OCT – Introduction and Macular disorders

General OCT working principle
Introduction to Macular Disorders
1. CME
2. CSR
3. PED
4. Druscen
5. CNV
6.ARMD
Recent advances
OCT-Angiography

1. OCT – Introduction & Macula Dr . Sajjan Sangai Dept. Of Ophthalmology MGM Medical College and Hospital , Aurangabad

2. Introduction Retina is a multi layered tissue with each layer having a different reflectance pattern thus by this principle OCT permits recognition of multiple retinal layers in vivo.

3. O ptical C oherence T omography Non-Excisional Optical Biopsy

4. Normal Retinal Anatomy

5. Macular Anatomy

6. Retina Framework Hyper reflective Hypo reflective

7. Retinal Anatomy & OCT

8. Optical Principles of OCT Imaging with OCT is based on Michelson's Interferometer and includes complex analysis of reflections of LOW COHERENCE LIGHT from the ocular tissue ( low coherence interferometry)

9. Optical Principles of OCT

10. 840 nm

11. Optical Principles of OCT INTERFERENCE PATTERN This interference pattern is processed into a signal

12. Image formation The signal is analogous to that obtained with A Scan Ultrasonography. A 2D image is built as the light source is moved across the retina and then the series of stacked and aligned A scans produce a 2dimensional cross sectional image resembling a HISTOLOGIC SECTION

13. Image formation

14. Basic Concepts The infrared image has a field of 30˚ . OCT operates like a fundus camera but resolves like a USG machine . USG OCT Source Sound waves Infrared light waves Resolution 150µ 10µ Patient Contact Needed Non- Invasive

15. Indications of OCT http://www.aao.org/eye-health/treatments/what-does-optical-coherence-tomography-diagnose

16. Advantages of OCT

17. Limitations of OCT

18. Types of OCT Time domain OCT Spectral domain OCT

19. Optical Principle – TD vs. SD OCT

20. Time Domain OCT - Principle Time-domain devices can provide 400 A scans per second with a maximal axial resolution of 8-10µm High quality images require longer time to create. Therefore time is the major limitation of this technique.

21. Spectral Domain OCT- Principle Absence of movable mirror speeds up the image acquisition up to 50 times. This technique enables to obtain large numbers of A-scans that allows creating high resolution images. SD devices can provide 20.000-52.000 A-scan per second with a 5-7µm resolution Such a speed reduces the eye movement artefacts.

22. TD OCT vs. SD OCT

23. TD OCT vs. SD OCT TIME DOMAIN OCT SPECTRAL DOMAIN OCT RESOLUTION : 10 µ 5-7µm 2 Dimensional images 2 D and 3 D Low coherence Interferometry Low coherence interferometry Uses fixed wavelength Broad wavelength spectrum Lower speed 400-512 A scan/sec High speed : 52000 A scans/ sec

24. Scanning protocols TOPCON

25. Scanning protocols Zeiss

26. Retinal scan protocol Scan Utility Line Multiple line scans can be obtained without returning to main window Radial Lines Determines entire macular thickness/ volume Raster lines Entire area of pathology can be scanned Repeat scan Monitoring change during follow-up Macular thickness Determines entire macular thickness/ volume Fast macular thickness Allows comparative thickness/ volume analysis

27. Analysis

28. Patterns of Abnormalities

29. Patterns of Abnormalities High Reflectivity: (Red and Yellow): Superficial : Epiretinal / vitreal membranes Sub hyaloid / Sub ILM haemorrhage Cotton Wool Spot’s Myelinated nerve fibres. Epiretinal Membrane Sub Hyaloid hemorrhage Cotton Wool spots

30. Patterns of Abnormalities Intraretinal: Hard exudates, Intraretinal haemorrhages fibrosis and scarring Intraretinal Hemorrhage

31. Patterns of Abnormalities Deep : Drusen RPE Hyperplasia Scarring , atrophy Sub retinal neovascular membrane Deep pigmented lesion e.g. Nevus Drusen

32. Patterns of Abnormalities Low reflectivity: ( Black and Blue) Gross separation of cellular elements and fluid present either in form of cystoid spaces Neurosensory detachment RPE detachment results in decreased reflectivity

33. Patterns of Abnormalities Shadowing: Dense highly reflective elements produce a kind of blockage of light waves by attenuation This appears a shadow that conceals the element lying behind it E.g. Haemorrhage's, Hard exudates, cotton wool spots, dense pigmented lesion or scar, retained foreign body.

34. Diseases of Macula Age related Macular Degeneration Dry / non-neovascular AMD: Drusen Wet / neovascular AMD: CNV and PED Epiretinal Membrane Full Thickness Macular Hole Central Serous Chorioretinopathy Cystoid Macular Edema

35. Age related Macular Degeneration Degenerative disorder affecting macula Clinical classification of AMD: Category Definition, based on lesion ( within 2DD of fovea) No apparent ageing change No drusen No AMD pigmentary abnormalities Normal ageing changes Only druplets No AMD pigmentary abnormalities Early AMD Medium drusen (>63 m - < 125 m) No AMD pigmentary abnormalities Intermediate AMD Large drusen (>125 m) Any AMD pigmentary abnormalities Late AMD Neovascular AMD and/or any geographic atrophy Category Definition, based on lesion ( within 2DD of fovea) No apparent ageing change No drusen No AMD pigmentary abnormalities Normal ageing changes Only druplets No AMD pigmentary abnormalities Early AMD Intermediate AMD Late AMD Neovascular AMD and/or any geographic atrophy

36. Drusen Extracellular deposits located at the interface between the RPE and Brusch membrane. Derived from immune mediated and metabolic processes in RPE. On OCT: Medium sized and large drusen are seen as hyper reflective irregular nodules beneath the RPE

37. Drusen

38. Choroidal Neovascularisation Causes:

39. Choroidal Neovascularisation ( CNV) Types: Classified according to Macular Photocoagulation Study (MPS): Based on FA Classic CNV (20%): well defined lacy pattern during early transit of dye subsequently leaking to sub retinal space. Occult CNV (80%): Limits cannot be fully defined on FA Predominantly / Minimally classic CNV: Classic element is grater or less than 50 % of total lesion

40. Choroidal Neovascularisation ( CNV) On OCT: CNV is shown as thickening and fragmentation of RPE and Choriocapillaries Sub retinal, Sub-RPE fluid, Blood and scarring are demonstrated.

41. Choroidal Neovascularisation ( CNV)

42. Retinal Pigment Epithelial Detachment (PED) Thickened and dysfunctional Brusch membrane impending movement of fluid from RPE towards the choroid PED. On OCT : PED shows Separation of RPE from the Brusch membrane by an optically empty area Clinically: Orange dome shaped lesion FA: Well demarcated Hyperfluroscent pooling ICGA: Hypofluroscence OCT: Optically empty area below RPE

43. Epiretinal Membrane Sheet like fibro cellular structure that develops over surface of retina. Proliferation of cellular component and contraction of membrane leads to visual symptoms. On OCT- Highly reflective surface layer associated with retinal thickening. Useful to exclude significant VMT .

44. Epiretinal Membrane

45. Full Thickness Macular Hole Pathogenesis: The vitreofoveal traction is central to development of a full thickness macular hole. Gass: Proposed that contraction of prefoveolar cortical vitreous results in tangential traction

46. Full Thickness Macular Hole Classification: Gass classification scheme on Biomicroscopy, New OCT based classification- IVTS- (International Vitreomacular Traction Study)

47. Idiopathic Macular Hole

48. Gass Classification Gass Classification

49. Full Thickness Macular Hole

50. Full Thickness Macular Hole Differential Diagnosis Lamellar hole Pseudo hole ERM CME CSR with central yellow spot

51. Central Serous Chorioretinopathy Idiopathic Characterised by local serou s detachment of the sensory retina at the macula secondary to leakage from choriocapillaries through one or more hyper permeable RPE sites Affects young , middle aged men Risk factors: Steroid administration, Cushing syndrome, H. Pylori infection, pregnancy, psychological stress, sleep apnoea.

52. Central Serous Chorioretinopathy On OCT : Optically empty neurosensory elevation , Other findings – one or more smaller RPE detachments , precipitates on posterior surface of detached retina , thickened choroid. On FA: Hyperfluroscent spot that enlarges- Ink Blot Vertical column- Smoke stack

53. Central Serous Chorioretinopathy

54. Cystoid Macular Edema Accumulation of fluid in outer plexiform layer and inner layers of retina with formation of tiny cyst like cavities. Fluids may initially accumulate intracellularly in Müller cells with subsequent rupture.

55. Cystoid Macular Edema- Causes : Ocular Surgery and Laser. Retinal Vascular Disease: Diabetic retinopathy, Retinal Vein occlusions. Inflammation: Intermediate Uveitis Drug induced: topical prostaglandin derivatives. Retinal dystrophies: Retinitis pigmentosa Conditions having VMT: ERM CNV Tumours: Retinal capillary haemangioma Systemic diseases : CRF

56. Cystoid Macular Edema On OCT : Retinal thickening with cystic hypo reflective spaces , and loss of foveal depression. Lamellar holes may be demonstrated in advanced cases. On FA : A petalloid pattern is seen due to dye accumulation in microcytic spaces in outer plexiform layer

57. Recent Advances Various newer OCT systems are: Ultra high resolution OCT Doppler OCT CAS OCT- Visante OCT Combined FFA and en-face OCT Intraoperative OCT

58. Ultra high resolution OCT (UHR OCT) Axial resolution of 3 µm Transverse resolution of 15-20 µm Useful for visualization of External limiting membrane Ganglion cell layer Photoreceptor layer

59. Colour Doppler OCT Technique that combines laser doppler velocimetry and OCT for imaging the depth , diameter flow rate, retinal haemodynamic characteristic Only possible in larger vessels Not well suited for angiography of retinal and choroidal microvasculature, where vessels are nearly perpendicular to the OCT beam. 

60. Intraoperative OCT Surgical microscope integrated with OCT to perform simultaneous imaging and en face visualization Uses are: Macular hole surgery, ERM peeling, Sub retinal surgery Zeiss OPMI LUMERA® 700 and RESCAN™ 700

61. OCT Angiography Doppler OCT uses the Doppler phase shift to quantify blood flow in larger vessels and measure total retinal blood flow OCTA is more concerned about separating moving scatters from static background tissue to create angiograms .

62. OCT Angiography

63. Bibliography Principles and Practices of Ophthalmology, Vol. 2 , Third edition, Albert and Jacobiec’s. RETINA, Vol.1 , Fifth edition, Ryan.S.J. Kanski’s Clinical Ophthalmology, 8 th edition, Bowling B. Practical Handbook of OCT , Lumbroso.B, Rispoli M. Step by Step Optical Coherence Tomography.