Oct in post seg disorders

1. USES OF OCT IN POSTERIOR
SEGMENT DISEASES
DR.M.DINESH

2. OCT is an invivo diagnostic imaging technique
• non contact
• non invasive that enables
• cross-sectional study of retina in
• Micron resolution &
• correlates very well with the retinal histology
• With the currently available machine the resolution is of 7- 10
microns, which allows imaging of the neurosensory retina, the
retinal pigment epithelium (RPE) and the choriocapillaris.
• Carmen Puliafito described the concept of Optical coherence
tomography (OCT) in 1995 for ocular imaging. He described OCT
as the first optoelectronic eye imaging system.

3. OCT advantages:
• rapid, easy (very short learning curve),
• non-contact, non-invasive,
• sensitive (7-10 microns resolution) and
• Highly reproducible and repeatable.
OCT software facilitates qualitative and quantitative analysis;
comparison of scans during subsequent follow-up examination.
It allows detection and measurement of:
• Morphological changes in retina
• Retinal thickness
• Retinal volume
• Retinal nerve fiber layer thickness (RNFL)
• Various parameters of the optic nerve head (ONH)

4. Limitations of OCT
• difficulty in scanning in presence of
• corneal edema,
• significant lens opacity,
• vitreous opacity and haemorrhage
• exploration is limited to the posterior pole.

5. Optical Principles
• Imaging with OCT is based on Michelson interferometer and
includes complex analysis of reflections of low coherence light from
the ocular tissue (low coherence interferometry).
Michelson Interferometer
• A beam of light passes through a semi-transparent mirror that
splits the beam into two.
• These two beams of light are then thrown on two equidistant
mirrors;
reflected light from these mirrors is then picked up and summed up
by a detector.
• The equidistant mirrors reflect the light wave in same phase

6. • If one of the mirrors is moved by a distance less than the
wavelength of the incident light, the reflected lights from the two
mirrors will then possess a phase difference.
• This phase difference then produces an interference pattern at
the level of the detector

8. OCT Machine
• uses a low-coherence infrared (830 nm) light coupled to a fiber
optic system.
• Light passing through the eye is reflected by structures in different
retinal tissue layers.
• The distance between the beam splitter and reference mirror is
continuously varied.
• When the distance between the light source and retinal tissue is
equal to the distance between the light source and reference
mirror, the reflected light from the retinal tissue and reference
mirror interacts to produce an interference pattern. The
interference pattern is detected and then processed into a signal.

9. • The signal is analogous to that obtained by A-scan
ultrasonography.
• A two-dimensional image is built as the light source is moved
across the retina and then a series of stacked and aligned A-scans
produce a 2-D cross-sectional retinal image resembling histologic
section
• An infrared-sensitive charge-coupled device video camera
documents the position of the scanning beam on the retina.
• The OCT image can be displayed on a gray scale where more
highly reflected light is brighter than less highly reflected light.
Alternatively, it can be displayed in color

11. • OCT operates like a fundus camera but resolves like a USG
machine.
• Has +78 D condensing lens images retina & infrared image with
field 300
USG OCT
Source Sound waves Infra red light waves
Resolution 150 microns 10 microns
Patient contact Needed Not needed

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

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

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

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

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

17. Types of machine scans
• posterior segment scan
• macular scan
• optic disc scan
• glaucoma RNFL thickness analysis scan
• anterior segment scan

18. Technique :
• In the presence of clear media and cooperative patients
an OCT can acquire quality images even with a 3 mm pupil
• The patient is seated comfortably in front of the OCT machine
with chin positioned on the chin rest.
• He is asked to fixate on the fixation target(green color light)
• Those patients who are unable to fixate with macula can focus
with the opposite eye on an external target.
• After Fixation the operator selects the desired scan and aligns
the instrument so that fundus image and scan beam is displayed
on the
screen

19. Normal retinal scan:
• The posterior hyaloid -very faint, fine and slightly reflective line
• The fovea shows a characteristic depression on the macular scan.
• Internal limiting membrane is clearly defined in the OCT scans
due to contrast between the reflective retina and non-reflective
vitreous.
• The outer retina is bounded by a highly reflective band (70µ
thick) that represents RPE

20. • The NFL and RPE highly reflective than the other layers of the
retina
• RNFL – thicker on nasal side of macula(side due to the
density of papillomacular bundle.)
• ONL – thickest portion
• The plexiform layers are hyperreflective than the nuclear
layers.
• The photoreceptors form a poorly reflective band
immediately anterior to the RPE, (d/t its vertical orientation)

21. Normal retina in oct

23. Highly reflective structures are shown in bright colours
(white and red) .
• Those with low reflectivity are represented by dark
colours (black and blue).
• Intermediate reflectivity is shown Green

24. • The Bruchs’ membrane and the choriocapillaris are generally
seen as a single less reflective structure but in some scans the
choriocapillaris may be visible separate from the RPE and the
Bruchs’ membrane.
• The larger retinal vessels are located indirectly by the shadow
cone that they form on the posterior layers.
Scan analysis
• has both qualitative and quantitative aspects.
• Qualitative analysis includes morphological & reflectivity study.
Morphological changes include addressing
• changes in contour,
• changes in retinal layers and
• location of changes (preretinal, intraretinal, subretinal)

25. • Qualitative Reflectivity changes include identifying increased or
decreased reflectivity or shadowing and noting its location
(Superficial, intraretinal and deep).
• Quantitative analysis can be performed with regard to
thickness, volume and surface mapping.
• The color codes used depict varying thickness
• Blue 150-210 microns,
• green 210-270 microns,
• Yellow 270-320 microns,
• orange 320-350 microns,
• red 350- 470 microns and
• white greater than 470 microns.

26. Patterns of Abnormalities
Increased thickness:
• Retinal edema is the main cause of increase in macular
thickness.
• Focal or diffuse spongy edema and cystoid edema
• Vitreoretinal traction may also result in retinal deformation and
intraretinal edema
Decreased thickness:
• retinal atrophy secondary to laser,
• trauma or inflammations.

27. High reflectivity
Superficial:
• Epiretinal or vitreal membranes,
• subhyaloid/sub-internal limiting membrane hemorrhage,
• cotton wool spots and Myelinated nerve fibers
Intraretinal:
• Hard exudates, intraretinal hemorrhages,
• fibrosis and scarring
Deep:
• RPE hyperplasia, drusen, scarring, atrophy,
• subretinal neovascular membranes,
• deep pigmented lesions like nevus.

28. Low reflectivity
• Gross separation of cellular elements and fluid present either in
form of cystoid space,
• neurosensory detachment or
• retinal pigment epithelium detachment
• Impending macular holes (cystic appearance)
• Usually the cystic spaces are optically clear but slight haze can be
created by accumulation of cells, fibrin, blood and inflammatory
exudates.
Shadowing
• Dense highly reflective elements produce a kind of blockage of
light waves by attenuation that appears as a shadow which
conceals the elements lying behind it.
• Eg :hemorrhages, cotton wool spots, large hard exudates, dense
pigmented lesion or scar and retained foreign body

29. Clinical applications of posterior segment scan
Vitreoretinal Interface Disorders
• Idiopathic epiretinal membranes (ERMs), a layer of
fibrotic tissue develops on the surface of the retina,
usually after a posterior vitreous detachment.
• vitreomacular traction (VMT) syndrome or idiopathic
macular hole, there are abnormal attachments between
the
vitreous and the retina ,resulting traction exerted on
the
retina causes anatomical alteration and subsequent
visual loss.

30. • Vitreomacular adhesion is defined on OCT as “perifoveal vitreous
separation with remaining vitreomacular attachment and
undistorted foveal morphologic features.”
• Vitreomacular traction is defined by “anomalous posterior
vitreous detachment accompanied by anatomic distortion of the
fovea.”
• Pseudocysts, cystoid macular edema, macular schisis, and
subretinal fluid are typical fndings of VMT.

31. PVD
Vitreomacular adhesion

32. Vitreo –macula traction syndrome

33. Epiretinal Membrane
• Most idiopathic ERMs are thought to result from fibroglial
proliferation on the inner surface of the retina secondary to a
break in ILM occurring during posterior vitreous detachment.
• Secondary ERMs result from an already-existing ocular pathology
such as CRVO/BRVO , diabetic retinopathy, uveitis, and retinal
breaks with or without detachment.
• Glial cells, RPE cells, and myofibroblasts are shown to be mostly
involved in ERM formation.
• ERM may lead to loss of normal retinal anatomy, with the patient
experiencing metamorphopsia, micropsia, monocular diplopia,
and decreased visual acuity.

34. Epiretinal membrane
Oct features
• Epiretinal membranes are seen as linear, increased reflectivity
structures located anterior to retina.
• loss of the normal foveal contour, increased retinal thickness,
and the presence of cystoid changes

35. Macular hole :
• is partial or full thickness dissolution of retinal tissue at the
foveal region.
• It may occur following blunt trauma, long-standing macular
edema or as an idiopathic condition.
• OCT has become the gold standard in diagnosing and
monitoring macular holes.
• OCT has been instrumental in the classification of macular
hole development, following the sequence of events
from antero-posterior vitreofoveal traction to full-thickness
macular hole (FTMH)

36. Macular hole, Stage-1
• Foveolar detachment with yellow spot.
• Stage I: OCT shows reduced or absent
foveal pit (a cystoid space occupying the
inner part of the foveal tissue.)

37. Macular hole stage II
• Partial break in the retinal surface with small
full-thickness loss of retinal tissue with cystic
spaces in the retina (Full thickness eccentric
defect with operculum )

38. Macular hole, Stage III
• Full thickness macular hole with or without
operculum.
• OCT shows a central full thickness macular
hole with detached posterior vitreous

39. Macular hole stage-IV
• stage III hole with a complete PVD
• macular hole with surrounding narrow
cuff of subretinal fluid, cystoid changes at
the edges with pigment deposit at the
base of macular hole

40. Pseudo-macular hole
• Macular ‘pseudohole’ is a result of anterior and central
displacement of the perifoveolar retina during contraction of
epiretinal membrane
• Oct findings include
• wrinkling of the inner retinal surface surrounding the hole,
• apparent retinal tissue in the base of the pseudohole(an
intact photoreceptors layer )
• absence of yellow RPE deposits
• overlying operculum or pseudo-operculum.

41. Pseudo-macular hole

42. Lamellar -macular hole
• The four characteristics of a lamellar hole
on OCT include:
• an irregular foveal contour
• a break in the inner fovea
• separation of the inner from the outer
foveal retinal layers
• absence of a full-thickness foveal defect
with intact foveal photoreceptors

43. Central serous chorioretinopathy
• is a noninflammatory, idiopathic serous detachment of the macula
with or without associated retinal pigment epithelial detachment
OCT –
• method of choice to detect subtle serous detachments of the
macula
• The serous detachment appears as
• a hypo-reflective, shallow separation of the neurosensory retina
from
the retinal pigment epithelium
• margins have a gradual slope compared to pigment epithelial
detachments.
• Overlying neurosensory retina may be thickened in the acute
phases.

44. Central serous chorioretinopathy

45. Central serous chorioretinopathy
Retinal pigment epithelial detachment appears as
• a well defined, dome shaped hypo-reflective elevation of the RPE
with cystic hypo-reflectivity.
• Such detachments may be present within the area of serous
detachment or in an adjacent area

46. • Oct is more sensitive for detection of early retinal thickening
compared to slit-lamp biomicroscopy.
• Hard exudates ,nerve fiber layer microinfarcts (soft exudates) and
intraretinal hemorrhages have characteristic features. All three are
hyper-reflective on OCT and may show posterior shadowing.
• Thickening of the retina with no evident cystoid changes and
affecting a significant area of the retina gives rise to a ‘spongy’
pattern of edema
• The spongy areas are thought to represent altered Mueller cells.
• Thickening with cystoid changes are thought to denote necrosis of
Mueller cells from chronic edema .These changes may also
be associated with foveolar detachment
Diabetic macular edema(CSME)

47. Diabetic macular edema, CME Type

48. Diabetic macular edema: CME with NSD

49. (A) Fundus photograph showing clinically significant macular
edema,
(B) OCT line scan shows loss of macular contour due to spongy
macular edema with hyporeflective thickening of the retina and
small areas of increased reflectivity denoting hard exudates

50. Diabetic macular edema with taut posterior hyaloid

51. CRAO
OCT Features
• Fresh cases show diffuse thickening of the neurosensory retina
• Increased reflectivity is seen in the inner retinal layers with
decreased reflectivity of the photoreceptor layers and the RPE
secondary to the shadowing effect.
• Involvement of macular may have appearance of cystoid
changes in the macular area with loss of the macular contour
• In old cases decrease in macular thickness is noted

52. • Acute CRAO showing opacification of retina and a cherry red
spot;
• OCTshowing increase reflectivity on the inner retinal layers and
hypo-reflectivity in the outer retinal layers, increased thickness of
neurosensory retina, loss of normal macular contour with
cystoid changes in the macular area,

53. CRVO
OCT Features
• Retinal thickening and Cystoid Macular Edema (CME)
• Increase in retinal thickness is seen as loss of macular contour on
OCT.
• In the area of retinal edema, presence of cystoid spaces with
reduced reflectivity depicts CME
• Intraretinal and subretinal hemorrhages are seen as focal areas
with bright and high reflectivity with back scattering.
• Area of shadowing appears as black spaces in the RPE &
choriocapillaris layer

54. CRVO

55. BRVO

56. Nonexudative ARMD
1. Drusens
2. Drusenoid PED
3. Outer retinal atrophy/degeneration(Geographic atrophy)
4. Pigment migration in drusenoid PED
5. Outer retinal tubulation
6. Pseudocyst

57. Nonexudative ARMD

58. Non-exudative AMD with large drusen. Mild disruption of
the EZ line is visible. No signs of subretinal fluid or
CNVM. Foveal contour is intact.

59. Drusenoid pigment epithelial detachment (DPED)
Well-defined drusen at least 350 microns in the narrowest diameter
and appears elevated on stereoscopic fundus photographs. Has a
high rate of progression to both geographic atrophy (GA) and
neovascular AMD.

60. Drusenoid pigment epithelial detachment (DPED) with RPE
migration

61. Geographic atrophy
As non-exduative AMD progresses in more advanced stages, the outer
retinal layers become disrupted and develops atrophy. Drusen is
reabsorbed and geographic atrophy develops that corresponds to
decrease in central vision. SD-OCT scans of geographic atrophy reveals
RPE thinning, loss of EZ and IZ lines, depression of the inner retinal layers
as the outer layers are loss, and increase visibility of Bruch's membrane and
the choroid.

62. Outer retinal tubulation

63. Pseudocysts in a patient with nonexduative age-related
macular degeneration. The hyporeflective space does not
indicate a CNVM but a degenerative process

64. Exudative age-related macular degeneration

65. Exudative age-related macular degeneration

66. Retinal Angiomatous Proliferation
• Occult CNV associated with proliferation of intraretinal capillaries
in the paramacular area and a contiguous telangiectatic response
that has a progressive vasogenic sequence.
• Six distinctive findings of OCT included drusen (100%), inner
retinal cyst (80%), outer retinal cyst (68%), fibrovascular PED
(84%), serous retinal detachment (40%), and PED (68%).

67. Stage I: intraretinal neovascularization. Stage II: subretinal neovascularization with a retinal-
retinal anastomosis.
Stage II: subretinal neovascularization
with a serous PED
Stage III: Choroidal neovascularization with a
vascularized PED and a retinal-retinal anastomosis.

68. minimally reflective spcae in NSR sourrounded
by hyperreflective dot like structures
Retinal Angiomatous Proliferation

69. OCT: Hyper-reflective tissue with,
SRF and cystoid changes in NSR
Retinal Angiomatous Proliferation

70. Fundus photograph shows shallow retinal
detachment with involvement of macula
OCT scan confirms macular detachment
with increased thickness of detachment
macula.
Retinal detachment

71. THAN Q
References :
• Retina ryan 6th ed
• Yanoff 4th ed
• Step by Step Optical Coherence Tomography Parul Sony (RP centre )

75. 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.

77. SD- OCT