Optical coherence tomography

Optical coherence tomography

1. OPTICAL COHERENCE TOMOGRAPHY PART-1 OPTOM FASLU MUHAMMED 1

2. Optical: relating or involving light and optics Coherence: Constant phase difference in 2 or more waves overtime Tomography: imaging by sectioning or slicing 2

3. INTRODUCTION OCT is the new diagnostic tool that can perform cross- sectional images of biological tissues within less than 10 micron axial resolution. It provide non contact, real time, high resolution, cross- sectional imaging of the eye 3

4. PRINCIPLE interferometry and low coherence light in near infrared range (820nm) probe beam Reflected light from each structures are according to their optical property Based on interferometry involves interference between the reflected light and the reference beam 4

5. 5 L.S REFERENSE MIRROR BEAM SPLITTER DETECTORE EYE REFLECTED MEASSUREMENT BEAM

6. The echo time delay of the light reflected from various layers of retina is compared with echo time delay of the light reflected form the reference mirror positive interference - light reflected from the retina and the reference mirror- within short coherence length of each other. 6

7. photo detector -range of time delays for comparison Different colors represent light backscattering from different depths of retina. The low- coherence light source determines the axial resolution. 7

8. Oct system comprises Fundus viewing unit Interferometry unit Computer display Control panel Color printer 8

9. Resolution 10 m 2 dimensional images Low coherence interferometry using fixed wavelength Lower speed Upto 512 A scan/sec 9 Resolution 3m 2 or 3 dimensional images Low coherence interferometry using broad wavelenth spectrum High speed – Upto 16000A scan/sec TIME DOMAIN OCT SPECTRAL DOMAIN OCT 2 TYPE OCT

10. spectral Domain OCT Advantages High speed reduces eye motion artifacts present in time domain OCT High resolution provides precise detail, allows more structures to visualized Layer by layer assessment Larger scanning areas allow data rich maps 3-D scanning improves clinical utility 10

11. PROCEDURE Activation of the machine and entering of patient data is the first step. Patient position: Patient is asked to look in to the internal fixation target light. Protocol for scan is selected as per the case requirement. The scanning beam is placed on the area of interest and scans are obtained . 11

12. 12 Advantages Disadvantages Non contact Media clarity Easy tolerance skill of operator Quantitative retinal pt. cooperation Information Teaching tool non-centered scans- inaccurate measurements.

13. NORMAL OCT SCAN OF RETINA The OCT scan of retina allows cross-sectional study of the macular , peripapillary region including RNFL and ONH region 13

14. PHOTORECEPTORS RPE CHORIOCAPILLARIS NF L FOVEOLA GCL ELM ONL OPL INL IPL

15. Normal OCT 15 High reflective (Red) - NFL & RPE Medium reflective ( yellow / Green ) - Plexiform >Nuclear Low reflective ( Blue -Black) - photoreceptors Photoreceptor layer - thickest at fovea NFL- increased thickness nasally

16. OCT SCANS Line scan : It gives an option of acquiring multiple line scans without returning to main window. . Default angle is 0* and length of scan is 5mm The length of the scan and angle can be altered to acquire multiple scans of different parameter. 16

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18. Radial line: Consists 6-24 equally spaced line scans that pass through a central common axis; the length of these line scans can be changed by adjusting the size of aiming circle The radial lines are useful for acquiring macular scan and retinal thickness /volume analysis. 18

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20. Macular thickness map ; same as radial lines except that the aiming circle has a fixed diameter of 6mm . protocol helps in measuring macular thickness Fast macular thickness map a quick protocol that takes only 1.92 seconds to acquire six scan of 6mm length each , when done in both the eyes used for comparative retinal thickness / volume analysis 20

21. EMM5 (MACULAR THICKNESS SCAN) 21

22. Thickness map 22

23. Raster lines ; it provides options of acquiring series of lines that are parallel , equally spaced and are 6-24 in number This scan is especially useful in choroidal neovascular membrane where one wishes to obtain scan at multiple level. Not only CNVM to scan ,all macular disease 23

24. Raster line scan 24

25. Cross line scan 25

26. Optic disc scan: Consits of equally placed line scans 4 mm length ,at 30* intervals and centered on disc Accurate assessment of size ,area ,C:D ratio ,volume of cup can be meassured RNFL scan: Circular scan of 1.34mm radius centered on ONH The mean RNFL Thickness meassured using age adjusted RNFL thickness average analysis protocol In case of glaucoma progression, neuro ophthalmic diseases. 26

27. OCT SCANS 27

28. TO BE CONTINUED… 28

29. ANY DOUBTS ???? 29

30. REFERENCE Ophthalmology investigation and examination techniques – bruce james larry benjamin -pg no.232-239 RTVue users manual OF OCT Diabeticeye disease-Alejandro espaillat-pg.75 www.opsm.com 30

31. PROFICIENCY TEST 31

32. 1.BASIC PRINCIPLE OF OCT ? SCATTERING POLARIZATION INTERFERENCE DIFFRACTION 32

33. 2.In normal OCT ,Nerve fiber layer increased thickness at which area? NASALLY TEMPORAL SUPERIOR INFERIOR 33

34. 3. RNFL scan Circular scan of ………..radius centered on ONH 3.5 mm 2mm 3mm 1.34mm 34

35. 4.Radial line consists of equally spaced line scans of ………. 6-24 line scan 1-20 line scan 1-6 line scan None of the above 35

36. 5.Identify the scan? 36 Line scan Cross line scan RNFL Scan None of the above

37. THANK UUUUU… 37