Optical Coherence Tomography (OCT)

Introduction, Principle, OCT setup, Types of OCT, Features, Limitations, Uses, Interpretation, Types of Edema, RNFL assessment, Macular Hole, CNVM, ERM,RD, ARMD OCT images

1. Optical Coherence Tomography Presented By Shruti Dagar Amity University

2. I ntroduction Optical coherence tomography, or OCT is a non- contact, noninvasive imaging technique used to obtain high resolution 10 cross sectional images of the retina and anterior segment. Reflected light is used instead of sound waves. Infrared ray of 830 nm with 78D internal lens.

3. Principle of OCT OCT is based on low coherence (white light) interference of electromagnetic waves, which was initially used in the measurement of optoelectronic components. And the first biological application of low coherence interferometry was in ophthalmic biometry. Principle of OCT is based on Michaelson’s interferometer.

4. The OCT Setup

5. Types of OCT Time domain A scan generated sequentially, one pixel at a time of 1.6 seconds. Moving reference mirror 400 scans/sec Resolution 10 microns Slower than eye movement Fourier domain Entire A scan is generated at once based on Fourier transformation of spectrometer analysis. Stationary reference mirror 700,00 scans/sec Resolution 5 microns Faster than eye movement

6. Features It is Non-Invasive technique and it gives resolution level of <10 im which is of the level of histopathology through light microscopy. More resolution because of shorter wavelength because of shorter wavelength used as compared to ultrasound or light waves. OCT provides cross-sectional biopsy of the tissue in-vivo .

7. It uses infrared radiation that does not get focused by ocular refracting elements and does not interfere with patient’s attention or cause glare during testing or cause any photic retinal injury. OCT is the most suitable diagnostic tool to ophthalmic use, as it not only images anterior parts of the eye but posterior segment can also be scanned because the light rays can easily penetrate the ocular tissues.

8. Limitations of OCT Despite its varied usage OCT has certain limitations like: Clear ocular media is needed for better performance Minimum pupillary size of 4mm is required. It is a costly apparatus.

9. Uses of OCT Oct is used for diagnosis , monitoring, quantitative and qualitative assessment of macular pathology and is used in most of the Vitreo -retinal conditions, some of them are listed. Posterior Vitreous Detachment (PVD) Vitreo -Macular Traction Syndrome (VMT) Asteriod Hyalosis Intra-retinal Hemorrhage.

10. Macular Edema ( CME, CSME) Macular Holes and cysts. Epiretinal Membrane in Diabetic Retinopathy. Central Serous Retinopathy. Foveal thining in Retinitis Pigmentosa and in Myopic Degeneration. Age Related Macular Degeneration. Post Retinal Detachment Surgery .

11. Interpretation Following things need to observed in OCT: Vitro-retinal interface. Retinal Thickness:           Increases :   Edema , Traction.           Decreases : Foveal atrophy. Reflectivity: Hyper-reflective lesions : Hard Exudates,   Blood , Scars. Hypo-reflective lesions :  Serous Fluid, Hypo- pigmented lesions of Retinal Pigment Epithelium, Media Hazy .

12. Foveal Contour. Continuity of tissues Distinction between: Serous fluid and blood. Detachment of neurosensory retina & RPE .

13. Normal retinal structures  Highly reflective structures are shown in bright colures (white and red) . Those with low reflectivity are represented by dark colors (black and blue). Intermediate reflectivity is shown Green.

14. Diabetic Macular Edema has different type of patterns : Sponge like retinal thickness. Macular edema and Cystoid Macular Edema . Serous Retinal Detachment. Epi -retinal Membrane. Vitro-macular traction.

15. Spongy Macular Edema

16. Macular Edema

17. Cystoid Edema

18. Spongy and cystoid macular edema

19. E xudates

20. Epi -Retinal Membrane

21. Tractional Retinal Detachment

22. OCT patterns in ARMD                                             Focal elevation of Retinal Pigment Epithelium. Large drusen shows irregular elevation of Retinal Pigment Epithelium with shadow from underlying choroid. Large drusen carry high risk of Choroidal Neo-Vascular Membrane.

23. Irregular RPE

24. Choroidal Neo-vascular membrane

25. Retinal Thinning in Scarred CNVM

26. Retinal thinning due to retinal Scar in Choroiditis

27. Retinal Thinning in Myopic Degeneration:

28. Macular hole There are three type of macular hole we can see: Impending Macular Hole. Lamellar Macular Hole. Full Thickness Macular Hole.

29. Impending Macular Hole

30. Lamellar Macular Hole

31. Full Thickness Macular Hole

32. Serous Retinal Detachment with Spongy Macular Edema in Supro -temporal Branch

33. Cystoid Macular Edema in Central Retinal vein Occlusion

34. RNFL assessment OCT can be used to rapidly evaluate the integrity of the RNFL and the macula for the purpose of tracking disease progression, and could also potentially be used to visualize neuro protection.

35. The clinical indications of RNFL measurement are : A sensitive indicator of glaucomatous damage. Quantification of RNFL loss which is highly correlated with visual field loss. Quantification of diffuse loss of ganglionic cells. Identification of early focal defects

36. BIBLIOGRAPHY https:// optometryeducation.blogspot.com/2011/12/oct.html?view=magazine https:// www.slideshare.net/aryalmanu/optical-coherence-tomography-37170447 Optometric Instruments Book

37. THANKYOU!