OCT.pptx
- 1. OCT Dr David Khiangte S4 Jr 2 23/9/2020
- 2. OCT OPTICAL : relating or involving light and optics Coherence : constant phase difference in 2 or more waves overtime Tomography : Imaging by sectioning or slicing.
- 3. The advantage of OCT is that it is giving us diagnostic capability at cellular level
- 4. It also gives us a lot of histological details of Retina and Choroid
- 6. • Quick • Non Invasive • Reproducible
- 7. Todays talk : • PRINCPLE OF OCT • EVOLUTION OF OCT • COMMON PROTOCOLS FOR IMAGING • HOW TO READ AN OCT SCAN • COMMON RETINAL CONDITIONS • GALUCOMA • PAPILLEDEMA VS PSEUDOPAPILLEDEMA
- 8. Principle of OCT : Interferometry • Like an Optical analogue of ultrasound • Uses low coherence light source to produce cross sectional images of Retina
- 9. PRINCIPLE • It is based on the principle of optical reflectometry(interferometry), which involves the measurement of intensity and echo time delay of light back- scattering through transparent or semi-transparent media such as biological tissues • Light from a broadband light source is broken into two arms, a reference arm and a sample arm that is reflected back from structures at various depths within the posterior pole of the eye. The echo time delay of the light reflected from various layers of retina is compared with echo time delay of light relected from reference mirror
- 10. TD OCT SD OCT SS OCT EVOLUTION OF OCT
- 12. Time domain(TD) vs Spectral (SD) vs Swept source(SS) OCT
- 14. • Fundus viewing unit • Interferometry unit • Computer display • Control panel • Colour printer
- 15. Scan Acquisition Protocol : Each commercially available OCT device has unique scan patterns that are programmed into the machine
- 16. Scanning Protocols line scans are a single B-scan composed of generally a higher number of A-scans than the cube scans. This higher sampling density allows higher resolution scans of the retinal tissue to be acquired Line Scan
- 17. Raster scan • Series of parallel line scans that can be obtained in any angle • Higher resolution (resolution of 5-line or 7 line raster scans provides an excellent image for viewing macular pathologies in the retinal layers)
- 18. Radial scan 6-12 line arranged in equal angles with a common axis When the axis coincides with the fovea, the relationship of the lesion to the fovea is documented It gives relationship of the lesion with respect to the fovea
- 19. 3D SCAN A number of horizontal line scans co mposing a 6x6 mm or 7x7 mm or 12X9 mm rectangular box 3D view – implementation of advanced , complex analysis – topographic maps and cystic volume These types of scans, however, are more prone to artefact caused by eye movement
- 20. Steps : • Machines is activated • Patients pupils are dilated (3mm minimum) • Patient is seated comfortably • Asked to look into target light in the ocular lens • Discouraged to blink • Protocol selected as per case requirement – A protocol is simply a pre- determined procedure or method • OCT image – upright and straight and the reference scan pattern should center on the fovea or area of interest
- 24. How to read an OCT Scan
- 25. CHECK LIST
- 29. Direction line of scan
- 30. For purposes of analysis , the OCT image of the retina can be subdivided vertically into four regions Pre retina Epi retina Intra retina sub retina
- 31. NORMAL OCT
- 32. OCT MACULA
- 33. Reflectivity
- 34. HYPERREFLECTIVE • Hard Exudates • Hemorrhage • Drusen, PED • Epiretinal Membrane • CNVM Lesion • Disciform scars
- 36. HYPER REFLECTIVE HYPOREFLECTIVE ILM RNFL IPL,OPL,ELM,EZ RPE RPE – CHORIOCAPILLARIS COMPLEX GANGLION CELL LAYER INNER NUCLEAR LAYER OUTER NUCLEAR LAYER DRUSEN, PED EPIRETINAL MEMBRANE CNVM DISCIFORM SCARS HARD EXUDATES HEMORRHAGE INTRARETINAL/SUBRETINAL FLUID
- 37. QUALITATIVE ANALYSIS OF OCT • Description by location • Description of form and structure • Identification of anomalous structure • Observation of the reflective qualities – Hypo/Hyper reflective
- 38. QUANTITATIVE ANALYSIS • Thickness • Volume • Shadow areas
- 41. Retinal layers absent causing light to pass easily and choroid gets highlighted Lesion on top of retina not allowing light to pass through Choroidal lesion not allowing light to pass through
- 42. Retinal vascular disorders Role of OCT : Retinal thickness assessment Patterns of DME Deciding Rx protocol in DME Quantification of CME in vein occlusion Monitoring response to treatment in DME, RVO Prognostic indicators
- 43. Diabetic Macular Edema Key OCT Features • Sub- and intra-retinal fluid accumulation are the key features • There is decreased reflectivity of outer retinal layers on OCT due to increased foveal thickness. • Exudates can be seen as hyper-reflective spots within the retina.
- 44. Spongy macular edema cystoid macular edema Posterior hyaloidal traction without TRD Serous retinal detachment Posterior hyaloidal traction with TRD Types of DME (OCT Classification)
- 45. Vein occlusions Role of OCT • CME , SRD • Prognostic aid • Great follow up tool • Complications – ERM, Lamellar hole , RPE changes
- 46. Key OCT Features • Macular edema • Visual acuity inversely correlates with macular thickening measured with OCT. • After treatment of macular edema, discontinuity of the photo- receptors (especially the ellipsoid zone) and retinal architecture correlate with worse visual acuity. CRVO
- 47. Key OCT Findings • OCT is key to diagnosing associated macular edema, deter- mining if the fovea is involved, and determining response to therapy. • OCT findings include cystoid macular edema, intraretinal hyperreflectivity from hemorrhages, shadowing from edema and hemorrhages, and subretinal fluid • Even with resolution of cystoid macular edema, disruption of the foveal photoreceptor layer, specifically the ellipsoid layer and external limiting membrane, have been associated with a poorer visual prognosis. BRVO
- 48. CRAO Acute phase Chronic phase Key OCT Findings • OCT in acute CRAO demonstrates inner retinal thickening, and the RPE, photoreceptors, and outer nuclear layer appear relatively unaffected • Chronic CRAO demonstrates inner retinal atrophy and loss of the foveal depression
- 49. BRAO Oct shows one half normal Key OCT Findings • structural damage to the inner retina • Increased hyperreflectivity in the affected inner retinal layers and retinal thickening where the occlusion occurred. • In chronic BRAO, OCT reveals atrophy in the nerve fiber layer and inner retina, while the outer nuclear layer and adjacent photoreceptor/RPE layers retain their physiologic thickness
- 50. Non Exudative/Dry AMD Extent of disease Monitoring of disease progression Staging and prognosis OCT – Drusens, loss of RPE and morphological alterations, increased hyperreflectivity Outer retinal tubulations
- 51. Geographic atrophy Key OCT Points • GA is characterized on OCT by loss of the hyperreflective external band (attenuation of the RPE layer) and/or by the hypertransmission effect secondary to loss of outer retinal layers, RPE and choriocapillaries • Nascent GA is a recently described entity, based on specific OCT features that precede manifestations on clinical examination or other imaging modalities RPE affected/loss with hypertransmission in geographic atrophy
- 52. Exudative AMD CNVM lesion type/location/extent FFA/ICG correlation Subretinal / Intraretinal fluid PEDs – types Response to anti VEGFs
- 53. Exudative AMD If choroid thickened – more likely PCV If choroid not thickened - typical AMD Choroid extremely thin – Myopic CNVM Key OCT Points • Type 1 CNV is classified based on its anatomic location, being present above Bruch’s membrane but below the RPE. • Type 2 CNV refers to vessels expanding into the subretinal space between the neurosensory retina and the RPE On OCT type 1 CNV manifests as PED and commonly multi- lobulated with variable internal reflectivity. OCT CNVM
- 54. Central Serous Chorioretinopathy Extend , nature of SRF PED Follow up Response to treatment Complications Acute/chronic CSCR Prognostic aid Role of OCT
- 55. CSR Subretinal fluid with elevations in RPE in a patient with CSR OCT Key Features • Serous macular detachment along with retinal pigment epithelium detachment • Choroidal thickening • Outer retinal granulations
- 56. Myopia • Staphylomas • Haemorrhages and scars • Myopic CNVMs • Myopic foveoschisis • Macular and lamellar holes • ERMs Above image showing alteration of contour of eye in Myopia Key OCT Features • Myopic CNVMs appears as a highly reflective, well- circumscribed, round complex on OCT • Typically, minimal associated exudation such as cystoid macular edema or subretinal fluid is present. Role of OCT
- 57. Retinoschisis type Foveal detachment Macular hole type Key OCT Features • Schisis may occur in multiple layers of the macula; however, the outer layers are most commonly affected leaving a thicker inner retina and thinner outer retina. • Perpendicular strands stretching within the schisis cavity are thought to be Müller cells. • Other associated features of myopia may be noted on OCT, such as staphyloma, RPE atrophy, and vitreomacular interface abnormalities
- 58. Ocular trauma • Macular hole • Outer retinal changes • Choroidal ruptures • Prognostic aid • Descision making
- 59. Retinitis Pigmentosa Diffuse loss of outer retinal layer
- 60. COMMON RETINAL DISORDERS VITREO MACULAR DISORDERS • Asymptomatic • Metamorphosia/DV • Altered fovea • CME/SRD • Surgical treatment/observation
- 61. VMA Vitreomacular adhesion key OCT features • Vitreomacular adhesion is a benign physiologic finding that should be distinguished from similar, often pathologic states of the vitreomacular interface. • In a patient with a history of full-thickness macular hole in one eye, if vitreomacular adhesion is present in the fellow eye, there is a risk for future full-thickness macular hole (FTMH) formation in that eye
- 62. VMT VMT Key OCT Features • VMT is due to an abnormally strong focal adhesion of the posterior hyaloid to the macula. VMT is distinguished on OCT by disruption of the normal macular contour at a focal point with overlying vitreous insertion. • VMT may resolve spontaneously or progress to visually impact- ful sequela, including lamellar macular hole and FTMH.
- 63. Macular hole • Provides confirmation of clinical findings • Further anatomic characterization • Means of educating patient • Improved staging of MH Role of OCT
- 64. Stage 0 – vitreomacular adhesion Stage 1a – impending macular hole With underlying yellow spot Stage 1b – occult macular hole Stage 2 – small full thickness macular hole (<400 micrometer in diameter) Stage 3 – full thickness macular hole ( > 400 micrometer in diameter) Stage 4 – full size macular hole with complete PVD.
- 66. Lamellar hole Key OCT Features • Irregular foveal contour • Defect of inner fovea • Separation of the inner and outer retinal layers • Lack of a full-thickness retinal defect Lamellar macular holes typically remain stable over time, and surgical treatment is rarely required.
- 67. Lamellar macular hole • Intra retinal split with separation of the inner and outer foveal retinal layers Pseudo hole • An appearance of the retina due to contraction (or pulling) from the ERM
- 68. Epiretinal membrane Group 1 – Fovea involving 1A – with outer retinal thickening and minimal inner retinal change 1B – with outer retinal inward projection and inner retinal thickening 1C - with prominent thickening of the inner retinal layer Group 2 – Fovea sparing 2A – with formation of a pseudohole 2B – with schisis like intraretinal splitting
- 69. Key OCT Features • ERM appears as a hyperreflective, thickened membrane on the inner surface of the macula. • An ERM may take on a corrugated or undulating contour in cross section. • In the presence of ERM, the macular contour may appear normal or become highly disorganized on OCT.
- 70. VKH septa inside the sub retinal fluid, denotes inflammatory pathology eg VKH Loss of choroid architecture in uveitic condition eg : VKH
- 72. GLAUCOMA • Structural damage precedes functional loss • 50% RNFL loss before VF defect • RNFL thinning can be detected in 60% cases up to 6 years before appearance of VF defect • Visual fields have poor repeatability (85.9% of abnormal and reliable fields not confirmed on retest in OHTS • 3 or more consecutive fields required to reliably confirm diagnosis OCT - DIAGNOSE AND FOLLOW UP PRE PERIMETRIC GLAUCOMA - HELPS TO CONFIRM WHETHER VF DEFECTS IS REAL OR ARTEFACT - MONITOR PROGRESSION
- 73. Glaucoma affects 3 areas in the posterior segment of eye
- 74. RNFL Analysis White , Green , Yellow, Red compared to normative data base RNFL axon bundles are thickest superiorly and inferiorly Most significant in IT and ST quadrant
- 75. Macular Analysis – uses 6mm radial line scans centered on fovea RFNL Analysis – uses 3.4 mm circular scan centered on the optic disc Optic Nerve Head Analysis - uses six 4mm radial scans around optic disc
- 76. Optic Nerve Head (ONH) evaluation Outlines • Optic Nerve Head • Optic cup and Disc borders Objectively measures • Optic Disc area • Cup volume • Cup:disc ratios • Average • Vertical • Horizontal
- 77. Oct Macula
- 81. There are three important parameters that can affect the interpretation of a scan. They are signal strength, centration, and scan alignment
- 82. Complications that can decrease signal strength : 1. Poor Fixation or disease that can prevent fixation 2. Lack of patient cooperation 3. Dry Eye 4. Corneal opacity 5. Cataract 6. Vitreous opacities i.e., silicone oil, blood, floaters, and asteroid hyalosis. 7. Blinking Signal Strength
- 83. Signal strength • Signal strengths of ten are most desirable. • A strength of six or higher are acceptable. • If the signal strength is less than ten, you should save and then repeat the scan as the one you saved may be the best scan of all future scan Problem?
- 84. Alignment • Not only does the eye have to be aligned on the visual axis, but the depth of the scan has to be correct • Ask your patient to look directly at the center of the green cross or star, where the lines come together in the middle, will help with this alignment Problem?
- 85. Scan centration The scan circle should be centered around the optic nerve Problem? This is an error that you won’t pick up by looking at the scan quality and signal strength * Newer oct have auto-tracking feature to maintain scan centration
- 86. Decentration
- 93. Favouring pseudopapilledema • RNFL thickness normal in all 4 quadrans • Direct Optic Nerve Head Drusen visualization in OCT (buried drusen) • Nasal RNFL thickness has the highest diagnostic ability to differentiate TP from pseudopapilledema
- 94. Spectral domain optical coherence tomography can differentiate between papilledema, pseudopapilledema, and a normal disc (a) If the RNFL thickness is normal in all four quadrants, it is more in favour of pseudopapilledema as none (0%) of the patients with TP had a normal RNFL thickness in all four quadrants. Similarly, increased RNFL thickness in all four quadrants is more suggestive of papilledema. (b) The direct visualization of the ONHD is the most important feature on SD-OCT to differentiate between pseudopapilledema and papilledema as the ONHD could be visualized on OCT in all (100%) eyes with buried drusen. c).
- 95. Advantages of OCT • Non contact , non invasive, real time • Histological images in vivo • High resolution images • Uses harmless radiation • Children can tolerate it • Very helpful for quantitative information about macular thickness • Valuable teaching tool for ophthalmologist and patients
- 96. Disadvantages of OCT • Media opacity • Scan quality depends on skill of OCT operator • Not possible with uncooperative patients • Measurement of foveal thickness not accurate if scan not through center of fovea