OCT in glaucoma ppt;1
- 1. OCT in Glaucoma LT. COL. RASHED-UL-HASAN FELLOW TRAINEE (GLAUCOMA)
- 2. Various imaging techniques Anterior Segment: AS-OCT UBM Posterior Segment: OCT HRT GDx ONH imaging
- 3. Quantitative Imaging Principles Clinical Parameters Measured OCT Interferometry Retinal Nerve Fiber Layer Thickness HRT Confocal Scanning Laser Ophthalmoscopy Optic Disc Tomography GDx Scanning Laser Polarimetry Retinal Nerve Fiber Layer Thickness
- 4. Structural damage precede functional loss About 50% of RNFL has to be lost* Window ofabout 6 years Dr. Harry Quigley. Kerrigan- Baummen, Quigley et al. IOVS 2000
- 6. New diagnostic imaging tool Non invasive, real-time, high resolution Principle – light interferometry Uses low coherence light in the near-infrared range (820nm) to perform cross-sectional images of biological tissues Axial resolution – 10µ Transverse resolution – 20µ INTRODUCTION
- 7. Optical Coherance Tomography Normal scan: Very unlikely there is glaucoma 8 Physiological cupping from early glaucoma Diagnose and follow up pre perimetric glaucoma Monitor progression confirm whether VF defect is real or an artifact
- 8. Various OCT instruments are available - Zeiss - Topcon - Optovue - Heidelberg - Nadik 9
- 9. PRINCIPLE OF OCT Near infra-red beam (820 nm) split into two components: Probe beam: To the tissue of interest (retina) Reference beam: Travels to a reference mirror at a known variable position
- 10. PRINCIPLE OF OCT Light reflected back from the boundaries of the microstructures Echo time delay of this light (reflected from the retina) is compared with the same of the reference mirror and the interference pattern is noted
- 11. PRINCIPLE OF OCT Interference measured by a photodetector Real time tomogram using a false colour scale
- 12. PRINCIPLE OF OCT
- 13. Types of OCT OCT TIME DOMAIN OCT FOURIER DOMAIN OCT SPECTRAL DOMAIN (SD) OCT SWEPT SOURCE (SS) OCT
- 14. TIME DOMAIN OCT FOURIER DOMAIN OCT A scans generated sequentially one pixel at a time in depth Entire A scan generated at once based on Fourier transformation of spectrometer analysis Moving reference mirror Stationary reference mirror 400 A scans per second 26000 A scans per second 10 micron depth resolution 5 micron depth resolution B scan (512 A scans) in 1.28 seconds B scan (1024 A scans) in 0.04 seconds Slower than eye movement Faster than eye movement
- 16. TIME DOMAIN OCT SLD Detector DataAcquisition Processing Combines light from reference with reflected lightfrom retina Distancedetermines depth in Ascan Reference mirror moves back andforth Lens Scanningmirror directs SLD beam onretina Interferometer Broadband LightSource Creates A- scan 1 pixel at a time FinalA-scan Process repeated many times tocreate B-scan
- 17. FOURIER DOMAIN OCT SLD Spectrometer analyzes signal bywavelength FFT Gratingsplits signal by wavelength Broadband LightSource Combines light from reference with reflected light fromretina Interferometer Spectral interferogram Fouriertransform converts signal to typical A-scan EntireA-scan created at a singletime Process repeated many times tocreate B-scan Referencemirror stationary
- 18. SD-OCT use Broadband near-infrared superluminescent diode , SLD (840 nm) as a light source Spectrometer as the detector SS-OCT use Tunable swept laser of 1050 nm Single photodiode detector SD OCT & SS OCT
- 19. • Optic nerve head (ONH) • Peripapillary retinal nerve fibre layer (RNFL) • Macular ganglion cell complex (GCC) • 03 innermost layer of retina (RNFL+ GCL+ IPL) ANALYSIS FROM OCT
- 20. RNFL ANALYSIS RNFL analysis helps to identify early glaucomatous loss Circular scans of 3.4 mm diameter in the peripapillary region (cylindrical retinal cross-section) Itisgraphed in a TSNIT orientation Compared to age-matched normative data
- 21. OPTIC NERVE HEAD ANALYSIS • Radial line scans through optic disc provide cross-sectional information on cupping and neuroretinal rim area • Disc margins are objectively identified using signal from "End of RPE (BMO)” • Parameters: • Disc • cup and rim area • horizontal and vertical cup-to-disc ratio • vertical integrated rim area • horizontal integrated rim width
- 23. COLOUR CODE Colour Code A : RNFL thickness map Warm colour (yellow, red) : Thicker Cold colour (blue, green): Thinner Colour Code B: All other zone other than 8 & 9 Compared to age-matched normative data Colour Code C : zone 8 & 9 False colour code based on tissue reflectance Warm colour (yellow, red) : High reflectance Cold colour (blue, green): Low reflectance
- 24. ZONES OF OCT Zone-1 : Pt. I.D & Signal strength Zone-2 : Key parameter table Zone-3 : RNFL thickness map Zone-4 : NRR thickness plot Zone-5 : RNFL deviation map Zone-6 : RNFL thickness TSNIT PLOT Zone-7 : RNFL Quadrant & RNFL Clock-hour thickness measurement Zone-8 : Extracted vertical & horizontal tomogram Zone-9 : RNFL circular tomogram
- 25. Zone-1. SIGNALSTRENGTH • Determines the reliability • Cirrus OCT: >/= 6/10 • Optovue: 40 and above
- 26. Zone-1. SIGNALSTRENGTH • Poor signal strength causes • Media opacities • Dry eye • Fixation inability • Poor OCT lens cleaning • Older device • Poor centration • Inexperienced operator
- 27. Zone-2 : Key parameter table Results are compared with normative database values & colour coded according to distribution
- 28. Normal – hour-glass or butterfly wing appearance, yellow and red Only map without any relation with normative database Abnormal – 1. Asymmetry between superior and inferior sectors 2. Early signs of a peripheral defect - blue notch in yellow red sectors Zone - 3 : RNFLTHICKNESS MAP
- 29. RE– Continuous line LE – Dotted lines Normal zones - Green Abnormal zones - Yellow and red Zone - 4 : NRR THICKNESS PLOT
- 30. Enface infrared image 3.46 mm in diameter, used as a reference zone for evaluation of RNFL thickness. Outside normal limits – yellow and red Zone - 5 : RNFLDEVIATION MAP
- 31. HEALTHY GLAUCOMA SUSPECT MODERATE GLAUCOMA SEVERE GLAUCOMA
- 32. Thickness of the RNFL in different regions ( TSNIT : temporal, superior, nasal, inferior, temporal) at 3.4 mm from centre of the optic nerve Normal zones - Green Abnormal zones - Yellow and red Zone - 6 : RNFLTHICKNESS TSNIT PLOT
- 33. Typical “Double hump” Carefully look for artifacts or anatomical variations Zone - 6 : RNFLTHICKNESS TSNIT PLOT
- 34. Pie graph summery of TSNIT plot Avg RNFL thickness Inf: 120 micro m Sup: 112 micro m Nasal: 72 micro m Temporal: 70 micro m Zone-7 : RNFLQuadrant & RNFLClock-hour thickness measurement
- 35. To check the correct localization of the BMO (black), which define the limits of the ONH and on the projections on to the surface of the internal limiting membrane (red) to determine the edge of the NRR To identify artifact related to NRR Zone-8 : Extracted vertical & horizontal tomogram
- 36. Zone-9 : RNFLcircular tomogram To look for Artifacts Segmentation errors Retinal diseases that can cause green disease
- 38. OCT OF MACULAR GANGLION CELLS • The macula is densely populated by RGCs, containing 50% of the total number of these cells while occupying only 2% of the retina’s area. • GCL comprises 30-35% of total macular thickness • Loss of RGC'sin early glaucoma is more likely to occur in macula
- 39. OCT OF MACULAR GANGLION CELLS • GCC composed of • Innermost retinal layers • RNFL + GCL + IPL • Zeiss’ Cirrus HD-OCT • GCL+IPL
- 41. OCT OF MACULAR GANGLION CELLS Zone-1 : Pt. I.D & Signal strength Zone-2 : Thickness map Zone-3 : Deviation map Zone- 4 : Sector map Zone- 5 : Thickness table (Avg thickness: 75 micro m) Zone- 6 : Macular Horizontal Tomogram
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- 43. OCT Panomap Analysis : Right Eye Combination of 200 × 200 Optic Disc Cube and 512 × 128 Macular Cube scans Macular full thickness map
- 44. Normative database of OCT Glaucoma Protocol 1) 284 healthy adults 2) Age range of 18–84 years 3) Refractive error of −12 to + 8D/ +6 D 4) Ethnicity includes Caucasians 43%, Asians 24%, African America 18%, Hispanic 12%, mixed ethnicity 6% and Indian 1%. 5) Disc area is < 1.3 mm2 or > 2.5 mm2 rim area 6) Vertical C:D >2.5
- 45. LIMITATIONS OF OCT Limited applications in poor media clarity Corneal edema Dense cataracts Vitreous hemorrhage Asteroid hyalosis High astigmatism and decentered IOL may compromise the quality