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Optical coherence tomography
Optical coherence tomography (OCT) uses low-coherence interferometry to perform high-resolution, cross-sectional imaging of biological tissues. It provides non-contact, real-time imaging of the retina with axial resolutions of 3-10 micrometers. OCT works by measuring the echo time delay and magnitude of light reflected from retinal layers compared to a reference beam, using interference of light. This allows visualization of the internal microstructure of the retina and optic nerve head. Common scan patterns include line scans, radial scans, and macular thickness maps. OCT is an important tool for diagnosing and monitoring retinal and optic nerve diseases.
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Optical coherence tomography
- 1. OPTICAL COHERENCE TOMOGRAPHY PART-1 OPTOMFASLU MUHAMMED 1
- 2. Optical: relating orinvolving light and optics Coherence: Constant phase difference in 2 or more waves overtime Tomography: imaging by sectioning or slicing 2
- 3. INTRODUCTION OCT isthe 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 andlow 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
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- 6. The echotime 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 10m • 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 OCTADVANTAGES • 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 themachine 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 contactMedia clarity Easy tolerance skill of operator Quantitative retinal pt. cooperation Information Teaching tool non-centered scans- inaccurate measurements.
- 13. NORMAL OCT SCANOF RETINA The OCT scan of retina allows cross-sectional study of the macular ,peripapillary region including RNFL and ONH region 13
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- 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 Linescan: 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 thicknessmap ; 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 THICKNESSSCAN) 21
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- 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
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- 26. Optic discscan: 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
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- 30. REFERENCE Ophthalmology investigationand 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
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- 32. 1.BASIC PRINCIPLE OFOCT ? A. SCATTERING B. POLARIZATION C. INTERFERENCE D. DIFFRACTION 32
- 33. 2.IN NORMAL OCT,NERVE FIBER LAYER INCREASED THICKNESS AT WHICH AREA? A. NASALLY B. TEMPORAL C. SUPERIOR D. INFERIOR 33
- 34. 3. RNFL SCANCIRCULAR SCAN OF ………..RADIUS CENTERED ON ONH A. 3.5 mm B. 2mm C. 3mm D. 1.34mm 34
- 35. 4.RADIAL LINE CONSISTSOF EQUALLY SPACED LINE SCANS OF ………. A. 6-24 line scan B. 1-20 line scan C. 1-6 line scan D. None of the above 35
- 36. 5.IDENTIFY THE SCAN? 36 A.Linescan B.Cross line scan C.RNFL Scan D.None of the above
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