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![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](https://image.slidesharecdn.com/opticalcoherencetomographyinglaucoma-191011141536/75/Optical-coherence-tomography-in-glaucoma-Dr-Shylesh-Dabke-69-2048.jpg)
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Optical coherence tomography in glaucoma - Dr Shylesh Dabke
This document discusses optical coherence tomography (OCT) in evaluating glaucoma. It begins by outlining the importance of early glaucoma detection to prevent vision loss. OCT is described as the most appropriate technology for detecting glaucoma as it can assess retinal nerve fiber layer (RNFL) thickness before visual field or optic disc changes occur. RNFL thinning is an early sign of glaucoma. The document then provides details on OCT technology and analysis of RNFL thickness, optic nerve head, and macula to diagnose and monitor glaucoma. RNFL analysis, especially of the inferior quadrant, is highlighted as the most useful OCT assessment for detecting early glaucoma.
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Optical coherence tomography in glaucoma - Dr Shylesh Dabke
- 1. Optical Coherence Tomography inGlaucoma 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 youdiagnose 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 progressiveoptic 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 appearancein 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 progressiveoptic 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 • Subjectivepsychophysical 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, FDTmore 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 progressiveoptic 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 ONHchanges 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 ofretinal ganglion cells is irreversible.
- 13. “Not sufficient todiagnose Pre perimetric glaucoma”
- 14. So, A technology thatassesses the • Health • Structure • Thickness of RNFL is clearly the most appropriate choice to detect and follow glaucoma.
- 15. Changing paradigm inONH evaluation
- 16. The Glaucoma Continuum RiskFactors 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 • RNFLdefects - 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 FreeRNFL 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 technologythat 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 :
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- 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 Imageof 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 helpsus 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™
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- 33. • Scattering isa fundamental property of a heterogeneous medium, and occurs because of variations in the refractive index within tissue.
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- 36. Image Formation Vitreous • Zaxis: 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 • Resolutionof 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 weuse 3 scan protocol only • Macular Analysis • RNFLAnalysis • Optic Nerve Head Analysis
- 45. Macular Analysis Uses six 6mm radialline 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 & ONHAnalysis
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- 48. 3.4 mm diametercircles 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 isthicker 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
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- 63. • To monitorRNFL 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 hasthe 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 withAge 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 • ONHevaluation 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 ANALYSISREPORT • 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 • Ganglioncell 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 scandata 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.
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- 72. GCC and clinicalpractice… SAP 30-2 ONH module (RNFL) GCC module
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- 81. Bipolar Notch withNFLDs
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- 86. Bipolar Notch withNFLDs
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- 90. Bipolar Notch withNFLDs
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- 101. Ophthal. - 2001Sanchez / 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 • Differentiatesnormal from glaucomatous eyes • Age matched normative data • Serial change analysis
- 103. Disadvantages • Expensive • Impairsperformance 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 TomographyAngiography & 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 opticnerve head vasculature - OCTA
- 107. • Glaucomatous eyewith 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 clinicalexamination 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.
Editor's Notes
- #14 Need not wait for the field loss to occur or progression
- #35 The interferometer integrates several data points over 2mm of depth to construct a tomogram of retinal structures
- #36 The interferometer integrates several data points over 2mm of depth to construct a tomogram of retinal structures
- #44 FD-OCT is also fast enough for sequential image frames to track the pulsation of blood vessels during the cardiac cycle.
- #51 ONH – Age & Disc size, RNFL - Age
- #52 ONH – Age & Disc size, RNFL - Age
- #53 ONH – Age & Disc size, RNFL - Age
- #54 ONH – Age & Disc size, RNFL - Age
- #56 ONH – Age & Disc size, RNFL - Age
- #57 ONH – Age & Disc size, RNFL - Age
- #58 ONH – Age & Disc size, RNFL - Age
- #59 ONH – Age & Disc size, RNFL - Age
- #70 Two recent studies from our group found that glaucoma diagnostic accuracy could be improved if macular measurements by OCT are focused on the inner retinal. Glaucoma preferentially affects the three innermost retinal layers: the nerve fiber, ganglion cell, and inner plexiform layers, which contain, respectively, the axons, cell bodies, and dendrites of the ganglion cells. Therefore, we refer to the combination of these three layers as the ganglion cell complex (GCC)
- #73 Pre-perimetric glaucoma → structural damage before functional
- #107 (OCT RT XR Avanti with the AngioVue software, OptovueInc Fremont, CA, USA).
- #109 Clinical ophthalmoscopy can't be replaced