OCT in Glaucoma umesh- showing a Glaucoma

OCT in Glaucoma umesh- showing Glaucoma

1. OCT in GLAUCOMA Dr. Umesh

2. PRINCIPLE Michaelson’s (Low-Coherence) Interferometry

3. Constructive Interference Destructive Interference (A) (B) INTERFERENCE Wave X Wave Y Resultant wave

4. Super-luminescent Diode (810nm near-infrared) laser

5. TYPES

6. TIME-DOMAIN OCT Axial Resolution – 10-15 microns Scanning speed – 400 A-scans/sec (Due to continuous need for moving mirror!)

7. FOURIER-DOMAIN OCT Spectral-Domain (SD)-OCT Swept-Source (SS)-OCT 18,000-70,000 A scans/sec x 200-400 faster Fixed mirror and spectrometer Axial resolution – 5 microns Reduced artefacts Time encoded frequency domain, No spectrometer required Narrow bandwidth light source (changes wavelengths and sweeps across a narrow band in time ) Deeper penetration, wider imaging, improved Signal to Noise Ratio , 1lakh A scans/sec Lower axial resolution than SD-OCT

8. Type Image Acquisition Scanning Speed (A-scans/second) Axial Resolution Transverse resolution Range of Imaging TD-OCT Super luminescent diode (810nm) single photon detector, moving mirror 400 10 20 Vitreoretinal interface to RPE SD-OCT Broadband super luminescent diode source (840nm), array of detectors, fixed mirror 27,000-70,000 5-7 14-20 Posterior cortical vitreous to sclera using EDI mode SS-OCT Swept source tunable laser (1050nm), single detector 1,00,000-40,00,000 5 20 Posterior cortical vitreous to sclera (superior to SD-OCT with EDI mode)

9. OCT in GLAUCOMA

10. RNFL loss - First sign of structural damage in pre-perimetric disease Structural damage precedes functional loss

11. Why OCT? Non-Invasive, Objective Fast, Non-Contact procedure Detects early structural damage – RNFL, ONH and Macular GCC changes, all at once Quantitative assessment with low test-retest variability Detects progression at pre-perimetric stage Highly reproducible and reliable

12. Interpreting an OCT Printout

13. Patient Data & Signal Strength Check DOB – age matched data Signal strength (quality control measure) - > 7 (essential) ( optopol - Poor Signal strength d/t Lenticular opacification Posterior Capsular Opacification Ocular surface disease Poor quality scan – poor centration, inexperienced operator, poor lens cleaning

14. 2. Key Parameters Table Color Code B

15. 3. RNFL Thickness Map Raw RNFL thickness data Only map WITHOUT any relation to the normative database Color Code A 350 175 Warm Thick, Cold Thin Black – can’t be scanned/measured

16. Neuro-retinal Rim Thickness Plot 4. Compared with age- and disc size- matched data of the normative database TSNIT Configuration Right eye (Clockwise)

17. RNFL Deviation Map 5. Any region not red or yellow – WNL Purple circle – Calculation circle Black circle – BMO circle Red circle – Cup Border Normal thickness – No overlay color code, otherwise complete green – Obscures the anatomical detail of OCT image

18. Bruch’s Membrane Opening – Minimum Rim Width (BMO-MRW)

19. 6. RNFL Thickness TSNIT Plot Foundation of RNFL analysis Uses 3.46mm calculation circle Normal eyes = Typical “ Double Hump” configuration

20. RNFL Quadrant and Clock-hour graphs 8. Summarizes the RNFL thickness TSNIT plot

21. 8. Extracted Vertical and Horizontal Tomograms Horizontal and Vertical B-scans of Optic Disc, extracted from the 6 x 6 data cube. Helpful for Verifying cup configuration Identifying artifacts related to NRR measurements Color code C (Based on reflectance) HOT – High COLD - Low

22. RNFL Circular Tomogram 9. Raw OCT image of the calculation circle Look for Artifacts Segmentation errors Vitreo -Retinal Pathologies = “GREEN Disease”

23. Interpreting an OCT Printout MACULA REPORT

24. Patient Data and Signal Strength Thickness Map Deviation Map Sector Map Thickness Table Horizontal tomogram of macula

25. (2) Thickness Map Raw GCL+IPL thickness Not related to values from normative database 0 – 225 microns range of measurement (0-350micron in ONH & RNFL) Normal value-92.11+- 5.48 micron Color Code A

26. (4) Sector Map Central elliptical region, 1.2 x 1.0mm, representing fovea where GCL+IPL thickness minimum Outer elliptical area where sectoral measurements provided Color Code B

27. (6) Horizontal Tomogram Tomogram must pass through fovea Detection of Macular pathologies Color Code C

28. Concept of Test-Retest Variability A change of 4 or more from baseline is considered statistically significant, when comparing the same eye from two visits

29. Floor Effect RNFL thickness does not go beyond 30-40 microns (Glial tissue, vasculature) No use of OCT in advanced disease VF supersedes OCT for monitoring in advanced glaucoma FLOOR EFFECT

30. Imaging Artefacts Poor Quality Scan due to Lenticular opacification Poor Device performance Ocular Surface Disease Poor centration Motion Artefact – Check for break in BVs Segmentation error – RED disease in high myopes and tilted disc , GREEN disease in MNF

31. MOTION ARTEFACT Look for discontinuity of BVs

32. Artefacts can still be present even when Signal Strength is good!

33. GREEN DISEASE

34. RED DISEASE Segmentation errors extremely common in high myopes, PPA BE CAUTIOUS

35. Split RNFL MCC of RED disease in a young patient with good quality OCT Anatomical variation rather than artefact Masquerades as a local RNFL defect Suspect when – Normal GCA, Normal ONH parameters, typical RNFL split pattern

36. Shifted RNFL Peaks

37. WEISS RING – RED DISEASE (BLOCK SIGNAL)

38. OCT AND MYOPIA Why the special mention? Visual field changes – mimic that of glaucoma Corneal hysteresis – affect IOP measurements Distinguishing Gamma zone from Beta zone in PPA OCT values Outside normative database Normal volume scan – depth of focus 2mm, Myopic eyes – Exceed the limit

39. OCT in Myopic Eyes

40. OCT and Glaucoma Progression Timely Diagnosis , thereby preventing functional loss – First step Detection of progression – Next Important step Event and Trend Analysis – evaluates functional progression

41. Patient is his own “ best normal ” – monitor progression over time Ability to detect significant progression while the patient is still “GREEN”

42. GUIDED PROGRESSION ANALYSIS

43. GUIDED PROGRESSION ANALYSIS Individual’s parameters compared over time No normative database used Assess – Patient details, Quality check, Event and trend analysis and summary boxes If GPA detects progression, evaluate clinical relevance

44. Thankyou