) comprised of
cells directly affected by glaucoma.
 GCC measured from inner limiting membrane((ILM)
to outer inner plexiform layer.
 Diffuse loss of GCC in macula in primary open
angle glaucoma (POAG) patients.

96.  Peripapillary NFL thickness and macular GCC
thickness have similar structure function
relationship with visual field sensitivity and similar
diagnostic values for glaucoma detection.
 Macular GCC measurements have a theoretical
advantage over peripapillary NFL measurement in
diagnosis of early stage glaucoma, because RGC
loss occurs early in the pathogenesis of glaucoma.

98. ACUTE OPTIC NEURITIS
 Acute optic neuritis is characterised by optic nerve
oedema.
 Subsequently, optic disc pallor and RNFL loss
develop.

99. Initial OCT shows retinal nerve fiber layer (RNFL) swelling.

100. LIMITATIONS OF SPECTRAL DOMAIN
OCT
 Despite many improvements over time-domain
OCT, spectral/Fourier domain OCT still has some
limitations.
 Media opacities, such as dense cataracts or
corneal edema, decrease image quality; in some
cases, time-domain OCT images have better
quality than spectral/Fourier domain OCT images of
the same patient.

101. Comparison of time-domain OCT image (above) and spectral/Fourier
domain OCT image (below) of a patient with cystoid macular edema (CME).
Because of a dense cataract, there is impaired visualization of CME and
intraretinal structures in the spectral/Fourier domain OCT image, but the
CME is easily identified in the time-domain OCT image.

102. THANK
YOU