OCT

• What does OCT stand for?

  Optical Coherence Tomography

  
• What are the characteristics of OCT images?

  • Real-time, cross-sectional images of the retina (2D or 3D)
  • High correlation to retinal physiology
  • Micron resolution

  
• What is the resolution of OCT images?

  Micron resolution

  
• What are the benefits of OCT?

  • Rapid
  • Non-contact
  • Non-invasive
  • Identifies early stages of disease before symptoms
  • Understands retinal disease pathogenesis
  • Monitors disease progression
  • Monitors response to therapy
• When was the first paper describing OCT published?

  1991
• What was the first commercially available OCT device?

  OCT 1, TD-OCT
• What are the differences between Time-domain (TD-OCT) and Spectral-domain (SD-OCT)?

  Time-domain (TD-OCT):

  • Reference mirror moves
  • Depth info collected as function of time
  • Axial resolution: ≈15µm
  • Scan speed: 400 A scans/sec

  
  

  Spectral-domain (SD-OCT):

  • Reference mirror stationary
  • Depth info calculated from light spectrum data
  • Axial resolution: ≈5µm
  • Scan speed: 100,000 A scans/sec
• How does OCT work?

  • Light beam scanned through tissue
  • Comprised of Axial scans (A scans)
  • Measures echo, delay, and intensity of backscattered light from retina
  • Lateral A scans combined into bidimensional scan (B scan)

  
• What types of OCT scans are there?

  • Line
  • Radial lines
  • Circle
  • Volume scan
  • Raster scan

  
• What is a volume scan in OCT?

  • Combines multiple B scans to create a 3D volume scan
  • Sacrifices resolution for increased area
  • Can generate thickness maps
• What is a raster scan in OCT?

  • Combines multiple B scans at regular intervals to obtain HD images
  • Sacrifices area for increased resolution
  • Example: 5-line raster
• What are the main parts of the OCT device?

  • Fixation light
  • Dioptre compensation lens selector
  • Focusing knob
  • Forehead rest
  • Chin rest
  • Touch display
  • Photography button
  • Control lever
  • Base clamping knob
• What is the first step in setting up a patient for an OCT scan?

  1. Ask the patient to remove their glasses/CLs
  2. Swab the equipment
  3. Seat the patient comfortably with chin centred on chinrest
• What is the purpose of the dioptre compensation lens selector in the Topcon DRI OCT Triton?

  • Adjusts for different refractive errors
  • Ensures clear imaging of the retina
• What is the procedure for taking a scan with the Topcon DRI OCT Triton?

  1. Hold the control lever and pull the instrument back towards the operator
  2. Center the patient’s eye in the fundus live image area
  3. Bring the scale towards the patient’s pupil
  4. Move the base towards the patient until the fundus image appears
  5. Ask the patient to look at the green light
  6. Adjust the brightness of the image
  7. Align the bright spots
  8. Center the alignment spot
  9. Adjust the focusing knob

  10. Capture the image
• What are the OCT layers?

  • Nerve Fibre Layer
  • Neural Retina
  • Ellipsoid Zone
  • RPE/Bruch’s membrane complex
  • Retinal pigmented epithelium
  • Photoreceptors

  
• What conditions can OCT be used to diagnose?

  • Macula conditions (e.g., macular oedema, macular hole)
  • Age-related macular degeneration
  • Optic nerve conditions (e.g., glaucoma)
  • Peripheral retina conditions (e.g., tumours, retinal detachment)

  
• What does the traffic light system indicate in OCT reports?

  • Normal: Observed in 95% of normals
  • Borderline: Observed in 5% of normals
  • Abnormal: Observed in 1% of normals
• What is Enhanced Depth Imaging (EDI) OCT?

  • Objective lens moved closer to patient
  • Reveals structural details of choroid
  • Increased signal depth through computerized image averaging
• What is OCT angiography?

  • Non-invasive visualization of retinal and choroidal vasculature
  • Maps erythrocyte movement over time
  • Compares sequential B scans at a given cross-section

  
• What is the axial resolution of SD-OCT?

  ≈5µm
• What is the scan speed of SD-OCT?

  100,000 A scans/sec
• What is the axial resolution of TD-OCT?

  ≈15µm
• What is the scan speed of TD-OCT?

  400 A scans/sec
• What is the purpose of the control lever in the OCT device?

  To adjust the position of the instrument relative to the patient's eye
• What should the patient do during the OCT scan?

  Keep watching the green cross and not blink

  
• What is the purpose of the photography button on the OCT device?

  To capture an image of the retina

  
• What is the significance of the nerve fibre thickness measured in the optic disc scan?

  It helps in diagnosing conditions like glaucoma

  
• What does the TSNIT plot represent in the optic disc scan printout?

  Nerve fibre thickness measured in a ring around the optic nerve head
• What is the purpose of the alignment bright spot during the scan?

  To ensure proper alignment of the OCT device with the patient's eye

  
• What is the role of the fixation light in the OCT device?

  To help the patient focus their gaze during the scan

  
• What is the purpose of the chin rest in the OCT device?

  To stabilize the patient's head during the scan
• What is the purpose of the forehead rest in the OCT device?

  To provide support and stability for the patient's head
• What is the significance of the retinal pigmented epithelium in OCT?

  It is one of the layers visualized in OCT imaging

  
• What is the purpose of the lateral A scans in OCT?

  To create a bidimensional scan (B scan)
• What is the purpose of the echo measurement in OCT?

  To assess the backscattered light from the retina

  
• What does the term "macular oedema" refer to in OCT?

  A condition diagnosed using OCT that involves swelling of the macula

  
• What does "choroidal neovascularization" indicate in OCT findings?

  A condition where new blood vessels form in the choroid

  
• What is the significance of the ellipsoid zone in OCT imaging?

  It is one of the layers visualized in OCT imaging

  
• What does the term "drusenoid deposits" refer to in OCT findings?

  Deposits that can be visualized in the retina using OCT