OPTICAL COHERENCE TOMOGRAPHY
(OCT)
l Imaging & Biometry key elements - - Spatial
- Temporal
- Depth resolution
Principle of O C T - - Near-infrared light waves to measure distances of anatomical structures
- Low-coherence interferometry
Near infra-red light - - 800-1,310nm
• 830nm: increases the transparency of the aqueous and vitreous humors.
•1,310nm: typical penetration depths in tissues between 1-3mm.
- A beam of light is directed onto the structure and the echo time delay of light is then recorded.
Low coherence interferometry - - Light reflected from the eye is compared to a reference value of a
known length.
- A series of A-scans are combined to form 2-D images of the ocular structures.
- Cross-sectional images are then generated by scanning the incident optical beam.
- The resultant scans are displayed in a color scale.
Types of O C T - - Time domain
• Example: Stratus O C T (carl zeiss)
- Fourier domain
• Spectral domain O C T (SDOCT)- collecting 25,000- 50,000 A-scans/sec with 5-7 microns.
• Optical frequency domain or swept source O C T (SSOCT)- collecting 200,000+ A-scans/sec with 5-7
microns axial resolution at 1,050nm.
• Example: Cirrus HD- O C T
Time domain - - Measures time-of-flight of light of the optical signal reflected off the retinal tissue.
(OCT)
l Imaging & Biometry key elements - - Spatial
- Temporal
- Depth resolution
Principle of O C T - - Near-infrared light waves to measure distances of anatomical structures
- Low-coherence interferometry
Near infra-red light - - 800-1,310nm
• 830nm: increases the transparency of the aqueous and vitreous humors.
•1,310nm: typical penetration depths in tissues between 1-3mm.
- A beam of light is directed onto the structure and the echo time delay of light is then recorded.
Low coherence interferometry - - Light reflected from the eye is compared to a reference value of a
known length.
- A series of A-scans are combined to form 2-D images of the ocular structures.
- Cross-sectional images are then generated by scanning the incident optical beam.
- The resultant scans are displayed in a color scale.
Types of O C T - - Time domain
• Example: Stratus O C T (carl zeiss)
- Fourier domain
• Spectral domain O C T (SDOCT)- collecting 25,000- 50,000 A-scans/sec with 5-7 microns.
• Optical frequency domain or swept source O C T (SSOCT)- collecting 200,000+ A-scans/sec with 5-7
microns axial resolution at 1,050nm.
• Example: Cirrus HD- O C T
Time domain - - Measures time-of-flight of light of the optical signal reflected off the retinal tissue.
