OCT in Glaucoma

1. Optical Coherence
Tomography in Glaucoma
Dr Shylesh Dabke
Glaucoma Consultant,
Aravidn Eye Hospital,TVL

2. Impact of Glaucoma
• Glaucoma is the 2nd leading cause of blindness worldwide.
• Most common irreversible cause of vision loss.
• In its chronic forms, no symptoms develop until vision loss is advanced.
• Therefore, prevention of vision loss requires early detection.

3. “ If you diagnose glaucoma early –
you can treat it early
If you treat it early –
you can slow the rate of progression
If you slow the progression –
you prevent blindness.”
- Robert Weinreb

4. Definition of Glaucoma
• 1960 :
Glaucoma is a condition characterised by raised IOP. Optic disc cupping
and visual field defect.
• 1980 –
is an optic neuropathy characterised by ONH changes, visual fields with IOP
as a risk factor.
• 2004 –
is recognized and defined by changes in the ONH and RNFL as a result of a
characteristic acquired loss of retinal ganglion cells.

5. • Chronic progressive optic neuropathy associated with accelerated apoptosis
of the RGCs , resulting in characteristic optic disc cupping , RNFL thinning &
visual field abnormalities, that may or may not be associated with IOP rise”.
with IOP rise”.

6. • Variable appearance in normal population.
• Subjective : Clinician interpretation.
• C/D ratio = not reliable (tremendous variability in the size of normal disc.
• Photography – relatively high inter-observer and intra-observer
variability.
“Progressive change in appearance compared to the baseline is more
diagnostic of glaucoma damage.”

7. • Chronic progressive optic neuropathy associated with accelerated apoptosis
of the RGCs , resulting in characteristic optic disc cupping , RNFL thinning &
visual field abnormalities, that may or may not be associated with IOP rise”.
with IOP rise”.

8. Automated Perimetry
• Subjective psychophysical test.
• Demand high degree of performance by patient.
• VF damage relatively late phenomenon.
• Need 30-45% death of RGC to produce a demonstrable field defect.
Dr. HarryQuigley.
Kerrigan- Baummen, Quigley et al. IOVS 2000

9. • SWAP, FDT more sensitive to early glaucoma damage.
• but false +ve , poor specificity
PredictiveValue of Frequency DoublingTechnology Perimetry for Detecting Glaucoma in
Developing Country Mansberger SL, J Glaucoma 2005

10. • Chronic progressive optic neuropathy associated with accelerated apoptosis
of the RGCs , resulting in characteristic optic disc cupping , RNFL thinning &
visual field abnormalities, that may or may not be associated with IOP rise”.
with IOP rise”.

11. • Identifiable ONH changes and RNFL defects with as minimal as 5% retinal ganglion
cell loss - Harry Quigley.
• Structural alterations in ONH and retinal NFL precede functional and psychophysical
changes.
• Objective ONH and RNFL evaluation by clinical examination or Imaging provides vital
clues in diagnosis of Pre perimetric glaucoma.

12. • Loss of retinal ganglion cells is irreversible.

13. “Not sufficient to diagnose Pre
perimetric glaucoma”

14. So,
A technology that assesses the
• Health
• Structure
• Thickness of RNFL is clearly the most appropriate choice to detect and follow
glaucoma.

15. Changing paradigm in ONH evaluation

16. The Glaucoma Continuum
Risk Factors
Accelerated/Initiated
Apoptotic process
Ganglion cell death
and axon loss
ONH change
(undetectable)
ONH change
(detectable)
SWAP Changes
SAP VF Change
VF change
(moderate)
VF change
(severe)
BLINDNESS
IOP Age
CCT Race
CD Ratio Fam Hx
Myopia Exfoliation
Pre-perimetric
Perimetric

17. RNFL Assessment
• RNFL defects - earliest sign of glaucoma
• 88% of ocular hypertensives who converted to glaucoma had RNFL defects
along with VF defects.60%of these converters had RNFL defects 6 years prior
to VF defects (Sommer et al).
• RNFL changes are detected more frequently than ONH changes in eyes
converted from ocular hypertension to glaucoma (Quigley et al).
• RNFL damage occurs earlier than VF defects and ONH damage.

18. RNFL Assessment
Red Free RNFL Photography
• Subjective method
• High resolution monochromatic images of RNFL
• Diffuse RNFL loss difficult to detect
• Clear media
• Dilated pupil
• Skilled photographer
• Results not immediately available
• Sensitivity and specificity - 70 to 80%.

20. So a technology that assesses the health, structure and thickness of RNFL is
clearly the most appropriate choice to diagnose and follow glaucoma.
OCT
HRT GDx
To assess RNFL thickness we have 3 choices :

22. OCT

23. • Non-invasive : without entering the tissue
• Non-contact :without touching the eye
• Trans-pupillary :scan is taken through the pupil
• High resolution
• Cross-sectional
• Quantitative
• Analogous ultrasound B-scan imaging except the optical rather than
acoustic reflectivity .

24. • Cross-sectional Image of Retinal Tissue in Vivo – Virtual Biopsy
• The in situ imaging of tissue
microstructure with a resolution
approaching that of histology, but
without the need for tissue
excision and processing

25. • OCT helps us to view superficial layer of retina,layer by layer
Identification of Retinal Layers by OCT
IS/OS RPE/CC
ILM GCLNFL
Choroid
IPL OPL
NFL: Nerve Fiber Layer
ILM: Inner Limiting Membrane
GCL: Ganglion Cell Layer
IPL: Inner Plexiform Layer
OPL: Outer PlexiformIS/OS: Junction of inner and outer
photoreceptor segments
RPE: Retinal Pigment Epithelium
CC: Choriocapillaris
Stratus
OCT™

30. Interference

31. Detector
OCT
Reference Mirror
Reference Beam
Measurment
Beam

32. Detector
OCT
Reference Mirror

33. • Scattering is a fundamental property of a heterogeneous medium, and
occurs because of variations in the refractive index within tissue.

34. Detector
OCT
Reference Mirror

35. Detector
OCT
Reference Mirror
Interferometer

36. Image Formation
Vitreous
• Z axis: 1024 data points
are captured over a 2 mm
depth to create a tissue
density profile, with
resolution of 10 microns
• X-Y axis: tissue density
profile is repeated up to
512 times - every 5-60
microns - to generate a
cross sectional image
2mm

38. Image Display
• Resolution of 10 micrometers in tissue
• Display is in gray scale or false color scale
• red-white - high reflectivity (RPE and RNFL)
• blue-green - low reflectivity (Ganglion cells,
Photoreceptors and Choroid)
• black – very low reflectivity (Vitreous)
• A real time tomogram using false color scale
• Different colours represent the degree of light
backscattering from different depths of retina
31 dB
250
µm
Log Reflection
mporal Nasal
#10
12/18/98

42. Time Domain OCT
• 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.

43. Fourier domain OCT
• 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 reflections.
• No physical scanning of the reference mirror is required; thus, FD-OCT can be much
faster than TDOCT.

44. FOR GLAUCOMA we use 3 scan protocol only
• Macular Analysis
• RNFLAnalysis
• Optic Nerve Head Analysis

45. Macular
Analysis
Uses six 6mm
radial line scans
centered on fovea
RNFL
Analysis
Uses 3.4 mm
circular scan
centered on the
optic disc
Optic
Nerve Head
Analysis
Uses six 4mm
radial line scans
Around optic
disc
Stratus OCT in Glaucoma

46. RNFL & ONH Analysis

47. Printout

48. 3.4 mm diameter circles for RNFL thicknessRNFL ANALYSIS
• Retina is mostly NFL.
• Large enough to avoid the
edge of ONH.
• Large enough to avoid
peripapillary atrophy.

49. Healthy RNFL is thicker at
superior and inferior quadrants
 DOUBLE- HUMP

59. Average RNFL Thickness
• Normal 95.9 ± 11.4
• Early glaucoma 80.3 ± 18.4
• Advanced glaucoma 50.7 ± 13.6
Schuman,J et al, Ophthalmology, January 2003

60. Early Glaucoma

61. Moderate Glaucoma

62. Advanced Glaucoma

63. • To monitor RNFL thickness changes over time.
• It can be used for 4 scan groups analysis simultaneously of both eyes .
RNFL Serial Analysis

64. RNFL Thickness & Glaucoma Diagnosis
• Mean RNFL thickness alone : 84% sensitivity and 98%
specificity.
• Infero-temporal and Supero-temporal : higher
predictability.
Budenz DL, et al. Sensitivity and specificity of the Stratus OCT for perimetric glaucoma.
Ophthalmology 2005; 112:3–9.

65. Inferior Quadrant has the best discriminating
ability for early detection of glaucoma , followed by
Vertical C/D Ratio.
- Sihota R, et al. Diagnostic capability of optical coherence tomography in evaluating the degree of
glaucomatous retinal nerve fiber damage. Invest OphthalmolVis Sci 2006.
- Naithani P, et al. Evaluation of optical coherence tomography and Heidelberg retinal tomography
parameters in detecting early and moderate glaucoma. Invest OphthalmolVis Sci 2007.

66. RNFL Decay with Age
Clinical Implications
• RNFL thickness decrease 2 µ / decade(0.2% /year).
(Sekhar GC, et al. Normal age-related decay of retinal nerve fiber layer thickness. Ophthalmology 2007.
• Inferior Quadrant : resistant to age-related decay : any amount of thinning in
inferior quadrant considered pathologic.
In glaucoma suspects : inferior quadrant
should be followed very closely.

67. ONH Analysis
• ONH evaluation is less useful.
• There is difficulty in standardizing ONH Parameters
• It is limited without normative morphometric data.
- Robert Chang etal Current Opinion in Ophthalmology 2008,19:127–135.
- Iliev ME, Meyenberg A, Garweg JG. Morphometric assessment of normal,suspect and
glaucomatous optic discs with Stratus OCT and HRT II. Eye2006
• Average RNFL has the best discriminating ability compared with
optic disc parameters.
Naithani P, et al. Evaluation of optical coherencetomography and Heidelberg retinal
tomography parameters in detectingearly and moderate glaucoma. Invest Ophthalmol
Vis Sci 2007.

68. OCT MACULAR ANALYSIS REPORT
• OCT scans of the macula involve a strategy of six intersecting lines that intersect at
the foveal center.
• Assessment of the macular region in glaucoma is necessary because over 50% of
retinal ganglion cells lie in the macular region and hence it is the ideal region to
detect early cell loss.
• The Ganglion Cell Complex (GCC) which includes
1) RNFL
2) Ganglion cell layer (GCL)
3) Inner-plexiform layer (IPL)
becomes thinner due to ganglion cell loss in glaucoma.

69. Macular Analysis
• Ganglion cell are arranged in later of 4 to 6 cells in macula. [One cell thick
outside the macula].
• Tan et al (2009) documented that glaucomatous damage occurs only in these 3 layers

70. • GCC scan data is displayed as thicknes map of GCC layer.
- Thicker regions - Hot colours (yellow and orange )
- Thinner regions - Cooler colours (blue and green).
• GCC map for a normal eye shows a bright circular band surrounding the
macula representing thick GCC as depicted below.

71. Normal thickness Glaucomatous patient

72. GCC and clinical practice…
SAP 30-2 ONH module (RNFL) GCC module

73. Case 1

75. 10/11/2019
OD

76. 10/11/2019
OS

77. 10/11/2019
Healthy vs Glaucoma
1 3
4
2

78. RNFL
Glaucomatous MaculaHealthy Macula

79. Superior Notch with NFLD

80. Inferior NFLD

81. Bipolar Notch with NFLDs

82. Inferior NFLD with
notch

84. Superior Notch with NFLD

85. Inferior NFLD

86. Bipolar Notch with NFLDs

87. RNFL Map

88. Inferior NFLD with
notch

89. Superior Notch with NFLD

90. Bipolar Notch with NFLDs

91. Inferior NFLD

92. Inferior NFLD with
notch

101. Ophthal. - 2001 Sanchez /
Bluementhol / Weintreb et al
Sensitivity Specificity
• HRT 64 to 75% 68 to 80%
• GDx 72 to 82% 56 to 82%
• OCT 76 to 79% 68 to 81%

102. Advantage
• Reproducible
• Differentiates normal from glaucomatous eyes
• Age matched normative data
• Serial change analysis

103. Disadvantages
• Expensive
• Impairs performance in undilated pupils and media opacities
• Cant do in patients with poor fixation

104. Future of OCT
• The newest iteration - swept source (SS) OCT technology
- SS-OCT has improved acquisition speed, volume and depth of ocular tissue measurements.
• OCT has also been adapted to surgical suites for intraoperative use, and portable models have
been incorporated into neonatal ophthalmologic care. Handheld OCT models have been used
for screening purposes in primary care settings.
• The combination of Doppler and OCT—referred to as phase variable OCT—and other similar
technologies collectively referred to as OCT-angiography (OCT-A), can give a representation of
retinal blood flow and provides the ability to define capillary networks in tissue.

105. Optical Coherence Tomography Angiography &
Glaucoma
Various vascular parameters have been investigated
1) Vascular density in the optic nerve head.
2) Flow index of the optic disc.
3) Vascular density in the peripapillary retina.
4) Vascular density in the macula.

106. Macular and optic nerve head vasculature - OCTA

107. • Glaucomatous eye with localized damage in the inferotemporal sector.
• Marked capillary drop-off is obvious on OCTA and is demarcated with yellow arrows.
• There is a corresponding inferotemporal retinal nerve fiber layer(RNFL) loss and a
superior nasal step.

108. Words of wisdom
• Diagnostic testing
- Not a substitute for a poor clinical skills but a complement to a GOOD clinical
evaluation.
- Devices cannot diagnose our patients conditions, but the findings they provide
frequently alter the probability that a subject has a particular condition

109. Conclude
• While clinical examination of the optic disk is indispensable.
• RNFL evaluation is important in confirming the diagnosis and monitoring the
progression.
• Measurement of RNFL with OCT may be even more sensitive than optic disk
measurement.
• With the recent availability of GPA, progressive changes of RNFL can be
analyzed statistically.
• Information obtained from OCT, however, should always be
interpreted carefully with reference to the image quality, scan
location and reliability of RNFL segmentation.
• Further innovations in both hardware and software technologies are
expected to aid in the assessment.