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

2. Introduction

3. OCT Determining and visualizing structure that absorb and scatter light Noninvasive in vivo analysis of retinal tissue 1 mm1 cm 10 cm Penetration depth (log) 1mic 10mic 100mic ronm Resolution (log) Ultrasound OCT Confocal microscopy Standard clinical CT and MRI

4. Principle Michelson Interferometer

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

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

7. Time Domain OCT

8. CHORIOCAPILLARIS NFL GCL FOVEOLA IPL INL OPL ONL RPE PHOTORECEPTORSELM 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. Vs Histological retina Vs SD-OCT

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

12. 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 VV VV V CC RPE CC RPE V CC RPE

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. 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 RNFL GCL IPL

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.