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Optical Coherence Tomography (OCT)

Optical Coherence Tomography (OCT). Gella Laxmi 2009PHXF013P. Introduction. Standard clinical. Resolution (log). Ultrasound. 100micronm. CT and MRI. 10mic. OCT. 1mic. Confocal microscopy. Penetration depth (log). 1 mm. 1 cm. 10 cm. OCT.

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Optical Coherence Tomography (OCT)

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  1. Optical Coherence Tomography (OCT) Gella Laxmi 2009PHXF013P

  2. Introduction

  3. Standardclinical Resolution (log) Ultrasound 100micronm CT and MRI 10mic OCT 1mic Confocalmicroscopy Penetration depth (log) 1 mm 1 cm 10 cm OCT • Determining and visualizing structure that absorb and scatter light • Noninvasive in vivo analysis of retinal tissue

  4. Principle • Michelson Interferometer

  5. Reference beam Diode 820 Beam splitter Detector Patients eye OCT software DVD

  6. Combination of multiple A scans to produce…..

  7. Time Domain OCT

  8. IPL INL GCL NFL FOVEOLA OPL ONL RPE PHOTORECEPTORS ELM CHORIOCAPILLARIS Spectral Domain OCT

  9. Features of SD-OCT • Better anatomic representation • High resolution (6 microns) • Fewer movement artifacts • Live cross-sectional movies of various details • High Signal to noise ratio • Scanning speed 25, 000 A-scans per second • 3D imaging

  10. Histological retina Vs SD-OCT Vs

  11. Retinal Structures on SD-OCT • Horizontally oriented structures – hyperreflective • Vertically oriented structures (layers containing nuclei) – hypo reflective

  12. V V CC RPE • Choriocapillaris: • Innermost limit of the vascular layer of the eye • Thin and hyper-reflective layer • Larger vessels of choroid – hyporeflective • Inconsistently identified • Bruch’s membrane: • Not visible on SD-OCT V V CC CC RPE RPE V V

  13. Retinal Pigment Epithelium: • RPE-CC complex divided into 3 parallel strips • 2 are thick, hyperreflective separated by thin hyporeflective line • Verhoef’s membrane

  14. Photoreceptors: • Rods and cones contain inner and outer parts • Inner part: nuclei (outer nuclear layer) • Outer part: inner and outer segment • Connection b/w inner and outer segment forms a hyper-reflective strip (result of diff in RI) • Sharply raised at the foveola • External limiting membrane

  15. Outer plexiform layer: • Visual cells connect to the bipolar cells • Horizontal axons of the horizontal cells • Hyper-reflective strip • Inner nuclear layer: • Nuclei of bipolar, horizontal, muller and amacrine cells • Hyporeflective layer

  16. GCL RNFL IPL • Inner plexiform layer: • Synapses b/w ganglion cells and amacrine cells • Hyper-reflective owing to their horizontal structure • Ganglion cell layer • Bulky cells are multilayered • Hyper-reflective • Nerve fiber layer • Nerve axons • Very high reflective layer

  17. Internal limiting membrane • Difficult to distinguish • Hyaloid and vitreous • Various pathologic structures clearly visible

  18. Reporting SD-OCT • Comment on each layer • Reflectivity • Morphological features • Measurements of thickness

  19. Take-home message • Retinal anatomy and virtual histology can be studied with the SD-OCT • The SD-OCT shows more detail at the vitreoretinal interface, and there is better delineation of all retinal layers

  20. References • Bruno Lumbroso. SD-OCT Reveals Details of Posterior Segment Structures. Cataract & refractive surgery today Europe. June 2008. Pg 27-28 • Wolfgang Drexler, et al. State-of-the-art retinal optical coherence tomography. Progress in retina and eye research. 2008.Jan; 27(1): 45-88 • Bruno Lumbroso, et al. Understanding Spectral OCT. I.N.C Innovation-News-Communication. 2007. • Michael R. Hee, et al. Optical Coherence Tomography of the Human Retina. Arch Ophthalmol. 1995; 113: 325-332.

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